Event Related Slow Potential Changes in Human Brain Stem

A SLOW negative shift of brain electrical potential can indicate association made between paired stimuli when one acts as a warning and the other an imperative stimulus 1 . This is termed the contingent negative variation (CNV). Intracerebral recording in man confirmed the cortical origins of the change seen at the scalp. There have, however, been suggestions based on animal studies 2–5 that, although essentially a cortical change, the CNV might be mediated by the action of sub-cortical centres, possibly in the thalamus and/or the brain stem and midbrain reticular system. Haider et al. recording from electrodes in thalamus and on the cortex of patients undergoing acute thalamic surgery, have reported characteristic changes in evoked potentials from the ventro-oral nucleus accompanying the appearance of the CNV at the cortex 6,7 .