Biology subjects

Hahamy, A.

Publications and source records attributed to Hahamy, A..

3 recordsLinked to original sources

bioRxiv2023

Flexible and abstract neural representations of structural knowledge

Humans ability for generalisation is outstanding. It is flexible enough to identify cases where knowledge from prior tasks is relevant, even when many features of the current task are different, such as the sensory stimuli or the size of the task state space. We have previously shown that in abstract tasks, humans can generalise knowledge in cases where the only cross-task shared feature is the statistical rules that govern the tasks state-state relationships. Here, we hypothesized that this capacity is associated with generalisable representations in the entorhinal cortex (EC). This hypothesis was based on the ECs generalisable representations in spatial tasks and recent discoveries about its role in the representation of abstract tasks. We first develop an analysis method capable of testing for such representations in fMRI data, explain why other common methods would have failed for our task, and validate our method through a combination of electrophysiological data analysis, simulations and fMRI sanity checks. We then show with fMRI that EC representations generalise across complex non-spatial tasks that share a hexagonal grid structural form but differ in their size and sensory stimuli, i.e. their only shared feature is the rules governing their statistical structure. There was no clear evidence for such generalisation in EC for non-spatial tasks with clustered, as opposed to planar, structure.

neuroscience↗

bioRxiv2022

The human brain reactivates context-specific past information at event boundaries of naturalistic experiences

Although we perceive the world in a continuous manner, our experience is partitioned into discrete events. However, to make sense of these events, they must be stitched together into an overarching narrative - a model of unfolding events. It has been proposed that such a stitching process happens in offline neural reactivations when rodents build models of spatial environments. Here we show that, whilst understanding a natural narrative, humans reactivate neural representations of past events. Similar to offline replay, these reactivations occur in hippocampus and default mode network, where reactivations are selective to relevant past events. However, these reactivations occur, not during prolonged offline periods, but at the boundaries between ongoing narrative events. These results, replicated across two datasets, suggest reactivations as a candidate mechanism for binding temporally distant information into a coherent understanding of ongoing experience.

neuroscience↗

bioRxiv2018

Reorganization in cerebral and cerebellar cortices is not restricted by proximity between body-part representations

A fundamental organizing principle in the somatosensory and motor systems is somatotopy, where specific body parts are represented separately and adjacently to other body parts, resulting in a body map. Different terminals of the sensorimotor network show varied somatotopic layouts, in which the relative position, distance and overlap between body-part representations differ. Since somatotopy is best characterized in the primary somatosensory (S1) and motor (M1) cortices, these terminals have been the main focus of research on somatotopic remapping following loss of sensory input (e.g. arm amputation). Cortical remapping is generally considered to be driven by the layout of the underlying somatotopy, such that neighboring body-part representations tend to activate the deprived brain region. Here, we challenge the assumption that somatotopic layout restricts remapping, by comparing patterns of remapping in humans born without one hand (hereafter, one-handers, n=26) across multiple terminals of the sensorimotor pathway. We first report that in the cerebellum of one-handers, the deprived hand region represents multiple body parts. Importantly, the representations of some of these body parts do not neighbor the deprived hand region. We further replicate our previous finding, showing a similar pattern of remapping in the deprived hand region of the cerebral cortex in one-handers. Finally, we report preliminary results of a similar remapping pattern in the putamen of one-handers. Since these three sensorimotor terminals (cerebellum, cerebrum, putamen) contain different somatotopic layouts, the parallel remapping they undergo demonstrates that the mere spatial layout of body-part representations may not exclusively dictate remapping in the sensorimotor systems.\n\nSignificance StatementWhen a hand is missing, the brain region that typically processes information from that hand may instead process information from other body-parts, a phenomenon termed remapping. It is commonly thought that only body-parts whose information is processed in regions neighboring the hand region could \"take up\" the resources of this now deprived region. Here we demonstrate that information from multiple body-parts is processed in the hand regions of both the cerebral cortex and cerebellum. The native brain regions of these body-parts have varying levels of overlap with the hand region across multiple terminals in the sensorimotor hierarchy, and do not necessarily neighbor the hand region. We therefore propose that proximity between brain regions does not limit brain remapping.

neuroscience↗