Biological Psychology

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The nervous and endocrine systems

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THE SYNAPSE (enlarged) The electrochemical message is transmitted across the synaptic gap by neurotransmitters released from vesicles in the pre-synaptic end bulb.

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Post synaptic membrane

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Neurones (or neurons) Neurones are cells that process and transmit information. One neurone can be connected to thousands of other neurones. Each neurone has a threhold of respo respons nse e - th the e amount of stimulation it needs to receive from other neurone neurones s to 'fire' its own electrochemical message.

THE NERVOUS SYSTEM

The nervous system is made up of 10-12 billion neurones of 3 main types: types: • Sensory neurones, which respond to external stimuli such as touch and light. • otor neurones, which carry messages to muscles, organs or glan glands. ds. • Assoc iation neurones (by far the most common type), type), which transmit and integrate informati on between other neurones. neurones. The nervous system includes: The central nervous system (CNS) which consists of the brain and spinal cord. The peripheral nervous system (PNS) which consi consists sts of 43 pairs of peripheral

nerves whose function is to link the senses to the CNS and the CNS to the muscles and organs. The PNS functions through two main systems: 1 The soma tic nervous system  this allows communication and voluntary interaction with the outside world vi the sensory and motor neurones. The autonomic nervous system  this connects the CNS to internal glands, organs and involuntary muscles in order to regulate internal processes without conscious control. It has two branches that interact to govern many aspects of behaviour, e.g. homeostasis: a The The sy sympathetic mpathetic branch - prepares prepares the body for action

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by increasing heart heartbeat, beat, breathing, blood sugar levels, and adrenaline release. The parasympathetic branch - ac acts ts to conserve conserve an and d restore body energy when relaxed.

78 Biopsychology

THE ENDOCRIN E SYSTEM

The endocr ine glands secrete hormones into the bloo d stream stream to affect behaviour. There Ther e are many en docrine glands throughout the body which are regulated by the pituit ary gland (sometimes referred to as the 'master gland'), which is itself controlled by the hypothalamus of the brain.

Pituitary gland - secretes many hormones from its anterior and posterior sections, e.g. for growt h, materna l care, etc.

Pineal gland - secretes melatonin involved in regulating body rhythms. Thyroid gland - secretes thyroxin, which affects body metabolism.

Pancreas - secretes insulin and glucagon to control blood sugar levels. Adrenal glands - secrete corticosteroids involved in muscle development and epinephrine/norepinephrine involved in activating the . sympathetic nervous sys system tem.. Gonads - secrete androgens involved in masculine characteristics (and possibly behaviour) and oestrogen and progesterone which regulate the female menstrual cycle.

 

8 2 Meth Methods ods of invest investig igati ating ng brain brain functi function on - measurement MEASURING/OBSERVATIONAL MEASURING/ OBSERVATIONAL TECHNIQUES DIRECT RECORDING OF NEURONAL ACTIVITY

Microelectrodes are inserted into single neuronal cells and record their electrochemical activity, e.g. Hubel and Wiesel measured the activity of single neuronal cells in the visual cortex of monkeys. By keeping the l-read still, various visual stimuli could be presented to different areas of the retina to discover both the area the cell represented and the stimuli it most responded to.

EVALUATION

Advantages

• Extremel Extremely y precis precise e - a very accurate accurate way of studying the living function of neurones.

Disadvantages • Very time-co time-consumi nsuming ng - tho thous usan ands ds of neurones occupy even a tiny area of brain. • Too focused focused - it neg neglects lects the the interactions between nerve cells that are responsible for brain functions. • Invasive Invasive method - it, thu thus, s, has ethical problems, especially if applied to humans.

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EXTERNAL RECORDING OF BRAIN ACTIVITY

Aims to detect brain activity from measurements made at the surface of the skull, e.g. • electroencephalograms EEG) - ele electr ctrode odes s are attached to areas of the scalp, and the electrical activity of the brain beneath that they detect is amplified to reveal the frequency of the 'brain wave'. The frequency is the number of oscillations the wave makes in a second and ranges from 1 3 hertz (delta waves) to 13 hertz or over beta waves). • evoked evoked potentials potentials - record the cha change nge in the the electrical electrical activity of an area of brain when an environmental stimuli is presented or a psychological task is undertaken. Electrooculargrams (EOG) measure electrical activity of eye movements, whereas Electromyograms (EMG) record activity from muscles to measure tension or relaxation.

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EVALUATION

Advantages • •

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Non-invasive techniques techniques - no alteration or or intervention intervention mak makes es these methods of measuring brain activity more natural measuring natural and ecologically valid. Practically useful useful - these methods can distinguish between levels of sleep and different types of subject, e.g. brain damaged, epileptic, those with Alzheimer's disease, etc.

Disadvantages •

Crude measure - the activity of millions of neurones is measured and averaged. EEGs indicate the activity level but not the precise function of the neurones involved.

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SCANNING TECHNIQUES

1 STILL PICTURES - detailed three dimensional or cross-sectional images of the brain can be gained by the foll owing non-invasive techniques techniques:: a Computerised xial Tomography (CAT scan) - is produced by X-ray rotation. b Magnetic Resonance Imaging (MR (MRII scan scan)) - where magnetic magnetic fields are rotated around the head to produce an extremely detailed picture.

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2 DYNAMIC PICTURES - moving coloured images of brain activity levels in different parts of the brain over time can be gained by techniques such as: a Positron Emission Tomography PET s,can) - which detects the metabolism level of injected substances e.g. glucose glucose)) made mildly radioactive to show which parts of the brain are most active (using up energy) over a period of minutes. b Functi Functional onal Magnetic Resonance Imaging (F(F-MR MRII scan) scan) - sho shows ws metabolic activity second by second without injected tracers. c Magnetoencephalography (MEG scan) - detect detects s actual actual nerve cell firing over thousandths of a second.

MRI SCAN

CAT SCAN

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EVALUATION

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Advantages •

Detailed knowledge - scans can gain informat ion about the brain structure and function of conscious patients, some while they are performing psychological tasks.

Disadvantages •

Scanning techniques - are expensive and scans can be difficult to interpret and are sensitive to disruption, e.g. by small movements.

