Influence of stimulus control on the excitability of the electrically elicited blink reflex in patients with schizophrenia

Background: In humans, the excitability of the electrically evoked blink re flex is influenced by the subject's attention to the stimulus. The early re flex component RI has been found to be facilitated in conditions of increas ed selective attention, whereas the late components R2 and R3 exhibited a m arked suppression. Distraction from the stimulus lends to enhanced R2 and R 3 magnitudes. Methods: We investigated the excitability of the distinct reflex components in 19 patients with schizophrenia and 19 healthy control subjects. In the control condition (EE), stimulation was elicited by the experimenter; in a second condition (SE), subjects released a key to evoke the reflex themselv es, Results: The SE patients with schizophrenia exhibited an abnormally increas ed RI facilitation and an impaired R2 inhibition in comparison with normal control subjects. An R3 component could be registered in EE in 13 of 19 pat ients brit only in one control subject; SE resulted in a complete suppressi on of this component in all but Two patients with schizophrenia. Conclusions: The abnormal RI facilitation and the impaired R2 inhibition ma y be regarded as neurophysiological markers of defective information proces sing in a condition of increased selective attention to a self-controlled s timulus in patients with schizophrenia, The enhanced excitability of the R3 component under standard conditions indicates defective attentional mechan isms in patients with schizophrenia in an uninstructed passive condition at tending a stimulus triggered by the experimenter.