EEG and slow brain potentials during anticipation and control of painful stimulation

Abstract

Cerebral responses in anticipation of painful stimulation and while coping with it were investigated in a ‘fakir’ and 12 male volunteers. Experiment 1 consisted of 3 periods of 40 trials each. During period 1, subjects heard one of two acoustic warning stimuli of 6 sec duration signalling that either an aversive noise or a neutral tone would be presented at S1 offset. During period 2, subjects were asked to use any technique for coping with pain that they had ever found to be successful. During period 3, the neutral S2 was presented simultaneously with a weak electric shock and the aversive noise was presented simultaneously with a strong, painful shock, again under pain coping instructions. EEG activity within the theta band increased in anticipation of aversive events. Theta peak was most prominent in the fakir's EEG. A negative slow potential shift during the S1–S2 interval was generally more pronoounced in anticipation of the aversive events than the neutral ones, even though no overt motor response was required. Negativity tended to increase across the three periods, opposite to the usually observed diminution. In Experiment 2, all subjects self-administered 21 strong shock-noise presentations. The fakir again showed more theta power and more pronounced EEG negativity after stimulus delivery compared with control subjects. Contrary to the controls, self-administration of shocks evoked a larger skin conductance response in the fakir than warned external application.