Biopsychology 79

 

8.3 Navigation Navigation related structural structural change chang e hippocampi of London taxi drivers. Maguire t al. 2000)

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INTRODUCTION

AIMS

The hippocampus is a structure found inside each hemisphere of the brain that is thought to playa role in spatial memory and navigation. Maguire et al report that previous research has found: • Certain birds and small mammals that show behaviour requiring navigation and spatial memory e.g. food storage) have increased

In general, the authors aimed to investigate: 1 navigatio nal experience and the the role played by the the hippocampus in humans 2 whether the the healthy human brain can undergo 'plastic' (structural) changes in response to extensive

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hippocampal volumes relative to their brain and body size, and can even show a greater increase in volume during seasons that demand more spatial ability. • Differences in the structure of the healthy human brain exist between different groups of subjects, e.g. males and females, or musicians and non-musicians. However, there are still questions surrounding: • The precise role of the hippocampus in humans. • Whether human hipp ocamp i can can undergo structural changes changes with extensive experience of spatial/navigational behaviour. • Whether differences in human brain structure are predetermined e.g. by the genes) or the result of 'plastic'/morphological/st ructural change change caused by environmental stimulation. London taxi drivers are ideally suited for a study of the effects of spatial navigation experience on the human hippocampus since they have to acquire extensive spatial/navigational information ('The Knowledge') on the city of London to pass their licensing test and carry out their job.

" METHOD

I Design

Natural experiment Independent measure measures s design/matched pairs

Independent variable: mount o f navigational experience tested in two conditions: • Licensed Licensed London taxi drivers wit h a min imu m of 18 months job experience (in addition to an average of about two years acquiring 'The Knowledge') • Non-tax i drivers (control group). Dependent variable: Volume of the hippocampi including their anterior, body and posteri or sections.

N.B. A correlation was also conducted on the taxi drivers between the amount of time spent as a taxi driver (training + job) and their hippocampal volume.

the brain between the two groups, taxi drivers had significantly increased grey matter volume in the right and left posterior hippocampus compared to controls.



taxi drivers had a significantly larger volume in the posterior hippocampi compared to controls. controls had a significantly larger volume in the anterior hippocampi compared to taxi drivers.

80 Biopsychology

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DISCUSSION Taken together, the experiment and correlation indicate: • •





Correlations Correla tions - a signific significant ant positive correlation was found between time as a taxi driver and right posterior hippocampal volume (but a negative one for the right anterior section).

Hippocampus

identities and the VBM results) compared the volume of anterior, body and posterior cross-sections of the taxi drivers' hippocampi with those of a precisely matched matched control group.

Pixell counting - despite Pixe despite no significant difference difference in the overall volume of the hippocampi between the two groups: •

In particular, based on past research, they expected taxi drivers to show significant (p<0.05) structural differences in their hippocampi compared to non-taxi drivers.

Procedure Structural MRI (magnetic resonance imaging) scans of taxi drivers and non-taxi drivers were analysed by: VBM (voxel-based (voxel-based morphometry) - an automatic procedure that 'normalised' the scans to a template (to eliminate overall size of brain as a variable) and compared the taxi drivers' brains with a control group of 50 non-taxi drivers to see if any differences in structure were to be found anywhere in the brain. Pixel counting - an experienced observer (blinded to the subjects'

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navigational experience.

Participants Taxi drivers - 16 healthy, right-handed, male, London taxi drivers. Average age 44 (range 32 to 62 years), average time as a taxi taxi dr iver 14.3 years (range 1.5 to 42 years). Controls - (50 for the VBM template, 16 for the pixel counting) matched for health, handedness, sex, average age, and age range.

RESULTS V M anal analysis ysis - despite despite no significant differences elsewhere in

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Human spatial spatial representations representations and navigat ional experience are stored in the posterior hippocampus. The structural rearrangement rearrangement of the hippocampi in taxi drivers reflects, rather than causes as a pre-existing, predisposition), the amount of navigational ability. The healthy human brain can can change change in structure in response to environmental sti mulation. This Bas implications for rehabilitation after brain damage, although this study only applies to the hippocampus. The methods of measurement were objective and well controlled (by computer or blind assessment). The study does not sho w how the brain changes occur.

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8.4 Me Meth thod ods s of investigating brai brain n function

alteration

ALTERATION/EXPERIMENTAL ALTERATION/EXPERIME NTAL TECHNIQ TECHNIQUES UES ACCIDENTAL DAMAGE

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Researchers use these natural experiments to compare the alteration in psychological functioning with the location of damage (by scan, surgery or autopsy). Damage may be caused by • stroke strokes/tumo s/tumours urs - e. e.g. g. blood clot damage has revealed much about the location of motor, sensory, and linguistic functioning in the brain. • head trauma - e. e.g. g. a railroad construction accident blew a foot long metal rod th through rough P Phin hineas eas Gage's left frontal lobe in 1848, changing his personality to make him impulsive and irritable. • virus - e. e.g. g. the the vi virus rus herpes herpes simplex damaged the temporal lobe and and hippocampus of Clive Wearin g causing anterograde amnesia.

EVALUATION Advantages • The altering damage damage occurs 'natu rally ' so there are less ethical problems compared to other methods. Disadvantages

• • •

Lac Lack k of precision - the exact extent of damage is not controllable and may be difficult to assess. Compari Comparison son problem problems s - compari comparison son of the functioning in the individual before and after the damage is less objective, since it is often based on retrospective accounts of previous behaviour and abilities. Confo undin g va variables riables - other non-physical effects effects of th the e dam damage age may be rresponsible esponsible for behavioural differences. Social reactions to Phineas Gage's physical deformity may have affected his personality.

DELIBERATE DAMAGE

ABLATION/LESION STUDIES - aim to investigate function

by removing areas of the brain or destroying links between areas. Some of the psychological functions investigated have included

• • • • •

Motivation - ablation studie studies s on th the e hypothal hypothalamus amus of rats have caused disrupted eating

behaviour. Aggressi Aggression on - removing the the amygd amygdala ala of some animals has reduced their aggression. Memory - Las Lashle hley y removed removed large port portions ions of rat brains to find the location of memory. Consci Consciousnes ousness s - Sper Sperry ry cut tthe he corpus callosum of epileptic patients, producing a 'split mind'. Psychopathology - prefrontal lobotomy was performed on mental inmates to control behaviour.

EXPERIMENTAL EXPOSURE EFFECTS - aim to influence brain physiology by using environmental distortion or deprivation. Common examples are found in perceptual studies, e.g. Blakemore and Cooper's study of the visual cortex of cats exposed to an environment of vertical lines. and

EVALUATION

Advantages • Greater control - greater precision in in the location of damage and the ability to compare behaviour before and after alteration leads to higher certainty over the effects of the damage.

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Disadvantages

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Ethical problem s of interve intervention ntion - the the deliberat deliberate e chan change ge of behaviour is radical and irreversible. Non-human find findings ings - may not be legitimately generalised to humans due to qualitative diffe difference rences. s.



