Neuropsychological Methods

Neuropsychological Methods

1. EEG / ERPs

   • Event Related Potentials (ERPs): The ERP technique involves electrical activity being measured. The time of presentation of stimulus is recorded.
     • The activity from many different trials is averaged together and a pattern of voltages is examined (pattern is related to the onset of stimulus (or event))
       • However, cannot be directly lined with underlying brain source! There are many potential sources of electrical activity in the brain that could give rise to the observed pattern of relative potentials on the scalp
         • For instance, positivity in frontal regions may produce the same pattern of activity on the scalp as that produced by a negative in a posterior brain region
           • This leads to POOR SPATIAL RESOLUTION for brain generators, yet TEMPORAL RESOLUTION IS VERY GOOD.
   • ELECTROENCEPHALOGRAPHY
     • Electrodes placed on scalp, electrical activity from neural activity is recorded
       • Good temporal resolution but poor spatial resolution
       • Voltage at each electrode is measured relative to a reference electrode - thus some electrodes will be relatively positive
       • Good for studies of BRAIN STATE: -Frequency band power over spatial locations (different brain processes will occur within different frequency bands)
         • States are long periods of time - psychology is more rapid than this...

2. MEG

   • Non-invasive functional imaging tool - localises sources of magnetic fields produced by the brain
   • No contact with the scalp - just sit in a machine
   • Better temporal resolution than EEG / ERP Better temporal resolution than fMRI
     • Very expensive, requires low noise environment (away from magnetic disturbance)
     • MEG provides unique combination of both fine spatial and temporal resolution - allowing users to not only LOCALISE where in the brain a specific function originates but also TRACK FUNCTION as it occurs
   • Magnetoencephalography

3. Transcranial Magnetic Stimulation (TMS)

   • Stimulates small areas of the brain by producing small electrical currents, which generate a focused magnetic field. Works by altering and disrupting neural activity
     • Neurons respond to TMS instead of responding to other neurons
       • Safe and non-invasive
         • Limitations - Effects are brief and only for superficial surface of the brain (ones that can be reached by pulse)
       • Stimulation of motor cortex causes movement of hand, stimulation of visual cortex causes problems in ability to identify letters

4. Positron Emission Photography (PET)

   • Relatively direct indicator of nerve cell metabolism
     • Good spatial resolution, but poorer than fMRI
       • Only group comparisons can be made
         • Precautions apply - RADIOACTIVE MATERIAL
   • Mean blood flow difference in images
   • Injection of radioactive tracer, decay leads to emission of photons which annihilates with electrons, emitting GAMMA RAYS
     • Can label neurotransmitters
       • Tracer accumulates in regions of high cerebral blood flow
   • Very expensive

5. Convergent techniques

   • Each technique is weak in isolation
     • Convergent findings from different techniques can be more reliable for brain-behaviour relationship

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