Thalamocortical Circuits Governing Egocentric-Allocentric Spatial Reference Frame Transformations

Boston University (Charles River Campus), Boston MA

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Abstract

PROJECT SUMMARY/ABSTRACT Sensory information enters the brain from a first-person, egocentric perspective. However, behavioral studies of spatial memory, and the discovery of spatial cell types such as place cells in the hippocampus and grid cells in the medial entorhinal cortex (MEC), imply that the brain binds such egocentric information to a world-centered, allocentric reference frame. One potential framework for this transformation involves a recently characterized, evolutionarily ancient pathway that conveys visual information from the superior colliculus to the postrhinal cortex (POR; homolog of the human parahippocampal cortex) via the lateral posterior thalamus (LP; homolog of the pulvinar). POR in turn sends strong projections to MEC, thought to contribute to the construction of allocentric spatial maps. While egocentric and allocentric spatial correlates have been discovered among POR neurons, the specific LP inputs that produce POR spatial firing are unknown, as are the mechanisms involved in transforming POR egocentric representations into MEC allocentric representations. The proposed experiments will seek to elucidate the neural mechanisms involved in transforming egocentric visual information into allocentric spatial representations along the pathway involving LP, POR, and MEC. Dual-site in vivo electrophysiology along with chemogenetic silencing of neural activity will be used to characterize functional and temporal connectivity between LP and POR, as well as the reliance of POR spatial representations on LP function. We also propose experiments combining computational modeling with simultaneous Neuropixels recordings from POR and MEC neurons during visual cue manipulations to identify the elements of POR cell firing that may create or support the firing of grid and non-grid spatial cells in MEC. The completion of these experiments will provide significant insight into how sensory information undergoes neural processing to guide spatial memory and behavior, as well as the mechanisms underlying deficits seen with damage to these brain areas including Alzheimer’s disease and topographical disorientation.