Prolonged medial forebrain bundle unit responses to rewarding and aversive intracranial stimuli

In unanesthetized cerveau isolé rats, brief medial forebrain bundle (MFB) and dorsal midbrain reticular (RET) stimulus trains elicited prolonged MFB unit responses lasting up to ten or more seconds. On the MFB unit responses studied, the effects of MFB and RET stimuli were basically similar, although the stimulations were probably rewarding and aversive respectively. These data agree with the previously reported anatomical localization, in medial regions of thalamus and pallidum, of opposite single cell responses to the behaviorally opposite inputs, and suggest that unit responses to rewarding stimuli should not be characterized as reward-related when aversive stimuli elicit similar responses in the same unit.