Transcript No Slide Title

Biological Bases of Behaviour.
Lecture 7: Techniques for Understanding
Brain Structure & Function.
Kalat (2000) p72
Learning Outcomes.
 At the end of this lecture you should be able to:
 1. Describe a range of techniques used to determine brain
structure and function.
 2. List the advantages and disadvantages of each of the
techniques described.
The Techniques
 Many techniques have been developed to enable biological
psychologists to understand how the brain works, each
having their own advantages and disadvantages.
 It is rare that a single method will provide a convincing
explanation, more often one or more techniques are
utilised to provide a clearer picture.
 This is referred to as 'converging operations' (Carlson,
1994).
1. Neuroanatomical Techniques.
 These tell us about the anatomical structure of the brain.
 a) Histological Procedures: Gross examination of the brain
does not allow us to study details of cell structure and
connectivity, to do so we need to selectively stain thin
slices of the brain.
 Preservation: After death the soft brain tissue is destroyed
by autolytic enzymes, so the brain must be preserved with
a fixative, such as formalin.
 The brain is then embedded within a paraffin block that can
be sliced thinly using a microtome and mounted on slides.
 Histological stains have been developed so that cell bodies,
nerve fibres and membranes can be selectively viewed
Staining.
 3 types are used:
 i) Cell-body stains.
 Developed by Franz Nissl
who discovered that dyes
such as cresyl violet would
selectively reveal the cell
bodies of brain tissue.
 ii) Myelin stains.
 These selectively colour
the myelin sheath that
surrounds nerve cells and
so fibre bundles are
revealed.
Carlson (1994) p 110
Membrane Stains
 These contain salts of
various heavy metals that
interact with the axon
membranes.
 The commonly-used GolgiCox stain uses silver.
 This enables us to see the
branching of individual
neurons and trace their
connections.
Carlson (1994) p 111
b) Tracing Connections.
 The structures of the CNS are interconnected by complex
systems of axons, finding out what nuclei are connected to
what others and the routes taken can be solved by:
 i) Anterograde (forward) tracing: Certain proteins are taken
up by cell bodies are transported through axons until they
reach the terminal buttons. Lectins such as phaseolus
vulgaris leukoagglutinin (PHA-L) are often used.
 ii) Retrograde (backward) tracing: Dyes such as flurogold
are injected into the terminal buttons and are then carried
back through the axons to the cell bodies where they can
be seen.
PHA-L Anterograde Tracing.
PHA-L injected and taken up
by dendrites and cell bodies
Transported to
terminal buttons
Carlson (1994) p 111
PHA-L labelled axons and
terminal buttons can be
seen under the microscope
c) Histochemical Techniques.
 These tell us the location of
specific neurons that produce
and secrete particular
neurotransmitters.
 Antibodies for a specific
neurotransmitterare injected
into a region and the slides
are viewed under ultraviolet
light.
 Alternatively radioactive 2deoxyglucose (2-DG) is taken
up by active neurons.
Vasopressin-containing axons
and terminal buttons
Carlson (1994) p 114
2. Imaging the Living Brain.
 The methods previously described have all required the
brain to be removed.
 The following techniques enable neural structure and
function to be viewed in the living brain.
 Computerised Axial Tomography (CAT): Consists of a
circular arrangement of x-ray emitters and detectors in
which progressive scans through the brain can be taken.
 A 2-dimensional image of horizontal sections can then be
produced.
 This technique is used mainly to diagnose neurological
conditions such as tumours, blood clots, degenerative
disease and the location of strokes.
CAT scan from a patient with a lesion
in the right occipital-parietal area.
Lesion site
Carlson (1994) p 119
Magnetic Resonance Imaging (MRI).
 MRI takes detailed pictures,
using a strong magnetic field.
 It detects radiation from
hydrogen molecules present
in all brain tissue in different
concentrations.
 Sagittal,
horizontal
and
frontal images are produced.
 MRI has now been adapted to
show function as well - this is
called functional magnetic
resonance imaging (fMRI).
Carlson (1994) p 120
Positron Emission Tomography (PET).
 Radioactive glucose is taken up by active cells in the brain.
 As the radioactive isotopes decay, they emit positrons
which are detected by the scanner.
 In a typical experiment, images of blood flow or radioactive
counts during a control state are subtracted from images
taken during functional activation (i.e. when the individual
is performing some type of cognitive task).
 By subtracting measurements in the control state from a
task state it is possible to identify those areas of the brain
concerned with specific mental operations (Raichle, 1994).
PET Scan of Brain Activation.
Normal elderly control
Alzheimer’s patient
Rosenzweig et al (2002) p 53
Advantages/Disadvantages
of Brain Imaging.
 Advantages.
 Non-invasive (CAT, MRI).
 Provide very detailed knowledge about structure (CAT,
MRI) and function (PET, fMRI).
 Disadvantages.
 Mildly invasive (PET)
 Only provide horizontal pictures (CAT)
3. Recording Electrical Activity
in the Brain.
 Axons generate action potentials, and terminal buttons
elicit postsynaptic potentials.
 These electrical events can be recorded, and changes in
electrical activity can be used to determine whether a
structure or region of the brain is involved in a certain
behaviour.
 There are two types of measure:
 a) Microelectrodes: Are very small and can record electrical
activity within single neurons (single-cell recording).
