Mixed selectivity coding of content-temporal detail by dorsomedial posterior parietal neurons

Abstract

The dorsomedial posterior parietal cortex is part of a higher-cognition network implicated in elaborate processes underpinning memory formation, recollection, episodes reconstruction, and temporal information processing. Neural coding for complex episodic processing is however under-documented. Here we revealed a set of neural codes of neuroethogram in the primate parietal cortex. Analyzing neural responses in macaque dmPPC to naturalistic videos, we discovered several groups of neurons that are sensitive to different categories of ethogram-items and to low-level sensory features, and saccadic eye movement. We also discovered that the processing of category and feature information by these neurons is sustained by accumulation of temporal information over a long timescale up to 30 s, corroborating its reported long temporal receptive windows. We performed an additional behavioral experiment and found that saccade-related activities could not account for the mixed neuronal responses elicited by the video stimuli. We further observed monkeys scan-paths and gaze consistency are modulated by video content. Taken altogether, these neural findings explain how dorsomedial PPC weaves fabrics of ongoing experiences together in real-time. The high dimensionality of neural representations should motivate us to shift the focus of attention from pure selectivity neurons to mixed selectivity neurons, especially in increasingly complex naturalistic task designs. HIGHLIGHTSO_LINeural codes for "neuroethogram" in macaque dorsomedial parietal cortex C_LIO_LIParietal neural codes exhibit mixed selectivity of event features C_LIO_LIDorsomedial PPC neurons support a long temporal receptive window for episodes C_LIO_LISaccadic movement could not explain away mixed neuronal responses C_LIO_LIConsistency in scan-path and gaze shown across viewing repetitions C_LI