Brainstem mechanisms underlying variations in the occurrence of experimentally elicited rhythmic oral movements in...

Mechanical stimulation of the oral cavity of the decerebrate rat induces rhythmic oral movements in some animals but not in others. Reasons for this difference were sought using electrical stimulation of the lip to elicit a variety of responses which were capable of accurate quantification. Neither the digastric reflex threshold, size of suprathreshold response nor the ability to generate rhythmic activity within the brainstem differed in the two groups. Depression of the digastric reflex by an electrical stimulus applied 30-150 ms previously was, however, significantly greater in those animals not showing rhythmic oral movements. It is suggested that the two groups differed in their ability to produce rhythmic oral movements because of differences in the level of stimulus related inhibition rather than any tonic effects on trigeminal neuronal activity.