Psyc 362 Chapter 5 text Methods and Strategies of Research Experimental Ablation destroying part of the brain to evaluate the animal s subsequent behavior Evaluating the behavioral effects of brain damage lesion wound or injury brain lesion the damaged region of the brain lesion studies observation of an animal s behavior after brain damage the function of an area of the brain can be inferred from the behaviors that the animal can no longer perform after damage We want to find the functions of different regions and understand how the functions are combined to accomplish particular behaviors Functions are performed by circuits within the brain and each region performs a function that contributes to performance of behavior Goal is to understand the functions that are required for performing a particular behavior and to determine what circuits of neurons in the brain are responsible for each of these functions Producing Brain Lesions brain lesions of subcortical under the cortex regions can be produced by passing electrical current through a stainless steel wire coated with insulating varnish except at the very tip One guides the wire to the appropriate place then a lesion making device is turned on to produce a radio frequency RF current that produces heat killing cells in the region surrounding the tip of the electrode more selective method is to use an excitatory amino acid kainic acid to kill neurons by overstimulation producing excitotoxic lesions cannula small metal tube injected into a region of the brain that releases such chemicals to destroy neural cell bodies sparing axons that belong to different neurons Can also attach toxic chemicals to antibodies that bind with particular proteins found in only some neurons in the brain killing those specific cells With any of these methods we always cause additional damage to the brain even before creating the lesions We can determine if this incidental damage to the brain causes the behavior loss or if it was the lesion with sham lesions cut open the scalp drill the hole inset the electrode lower it to the proper depth done which involves doing everything but creating the lesion These lesions act as the control group Sham lesions are comparable to placebos in pharmacological studies Temporary brain disruption can be done with the injection of a local anesthetic blocks action potentials or muscimol drug which stimulates GABA receptors to inactivate a region of the brain by inhibiting neurons into the appropriate part of the brain Stereotaxic Surgery brain surgery using a stereotaxic apparatus to position an electrode or cannula in a specified position of the brain using a holder for the head and a carrier for the cannula electrodes Since no two brains are identical enough similarity allows us to predict the location of particular brain structures relative to external features of the head using a stereotaxic atlas It has photographs and drawings corresponding to frontal sections taken at various distances rostral and caudal to bregma and the sections are labeled according to the distance of the sections anterior or posterior to bregma Bregma is the junction of the sagittal and coronal sutures of the skull used as a reference point for stereotaxic brain surgery The atlas gives only an approximate locations due to variation in different strains and animals Stereotaxic apparatus device that positions an electrode or cannula into a specific part of the brain It has a head holder an electrode holder and a calibrated mechanism that moves the electrode holder in measured distances along 3 axes anterior posterior dorsal ventral lateral medial Process involves anesthetizing the animal and cutting the scalp open locating the bregma after obtaining coordinates from a stereotaxic atlas then dial in the coordinates and drill a hole through the skull Last lower the device into the brain by the correct amount Besides creating lesions Apparatus can also be used to stimulate neurons or block specific neurons by injecting drugs Even to reduce symptoms of Parkinson s disease Histological methods what we do after lesions fix slice stain examine to see the location of the lesion and study the tissue Fixation making sure the tissue can be observed in the form it had at the time of the organism death Placing the neural tissue in a fixative like formalin an aqueous solution of formaldehyde that halts autolysis hardens tissue and kills microorganisms that may destroy it can be used to destroy autolytic selfdissolving enzymes and preserve to prevent decomposition by mold or bacteria Slicing cutting brain into thin sections and with a microtome produces thin slices for either a light microscope 10 80 um in thickness or an electron microscope 1 um thickness Staining to see anatomical details of various cellular structures we attach the sections to glass microscope slides and put the entire slide into various chemical solutions Focus on cell body stains to verify locations of a brain lesion Methylene blue is a dye that is taken up by material such as RNA DNA and associated proteins in and out of the nucleus These materials categorized as Nissl substance cresyl violet is another dye Process made it possible to identify nuclear masses in the brain but the stain isn t selective for neural cell bodies As a result all cells are stained neurons and glia We cover the stained sections with a small amount of a mounting medium transparent liquid and place a thin glass coverslip over the section Examining with Electron Microscopy can be used to see synaptic vesicles and details of cell organelles It passes electrons through the tissue casting a shadow of the tissue onto a sheet of photographic film that was exposed to the electrons Scanning electron microscope produces 3D images but is less magnified than a standard electron microscope that would transmit the electron beam through the tissue Tracing Neural Connections focuses on VMH involvement in copulatory behaviors as studied in female rats allows us to understand discover circuits of interconnected neurons Usually pathways in one structure say VMH will affect neurons in other structures which influence those in other structures until motor neurons are eventually stimulated To understand these pathways we want to trace the efferent axons which can be done using an anterograde labeling method This method uses chemicals that are taken up by dendrites cell bodies and transported through the axons toward the terminal