Plasticity Plasticity - th the e brain is a very flexible system which can compensate for damage. Removing one part of it will only show the performance of the rest of the system, not necessarily the missing part.

STIMULATION OF THE BRAIN

ELECTRICAL ELECTRICA L STIMULAT ION - aims to stimulate brain areas

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with microelectrodes to reveal their function through behavioural c h n g ~ Examples include • animal studie studies s - Delgado stimulated areas of the limbic system to provoke aggression in monkeys and inhibit aggression in a charging bull (wh ile standing in front of it!) by remote control. • human stud studies ies - Penfield stimulated areas of the cortex in patients undergoing brain surgery and found locations that would produce body movement (primary motor cortex), body sensations (primary sensory cortex), memories of sound (temporal lobe) and visual sensations (visual cortex).

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EVALUATION

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Advantages • Less harmfu harmfull - the the aim is to stimulate the brain rather than damage it (therefore more ethical). • More valid - stim stimulat ulation ion seems a better way of investigating the living function of brain area areas. s. Disadvantages

• •

Invasive Invasive technique - the techni techniques ques still involve surgi surgical cal op operation, eration, which can be risky. Interconn Interconnected ectedness ness - it is not easy to know exactly how far the stimulation has spread to other areas and the behaviour produced may not be natural, indeed it is often more stereotype stereotyped. d.

Biopsychology 81

 

8.5 Locali Localisat sation ion of brai brain n fun functi ction on - exterior struct structure ure LEFT SIDE VIEW OF BRAIN FRONTAL LOBE OF CORTEX Involved in planning, initiative, and voluntary motor control. Th frontal cortex is a very highly developed area in humans c mpared to other animals animals.. Micro- electro de stimulati on of the primar y motor cortex produces twitches of movement in b dy par parts. ts.

PARIETAL LOBE OF CORT EX • Involved in sensin sensing g and monitor ing of body parts. • Micro-electrode stimulation to the primary senso sensory ry cortex produces sensations in variou various s parts of the body. • Contains many sens sensory ory association areas, such as the visual association area necessary for object recognition

Damag causes lack of insight, loss of pri miti ve reflex suppression, behavioural inertia (lack of spontan spontaneity eity and initiative), and a n ina bil ity to adjust behavio ur to make it appropriate to the situation.

(dam (damage age does not cause cause blindness but visual agnosia agnosia - the inabi lity to recognise the identity of whole objects by -sight -sight). ). Also integ integrate rates s info rmatio n from differe nt sensory sensory areas to enable cross-modal matching (e.g, pairing up the Sight and s o u ~ of an object).

Primary motor cortex

Primary sensory cortex

Strip invol ved in movement of body parts

Strip invol ved in sensation of body areas

Lateral Sulcus Central Sulcus Fissure dividing frontal and parietal cortex

Fissurefrom dividing temporal frontal and parietal cortex Broca s area Area involved in the production of language

AngUlar gyrus Area involved in written language comprehension

Primary auditory area

Area involved in the analysis of sound

Primary visual area

Area involved in the analysis of visual stimuli

Wernicke's area Area involved in language comprehension

Cerebellum Involved in balance and storage of motor movements

Brain stem

Link between nervous system and brain

Left side view

TEMPORAL LOBE OF CORTEX • Contains important importa nt areas for hearing, language and memory. • Micro-electrode stimulation of the temporal lobe association areas produces 'dream-like' memories of events. • Damage to specific brain areas in and around the edge of the temporal lobe produces specific deficits in language. Damage to Broca's area leads to mo tor aphasia (the disruption of spoken language production), damage to VVernicke's area leads to receptive aphasia (disruption to the comprehension of language) and damage to the angular gyrus disrupts reading comprehension.

OCCIPITAL LOBE OF CORTEX • Contains the the visual cortex a and nd primary visual area. • Micro-electrode stimulation of the primary visual cortex produces flickering patterns of light and colour. • Damage to areas of the primary visual cortex on one side of the brain will produce blind spots (scotomas) in the visual field of the opposite side, side, wh il e damage tto o the right parietal cortex can result in no visual conscious awareness

of the left side of an obje object ct - people people so affected will draw

only the right hand side of a clock face face or eat only the right half of food on their plate (visual neglect).

 

8.6 Localisation of brain function hemispheres

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LATERALISATION AND ASYMMETRY OF BRAIN FUNCTION

Most functions of the brain are contra contralatera laterally lly controlled - th the e sense information and functions of one side of the body are received and controlled by the hemisphere on the opposite side of the brain. Thus, touch, sound, and sight (but not smell) information received from the right side of the body is processed in the left hemisphere, which also controls right hand side body movements. Many functions are, therefore, duplicated in both hemispheres. However, there are some differences (asymmetries) in function between them. y

LEFT HEMISPHERE

RIGHT HEMISPHERE

The left hemisphere is usually

The right hemisphere is usually the dominant hemisphere for • visuospatial tasks such as drawing, face recognition, or visuospatial problems • synthe synthetic tic or holistic thought thought

the dominant hemisphere for • language (especially speech) and writing • logical, analytical, and calculating thought

MOTOR CORTEX FOR LEFT BODY AREAS

MOTOR CORTEX FOR RIGHT BODY AREAS 'Elbow.Jr.unk, knee H and, Digits , Thumb

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SENSORY CORTEX FOR LEFT BODY AREAS He Hand Digits Thumb Eyes Nose Lips Inner mouth Tongue Pharynx Inner abdomen

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TOP VIEW OF BRAIN Genitals

SENSORY AND MOTOR CORTEX LOCALISATION

The sensory and motor cortex show • contralateral contralateral localisation. • upside down orga organisa nisation tion - gen general erally ly the lower body areas are represented at the top of the cortex. • proportional representa representation tion - the gre greate aterr the sensitivity or motor control the body area

Hand Digits Thumb Eyes Nosa Lips Inner mouth

Tongue Pharynx Inner abdomen

the proportion of cortex requires, the greater that represents it.

Biopsychology 83

 

8.7 'Hemi 'Hemispher sphere e decon deconnecti nection on and unity in conscious awareness' Sperry (1968) IM To present studies investigating the behavioural, neurological and psychological consequences of surgery in which the two cerebral hemispheres are deconnected from each other by severing the corpus callosum. Sperry uses these studies to argue that the 'split brain' shows characteristics during testing that suggest each hemisphere • has sl ightly different functions • possesses an independen t stre stream am of conscious awareness and • has its own set of memories whi h are inaccessible to the other

METHOD Subjects: A handful

of patients reduce reduc e crippli ng epilepsy epilepsy..

