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Maimon, S. R.

Publications and source records attributed to Maimon, S. R..

2 recordsLinked to original sources

Multi-scale place fields provide a predictive basis for hierarchical control

Hippocampal place cells typically exhibit unimodal spatial selectivity in small enclosures, but express multiple, irregularly spaced fields in environments of naturalistic scale. However, existing predictive-map theories of the hippocampus do not scale well to large environments and do not account for these heterogeneous place field characteristics. Here, we introduce the factorised hierarchical successor representation (fHSR), a predictive map that supports hierarchical control using subgoal-directed subroutines. We show that the fHSR allows efficient generalisation across tasks, scaling favourably with environmental size, and it reproduces key statistical and topological characteristics of multi-scale CA1 place cell activity in rats and bats. Analyses of experimental data further confirmed a novel prediction of the fHSR: population firing rates exhibit spatial periodicity with a characteristic wavelength independent of environmental size. These results identify the integration of hierarchical control and predictive representations as a normative principle that unifies efficient navigation with the spatial organisation of hippocampal activity.

neuroscience↗

Antagonistic center-surround mechanisms for direction selectivity in the retina

A key feature in sensory processing is center-surround receptive field antagonism. Retinal direction-selectivity (DS) relies on asymmetric inhibition from starburst amacrine cells (SAC) to direction selective ganglion cells (DSGC). SAC exhibit antagonistic center-surround, depolarizing to light increments and decrements in their center and surround, respectively, but the role of this property in DS remains elusive. We found that a repetitive stimulation exhausts SAC center and enhances its surround and used it to distinguish center-from surround-mediated responses. Center, but not surround stimulation, induced direction-selective responses in SAC, as predicted by an elementary spatiotemporal model. Nevertheless, both SAC center and surround elicited direction-selective responses in DSGCs, but to opposite directions. Physiological and morphology-based modeling data show that the opposed responses resulted from inverted DSGCs excitatory-inhibitory temporal balance, indicating that SAC response time rules DS. Our findings reveal antagonistic center-surround mechanisms for DS, and demonstrate how context-dependent center-surround reorganization enables flexible computations.

neuroscience↗