Evoked potential studies (auditory, cognitive, visual, sympathetic) show changes in the electrical activity of the brain in response to certain stimuli. The amplitude of the evoked potentials is small and ranges from tenths of a microvolt to several microvolts.
When interpreting survey data, methods are used that are independent of the reporting point. Analysis of field strength, dipole signal curves is preferred. Time division into different components is used to isolate a single peak in the signal curve. Evoked potentials from stimulation with simple stimuli are usually investigated.
In psychiatric practice, stimuli are compared with the cognitive assessment of the signal, the degree of concentration of attention.
By modality, evoked potentials are divided into:
Auditory evoked potentials P50 appear in 50 msec . after clicking. The auditory cortex of the temporal lobe is responsible for the reaction.
Auditory evoked potential N-100 is induced in the superior temporal gyrus and is modulated by attention.
Auditory P300 evoked potentials arise in response to frequent stimuli. The patient must calculate these stimuli at the push of a button. Signals are divided into: P300a and P300b. P300a is a reflection of orientation response, P300b is associated with attention and cognitive ability. The temporal and parietal lobes are responsible for its occurrence. With depression, a change in the shape and amplitude of N100-P200 is observed and reflects serotonergic activity and the intensity of serotonin metabolism.