Neural Population Dynamics in Primate Multisensory Cortical Areas during Heading Discrimination

Cortical areas involved in self-motion perception process cues from multiple sensory modalities, primarily visual and vestibular, alongside choice-related activity. Neurons in these regions often respond to combinations of these factors-demonstrating a high degree of mixed selectivity. Moreover, self-motion is inherently dynamic, with each cue-visual and vestibular-comprising a mix of distinct motion signals, such as velocity and acceleration, that evolve over time. Here, we developed a time-varying targeted dimensionality reduction method to expose these dynamic motion and choice-related signals in neuronal populations. We applied this approach to recordings from the ventral intraparietal cortex (VIP), dorsal medial superior temporal cortex (MSTd), and parietoinsular vestibular cortex (PIVC), in six male rhesus macaques, performing a task of heading discrimination. Distinct configurations of dynamic signals were seen in the population activity across the different cortical areas. VIP exhibited all components-namely, velocity and acceleration, for visual and vestibular cues, along with strong choice-related signals that rose early and remained elevated throughout the stimulus period, well before the choice was reported. In contrast, MSTd and PIVC had weaker and later choice-related activity. MSTd primarily exhibited visual signals (velocity more than acceleration) with weak vestibular signals. PIVC predominantly exhibited vestibular signals (velocity and acceleration), yet visual signals were nonetheless present. The distinct configurations of time-varying parameters across VIP, MSTd, and PIVC likely reflect different functional specializations in heading discrimination.