Lecture 2: Techniques

Question 1

Methods of visualising and stimulating the living human brain

Answer 1

X ray photography is effective in characterising internal structures that differ substantially from their surroundings in the degree to which they absorb x –rays

Question 2

Methods of visualising and stimulating the living human brain

Contrast X-rays

Answer 2

Techniques involve injecting into one compartment of the body a substance that absorbs X –rays either less than or more than the surrounding tissue

• Injected substance heightens the contrast
• Cerebral Angiography: Uses infusion of a radio-opaque dye into a cerebral artery to visualise the cerebral circulatory system during x ray photography, most useful for localising vascular damage but the displacement of blood vessels from their normal position can also indicate the location of a tumour

Question 3

Methods of visualising and stimulating the living human brain

X-Ray Computed Tomography (CT):

Answer 3

Computer assisted X-ray procedure that can be used to visualise the brain and other internal structures of the living body (uses x-rays to create a CT scan of the brain)

• Patient lies with head positioned in centre of large cylinder
• On one side of cylinder is x-ray tube that projects an x-ray beam through the head to an x-ray detector mounted on the other side, tube and detector automatically rotate around head of patient at one level of brain, takes many individual x-ray photographs as they rotate
• Info from each photograph is combined by computer to generate CT scan of one horizontal section of the brain
• X-ray tube and detector are moved along axis of patient’s body to another level of brain and process repeated
• Scans of 8/9 horizontal brain sections are typically obtained producing 3D representation of brain

Question 4

Methods of visualising and stimulating the living human brain

Magnetic Resonance Imaging:

Answer 4

Procedure in which high resolution images are constructed from measurement of waves that hydrogen atoms emit when they are activated buy radio-frequency waves in a magnetic fiend

• Provides clearer images of brain than CT, provides relatively high spatial resolution (ability to detect and represent differences in spatial location)
• Structural MRI used to provide 3D images of entire brain

Question 5

Methods of visualising and stimulating the living human brain

Positron Emission Tomography:

Answer 5

First brain imaging technique to provide images of brain activity (functional brain images) rather than images of brain structure (structural brain images)

• Radioactive 2-deoxyglucose (2-DG) injected into patient’s carotid artery (artery of neck that feeds ipsilateral cerebral hemisphere), because of its similarity to glucose it is rapidly taken up by active cells, unlike glucose is not metabolised, accumulates in active neurons or associated astrocytes until it is gradually broken down
• Each PET scan taken of a patient who engages in 30 seconds of reading after injection will indicate areas most active during 30 seconds of activity
• Scan is coloured map of amount of radioactivity in each of the tiny cubic voxels (volume pixels) composing each scan
• Exactly how each voxel maps onto particular brain structure can be estimated by superimposing scan on brain image

Question 6

Methods of visualising and stimulating the living human brain

Functional MRI (fMRI):

Answer 6

• Most influential tool of cognitive neuroscience
• Produces images representing increase in oxygen flow in blood to active areas of brain
• Active areas take up more oxygenated blood than they need for energy requirements, oxygenated blood accumulates in active areas of brain, has magnetic properties (oxygen influences effect of magnetic fields on iron in blood), signal recorded is BOLD (blood oxygenation level dependent signal)

4 advantages over PET:
Nothing has to be injected, provides both structural and functional information in same image, spatial resolution is better, can be used to produce 3D images of activity over entire brain

Too slow to capture neural responses, takes 2-3 seconds to create image, neural responses i.e. action potentials however occur in milliseconds

Question 7

Methods of visualising and stimulating the living human brain

Magnetoencephalography (MEG):

Answer 7

Measures changes in magnetic fields on surface of scalp produced by changes in underlying patterns of neural activity

• Advantage over fMRI is temporal resolution, can record fast changes in neural activity

Question 8

Methods of visualising and stimulating the living human brain

Transcranial Magnetic Stimulation:

Answer 8

Used to show correlation between brain activity and cognitive activity but cannot prove causation as there are many explanations

• Is a technique for affecting the activity in an area of the cortex by creating a magnetic field under a coil positioned next to the skull
• Magnetic stimulation temporarily turns off part of brain while the effects of the disruption on cognition and behaviour are assessed
• Questions about depth of effect, safety and mechanisms of neural disruption although is often used to get around difficulty that brain imaging studies have in determining causation

Question 9

Recording Human Psychophysiological Activity:

Scalp Electroencephalography (EEG):

