The relationship between P3-latency and reaction time in depression.

A random series of frequencies and infrequent clicks was presented to 13 primary depressives and 13 healthy controls matched for age and gender. Subjects were instructed to press a button as fast as possible in response to the infrequent clicks. P3 amplitudes and latencies as well as correlations between P3 latency and reaction time were calculated on a single trial basis using Woody's adaptive filter. While reaction times were significantly longer in patients, neither P3 latencies nor P3 amplitudes differed between the groups. Thus, delayed reaction time of depressives seems to be a consequence of impaired selection, activation, or execution of the motor response rather than of delayed stimulus evaluation. The correlation between P3 latency and reaction time was significantly smaller in patients then in controls.