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underwent hemispheric deconnection to

Design: A natural experiment. Severing the corpus callosum prevents communication between the left and right hemispheres. Procedure: Since each hemisphere receives information from, and controls the functioning of, the opposite side of the body, the capabilities of each can be tested by • presenting presenting visu visual al informati on to either the leh or right visual field when the subject is focusing straight ahead. If this is done at fast speeds (about 1 tenth of a second) the eye does not have time to move and re-focus. Thus information presented to the leh visual field, will be received by the right hemisphere of the brain • presenting tactile infor mation to either the leh or right hand behind a screen (to remove visual identification). Thus tactile information from objects felt by the right hand will be received by the left hemisphere.

RESULTS Visual stimuli presented in one visual field

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Objects shown once to a visual field are only recognised if presented again in the same visual field, not the o th e r imp lyi ng differ ent visual perception and memory storage storage for each hemisphere. Objects presented presented in the right visual field, and therefore received in the leh hemisphere, can be named verbally and in writing, indicating the presence of speech comprehension and production as well as writing ability. Objects presented in the l h visual field, and therefore received in the right hemisphere, can not be named verbally or in writing, but can be identified through pointing, indicating that the right hemisphere has language comprehension but not speech or writing. These tests imply that the two hemispheres of the brain have different abilities and functions.

Different visual stimuli presented simultaneously to different visual fields • If differ ent visual visual stimul i are presented presented simulta neously to different visual fields, e.g. a dollar sign to the left, a question mark to the right, and the subject is asked to draw with the leh hand (out of sight) what was seen, the subject draws the stimuli from the left visual field (the dollar sign). If asked what the left hand has just drawn the subject's verbal, leh hemisphere replies with what was seen in the right visual field (the question mark).

EV LU TION Methodological:

alidity Being a natural experiment there is a lack of control over variables - in parti cular the subjects' mental abilities may have been atypical before the operation. to be functional There do seem asymme tries many Theoretical: between the hemispheres. However, research asymmetries has revealed

indivi dual differences - the above findings appear appear most most typical

84

iopsychology

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If two related words are are simulta neously presented presented to the different visual fields, e.g. 'key' to the left and 'case' to the right, the leh hand will select a key from amongst a variety of objects, whereas whereas the right hand will write what it saw in the right visual field (a case) without being influenced by the meaning of the word in the left visual field.

Tactile stimuli stimuli presented to different hands • If an object has been felt by the left hand only, it can be recognised by the left hand again but cannot be named by the subject or recognised by the right hand from amongst other objects. These tests tests i mply that on side of the brain does not know what the other side has seen or f lt

Tests of the non-dominant right hemisphere •

The l h hand can pick out semantically similar objects in a search for an object presented to the left visual field but not present in the search array of objects, e.g. a watch will be selected in response to a picture of a wall clock. The leh hand can sort objects into meaningful categories. • The right brain can solve simple arithmet ical problem s (pointin g out the correct answer) answer) and is superior in drawing spatial relationships. • The right brain appears appears to experienc e its own emotional reactions (giggling and blushing in embarrassment at a nude pin-up presented to the left visual field) and can show frustration at the actions of the left hemisphere.

right-handed men. It should not be forgotten that the leh and right hemispheres hemispheres share many functions and are highly integrated.

Applications: The research has implications for helping patients wit h brain damage. damage. Links: Cortical functions, consciousness, psychosurgery.

 

8 8 Evaluation of neurophysiologica neurophysiologicall findi findings ngs THE LIMITATIONS OF NEUROPHYSIOLOGICAL FINDINGS •

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Neurop hysio logy often often explains the hardwar e and funct ion of different parts of the brain but often ignores the effect of environmental experience upon it. Some studies have looked at this issue, h o w e v ~ r such as Blakemore Cooper's (1970) exposure of animals to environments of vertical lines, and the effect of this on the striate visual cortex. Physiological explanations have not dealt with the mind

hardware of the brain, but on the other hand, this biological complexity may also make a clear and useful explanation of perception impossible if the functions are spread in a parallel way over m illio ns of neu neurone rones. s. Focusing just on the physiology of the brain may lead researchers to ignore the important implications that psychological research and theory has for the functions of

body problem - the they y do not say how the physical structure

brain areas. Hubel and Wiesel's 'bottom-up' description of feature detection in the cells of the visual cortex only focused on the input from the retina, and thus ignored the 'top-down' influences of past experience and expectation that many psychologists such as Gregory (1970) have long pointed out. Recent investigations of the neural activity of cells that respond to the input of visual stimuli are now stressing the importance of the brain's background state of acti activity vity - 'It seems that the output of an individual neurone also depends on what the brain happens to be thinking about about at the time' (McCrone, cited from ew Scientist December 1997). Maunsell and Treue (1996), for example, found the visual movement detection cells of monkeys would show increase increased d activity to moving dots that they had been trained to pay attention to, compared to dots they could see but were not 'interested' in.

and activity of the brain gives rise to the apparently non physical conscious sensations and experience of mental life. There are many limitations of some of the methods used to identify brain activity, e.g. electrical stimulation of the brain may have a spreading activation effect to other areas see methods of investigating brain function). The idea that neuroph ysiolog ical explanations ar are e suffici ent to explain psychological functioning is dubious. In the case of visual perception, for example, Marr (1982) pointed out that the aims and cognitive processes of vision had to be considered rather than just the hardware. Indeed, once the processes by which perception occurs have been identified, the psychologist could change the hardware from the brain to a computer's circuits. There is, however, the possibility that vision could only be achieved by the complex biological

Integration of cortical areas devoted to speaking a written passage

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Retinal information sent to the primary visual cortex is analysed to deted the lines and curves of letters in the text. Words are distinguished in the angular gyrus and transformed into a form that can be recognised and interpreted for meaning by Wernicke's area. Once the written passage has been understood and held in memory, Broca's area is involved in the formation of spoken words and the motor cortex initiates the physical

Motor initiates bodycortex movements

auditory Primary area

Wernicke's area area language comprehension

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Angular wrihen language comprehension

Primary visual area

roca's area

analysis of visual stimuli

language production

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ARGUMENTS AGAINST LOCALISATION OF FUNCTION Localisation is not always dear cut. In the case of brain asymmetry, for example, there are many variations in the location of function in the two cerebral hemispheres between male and female subjects and left and right h a n d e d ~ s u b j e c t s The findings usually reported on the location of cerebral functioning are most representative of right-handed, male subjects. The brain shows 'plasticity'. According to some researchers, the brain is very flexible and can physically adjust the location of function if brain damage occurs (e.g. the recovery of language in children with left cerebral hemisphere damage), or specialisation specialisation to environmental conditions is required e.g. blind Braille readers show an increase in the sensory cortex surface area devoted to the right forefinger, compared to non Braille readers and their own left forefingers).

