Biology subjects

Savelli, F.

Publications and source records attributed to Savelli, F..

4 recordsLinked to original sources

bioRxiv2025

Prevalence and modulation of rat off-track head-scanning on linear tracks: possible implications for representational and dynamical properties of hippocampal place cells

(Re)mapping of different environments by hippocampal place cells is thought to reflect incidental learning. Rat "head scanning" is a spontaneous and presumed investigatory behavior that can trigger the onset of firing locations in place cells. This behavior was studied on (quasi-)circular tracks, and it was speculated that off-track head scans might have been overlooked or inadvertently discouraged in studies employing more common apparatus. To better understand the general prevalence and significance of off-track scanning, we investigated it in rats running laps on linear tracks in rooms featuring visual landmarks. Scanning spanned the length of the track, even in highly familiar conditions and in rats rewarded only at the two ends of the track. Thus, co-localized rewards are not necessary for the occurrence of this behavior. Scanning rate increased markedly in a novel room and then declined steeply during each daily session in this room over 3 days. Transient increases at the beginning of each daily session partially counteracted this decline, producing a "seesaw" profile that is reminiscent of previous observations on place cell plasticity. Therefore, the remapping that place cells are known to undergo in similar contextual changes could conceivably be facilitated by the putative surge of new place fields induced by increased scanning. Investigatory behaviors could thus be causally involved in the representational and dynamic properties of hippocampal representations. Addressing these possibilities offers insight into the incidental creation and update of a cognitive map. HIGHLIGHTSO_LIRat head scanning is known to trigger the onset of firing locations in place cells C_LIO_LIOff-track scanning occurs on linear tracks in familiar and novel conditions C_LIO_LICo-localized rewards are not necessary for scanning events C_LIO_LIResponse to a novel room resembles that seen in place cell dynamics C_LIO_LIRelationships between head scanning and place field formation could help uncover the incidental process of map making C_LI

neuroscience↗

bioRxiv2023

Spontaneous dynamics of hippocampal place fields in a model of combinatorial competition among stable inputs

We present computer simulations illustrating how the plastic integration of spatially stable inputs could contribute to the dynamic character of hippocampal spatial representations. In novel environments of slightly larger size than typical apparatus, the emergence of well-defined place fields in real place cells seems to rely on inputs from normally functioning grid cells. Theoretically, the grid-to-place transformation is possible if a place cell is able to respond selectively to a combination of suitably aligned grids. We previously identified the functional characteristics that allow a synaptic plasticity rule to accomplish this selection by synaptic competition during rat foraging behavior. Here, we show that the synaptic competition can outlast the formation of place fields, contributing to their spatial reorganization over time, when the model is run in larger environments and the topographical/modular organization of grid inputs is taken into account. Co-simulated cells that differ only by their randomly assigned grid inputs display different degrees and kinds of spatial reorganization--ranging from place-field remapping to more subtle in-field changes or lapses in firing. The model predicts a greater number of place fields and propensity for remapping in place cells recorded from more septal regions of the hippocampus and/or in larger environments, motivating future experimental standardization across studies and animal models. In sum, spontaneous remapping could arise from rapid synaptic learning involving inputs that are functionally homogeneous, spatially stable, and minimally stochastic. Significance StatementIn both AI and theoretical neuroscience, learning systems often rely on the asymptotic convergence of slow-acting learning rules applied to input spaces that are presumed to be sampled repeatedly, for example over developmental timescales. Place cells of the hippocampus testify to a neural system capable of rapidly encoding cognitive variables--such as the animals position in space--from limited experience. These internal representations undergo "spontaneous" changes over time, spurring much interest in their cognitive significance and underlying mechanisms. We investigate a model suggesting that some of these changes could be a tradeoff of rapid learning.

neuroscience↗

bioRxiv2022

Closed-loop control and recalibration of place cells by optic flow

Understanding the interplay between sensory input, endogenous neural dynamics, and behavioral output is key toward understanding the principles of neural computation. Hippocampal place cells are an ideal system to investigate this closed-loop interaction, as they are influenced by both self-motion (idiothetic) signals and by external sensory landmarks as an animal navigates its environment1-9. To continuously update a position signal on an internal "cognitive map", the hippocampal system integrates self-motion signals over time10,11. In the absence of stable, external landmarks, however, these spatial correlates of neuronal activity can quickly accumulate error and cause the internal representation of position or direction to drift relative to the external environment1,5. We have previously demonstrated that, in addition to their known roles in preventing and/or correcting path-integration error, external landmarks can be used as a putative teaching signal to recalibrate the gain of the path integration system6. However, it remains unclear whether idiothetic cues, such as optic flow, exert sufficient influence on the cognitive map to enable recalibration of path integration, or if instead an unambiguous allocentric frame of reference, anchored by polarizing landmark information, is essential for path integration recalibration. Here, we use principles of control theory12,13 to demonstrate systematic control of place fields by pure optic flow information in freely moving animals by using a neurally closed-loop virtual reality system that adjusts optic flow speed as a function of real-time decoding of the hippocampal spatial map. Using this "cognitive clamp", we show that we can not only bring the updating of the map under control of the optic flow cues but we can also elicit recalibration of path integration. This finding demonstrates that the brain continuously rebalances the influence of conflicting idiothetic cues to fine-tune the neural dynamics of path integration, and that this recalibration process does not require a top-down, unambiguous position signal from landmarks.

neuroscience↗

bioRxiv2018

Recalibration of path integration in hippocampal place cells

Hippocampal place cells are spatially tuned neurons that serve as elements of a \"cognitive map\" in the mammalian brain1. To detect the animals location, place cells are thought to rely upon two interacting mechanisms: sensing the animals position relative to familiar landmarks2,3 and measuring the distance and direction that the animal has travelled from previously occupied locations4-7. The latter mechanism, known as path integration, requires a finely tuned gain factor that relates the animals self-movement to the updating of position on the internal cognitive map, with external landmarks necessary to correct positional error that eventually accumulates8,9. Path-integration-based models of hippocampal place cells and entorhinal grid cells treat the path integration gain as a constant9-14, but behavioral evidence in humans suggests that the gain is modifiable15. Here we show physiological evidence from hippocampal place cells that the path integration gain is indeed a highly plastic variable that can be altered by persistent conflict between self-motion cues and feedback from external landmarks. In a novel, augmented reality system, visual landmarks were moved in proportion to the animals movement on a circular track, creating continuous conflict with path integration. Sustained exposure to this cue conflict resulted in predictable and prolonged recalibration of the path integration gain, as estimated from the place cells after the landmarks were extinguished. We propose that this rapid plasticity keeps the positional update in register with the animals movement in the external world over behavioral timescales (mean 50 laps over 35 minutes). These results also demonstrate that visual landmarks not only provide a signal to correct cumulative error in the path integration system, as has been previously shown4,8,16-19, but also rapidly fine-tune the integration computation itself.

neuroscience↗