PSYC 211 Lecture Notes - Lecture 5: Halorhodopsin, Optogenetics, Transcranial Magnetic Stimulation
11 Mar 2013
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PSYC211 Lecture 5 - Jan. 23
Experimental Approaches to Understanding Behaviour:
•Invasive physiological research methods
•Legion, electrical stimulation, neurophysiological recording)
•Behavioural paradigms that assess constituent cognitive processes
•Visuospatial attention, working memory, reversal learning)
•Pharmacological research methods
•Drug administration, chemical lesions, chemical activity of the brain)
•Genetic engineering
•Gene knockout, genetic replacement
•Visualizing the living human brain
•PET, fMRI
•Neuropsychological testing
•WCST, delayed response
Experimental Ablation (Lesion Methods):
•Experimental ablation
•A method used to investigate brain function by destroying part of the brain and
evaluating the animals subsequent behaviour
•The area of the brain that is damaged is called the brain lesion
•The goal of lesion methods is to discover what functions are performed by different
regions of the brain and how these functions are organized to produce complex
behaviour (i.e. Functional organization of the brain)
•Neural circuits in the brain perform functions (or a set of functions)
•Functions contribute to the performance of a behaviour
•Do not confuse functions with behaviour. (i.e. Behaviour act of reading requires
multiple functions such as eye movements, recognition of words, and processing of
information)
Brain Stereotaxy:
•The means by which the tip of an injector can reach the depths of certain brain
regions
•No two brains of any given species are identical. Enough similarities to predict
certain locations
•The skull is made up of several bones that join together and form sutures. The
junction at which the sutures meet at the front of the head is called bregma. The
junction at the cordial end at which the sutures meet at the back of the head is
called lambda
•Stereotaxic surgery is a form of surgical intervention. It uses a three dimensional
coordinate system to locate a target brain region and perform the lesion
•A stereotaxic atlas contains drawings that correspond to brain sections taken at
varying distances from bregma
Stereotaxic Apparatus for Performing Brain Surgery in Rats:
•Inject excitotoxins to create selective lesions to specific brain areas
•Create neurochemical lesions (e.g. Deplete acetylcholine in the frontal cortex)
•We can use it to place wires to stimulate neurons
•We can implant cannulae that allow the infusion of drugs that temporarily stimulate
neurons or block specific receptors
Different Lesion Methods (I):
•Excitotoxic lesions:
•An excitatory amino acid (e.g. Ibotenic acid, kainic acid, N-methyl-d-aspartic
acid) is injected into the target region of the brain
•The chemical destroys cell bodies (the somas) by stimulating them to death
•This method is highly selective; it destroys cell bodies only, and spares axons
of other neurons that pass nearby (fibres of passage)
•This method can create selective neurochemical lesions thereby depleting
dopamine, serotonin, norepinephrine or acetylcholine in specific brain areas
•Aspiration lesions:
•The brain area of interest is removed by suction (or aspiration) using a fine-
tipped hand-held glass pipette
•Can be performed under visual guidance
•This method can sometimes damage underlying white matter and major blood
vessels
•This is a nonselective method because it removes cell bodies and fibers of
passage
Different Lesion Methods (II):
•Radiofrequency lesions:
•Small subcortical lesions (i.e. Regions located beneath the cortex) are made by
passing a radiofrequency current through a stainless steel wire that is
insulated except the tip
•The wire is guided stereotaxically
•The electric current produces heat that destroys the cells in the region
surrounding the tip of the wire
•The size and shape of the lesion is determined by the duration and intensity
of the current
•Sham lesions (operated controls):
•When we create anatomical or neurochemical lesions, we can potentially cause
additional damage simply by inserting the electrode or injector into the brain
•For experimental comparisons, a group of animals will undergo the same
experimental procedure WITHOUT the excitotoxin, frequency or aspiration
•Animals with sham lesion serve as a control group
•Most lesions are permanent. Temporary (or reversible) lesions can be made
by infusing a local anesthetic (e.g. Lidocaine) which blocks action potentials,
or infusing a GAVA agonist (e.g. Muscimol) which is an inhibitory
neurotransmitter
•Permanent lesion experiments helps see what the long term effects (behaviour)
will be
•Temporary lesion experiments helps see what area of the brain affects what
functions
Histological Methods (1): Nissl Staining
•Historlogical methods allow:
•Location of structures
•How structures are connected
•Identify areas of the brain that are damaged (verify the lesion)
•Nissl staining:
•Histological stains allows us to visually identify specific substances within and
outside a cell
•The most commonly used stain is cresyl violet which stains cell bodies
•The dark regions represent cell bodies. The light regions represent axons or
fiber bundles
Histological Methods (2): Golgi Staining
•The golgi stain allows us to visually identify the external structure of neurons
•The neuron silhouettes are revealed in great detail but the internal structure of the
cells is invisible
The Electron Microscope:
•Electron microscopy allows us to see small anatomical structures (e.g. Synaptic
vesicles and details of cell organelles) using a special electron microscope
•Limited up to 1000x magnification
•Uses a beam of electrons which illuminate a specimen on a fluorescent screen
which you can then capture a picture of
•Very powerful in capturing images of small specimen
Document Summary
Brain stereotaxy: the means by which the tip of an injector can reach the depths of certain brain regions, no two brains of any given species are identical. Enough similarities to predict certain locations: the skull is made up of several bones that join together and form sutures. The junction at which the sutures meet at the front of the head is called bregma. The junction at the cordial end at which the sutures meet at the back of the head is called lambda: stereotaxic surgery is a form of surgical intervention. It uses a three dimensional coordinate system to locate a target brain region and perform the lesion: a stereotaxic atlas contains drawings that correspond to brain sections taken at varying distances from bregma. Histological methods (2): golgi staining: the golgi stain allows us to visually identify the external structure of neurons, the neuron silhouettes are revealed in great detail but the internal structure of the cells is invisible.