above shows how just some of the areas involved in language interact in a simple task. Researchers such as Lashley believe in holism - tha thatt many functions functions are distributed across the whole brain. Lashley (1929) destroyed virtually all parts of rat brains in varying amounts to find the location of memory, and concluded that the law of mass action' applied memory loss is related to the amount of damage inflicted upon a rat brain, not the location of it. Neuroscientists are currently accepting the view that the brain is a very dynamic system and that activity in one area of the brain is influenced by the background activity of the rest of the brain. We must 'stop thinking of neurones as if they are exchanging messages ... most of the 5000 input lines to the average brain cell are actually parts of feedback loops returning via neighbouring neurones, or those

The brain is hugely integrated. There are many different brain areas involved in abilities such as vision (Maunsell and Newsome, 1987, proposed there were at least 19 visual areas in macaque monkeys) and research needs to focus on how these areas interact together to produce function. The diagram

higher up the hierarchy. Barely a tenth of the connections come from sense organs or mapping levels lower in the hierarchy. Every neurone is plumbed into a sea of feedback' (McCrone, cited in ew Scientist December, 1997).

Biopsychology 85

 

8.9 The genet genetic ic basi basis s of behaviour GENETIC INFLUENCES ON BEHAVIOUR The inherited basis of human behaviour has long interested philosophers, genetic biologists, psychologists, politicians and the general public, and has generated a great deal of debate and controversy. An understanding of the assumptions and methods of the biological approach in this area can help explain the impl icati ons of research research int o the genetic basis basis of behaviour.

GENETIC RESEARCH METHODS

GENETIC RESEARCH ASSUMPTIONS

FamilylTwin resemblance correlations

Genotype and phenotype o

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The genotype refers to a person person's 's 'genetic blue print '  the total pattern o f chromosomes (each containing thousands of genes) inherited from each parent, with the DNA 'instructions for buil ding a new person'. The phenotype refers to the set of characteristics a realisation or person actually develops - the physical realisation embodiment of the genetic instructions based on the environmental resources available.

Behavioural Behaviour al geneti cs is the attempt to discover the influence of inherited genetic factors on individual differences in behaviour and mental abilities - based on the assumption that genetic factors must influence such characteristics to some extent, since they are produced by bodies which are constructed from the instructions contained in the DNA

Adoption studies

During human human reproduction, a fertilised fertilised egg (zygote) receives 23 chromosomes from the mother and 23 from the father. This means the average number of genes shared by two 'bloo d relatives' can be calculated. average age genetic makeup For example, in terms of aver (genotype), anyone individual shares

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Evaluation With these studies it is difficult to discover the relative effects of genet genetic ic and environmental environmental influences influences - the closer closer the genetic relatedness people have, the more likely they are to share similar family environments (especially for identical twins who are treated more alike than non identical, e.g. brother and sister, twins).

Family genetic relatedness

o

These measure the degree of similari ty (concordance) (concordance) of characteristics between genetically related e.g. parent/offspring, parent/offsp ring, sibling/sibling, etc.) and and unrelated individuals on the assumption that the closer the genetic relationship, the greater the similarity of traits. Comparing the concordance rates of monozygotic and dizygotic twins is particula rly valuable since twins are born at the same time to similar environments, but each type differs in the proportion of genes shared.

Adoption studies help control for the similar environments rela related ted indivi duals are more likely to share, especially if correlations are made between monozygotic twins raised in different families. families. Evaluation Since adoption studies are natural experiments, they can never completely cont rol environmernal eff effect ects, s, e.g. separated twins may be placed in similar adoptive families and still shared womb environment.

100% with a monozygotic same egg)/identical tvv tvvin. in. 50% with a dizygotic (different egg}/fraternal tvvin. 50% with a parent, brother or sister. 25% with a related uncle, aunt, niece or nephew.

Selective breeding studies

Animals with similar characteristics are mated to see if their offspring are more likely to show the trait when raised alone or by parents parents who do not possess it.

Evaluation

Researchers have differed in their assumptions over exactly how strong genetic influences are, creating an over simplified division of nature vs. nurture. n ~ n v i r o n m n t interaction is actually highly complicated, since research shows that: o

o

o

o

 

A variety of environmental factors, from womb and food nutrition to pollution and social stimulation, influence phenotype development from a genotype. Environmental facto factors rs can even affect the genotype itself - sw switc itchi hing ng genes on or off. A single human characteristic can be influenced by many genes (pleiotropy), not all of which may be present or expressed in a particular person. Some genes, e.g. those involved in Huntingdon's disease, have more direct and inevitable effects than others, e.g. those involved in Alzheimer's disease.

86 Biopsychology

Evaluation Controlled human breeding studies are not ethical.

Molecular genetics

Modern technology allows the extraction of genetic material from individuals with a certain characteristic to see how it differs from that of people without the characteristic. This can reveal the coding of the ge es correlated with the characteristics and their location amongst the 46 human chromosomes. Evaluation Molecular genetics research has found that individual s can possess the genes associated with a characteristic, without necessarily developing it themselves.

b  

91

Body rhythms 1

WHAT ARE BODY RHYTHMS AND WHAT CAUSES THEM? Bod}! rhythms are biological processes that show cyclical variation ov r time. Many processes show such cyclical variation in both plants and animals over a variety of time periods, ranging from hours or days to years, and reflect the influence of the Earth's rotation upon its living inhabitants through the physical changes in the environment it produces. Body rhythms seem governed by internal, inbuilt mechanisms (termed 'endogenous (termed 'endogenous pacemakers' pacemakers' or 'bo dy clocks') as well as external environmenta'i stimuli (termed 'zeitgebers' or 'time-givers'). :}

CIRCADIAN

R

YT

MS

Circadian rhythms cycle over 24 hours ('circa' = approximately, 'diem' day). Humans show physiological changes over a 24 hour cycle in hormone levels, body temperature and heart, respiration and etabolic rate. Of most interest to psychologists however, has been the circadian sleep-waking cycle because of the dramatic changes in behaviour it produces.

