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Neurotechniques Notes

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Study of the brain and behaviour in the laboratory: Neurotechniques Lesioning / ablation studies Ablation is the destruction (or less commonly, removal) of a certain part of the animal's brain. The idea is that if a behaviour cannot be performed after an ablation surgery, then that part of the brain was responsible for that behaviour. There are 4 main methods of lesion formation:

1. tissue removal is what it says on the tin, on the cortical area just underneath the skin

2. RF lesioning involves steel electrodes inserted into the brain, which then carry a radio frequency. This produces heat, which damages the target. This is a broad and non-selective method of lesioning.

3. excocitotoxic lesioning is similar to RF lesioning, but instead excitatory amino acids such as kainic acid, a glutamate receptor stimulant, are injected using a cannula which over-excites the area to death. This method is a lot more selective than RF lesioning as it only destroys the soma.

4. injection of anaesthetic such as muscimol which is a GABA receptor agonist. RF and excitotoxic lesioning are typically performed using stereotaxic surgery, which guides the electrodes or cannula into a specific area using a stereotaxic atlas (basically a map of the brain). However, as the atlas is produced based upon the average animal, numerous trials may be necessary with varying co-ordinates. Histological methods First pioneered (and rewarded by a Nobel Prize) by Santiago Ramon y Cajal in the early 20th century, histoligical staining is used to observe tissues (for eample, to check the location of a lesion). The procedure consists of the following stages

1. Perfusion replacing the animal's blood with another fluid, eg saline

2. fixing using a fixative such as formaline (an aqueous solution of gaseous formaldehyde) which preserves and prepares the tissue

3. Slicing using a microtome which is capable of slicing extremely thin segments of tissue

4. Staining using stains such as Nissi substance (nuclear) or cresyl violet (cell body)

5. microscopy Recording and stimulating neural activity I. Microelectrodes measure the electrical activity of a single neuron II. Macroelectrodes measure the electrical activity of the whole brain and produce an electroencephalogram (EEG) III. 2-Deoxyglucose autoradiography records the metabolic activity in the brain, highlighting specific areas of high and low activity. The brain and its activity, along with concentrations of particular chemicals, are then measured using positron emission topography (PET) which detects subatomic particles (positrons) that are emitted when 2-DG decays. As 2-DG decays fast, it must be made onsite using a particle accelerator called a cyclotron. Whilst the advantages are that PET shows functional areas of the

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