Clustering Of Vestibular Activity In The Ventral Intraparietal Area Of Macaque Cortex

"Structure determines function" was thought to be one of the basic principles in biology.Since the functional columns have been found in visual cortex,clustered organization was widely considered as a general organizational principle of the cerebral cortex.Neurons with similar response properties are clustered to facilitate information exchange by minimizing the wiring cost and improve signal reliability by reducing stochastic noise.Thus,understanding cells with which features are clustered in different brain areas may help to reveal the functional roles of these areas.The ventral intraparietal area(VIP)in macaque monkeys is a multimodal cortical region,in which neurons have responses to both optic flow and vestibular self-motion signals,and may play significant role in heading perception.Previous studies have demonstrated that tuning for optic flow stimuli in VIP is organized in a clustered manner,but the organization of neurons responsive to vestibular information is not known.Given that VIP receives considerable input from the dorsal medial superior temporal area(MSTd),which has a clustered organization for vestibular stimuli,we hypothesized that VIP may also contain a clustered representation of vestibular signals.In the current study,monkey behavioral task and electrophysiological recording were used to analysis the clustering of VIP neurons for vestibular selectivity,heading discriminability and choice-related signals.Therefore,we recorded the neuronal activities(single unit,SU)during fixation task and discrimination task,then we extracted the multiunit activities(MU)off-line,which correspond to the responses of several neurons neighboring the SU.The clustering was examined by comparing the activities of SU with that of simultaneously recorded MU,and the results were concluded as following:1.In the translation condition,425 pairs of SU and MU activities for vestibular stimuli were recorded during the fixation task.Then we examined the preferred direction and tuning strength,and found that the SU and MU translation preferences were well matched and tuning strength were significantly correlated.These results indicate that VIP neurons are clustered according to the translational selectivity.2.In the rotation condition,134 pairs of SU and MU responses for vestibular stimuli were recorded during the fixation task.Similar to the translation condition,the preferred directions were also well matched,and tuning strength were also significantly correlated,indicating that direction tuning for rotation stimuli in VIP is also organized in a clustered manner.3.For the heading discrimination task,we compared the neuronal discrimination thresholds between SU and MU responses for vestibular condition,and found that the thresholds of SU and MU activities were well correlated.Thus,the vestibular signals related to heading discriminability are clustered in VIP as well.4.The relationship between monkey behavior choice and neuronal responses recorded during heading discrimination task were also quantified by the choice probability(CP).The CP values for SU and MU were well correlated in vestibular condition,indicating that not only the sensory signals but the choice-related signals regarding self-motion are also clustered within area VIP.5.To further investigate whether the clustering of vestibular selectivity inherit from parieto-insular vestibular cortex(PIVC),the same analysis was conducted to the PIVC neural responses in fixation task.The results showed that PIVC neurons are also clustered according to the vestibular selectivity.Moreover,compared with VIP,the direction preferences of SU and MU were more consistent with each other and the tuning profiles were also related stronger to nearby neurons in PIVC.6.We further explored whether the statistical rules of vestibular-visual interaction are also clustered.We recorded the neuronal responses in visual posterior sylvian cortex(VPS),which was a multimodal cortical area being closer to the vestibular periphery compared with VIP.We examined the SU responses to the vestibular-visual stimuli,and found that multisensory neurons show weighted linear sums of unimodal response.Moreover,the neuronal activities showed cross-modal suppression when one of the two stimuli was presented at a non-preferred heading direction,but the bimodal responses were enhanced when both stimuli were presented at the preferred heading.The relevant MU activities are currently being analyzed.These results suggested a potential statistical exploration of neural response to bimodal stimuli.Thus,VIP neurons are clustered according to both the sensory and choice-related signals regarding self-motion.These results indicated that VIP may play important role in processing the vestibular and perception-related signals.Furthermore,the stronger clustering characteristic for PIVC neurons indicated that the clustering of VIP neurons may inherit from PIVC.This study provided foundational support for understanding the neural mechanism of how visual and vestibular signals regarding self-motion are encoded,and also provided a basic evidence for further exploring of clustering characteristics of statistical rule on population level.