Answer 9

Measure of the gross electrical activity of brain

• Recorded through large electrodes electroencephalograph (EEG machine)
• EEG activity recorded from disk shaped electrodes which are taped to scalp
• Signal reflects electrical events throughout head
• Events include action potentials, electrical signals from skin, muscle, blood, eyes and post synaptic potentials
• Diagnostic tool based on fact some EEG wave forms are associated with particular states of consciousness/particular types of cerebral pathology e.g. alpha waves with wakefulness, epilepsy
• EGG signals decrease in amplitude as they spread form source, comparison of signals recorded from various sites on scalp can sometimes indicate origin or particular waves, usual to record EEG activity from many sites simultaneously
• Interested in EEG waves that accompany certain psychological events (Event Related Potentials ERPs) than background EEG signals, commonly studied ERP is sensory evoked potential (change in the cortical EEG signal elicited by momentary presentation of sensory stimulus)
• Signal is part of any recording that is of interest, noise is part that isn’t
• Problem in recording sensory evoked signals is that the noise is often so great sensory evoked potential is masked
• Method to reduce noise of background EEG is signal averaging, when averages are plotted average response is apparent (background EEG cancelled out)
• Analysis of average evoked potentials (AEPs) focuses on various waves in averaged signal, each wave is characterised by direction, positive or negative and latency
• First few milliseconds after stimulus not influenced by meaning of stimulus for subject, small waves are far-field potentials because although they are recorded from scalp they originate far away in sensory nuclei of brain stem
• Score high on temporal resolution, computer software and many electrodes can accurately locate source of signal (spatial resolution)
• Spatial resolution is sufficient to enable evoked EEG signals recorded on cortex to be colour coded and plotted on surface of 3D MRI scan

Question 10

Recording Human Psychophysiological Activity:

Muscle Tension:

Answer 10

• Muscle fibres contract in all or nothing fashion when activated by motor neuron
• At any given time a few fibres in each resting muscle are likely to be contracting which maintains overall tone (tension) of muscle
• Movement results when large number of fibres contract at same time
• People who are anxious typically display high resting levels of tension in muscles (measure can be indicator of psychological arousal)
• Electromyography measures muscle tension (EMG), activity recorded between 2 electrodes taped to surface of skin over muscle of interest
• Increase in muscle contraction is an increase in amplitude of raw EMG signal reflecting number of muscle fibres contracting at any one time
• Raw EMG signals are converted into more workable forms, fed into computer that calculates total amount of EMG spiking per unit of time, integrated signal (total EMG activity per unit of time) is plotted resulting in smooth curve with simple continuous measure

Question 11

Recording Human Psychophysiological Activity:

Eye Movement:

Answer 11

• Electrooculography: Electro physical technique for recording eye movements producing an Electrooculogram (EOG)
• Based on fact there is a steady potential difference between the front (positive) and back (negative) of the eyeball, when eye moves change in electrical potential between electrodes placed around eye can be recorded
• Usual to record EOG activity between 2 electrodes placed on either side of eye to measure its horizontal movements and between two electrodes placed above and below eye to measure vertical movements

Question 12

Recording Human Psychophysiological Activity:

Skin Conductance:

Answer 12

• Emotional thoughts and experiences are associated with increases in the ability of the skin to conduct electricity
• Indexes of electrodermal activity are skin conductance level (SCL) and skin conductance response (SCR)
• SCL is measure of background level of skin conductance associated with particular situation
• SCR measure of transient changes in skin conductance associated with discrete experiences
• Sweat glands are active in emotional situations particularly hands, feet, armpit, head

Question 13

Recording Human Psychophysiological Activity:

Cardiovascular Activity:

Answer 13

• Blood vessels and heart (circulatory system)
• Heart Rate: Electrical signal associated with each heartbeat can be recorded through electrodes placed on chest, produces electrocardiogram (ECG) average resting heartrate for healthy adult is 70bpm
• Blood Pressure: Peak pressure during contraction (systoles) divided by measurement of minimum pressure during periods of relaxation (diastoles), expressed as millimetres of mercury mmHg, normal resting blood pressure is 130/70, chronic blood pressure of 140/90 is hypertension
• Blood Volume: Chances in volume of blood in particular parts of body measured by plethysmography techniques, one method involves wrapping strain gauge around target tissue although possibilities for employing are limited i.e. to fingers, other method is shine light through tissue under investigation, measure amount of light absorbed by it, more blood there is more light it will absorb

Question 14

Recording Human Psychophysiological Activity:

Stereotaxic Surgery:

Answer 14

• Means by which experimental devices are precisely positioned in depths of brain, requires atlas to provide direction to target site and instrument for getting there
• Stereotaxic atlas used to locate brain structures, represented by series of individual maps one per page each representing structure of single 2D brain slice, all distances given in mm from designated reference point (bregma) point on top of skulls where 2 major sutures (seams in the skull) intersect

Question 15

Recording Human Psychophysiological Activity:

Lesion Methods:

Answer 15

• Part of brain removed, damaged or destroyed then behaviour of subject carefully assessed in effort to determine functions of lesioned structure

Aspiration Lesions:
When a lesion is to be made in a area of cortical tissue that is accessible to the eyes and instruments of the surgeon, frequent method of choice, cortical tissue drawn off by suction through fine ripped handheld glass pipette, underlying white matter more resistant to suction than cortical tissue itself, skilled surgeon can delicately peel off layers of cortical tissue from surface of brain leaving underlying white matter and blood vessels undamaged

Radio Frequency Lesions:
Small subcortical lesions commonly made by passing radio frequency current (high frequency current) through the target tissue from tip of stereotaxically positioned electrode, heat from current destroys tissue, size and shape of lesion are determined by duration and intensity of current and configuration of electrode tip

Knife Cuts:
Sectioning (cutting) used to eliminate conduction in nerve or tract, tiny well placed cut accomplish task without producing extensive damage to surrounding tissue

Cryogenic Blockade:
Alternative to destructive lesions, coolant pumped through implanted cryoprobe, neurons near tip cooled until stop firing, temperature maintained above freezing level, no structural damage, tissue allowed to warm up, normal neural activity continues

• ‘Reversible lesions’
• Microinjections into the brain –> local anaesthetics (Lidocaine)

Question 16

Recording Human Psychophysiological Activity:

Interpreting Lesion Effects:

Answer 16

Difficult to interpret, structures of brain are small, convoluted and tightly packed together, high skilled surgeon cannot destroy a structure without producing significant damage to adjacent structures

Question 17

Recording Human Psychophysiological Activity:

Bilateral and Unilateral Lesions:

Answer 17

• Unilateral lesions (lesions restricted to one half of the brain) are milder than symmetrical bilateral lesions (lesions involving both sides of brain) particularly in non-human subjects
• Behavioural effects of unilateral lesions can be difficult to detect, most lesion effects are studies of bilateral

Question 18

Recording Human Psychophysiological Activity:

Electrical Stimulation:

Answer 18

• Function of neural structure obtained by stimulating electrically
• Stimulation delivered across 2 tips of bipolar electrode
• Weak current pulses produce immediate increase in firing
• Behavioural effects opposite to those produced by lesion to same site
• Can elicit eating, drinking, attacking, copulating, sleeping, depends on location of electrode tip and test environment

Question 19

Invasive Electrophysiological Recording Methods:

Intracellular Unit Recording:

Answer 19

• Provides a moment by moment record of graded fluctuations in one neurons membrane potential
• Mostly used on chemically immobilised animals, impossible to keep tip of microelectrode positioned inside neuron of freely moving animal

Question 20

Invasive Electrophysiological Recording Methods:

Extracellular Unit Recording:

Answer 20

• Microelectrode tip positioned in extracellular fluid, each time neuron fires electrical disturbance occurs, blip recorded, provides record of firing of neuron but no info about neuron’s membrane potential
• Difficult to record extracellularly from single neuron in free moving animal, can be accomplished with special flexible microelectrode
• Can now simultaneously record extracellular signals from 100 neurons

Question 21

Invasive Electrophysiological Recording Methods:

Multiple-Unit Recording:

Answer 21

• Electrode tip much larger, picks up signal from many neurons, slight shifts due to movement of subject have little effect on overall signal
• Many action potentials integrated by circuit

Question 22

Invasive Electrophysiological Recording Methods:

Invasive EEG Recording:

Answer 22

• Lab animals, EEG recorded through large implanted electrodes rather than scalp electrodes
• Cortical EEG recorded through stainless steel skull screws
• Subcortical EEG signals recorded through stereotaxically implanted wire electrodes

Question 23

Pharmacological Research Methods:

Routes of Drug Administration

Answer 23

• Fed
• Injected through tube into stomach (intragastrically)
• Injected hypodermically into peritoneal cavity of abdomen (intraperitoneally, IP) into large muscle (Intramuscularly, IM), into fatty tissue beneath skin (subcutaneously, SC) or into large surface vein (intravenously, IV)