** * * *

THE SLEEP-WAKING CYCLE The circadian sleep-waking rhythm determines our alertness and activity levels during the day and night. In humans it is regulated by: • The endogenous pacemakers or internal body clock of the suprachiasmatic nucleus SCN) and the pineal gland. The SCN is part of the hypothalamus that regulates sleep-waking patterns by sending messages to the pineal gland to re rele leas ase e melatonin - which is thought to stimulate the production of serotonin in the raphe nucleus to initiate sleep. Removal of the SCN in hamsters randomises their sleep- waking patter patterns. ns. The sleep-waking body clock seems to be the product of evolution and is largely inherited, SCN cells will fire in a rhythmic way even if removed and placed in culture. In humans it seems to naturally run on a slightly longer cycle than a day (around 25 hours) but there seem to be inherited individual differences between people. If the SCN of mutant hamsters which causes different sleep-waking patterns is transplanted into normal hamsters who have had their SCN removed, they adopt the mutant's circadian patterns. The sleep-waking circadian rhythm can be adjusted to a certain degree by zeigebers, but seems mostly regulated by the internal body clock. •

The major ex external ternal re-setter (zeitgeber) (zeitgeber) of the circadian body clock in humans is light, which is detected at the retina and can influence (via interconnecting nerve fibres) the SCN to synchronise our rhythms to the 24 hour cycle of the day. This has been demonstrated by studies that have removed the zeitgeber of light such as Siffre s cave study. However, while the cycle/rhythm can slowly adjust to new starting points as happens when zetigebers change due to human activities such as shift work or travel over time zones) and can be resisted with a struggle e.g. in sleep deprivation studies) the basic pattern or ratio of sleep-wa sleep-waking king activit y is remarkably consistent due to its biological basis. Similar sleep-waking patterns are found cross-culturally, despite cultural zeitgebers such as siestas and environmental zeitgebers in countries who experience whole summers or winters of lightness and darkness (such as those in the arctic circle). The inflexibility of the rhythm has also been demonstrated under controlled laboratory conditions, where exposure to different ratios of light and dark hours do not affect the sleeping patterns of subjects beyond certain limits.

PSYCHOLOGICAL AND PHYSIOLOGICAL CHANGES

OF

THE CIRCADIAN RHYTHM PHYSIOLOGICAL CORRELATES

PSYCHOLOGICAL EXPERIENCE WAKING

STATES

(Approx. 16 hours) hours) SLEEP STATES

l

(Approx. 8 hoursaround 80 NREM 20% REM in adults}

Alertness - involves open-eyed active consciousness ith the full ability to concentrate on a task. Relaxation - involves a passive but awake conscious xperience although the eyes may be shut shut..

EOG

EEG

EMG

Beta waves 13 hertz or above) Alpha waves 8 to 12 hertz)

Eye movements reflect task Eye movements reflect cogni tion

Muscle activity reflects task Muscle activity reflec reflects ts relaxation

Stage 1: Lightest stage of sleep. Easily awakened.

Theta waves (4-7 hertz)

Slow rolling eye movements

Muscles relaxed but active

Stage 2: Light sleep. Fairl Fairly y easily awakened. Some responsiveness to external and internal sti_muli - name calling produc produces es K-complex activity.

Theta waves sle sleep ep spindles spindles,, K-complexes K-complexes

Mini mal ey eye e movement

Little musc musc Ie

Stage 3: Deep sleep. Difficult to awaken. Very unresponsive to external stimul i.

Delta waves (1-3 Hz) 20-5 0% of the time

Virtuall y no eye movement

Virtuall y no muscle movement

Stage 4: Very deep sleep. sleep. Very dif fic ult to awaken. Very unresponsive to external stimuli.

Delta waves waves over 50% of the time

Virtua lly no

eye movement

Virtuall y no muscle movement

High levels of

Eye movement

Muscles in a

mixed wave brai brain n activ activity ity

- may may ref reflec lectt dre rea am co cont nten entt

state of virtual paral araly ysi sis s

NON-REM SLEEP - involves a se serie ries s of stages.

EM SLEEP It is difficult to awaken people from rapid

sleep. p. If woken, indi vidua ls report eye-movement REM) slee vivid dreaming far more often than if wo woke ken n fr from om nonnonREM sleep (Dement and Kleitman, 1957).

movement

Biological rhythms and sleep 87

 

9.2 Disrupt Disrupting ing biological rhythms

""

WHAT PHYSIOLOGICAL CONCEPTS ARE RELEVANT? Physiological research into body rhythms such as the human sleep-waking circadian rhythm has revea revealed led that both inner biologi cal factors endogenous pacemakers or body clocks) and external environmental factors zeitgebers) can influence our pattern of sleeping and waking activity. However, research has also shown that the sleep-waking body clock is fairly consistent and slow to adjust, while zeitgebers such as natural body rhythms and work patterns and travel across time zones can change very quickly. Such a mismatch between our natural activity patterns can produce negative effects, which have been investigated by physiologically orientated psychologists. The pattern adjustment is also important. Siffre, a French cave explorer, spent 6 months in a cave underground which effectively removed the external zeitgebers of the world above such as light levels and human activity patterns. No time cues were given via his telephone telephon e contact wit h the outside outside world and artificial lights were switched on when he woke up and off when he fell asleep. Under these conditions his natural body rhythms lengthened to around 25 hours so by the time he left the cave he had experienced fewer 'days' than everyone else. This means that adjustment to new zeitgebers is easier if they involve a lengthening of the day, since the circadian cycle itself seems to have a natural tendency to lengthen.

SHIFT WOR Much shift work has involved three 8-hour working period periods s rotating rotatin g anti-clockwise, e.g. from night shift to evening shift to day shift a 'phase advance' rather than 'phase delay' schedule), frequently on a weekly basis or less. Physiological research on body rhythms informs us this can produce long-term disorientation, stress, insomnia, exhaustion and negative effects on reaction speed, co-ordination skill, attention and problem solving, since such work schedules: 1 Create Create a mismatch or desynchronisatio n between the the body

Worst order of shift rotation (phase advance)

Best order of shift rotation (phase delay)

rhythms of arousal and the zeitgebers of activity levels. Do not allow enough adjustment time for body rhythms to catch up with (become 'entrained' by) new activity levels. 3 Delay the the catching up (entrainment) of body rhythms by shortening rather than lengthening the day. This increases the chances of accidents occurring due to human error, even when other factors such as reduced hours of sleep, night-time supervision levels, etc. are taken into account. Czeisler t al (1982) studied a group of industrial workers who were following such a shift pattern and their suggestion that they moved clockwise in shifts a phase delay schedule) on a three week rather than one week basis led to better worker health and morale, as well as higher producti vity lev levels els.. 2

l

I I

JET LAG Rapid air travel across across time zones can produce jet lag - general disorientation and symptoms similar to those described for shift work, though not always as severe. This also: 1 Results from a mismatch or desynchronisation between the body rhythms of the old time zone, stored in the body clock you take with you, and the zeitgebers of the new time zone, such as human activity levels e.g. mealtimes) and light levels. 2 Is harder to adjust to if the zeitgebers shorten the day and the circadian cycle - causing causing a phase phase advance advance.. This explains why rapid travel from the west to the east across many time zones tends to produce worse jet lag than travelling from east to west (which lengthens the day ar:td causes phase delay). The influence of zeitgebers and endogenous pacemakers on jet lag are harder to identify since many other variables involved in travelling could cause the symptoms, such as stress, excitement, unfamiliarity and restricted posture. Slower travel over fewer time zones as well as taking drugs that affect melatonin act ivity at appropriate times may reduce the severity of jet lag symptoms.

