Neuronal habituation in the vestibular nuclei of the cat

This is a study of the effects of repeated angular acceleration on the activity of vestibular nuclei units in anesthetized and in conscious cats. The experimental animals were subjected to trains of repeated and consecutive constant acceleration-deceleration ramps (4-8 degrees/sec2). In a few cases nystagmus was recorded along with extracellular unit activity. The effect of stimulus repetition on vestibular neuronal activity consisted of one of the following: 1. No change in response. 2. Progressive response decline. 3. An initial maintenance of a constant response level throughout the first part of the stimulus paradigm, followed by a progressive decline. 4. An initial gradual enhancement of response followed by a progressive decline. This classification is based on results of polynomial and non-linear broken-line regression analyses. Categories 3 and 4 were found predominantly in units recorded from conscious cats. The majority of neurons recorded from anesthetized cats that exhibited response changes upon stimulus repetition manifested a progressive response decline. The response decline in anesthetized cat units was usually on a faster time scale than in conscious cats. Correlations between unit response modification patterns and simultaneously recorded nystagmus were mostly of a moderate degree.