Lecture 5 - Jan 23.pdf

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 The electron Microscope (e.g. synaptic vesicles and details of cell organelles) using a special electron microscope. An electron A colour enhanced electron photomicrograph showing photomicrograph showing a the cross section of a neuron cell body (green) studded synapse with terminal buttons (orange). Tracing Neural Connections: •Brain regions do not work in isolation. They receive inputs from different structures and send outputs to other brain regions. The integration of these inputs and outputs leads to a network that requires activation for the appropriate 5 behaviour •Used to determine if information between two areas is reciprocal (reciprocally connected) •Anterograde labeling (tracing efferent axons) Used when tracing a path of axons projecting ‘away’ from the cell bodies • • The method employs chemicals such as PHA-L (an anterograde tracer) which is injected into the brain region of interest • The PHA-L molecules are taken up by the cell bodies and dendrites and transported down the axon to the terminal button •Retrograde labeling (tracing afferent axons) • Used when tracing a path of axons projecting ‘toward’ a particular brain area • The method employs chemicals such as fluorogold (a retrograde tracer) which is injected into the brain region of interest • The fluorogold molecules are taken up by the terminal buttons and transported back to the cell bodies Visualizing the Living Human Brain (I) - CT •Computerized Tomography (CT) A computer assisted X-ray procedure used to visualize the brain • • The patient lies with his or her head positioned in the center of a large cylinder An X-ray beam is projected through the head to an X-ray detector • • The X-ray bean scans the head from all angles • A computer translates the information received from the X-ray detector into a series of pictures of the skull and brain Visualising the Living Human Brain (I) - CT Visualising the Living Human Brain (I) - CT Computerised Tomograpy (CT) Computerised Tomograpy (CT) !  A computer assisted X-ray procedure used to !  A computer assisted X-ray procedure used to visualise the brain. visualise the brain. !  The patient lies with his or her head positioned !  The patient lies with his or her head positioned in the centre of a large cylinder. in the centre of a large cylinder. !  An X-ray beam is projected through the head to !  An X-ray beam is projected through the head to an X-ray detector. an X-ray detector. !  The X-ray bean scans the head from all angles. !  The X-ray bean scans the head from all angles. !  A computer translates the information received from the X-ray detector into a series of pictures !  A computer translates the information received of the skull and brain. from the X-ray detector into a series of pictures of the skull and brain. A series of CT scans from a patient with a lesion in the right occipital parietal area A series of CT scans from a patient with a lesion in the right occipital parietal area Visualizing the Living Human Brain (II) - MRI: • Magnetic Resonance Imaging (MRI) • Does NOT use X-rays. Instead, it uses strong magnetic fields • The patient lies with his or her whole body positioned in the center of a large cylinder • When the body is in a strong magnetic field, the hydrogen atoms in the body spin with a particular orientation • A radiofrequency wave passed through the body makes the hydrogen atoms emit their own radiowaves • The computer is tuned to detect radiation from hydrogen atoms because these atoms are present in different concentrations in different tissues • The result is a high spatial resolution, three-dimensional image of the brain Spontaneous Brain Activity: • The brain is constantly active even when a human is at rest Visualizing the Living Human Brain (III) - PET: • Positron Emission Tomography (PET) • Measures the metabolic activity of specific brain regions • The person is injected with radioactive 2-DG (2-deoxyglucose) into the carotid artery 2-DG is similar to glucose. It is taken up by active energy consuming molecules