2. Research Methods
• Experimental Ablation
– Evaluating the behavioural effects of brain damage
– Producing brain lesions
– Stereotaxic surgery
– Histological methods
– Tracing neural connections
– Study of the living human brain
• Recording and Stimulating Neural Activity
– Recording neural activity
– Recording the brain’s metabolic and synaptic activity
– Measuring the brain’s secretion
– Stimulating neural activity
– Behavioural effects of electrical stimulation
• Neurochemical Methods
– Finding neurons that’s produce particular neurochemicals
– Localizing particular receptors
• Genetic Methods
– Twin studies
– Adoption studies
– Targeted mutations
3. Experimental Ablation
• Investigating brain functions involves destroying parts
of the brain and evaluating the animal’s subsequent
behaviour.
• Evaluating the behavioural effects of brain damage-
– Lesion- Wound or injury.
– Lesion studies- Experiments in which part of the brain is
damaged and the animal’s behaviour is observed.
– Goal- To discover what functions are performed by
different regions of the brain and how these combine to
accomplish particular behaviours.
– Must be careful about interpretations of behaviour shown
by animals after brain damage.
– Differentiation between brain function and behaviour
4. • Producing brain lesions
– On the surface- Anesthetize -> Open scalp -> Remove part of the
skull -> Cut through dura mater -> Suction device to aspirate the
brain tissue.
– In the subcortical regions- Produced by passing electrical
currents through a stainless steel wire that is coated in
insulating varnish except for the tip. Guiding wire stereotaxically
-> Turn on the lesion making device -> Produces radio frequency
-> Generates heat that kills cells in the region surrounding the
tip of the electrode.
– Excitotoxic lesions- Killing neurons by using kainic acid that
overstimulates neurons to death. Allows for selective
destruction of neurons and spares axons of surrounding
neurons.
– Sham lesions- A placebo procedure that duplicates all the steps
of producing a brain lesion except for the one that causes the
brain damage. Done to establish a control group.
– Reversible brain lesion- Using muscimol to anesthesize a region
of the brain by stimulating GABA receptors.
5. • Stereotaxic surgery
– Brain surgery using a
stereotaxic apparatus
to position an
electrode or cannula in
a specified field
position of the brain.
Done using stereotaxic
apparatus.
– Stereotaxic atlas- A
collection of drawings
of sections of the brain
of a particular animal
with measurements
that provide
coordinates of
stereotaxic surgery.
6. • Histological methods
– Fixing, slicing, staining and observing the brain.
– Fixation and sectioning- Using formaldehyde to
harden the soft brain tissue and to avoid autolysis.
– Microtome- Used to cut thin slices of brain
– Staining- To reveal fine details and cellular
structures. Most common is a cell-body stain done
by using methylene blue or cresyl violet. The
substance that picks up the dye is called Nissl
substance after Franz Nissl. Consists of RNA, DNA
and other proteins.
7. • Electron Microscopy
– Helpful in observing small
anatomical structures
such as synaptic vesicles.
– A beam of electrons is
passed through the
tissues which casts a
shadow onto the
photographic plate
exposed by the electrons.
– Scanning electron
microscope- A microscope
that provides 3-d
information about the
shape of the surface of a
small object.
8. • Tracing neural connections
– Tracing efferent neurons-
• Anterograde labeling method- A histological method
that labels axons and terminal buttons of neurons
whose cell bodies are located in a particular region.
• PHA-L- A protein (lectins) derived from kidney beans
and used as an anterograde tracer, taken up by
dendrites and cell bodies, and carried to the ends of
the axons. Binds with specific complex molecule
present in the cells of the immune system.
• Immunocytochemical method- A histological method
that uses radioactive antibodies or antibodies bound
with a dye molecule to indicate the presence of
particular proteins of peptides.
9. – Tracing afferent neurons
• Retrograde labelling method-
A histological method that
labels cell bodies that give rise
to the terminal buttons that
form synapses with cells in a
particular region.
• Fluorogold- A dye that serves
as a retrograde label taken up
by the terminal buttons and
carried back to the cell
bodies.
– Transneuronal tracing-
Identifies a series of
multiple neurons that form
serial synaptic connections
with each other.
• Pseudorabies virus- A
weakened form of pig herpes
virus used for transneuronal
tracing, which labels
interconnected series of
neurons.
10. • Study of the living human
brain
– Computerized
tomography (CT scan)-
The use of device that
employs a computer to
analyze data obtained by a
scanning beam of X-rays
to produce a 2-d picture of
a slice through the body.