–>Problem with peripheral routes: Many drugs do not readily pass through blood-brain barrier, to overcome this drugs can be administered in small amounts through fine hollow tube (Cannula) that has been stereotaxically implanted in brain

Question 24

Pharmacological Research Methods:

Selective Chemical Lesions:

Answer 24

• Inject neurotoxins (neural poisons) that have affinity for certain components of nervous system
• Kainic acid or Ibotenic acid administered by microinjection, taken up by cell bodies at tip of cannula, destroys those neurons leaving neurons with axons passing through area unscathed
• 6-hydroxydopamine (6-OHDA) taken up only by neurons that release norepinephrine or dopamine, leaves other neurons at injection site undamaged

Question 25

Pharmacological Research Methods: Measuring Chemical Activity of Brain:

Answer 25

• 2-Deoxyglucose Technique: - Place animal injected with 2-DG in test situation in which it engages in activity of interest, taken up by active neurons but not metabolised, subject killed, brain removed and sliced, subjected to autoradiograph (coated with photographic emulsion, stored in dark for few days, left to develop), areas of brain that absorbed high levels of radioactive 2-DG appear as black spots on slides, density in various brain regions can then be colour coded • Cerebral Dialysis: - Method of measuring extracellular concentration of specific neurochemicals in behaving animals, fine tube with short semipermeable section implanted in brain, semipermeable section positioned in brain structure of interest so extracellular chemicals from structure will diffuse into tube, can be collected, frozen and stored for later analysis, carried in solution directly to chromatograph (device for measuring chemical constituents of liquids and gases)

Question 26

Pharmacological Research Methods: Locating Neurotransmitters and Receptors in the Brain:

Answer 26

• Immunocytochemistry: - Procedure for locating particular neuroproteins in brain by labelling their antibodies with dye or radioactive element and exposing slices of brain tissue to labelled antibodies, regions of dye/radioactive accumulation in brain mark locations of target neuroprotein - Foreign protein (antigen) injected into animal, animals body creates antibodies, bind to antigen, stock antibodies created of brain’s peptide neurotransmitters (neuropeptides) and receptors by neurochemists - Can be used to locate neurotransmitters by binding to their enzymes, done by exposing brain slices to labelled antibodies that bind to enzymes located only in neurons that contain neurotransmitter of interest • In Situ Hybridisation: - Nucleotide base sequences that direct synthesis of many neuroproteins identified, hybrid strands of mRNA with complementary base sequences artificially created, hybrid mRNA with complementary base sequence that directs synthesis of target neuroprotein obtained, hybrid RNA strands labelled with dye or radioactive substance, brain slices exposed to labelled hybrid RNA strands, bind to complementary mRNA strands marking location of neurons that release target neuroprotein

Question 27

Genetic Engineering: Gene Knockout Techniques:

Answer 27

- Procedures for creating organisms that lack a particular gene under investigation - Mice favoured mammal to be subjects (knockout mice) - Studies conducted to clarify neural mechanisms of behaviour - Melanopsin knockout mice research found Melanopsin contributes to control of circadian rhythms by light but is not only factor

Question 28

Genetic Engineering: Gene Replacement Techniques:

Answer 28

- Pathological genes from human cells can be inserted in other animals (e.g. mice, produce transgenic mice) - e.g. injecting human gene associated with schizophrenia into mice, transgenic mice displayed cerebral abnormalities (reduced cerebral cortex, enlarged ventricles) and abnormal behaviour, confirmed defective gene was causal factor of schizophrenia - Gene can also be replaced with one that is identical except for addition of few bases that can act as a switch (on/off) for gene at particular point in development, can mean faulty genes can be replaced in patients suffering from genetic disorders

Question 29

Genetic Engineering: Fantastic Fluorescence and the Brainbow:

Answer 29

- Green fluorescent protein (GFP) exhibits bright green fluorescence when exposed to blue light - Activate particular cells under investigation so that they can be readily visualised - Accomplished by inserting GFP gene in only target cells or by introducing GFP gene in all cells of subject but expressing the gene in only the target cells - Has now been expressed in many plant and animal species including humans, minor alterations mean GFP gene can synthesise proteins that fluoresced different colours, each labelled neuron has distinctive colour, produces Brainbow

Question 30

Behavioural Research Methods of Biopsychology

Answer 30

Produce behavioural paradigms, behavioural phenomenon under investigation and objective method for measuring it

Question 31

Behavioural Research Methods of Biopsychology: Neuropsychological Testing:

Answer 31

-Time consuming, prescribed to small portion of brain damaged patients, can help by assisting diagnosis of neural disorders, serve as basis for counselling and care, provides basis for objectively evaluating effectiveness of treatment and seriousness of side effects •Single-Test Approach: Detect presence of brain damage, discriminate between patients with psychological problems resulting from structural brain damage and those with psychological problems resulting from functional rather than structural changes to brain •Standardised-Test-Battery Approach: Used to identify brain-damaged patients but involves sets of test not just one, Halstead-Reitan is test that tends to be performed poorly by brain damaged patients in relation to healthy controls, scores on each added to make aggregate score, average aggregate below designated cut off leads to diagnosis, not so good at discriminating between neurological patients and psychiatric patients •Customised-Test-Battery Approach: Used to characterise nature of psychological deficits of each brain damaged patient, battery of tests selected to provide general nature of neuropsychological symptoms, customised tests then selected, specifically designed to measure aspects of psychological function that have been spotlighted by modern theories and data -Interpretation does not rest entirely on how good patient does, brain damage often changes strategy that neuropsychological patient uses without lowering score, requires right battery tests to expose deficits and qualitative differences in cognitive strategy

Question 32

Behavioural Research Methods of Biopsychology: Tests of Common Neuropsychological Test battery:

Answer 32

• Intelligence: - IQ poor measure of brain damage, general intelligence always included however in battery e.g. Wechsler Adult Intelligence Scale (WAIS), knowing patients IQ helps interpret results of subsequent tests, can draw inferences e.g. low scores verbal indicates damage on left hemisphere • Memory: - WAIS fails to detect memory deficits despite including digit span and information subtests however both forms of memory are least likely to be disrupted by brain damage • Language: - Deficits of language inferred from low aggregate score on verbal subtests on WAIS or token test • Language Lateralisation: - One hemisphere participates more, left hemisphere dominant but in some right hemisphere is, knowing which hemisphere is dominant is useful for interpreting results of other tests, test of language lateralisation always given to patients before any surgery that might invade cortical language areas, results used to plan surgery to avoid language areas if possible - Sodium Amytal Test involves injecting aesthetic sodium amytal into left or right carotid artery in neck, temporarily anesthetises ipsilateral (same side) hemisphere leaving contralateral (opposite) unaffected, tests administered and repeated for other side of brain, when injection on dominant patient is mute for 2 mins, on non-dominant few minor errors are made - Dichotic Listening Test, sequence of spoken digits presented through headphones, 3 digits presented in one ear at same time that 3 different digits are presented to other, subjects asked to report as many of 6 digits as possible, more correctly reported by ear contralateral to dominant hemisphere for language

Question 33

Behavioural Research Methods of Biopsychology: Tests of Specific Neuropsychological Function:

Answer 33

• Memory: - Following discovery of memory impairment, must answer does memory impairment involve LTM, STM or both, are LTM deficits anterograde (affect after), retrograde (affect before) or both, do LTM deficits involve semantic, episodic or procedural memory, are deficits in LTM explicit or implicit - Repetition priming tests used in amnesic patients, can complete fragments as well as healthy controls however often have no memory of any words in initial list or even of seeing list, display good implicit memory of experience without explicit memories of them • Language: - If language related deficit identified in common test battery, complex series of tests administered to clarify nature e.g. if speech is issue it could be phonology, syntax or semantics, must test each patient within each of the 3 capacities

Question 34

Behavioural Research Methods of Biopsychology: Frontal Lobe Function:

Answer 34

- Injuries to frontal lobes are common, Wisconsin Card Sorting Test sensitive to frontal lobe damage, patients with damage continue to sort cards on basis of one sorting principle for 100+ more trials after it has become incorrect, they have great difficulty in learning and remembering that previously appropriate guidelines for effective behaviour are no longer appropriate (problem = perseveration)

Question 35

Behavioural Methods of Cognitive Neuroscience

Answer 35

>Assumptions - Each complex cognitive process results from the combined activity of simple cognitive processes (constituent cognitive processes - Each constituent cognitive process is mediated by neural activity in particular area of brain - -> Goal is to identify parts of brain that mediate various constituent cognitive processes

Question 36

Behavioural Methods of Cognitive Neuroscience: Paired-Image Subtraction Technique:

Answer 36

- Involves obtaining PET or fMRI images during several different cognitive tasks, typically designed so pairs of them differ in terms of only 1 cognitive process, brain activity associated with that process can be estimated by subtracting activity in image associated with one of two tasks from the activity in image associated with other (obtain difference image) - Interpretation complicated by brains default mode (brain activity when humans sit and brain wanders), brain structures active in default mode are default mode network, comprises medial and lateral parietal cortex, medial frontal cortex and lateral temporal cortex - Also difficult due to noise associated with random cerebral events occurring during test, noise can be significantly reduced by signal averaging

Question 37

Biopsychological Paradigms of Animal Behaviour

Answer 37

- Behavioural paradigms used to study common behaviours - Species common behaviours are those displayed by virtually all members of a species or at least by all those the same age and sex (grooming, swimming, eating, drinking, copulating, fighting, nest building)

Question 38

Biopsychological Paradigms of Animal Behaviour: Open-Field Test:

Answer 38

- Subject placed in large barren chamber - Activity recorded either with automated activity recorder or by drawing lines on floor of chamber and counting number of line crossings during test - Common to count number of excrement (boluses), low activity and high bolus counts are indicators of fearfulness, are highly thigmotaxic (don’t venture, don’t groom) - Rats fearful when first placed in strange open field, declines with repeated exposure to same field

Question 39

Biopsychological Paradigms of Animal Behaviour: Tests of Aggressive and Defensive Behaviour:

Answer 39

- Observed and measuring during combative encounters between dominant male rat of established colony and smaller intruding male rat (colony-intruder paradigm) - Piloerection, sideways and biting approach indicate aggression, freezing, boxing and rolling over indicate defensiveness - Some test defensiveness to experimenter not another rat - Elevated plus maze is test of defensiveness used to study anxiolytic effects of drugs, many significantly reduce time rats spend in protected closed arms compared to exposed arms, maze effective in treatment of human anxiety

Question 40

Biopsychological Paradigms of Animal Behaviour: Tests of Sexual Behaviour:

Answer 40

- Male rat mounts female from behind, clasps, if female is receptive she assumes lordosis posture, bends back in a U, deflects tail to side - Cycles of mounting, intromitting (insertion), and dismounting occur about 10 times before male mounts, intromits and ejaculates - Common measures are number of mounts required to achieve intromission, number of intromissions to achieve ejaculation and interval between ejaculation an reinitiation of mounting - Most common measure of female rat sexual behaviour is lordosis quotient (proportion of mounts to elicit lordosis)

Question 41

Biopsychological Paradigms of Animal Behaviour: Traditional Conditioning Paradigms:

Answer 41

• Pavlovian Conditioning Paradigm: - Experimenter pairs initially NS with UCS which elicits an UCR, as a result of these pairings the CS eventually acquires the capacity when administered alone to elicit a CR, one that is often similar to the UCR • Operant Conditioning Paradigm: Rate at which a particular voluntary response is emitted is increased by reinforcement --> Self-stimulation paradigm, animals press lever to deliver electrical stimulation to particular sites in their own brains supported by pleasure centres in brain

Question 42

Biopsychological Paradigms of Animal Behaviour: Semi Natural Animal Learning Paradigms:

Answer 42

• Conditioned Taste Aversion: - Avoidance response that develops to tastes of food whose consumption has been followed by illness - Rats receive an emetic (nausea inducing drug) after they consume a food with an unfamiliar taste, on the basis of single conditioning trial rats learn to avoid the taste - Relationship established potentially increases chance of survival, subsequently become ill will not eat again, rats appear to have evolved to readily learn associations between foods and illness - Happens in humans, Cancer patients report developing aversions to foods consumed before nausea inducing chemotherapy • Radial Arm Maze: - Rats placed each day in maze that has same arms baited each day, after few days of experience rats rarely visit unbaited arms, rarely visit baited arms more than once in same day even when control procedures make it impossible for them to recognise odours left during previous visits to make their visits a systematic sequence - Arms are identical, rats must orient themselves in maze with reference to external room, performance can be disrupted by rotation of maze or changes in appearance of room • Morris Water Maze: - Rats placed in circular featureless pool of cool milky water, must swim until they discover escape platform (invisible beneath surface), rats allowed to rest on platform before being put back in water for another trial, despite starting point varying each trial, rats learned after few trials to swim directly to platform using spatial cues - Useful for assessing navigational skills of brain-lesioned drugged animals • Conditioned Defensive Burying: - Rats receive single aversive stimulus (shock, air blast, noxious odour) from object mounted on wall of chamber above floor, after single trial rats learn test object is threat, responds by throwing bed material at test object - Antianxiety drugs reduce amount of conditioned defensive burying (is used to study neurochemistry of anxiety)