88 Biological rhythms and sleep

 

9.3 Body rhythms 2 PSYCHOLOGICAL AND PHYSIOLOGICAL PHYSIOLOGICA L CHANGES CIRCANNUAL RHYTHMS (Rhythms lasting about a year)

• '

INFRADIAN RHYTHMS





(Rhythms lasting longer than 24 hours) of n



ly)

THE ROLE OF EN OGENOUS

PACEMAKERS AND ZEITGEBERS

Much behaviour in animals varies over a yearly



cycle, such as hibernation, mating and migration. Some humans show Seasonal Affective Disorder (SA (SAD) D) - a strong variat ion in m ood over the year, year, usually involving depression during the winter months.



The infradi an rhythm of menstruation in women occurs over a 28-day cycle and is associated with physiological changes and discomfort relating to the shedding of the lining of the uterus wall and the behavioural changes of pre menstrual syndrome PMS). The psycholo gical effects effects that are suggested to occur begin around five days before menstruation in some women and can include mood change, irritability, dizziness and changes in energy levels and eating habits. habits. The severity severity of the physiological symptoms varies among women and the extent of psychological changes





associated with PMS has been the subject of some debate between psychologists.

ULTRADIAN RHYTHMS

DIURNAL (day) RHYTHMS



(Rhythms lasting less than 24 hours) •

 

ift

k e,

jthe

e east .

jet in ent, that e

Individuals seem to vary in their activity levels, some being more alert and receptive to information in the morning, others in the evening. Horn e and Osterberg (1976) used their 'Morningness-Eveningness' questionnaire to confirm this distinction, although research findings on the effect of time of day upon performance have been mixed.

NOCTURNAL (night) RHYTHMS • The stages of sleep are cycled through around 5 times per night in the following way: Relaxation Relax ation to first cycle - may involve hypnagog hypnagogic ic experiences, e.g. dream images or falling sensations. Firs Firstt cycle - Desc Descent ent to deep deep stage 4 sleep (which lasts approx. 40 minutes), ends with a short REM period. Second Second cycle - Gradual descent descent to deep deep stage 4 sleep slee p ( approx. minutes), ends with a short REM period. Third Thir d cycle cycle - Most Mostly ly stage 2Jleep followed by up to 40 minutes of REM sleep. Fourth Fou rth cyc cycle le - Arou Around nd an hour of stage 2 sleep followed by around an hour of REM sleep. Fifth cycle - Stage 2 sleep followed by a shorter REM period or waking (possibly with hypnagogic experiences). • The level of dreaming and alertness is determined by when during the cycles a person is awoken . The deepest NREM NREM sleep usuall y of occurs in the first half a night, while the most vivid dreaming REM sleep usually occurs in the second half.

A key external zeitgeber that regulates physiology and behaviour in yearly cycles is light levels. Greater winter darkness darkness stimulates stimulates th the e pineal gland to produce produce melatonin - a hormone involved in controlling energy levels and mood. However , many environmental an and d psychological factors can lead to winter depression, e.g. the colder weather.

The endogenous pacemaker of tthe he pitu itar y gland and its triggering of hormones such as prostaglandin internally regulate the menstrual cycle. The endogenous regulation of PMS via cycles in the endocrine system is supported by the finding of PMS cross-culturally. The menstrual cycle can can be quite variable at first and is open to modification by external stimuli - ., zeitgebers such as light levels levels (indicating a role for melatonin) and the presence of other women (studies show frequent interaction with particular women can cause synchronisation of menstruation, possibly due to pheromonesreleased chemically active scents). Since not all women experience it, PMS may result from psychologica I factors factors too.





Morning types seem to reach their physiological peak as measured by body temperature, metabolic rate, etc.) earlier than evening types, indicating perhaps a 'phase advance' in their endogenously regulated circadian rhythms (Marks and Folkhard, 1985). However, these variations could be the result (rather than the cause) of zeitgebers such as the subject's lifestyle and activity levels during the day.



The ultradian rhythm of alternating NREM and REM sleep results from the alternating activity of the endogenous pacemakers of the: raphe nuclei (which releases inhibiting, NREM sleep-producing serotonin) and 2 locus coeruleus (which releases activating, REM sleep inducing acetylcholine and noradrenaline). • Destruction of the locus coeruleus stops REM sleep • Destruction of the raphe nuclei causes sleeplessness • Zeitgebers like alcohol can disrupt the cycle.

Awake Stage 1 Stage 2 Stage 3 Stage 4 Hours

2

3

4

5

6

7

Biological rhythms and sleep 89

 

9.4 'The re relation lation of eye movemen movements ts durin during g sleep to dream activity: an objective method for the study of dreams' Dement and 'Kleitman (1957) AIM



Aserinsky and Kleitman found a relationship between rapid eye movement REM) during sleep and reports of dreaming. Dement and Kleitman aimed to provide a more detailed investigation of how objective, physiological aspects of rapid eye movement relate to the subjective, psychological experience of dreaming reported by subjects, by testing whether:

METHOD

Subjects: 7 adult males and 2 adult females females - 5 of

which were

intensively studied, 4 of which were used to confi rm result results. s.

Design: Laboratory experimentation and observation. Procedure: Subjects slept individually in a quiet dark laboratory room after a normal day's activity (except that alcohol and caffeine were avoided during the days before testing). Electrodes were connected near the eyes to register eye movement and on the scalp to measur measure e brain waves dur ing slee sleep p - these these were th the e





significantly more dreaming occurs during REM sleep than non-REM sleep under controlled conditions. there is a significant positive correlation between the objective length of time spent in REM and the subjective duration of dreaming reported upon waking. there is a significant relationship between the pattern of rapid eye movements observed during sleep and the content of the dream reported upon waking.

objective measures of REM sleep. Subjects were awoken at various times during the I'light (fairly evenly distributed across the average sleeping time of the subjects) by a loud doorbell noise, and immediately reported into a recording device whether they had been dreaming and the content of the dream efore any contact with the experimenter to avoid bias). Subjects were never usually told whether their eyes had been moving before being awoken. Dreaming was was only counted if a fairly detailed and coherent dream was reported - vague impressions or as assertion sertions s of dreaming without recall of content were not counted.

