Habituation and modification of reticular formation neuron responses to peripheral stimulation in cats

Abstract

Reticular formation neurons have been shown to respond in a dynamic way to repetitive and changing sensory input. Extracellular, microelectrode recording was performed in 22 acutely prepared, unanesthetized, immobilized cats. Twenty-one of 36 midbrain and medullary reticular formation cells manifested response habituation after 5–15 min of repetitive sciatic stimulation at once per 3 sec. Two types of changes were observed in the post-stimulus time histograms and dot displays: decrease in the amplitude or change in the latency of the responses. Recovery of the prehabituated responses and comparison of responses to prehabituation and posthabituation control stimulation of either the other sciatic nerve or forepaw indicated that habituation resulted from the stimulus repetition. Ten of 18 neurons, tested completely, showed response modifications to stimulation of one sciatic nerve after pairing for 10–15 min with a stimulus to the other sciatic or forepaw. Extinction of the modified responses and comparison of control responses before and after pairing suggested that the response modifications were related specifically to the pairing experience. Stimulus pairing initially led to sensory interaction, i.e., the units responded in a different way to pairing of the stimuli than to either stimulus alone. Nine of 12 neurons manifesting sensory interactions later showed response modifications after pairing. Also six of seven cells that had previously displayed both habituation and sensory interactions subsequently demonstrated response modifications. Thus response modifiability appears to be characteristic of many reticular formation cells that also manifest other dynamic properties such as habituation and sensory interaction.