Spatial Information Encoding across Multiple Neocortical Regions Depends on an Intact Hippocampus

Abstract

There has been considerable research showing populations of neurons encoding for different aspects of space in the brain. Recently, several studies using two-photon calcium imaging and virtual navigation have identified "spatially" modulated neurons in the posterior cortex. We enquire here whether the presence of such spatial representations may be a cortex-wide phenomenon and, if so, whether these representations can be organized in the absence of the hippocampus. To this end, we imaged the dorsal cortex of mice running on a treadmill populated with tactile cues. A high percentage (40-80%) of the detected neurons exhibited sparse, spatially localized activity, with activity fields uniformly localized over the track. The development of this location specificity was impaired by hippocampal damage. Thus, there is a substantial population of neurons distributed widely over the cortex that collectively form a continuous representation of the explored environment, and hippocampal outflow is necessary to organize this phenomenon.

The spatiotemporal organization of experience dictates hippocampal involvement in primary visual cortical plasticity

“…Therefore, how the brain stores long-term representations of individual oriented gratings appears to vary depending on their relationship to other sensory stimuli. This conclusion is consistent with observations that neocortical representations of sensory stimuli are strongly influenced by other environmental cues, such as spatial position, and that this modulation requires the hippocampus (50).…”

Spatial coding in the hippocampus of flying owls

“…It is noteworthy also that although in mammals place cells have been primarily described as a hippocampal phenomenon, spatial modulation of firing-rates has been found also in several neocortical areas (Diamanti et al, 2021;Esteves et al, 2021;Long and Zhang, 2021). Thus, our finding of place-cells in HAp may be in-line with findings from mammals.…”

The spatiotemporal organization of experience dictates hippocampal involvement in primary visual cortical plasticity

“…This conclusion is consistent with observations that neocortical representations of sensory stimuli are strongly influenced by other environmental cues, such as spatial position, 49 and that this modulation requires the hippocampus. 50 One compelling model is that the hippocampus specifically encodes so-called successor representations that preserve relationships or transitions among sensory features 51 rather than the identity of each discrete stimulus.…”