 These are normally implanted chronically into the brain of
an animal thus allowing the monitoring of activity as the
animal responds to particular environmental stimuli.
Advantages/Disadvantages
of Microelectrodes.
 Advantages.
 Extremely precise.




Disadvantages.
Time consuming.
Too focused - it neglects neuronal interactions.
Invasive.
b) Macroelectrodes.
 The Electroencephalogram (EEG) was invented by Berger
(1929).
 Electrodes are attached to the scalp and the activity of
hundreds of thousands of neurons in the vicinity of the
electrodes recorded.
 Active electrodes are placed over the site of expected
neural activity and an indifferent electrode is placed at a
neutral spot (usually the earlobe).
 The recording simply measures the potential difference
between the two electrodes.
 In clinical studies, many electrodes are used and they are
placed over the lobes of the brain according to a
conventional scheme.
The EEG Record.
 Changes in electrical activity are evident in states such as
sleep, wakefulness, and arousal;abnormal electrical activity
can signal epilepsy or mental illness.
 Each individuals EEG pattern is distinctive, but there are
characteristic patterns of electrical activity:
 Alpha waves (8-13 Hz): Associated with relaxed wakefulness
 Beta waves (13-30 Hz): Seen in individuals who are awake,
alert, with eyes open, and who may be concentrating on
something.
 Delta waves (0.5-4 Hz): Associated sleep in adults but are
also seen in infants, their abnormal appearance in awake
adults can be indicative of a brain tumour.
 Theta waves (4-7 Hz): Also seen in adults sleeping and in
children. Their abnormal appearance in adults is typically
seen in psychopaths.
Advantages/Disadvantages
of Macroelectrodes.
 Advantages.
 Non-invasive
 Can differentiate between different neurological conditions
or behavioural states.
 Disadvantages.
 Time consuming.
 Very crude - the averaging of activity in many neurons
cannot establish precise activity in a particular region.
4. Brain Stimulation.
 In animals, direct electrical stimulation of the brain can
produce clear behavioural changes.
 E.g stimulation of the hypothalamus may produce feeding,
drinking, sexual arousal, and aggression suggesting an
activational role.
 Stimulation of the caudate nucleus often halts ongoing
behaviour which suggests an inhibitory role.
 In humans this technique was pioneered by Penfield and
Jasper (1954) in which they stimulated various regions of
cortex in conscious patients and noted down the
behavioural or sensory effects.
Electrical Stimulation of
the Human Brain
Carlson (1994) p 137
Advantages/Disadvantages
of Brain Stimulation.
 Advantages.
 Does not harm the brain.
 A valid way of investigating living function of brain areas.
 Disadvantages.
 Invasive.
 Crude - not easy to tell how far the stimulation has spread.
5. Experimental Brain Damage.
 An influential, though ethically controversial technique is to
cause localised brain damage in animals and note the
behavioural effects.
 If an animal no longer performs a specific behaviour
following brain damage to a particular area (a lesion) then
that area must be responsible for the behaviour.
 There are several methods:
 Aspiration (ablation): the surface of the cortex is removed.
 Radiofrequency lesion: an electrode is inserted to the
correct location and then the tip is heated destroying
nearby cells.
 Neurotoxic lesion: a neurotoxin such as ibotenic acid is
injected into a specific region, this destroys cell bodies but
leaves undamaged fibres of passage.
A Radiofrequency Lesion.
Bilateral radiofrequency lesion of the
cingulum bundle in a rat brain
Problems in Interpreting Results of
Brain Lesions in Animals.
 1. How do we know that the damage that has been caused
has actually interfered with the behaviour in question?
 2. All regions of the brain are interconnected at some level
and so by damaging a structure, we may also damage fibre
pathways between other areas.
 3. As the brain works as an integrated whole, disturbance at
one location may affect the functioning of other regions.
 4. Following damage, some form of regeneration may take
place or other brain regions may partly take over.
 5. We are generalising from a damaged animal to functioning
in normal animals.
6. Human Cases of Brain Damage.
 Head injuries occur in many different forms but rarely
produce localised damage.
 Case studies of individuals who do have circumscribed
damage can shed light on how the brain functions.
 Most cases show a dissociation of impairments, comparisons
can be made of the brain regions damaged in different cases.
 While it is unethical to administer selective neurotoxins to
humans and then observe the effects, some willingly selfadminister neurotoxic substances such as
ecstasy and
provide ready-made experiments on the effects of brain
damage on mood, memory, and behaviour.
Advantages/Disadvantages
of Brain Damage.
 Advantages.
 No ethical problems as the damage has occurred naturally.
 Disadvantages.
 Lack of precision - extent of the damage is not controllable.
 There are problems with comparison - ie if a person suffers
brain damage and behaves aggressively how do we know
that this is not how they behaved before?
References and Bibliography.
 Carlson, N.R. (1994). Physiology of Behaviour.
 Kalat, J.W. (2000). Biological Psychology.
 Penfield, W., & Jasper, H. (1954). Epilepsy and the
functional anatomy of the human brain. Boston: Little,
Brown & Co.
 Raichle, M.E. (1994). Imaging the mind: studies with
modern imaging techniques. Annual Review of Psychology,
45: 333 - 356.
 Rosenzweig, M.R., Breedlove, S.M., & Leiman, A.L. (2002).
Biological Psychology.
 Toates, F. (2001). Biological Psychology.