Neuroscience Methods

Neuroscience Methods

1. Neuroscience methods; brain imagining techniques in living humans. Neuropharmacological measurement, Artificially simulating the brain.

2. Brain imagining techniques in living humans; Computer tomography (CT) states, Magnetic resonance imaging (MRI) static. Positron emission tomography (PET) dynamic. Functional MRI (FMRI) dynamic, Electoencephalgraphy (EEG) dynamic, Magnetoencephalography (MEG) dynamic, Electocorticographology (EcoG) and single cell recordings.

3. CT scans; A computer assisted X-ray procedure, An X-ray scanner is rotated 1 degrees at a time over 180 degrees. Computer reconstruction. Reveal structural abnormalities, such as cortical atrophy or lesions caused by a stroke or trauma. Take about 10-20 mins for the image to form. CT images are acquired only in an avail plane. The axial data set can then be used to construct images in other planes, sagittal and coronal are the most common.

4. MRI scans; A strong magnetic field causes hydrogen atoms to align in the same orientation. When ratio frequency wave is passes through the head to nucleus of the hydrogen atoms spins and emits electromagnetic energy (i.e. nuclear radiation). The MRI scanner is tuned to detect this radiation emitted from the hydrogen molecules. Take about 20-30 mins for image to form.

5. MRI vs CT scans; Both methods produce a detailed image of the brain but; require a longish period in a confined space, No movement. Advantages of MRI; No ionising radiation exposure and better spatial resolution. Disadvantages of MRI; cost, noise, no ferrous metal.

6. PET scans; A position emitting radionuclide is injected. Positions interact with electrons which produce photons (gamma rays) travelling in opposite directions. PET scanner detects the photons. Computer determines how many gamma rays from a particular region and a map is made showing areas of high to low activity. Images can formed in 45-60 seconds with good spatial resolution (3mm-5mm betweens areas of brain tissue)

7. PET vs CAT; CAT scans show brain structures, PET scans reveal brain activity, CAT involves absorption of X-ray, PET involves emission of radiation by an injected or inhaled isotope, PET is relatively fast acting (45-60 seconds), CAT is slow acting (10-20 mins for image to form).

8. Functional MRI; imaging brain hemodynamics; Magnetic properties of oxygenated blood are different to deoxygenated blood. Produces detailed information about the flow of oxygenated blood to brain regions. Temporal resolution; Good (hemodynamic response takes 408 seconds). Spatial resolution; very good (2mm between areas of brain tissue and BOLD changed can be superimposed on to MRI images). Advantages over PET; no injections need to be given, shorter imagine time, better partial resolution, 3-D images.

9. EEG; a measurement of summated neuronal activity derived from cortical tissue beneath the electrode. Low amplitude alpha and beta link to attention and arousal. High amplitude theta and delta link to drowsiness and sleeping, Non invasive. High temporal resolution. Direct reflection of neuronal activity. Less expensive than FMRI or PET. poor spatial localisation due to recordings made at the scalp, better suited to answering questions about when cognitive processes work not where they work.

10. ECoG vs EEG; Advantages; both have excellent temporal resolution, ECog has much better spatial resolution. Disadvantages; ECog requires extensive invasive surgery, ECoG is typically only performed on ops who already have some severe neurological complaint, ECog is much more costly. Single cell recordings; micro electrode, these can be inserted into individual neutrons and record firing action potential. Macro electrodes; measure from a localised area of cortisol tissue comprising a number of neutrons (local field potentials-LEP).

11. Neuropharmacological methods; Cerebral display (in vivo micro dialysis); under anaesthesia and sterotaxi guidance, a cannula is inserted into a specific brain site. Following recovery, a small probe with semipermeable membrane is inserted into the cannula. Fluid is perfused through the probe and chemicals in the extracellular fluid diffuse across the membrane and are collected into a sample vial. The samples are then analysed.

12. Measuring chemical activity in the brain; 2-DG autoradiography; Radioactive 2 deoxyglouce is injected, Animal engages in behaviour in interest, Animal is euthanised, brain tissue is removed and sliced. Tissues slices are collected with photographic emulsion and stored in the east (much like film processing). Areas that absorbed high levels of radioactive substance will appear darker. Using computer imagine, differences in density can be colour coded.