[Clustering of vestibular direction-selective neurons in macaque parieto-insular vestibular cortex]

Neurons with direction-selectivity for vestibular stimuli are found in a number of cortical areas, and neurons in the ventral intraparietal area (VIP) and the dorsal subdivision of the medial superior temporal area (MSTd) of the macaque brain are clustered according to their direction preferences for vestibular signals. This raises the question where the clustering inherits from? Previous work has shown that VIP and MSTd most probably receive vestibular input from the parieto-insular vestibular cortex (PIVC), which processes vestibular signals at the earlier stage. Thus, PIVC is also supposed to show a clustered organization similar to that seen in VIP and MSTd. The present study was aimed to examine clustering properties of vestibular response in PIVC area. To address this issue, we compared the tuning of isolated single unit (SU) with the undifferentiated multiunit (MU) activity of several neighboring neurons recorded from the same microelectrode. When directional tuning was observed in MU activity, the direction preference generally agreed closely with that of a simultaneously recorded SU. These results suggest that PIVC neurons are indeed clustered according to preferred direction for both translational and rotational vestibular stimuli.