STUDY ONE

STUDY TWO

STUDY THREE

Subjects were awoken in one of four different ways during either REM or non REM sleep, and were compared to see if

Subjects were awoken either 5 or 15 minutes after REM sleep began and were asked to decide whether the duration of

Subjects were awoken as soon as one of four patterns of eye movement had occurred for 1 minute, and were asked

they had been dreaming. • 2 subjects subjects were awoken randomly • 1 subject was was awoken during 3 REM sleep periods followed by 3 non-REM periods, and so on • 1 subject wa was s awoken randomly, but was told he would only be awoken during periods of REM sleep • 1 subject was was awoke n at at the whim of the experimenter

their dream was closer to 5 or 15 minutes. The length of the dream (measured in terms of the number of words in their dream narratives) was also correlated to the duration of REM sleep before awakening.

exactly what they had just dreamt. ainly vertical eye movements • ainly horizontal eye movements • • Bot Both h vertical and horizont al e eye ye movements. • Very little or no eye movement

RESULTS

Generally, REM periods were clearly observed in all subjects and distinguished from non-REM sleep periods. REM sleep periods occurred at regular intervals specific to each subject (although on aver average age occur ring every 92 minutes) and tended to last longer later in the night.

STUDY ONE Regardless of how subjects were awoken, significantly more dreams were reported in REM than non-REM sleep. When subjects failed to recall dreams from REM sleep, this was usually early in the night. When subjects recalled dreams from non-REM sleep it was most often within 8 minutes after the end of a REM period.

STLlDYTWO

Subjects were significantly correct in matching the duration of their dream to length of time they had shown REM sleep for both the 5-minute periods 45 out of 51 estimates correct) and 15-minute periods (47 out of 60 estimates correct). All subjects showed a significant positive correlation at the P< 0.05 level or better between the length of their dream narratives and duration of REM sleep before awakening.

STUDY THREE There was a very strong association between the pattern of REMs and the content of dream reports. • The 3 verti cal REM periods were associ associated ated with dreams of looking up and down at cliff faces, ladders, and basketball nets. • A dream of two people throwing tomatoes at each other occurred in the only mainly horizontal REM period. • 21 periods of vertical and horizontal REMs were associated with dreams of looking at close objects. • 10 periods of very little or no REMs were associated with dreams of looking at fixed or distant objects.

..

EVALUATION Methodological: Dreams may be recalled easier in REM than non-REM sleep because the latter is a deeper stage of sleep  perhaps dreams occur in deeper sleep, but are more difficult to recall from it.

9

Biological rhythms and sleep

The study used a limited sample, mostly men, therefore showed a lack of generalisability.

Theoretical: The research provides support for the idea that dreams can be studied in an objective way. This then opens up areas of research for the effect of environmental stimuli on dreaming.

Links: Sleep and dream research. Laboratory studies.

5

 

9.6 Theories of the function of sleep SLEEP DEPRIVATION

IS

SLEEP NEEDED?

ANIMAL STUDIES:

HUMAN STUDIES:







9

Jouvet (1967) depri ved cats of sleep by putting them on a floating island in a pool of water so that when they fell asleep they fell in and woke up. The cats deve'loped abnormal behaviours and eventually died. Rechtschaffen et at deprived rats of sleep. They had all died after 33 days.



Psychological effects effects - increased desire to sle sleep ep,, diff icult y sustaining sustaining attention (however, (however, problem solving is less impaired), delusions, and depersonalisation. Physiological Physiological e effe ffects cts - minor chang changes, es, such such as problems with eye focusing, but no significant major adverse effects. Sleep after deprivation is not cumulative (not much longer th than an usual), usual), although more time is

I

spent in REM sleep a REM rebound effect). However, sleep deprivation studies are not indefinite.

v

THEORIES

OF

sel

SLEEP FUNCTION

in

RESTORATION THEORY

MEMORY

Oswald (1966) suggests that the function of sleep, especially REM sleep, is simply to restore bodily energy reserves, repair the condition of muscles and cells and to llow growth to occur. Sleep could also llow brain neurotransmitters to replenish and aid psychological recovery.

THEORY

Evaluation

Evaluation

For





Longer sleep sleep (part icular ly stage 4) occurs after large amounts of physical exercise, and in growing children REM occupies 50% of sleep in babies, 20% in adults). Growt h hormones are released during stage 4 sleep, deprivation of which



causes physical problems such as fibrositis. Sleep is greater after periods of stress and improves mood.

Against • Sleep duration is not reduced with lack of exercise. • Deprivation of REM sleep does not produce significantly adverse effects. • REM sleep involves an increase in energy expenditure and blood flow which inhibits protein synthesis.

CONSOLIDATION

Empson and Clarke (1970) propose that sleep, especially REM sleep, Facilitates the reinForcement of information in memory. For



Subjects exposed exposed to info rmat ion before sleep remember less in the morning if deprived of REM sleep rather than non REM sleep.



Perhaps more REM sleep occurs in younger humans because they have more to learn.

Against • There is little evidence against the theory, but memory consolidation can occur without sleep.

Z Z

EVOLUTIONARY EVOLUTIO NARY THEORY

Z

Z

Evaluation

All mammals sleep (the porpoise even shuts down one side of its brain at a time to do so), although the length of time varies according to the species. Given its universal nature and the fact that this unconscious and defenceless state seems a dangerous behaviour to show, sleep probably has an important evolutionary survival function, possibly to • conserve energy when food gather ing has been completed or is more difficult e.g. at night), and/or • avoid damage damage from nocturnal predators or accidents by

Lions (whi ch have few predators and meet their food needs needs in short bursts) and squirrels (who have safe burrows) sleep longer. • Cattle (whi ch have have many natural p{edators) and shrews (which hav have e high metabolic rates)sleep rates)sleep very little. Against • Some Some evolu tion ary arguments arguments sugges suggestt that animals who are highly preyed upon need to sleep little to keep constant

remaining motionless. Meddis (1975) suggests the duration of sleep a species shows depends upon its food requirements and predator avoidance needs.

vigilance for predators, however others suggest the opposite - that they n need eed to sleep sleep longer to keep keep them away from harm by remaining motionless.

92 Biological rhythms and sleep

For



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