Reaction time and heart rate response pattern: Effects of reticular stimulation in cats

Abstract

The effects of stimulation of the mesencephalic reticular formation and other midbrain sites on heart rate (HR) and reaction time (RT) performance were studied in unanesthetized cats. Without stimulation, four of five cats showed the human pattern of deceleration in the preparatory interval. There was no clear and consistent evidence that HR decreases and fast RTs were associated in the cats as they were in human experiments. Differences between the human and cat experiments which might account for this discrepancy were discussed. At some reticular sites stimulation facilitated HR decelerations during the foreperiod and lowered intertrial HR. Improvement in RT could be dissociated from effects on HR, and effects on task-related HR response could be dissociated from effects on intertrial HR level. Improved RT performance and similar HR effects were obtained from four midbrain electrodes clearly outside of the reticular formation. Three of these were in the Substantia Nigra. Reticular facilitation of the baroreceptor reflex was not confirmed. It was concluded that HR, tonic or phasic, cannot be used as an index of the reticular activity underlying behavioral arousal. Heart rate reflects, among other things, the attentive demands of the task; attentive behavior is often accompanied by HR slowing.