Sensory system neural activity during habituation of the pupillary orienting reflex

Abstract

The possible role of sensory system evoked activity in the habituation of the orienting reflex was examined by recording simultaneously multiple unit activity and pupillary responses to repeated tactile and acoustic stimulation. Cats bearing electrodes chronically implanted in the somatosensory and auditory systems were tested during neuromuscular paralysis in order to ensure constancy of stimulus intensity at the receptors and permit precise monitoring of pupillary size. Tactile and acoustic stimulation produced evoked responses in both of these sensory systems. Both tactile stimulation (1/3 sec) and acoustic stimulation (1/min) resulted in habituation of the pupillary dilation component of the orienting reflex which was accompanied by decrements in somatosensory and auditory system evoked activity. The cochlear nucleus was unresponsive to tactile stimulation, and did not exhibit response decrements during acoustic stimulation. Background activity increased in the auditory cortex during tactile habituation, and in the somatic cortex during auditory habituation. The results indicate that systematic decrements in sensory evoked multiple unit activity could be of functional significance to the habituation of the orienting reflex and that specific effects upon sensory cortex do develop during behavioral habituation.