In search of cerebral error detectors.

Multiunit activity was recorded from 124 different subcortical sites in 10 parkinsonian patients bearing gold electrodes for diagnosis and therapy. The patients participated in a visual recognition task in which the stimuli (digits) were presented on a LED-matrix at threshold, the exposure times so chosen that in about half the trials the patient failed to recognize the digit correctly. Peristimulus time histograms (PSTHs) for each neuronal population as well as profiles of reactions for all neuronal populations were calculated and statistically analysed, separately for the cases of correct, incorrect, and non-recognition. There are at least 3 groups of neuronal populations, each associated with one temporally separate neurophysiological process involved in the performance of the psychological recognition task. They can be differentiated by the parameters' 'onset' and 'peak' latency. This in itself suggests that they may be related to different psychological processes involved in the task's performance, the earlier components in feature detection and/or evaluation operations concerning the stimulus; the later components, presumably, in processes related to initiation of the actual response. By scanning the individual PSTHs, we found one neuronal population which might be considered an error detector. This population reacted robustly in the early stages of information processing (100-500 ms post-stimulus) only in the case of non-optimal behavior, suggesting that it might somehow be related to signalling an error.