Intracerebral events in humans related to real and imaginary stimuli.

Abstract Recordings were made from gold intracerebral electrodes in orbital and cingulate cortex and subdural electrodes on superior frontal cortex in five patients under treatment for chronic obsessional and anxiety disorders. The subjects were instructed to guess whether or not they would receive a stimulus in the form of a flash, click or electric shock to the finger. They were told to move a lever to the right when they expected a stimulus and to the left when they did not. A reward was offered for every three successive correct guesses. Movement of the lever in either direction started a LINC 8 averaging and provided a stimulus or not according to a switching programme operated by the experimenter. Sets of averages of eight trials each were collected in the four conditions: expectation-occurrence, expectation-non-occurrence, no expectation-occurrence, no expectation-non-occurrence. Averages were also taken of responses to random stimuli and of intrinsic activity when the lever was moved without guessing or stimuli. Clear cerebral events, termed “emitted potentials”, were observed when stimuli were expected but did not occur. The emitted potentials resembled those evoked when real stimuli were presented on switch closure, suggesting that they may reflect memory processes corresponding to the perception of real events. In some experiments the latency of the emitted potentials was significantly shorter than that of responses evoked by real random stimuli, suggesting a rise in cortical excitability with expectancy. A positive deflection peaking at about 300 msec often appeared following switch closure, particularly with expectancy, and a negative variation usually preceded and accompanied this action.