– Magnetic resonance
imaging (MRI)- A
technique whereby the
interior of the body can be
accurately imaged and it
involves the interaction
between radio waves and
a strong magnetic field.
Picks up radio waves
emitted by hydrogen
atoms.
11. Recording and stimulating neural activity
• Recording neural activity
– Studying the changes in the electrical activity of a particular region can be
used to determine if that region plays a role in various behaviours.
Recordings can be made:
• Chronically- over an extended period of time after the animal recovers
from surgery.
• Acutely- over a relatively short period of time during which the animal is
kept anesthetized.
– Recordings can be made using-
• Microelectrodes- Are very fine electrodes used to record activity of
individual neurons. Recording the activity of a single neuron is also
called single-unit recording.
• Macroelectrodes- An electrode used to record the electrical activity of
large number of neurons in a particular region of the brain. A form of
representation of data from macroelectrodes in ink-writing oscillograph
or polygraph. Recording from a person’s scalp are called
electroencephalograms (EEG).
• Magnetoencephalography- A procedure that detects groups of
synchronously activated neurons by means of the magnetic field induced
by their electrical activity. Uses an array of superconducting quantum
interference devices (SQUID).
12. • Recording the brain’s metabolic and synaptic activity
– 2-deoxyglucose (2DG)- A sugar that enters calls along with
glucose but is not metabolized. Done to see the rate of
metabolism in cells. High cell activity = high cell metabolism =
high absorption of 2DG.
– Autoradiography- A procedure that locates radioactive
substances in the slice of tissue. The radiation exposes a
photographic emulsion or a piece of film that covers the tissue.
– Immediately early genes and Fos- Particular genes in the
nucleus respond to nuclear activation by releasing proteins such
as Fos that bind with the chromosomes in the nucleus. These
proteins can be traced by using methods like staining.
– Positron emission tomography (PET)- The use of a device that
reveals the localization of a radioactive tracer in a living brain.
Mostly radioactive 2-DG or radioactive water that emit
positrons while decaying.
– Functional MRI (fMRI)- A modification of the MRI procedure
that permits the measurement of regional metabolism in the
brain. Detects levels of oxygen in brain’s blood.
13. • Measuring the
brain’s secretions
– Microdialysis- A
procedure for
analysing
chemicals present
in the interstitial
fluid through a
small piece of
tubing made of a
semipermeable
membrane that is
implanted in the
brain.
14. • Stimulating neural activity
– Electrical- By passing electrical current through
the wire inserted into the brain.
– Chemical- By injecting excitatory amino acids such
as kainic acid or glutamic acid.
• Disadvantage- Slightly more complicated than
electrical. Uses cannula, tubes, solutions of amino
acids.
• Advantage- Activates cell-bodies but not axons. This
effects can be studies in a more localized manner.
15. • Behavioural effects of electrical brain stimulation
– Electrical impulses can be used to generate
behaviours, however they are never truly as natural as
naturally occurring neural impulses. One of the ways
in which this can be achieved is by activating
modulators in the brain that help in secreting other
hormones such as activating acetylcholine that
activates cerebral cortex.
– Transcranial magnetic stimulation (TMS)- Stimulation
of the cerebral cortex by means of magnetic fields
produced by passing pulses of electricity through the
coil of wire placed next to the skull. It interferes with
the functions of the brain region that is stimulated.
16. Neurochemical methods
• Finding neurons that produce particular
neurochemicals. For ex., organophosphate insecticides
directly activate the neural circuits responsible for
dreaming. Are acetylcholinesterase inhibitors. Three
ways in which we can detect where the insecticide acts
in the brain:
– Look for neurons that contains acetylcholine (localize
neurotransmitters and neuromodulators)
• Localizing the chemicals themselves
• The enzymes that produce them
– Look for the enzyme acetylcholinesterase
– Look for acetylcholine receptors
• Autoradiography- Using radioactive ligand-brain tissue
interaction
• Immunocytochemistry- Using antigen-antibody
interaction
17. Genetic methods
• Twin studies- Studying concordance rate for a
particular trait in monozygotic and dizygotic twins.
– Concordant- If both twins are diagnosed with a disorder
– Discordant- if one out the two got a diagnosis of the
disorder.
– Any disorder with a genetic basis would have a higher
concordance in identical twins than fraternal twins.
• Adoption studies- Estimating the heritability of a
particular behavioural trait is to compare people who
were adopted early in their lives with their biological
and adoptive parents.
• Targeted mutation- Mutated genes (knockout genes)
produced in labs and inserted into chromosomes of
animals. Do not produce functional proteins.
