Biology subjects

Kalle Kossio, F. Y.

Publications and source records attributed to Kalle Kossio, F. Y..

3 recordsLinked to original sources

bioRxiv2025

Brain-wide representational drift: memory consolidation and entropic force

Memory engrams change on the microscopic level with time and experience as the neurons that compose them switch in a process termed representational drift. On the macroscopic level the engrams are not static either: numbers of engram neurons in different brain regions change over time, which is considered to reflect the process of memory consolidation. Here we predict a link between these two levels, using a novel statistical physics approach to engram modeling. Importantly, it is general as it makes only minimal assumptions on the engrams nature, does not rely on a specific architecture, and its fundamental implications hold for any representational drift with random component. Our first, analytically well tractable model shows that an entropic force emerges at the region level from random representational drift at the neuronal level. We refine the model by incorporating the interaction of the entropic force with biological processes that shape neuronal engrams. Here, the connectivity between the brain regions strongly influences the (quasi-)equilibrium engram distribution. The obtained distributions are in qualitative agreement with the ones of a biologically detailed drifting assembly model. Our engram description allows to predict the engram evolution in large neuronal systems such as the mouse brain. We find several predictions that are consistent across the valid tested parameter ranges, such as a strong tendency of the engram to leave the hippocampus. The results suggest that the brain operates in a regime where engrams drift, both deterministically and randomly, to allow for memory consolidation.

neuroscience↗

bioRxiv2025

Odour representations supporting ethology-relevant categorisation and discrimination in the Drosophila mushroom body

Neural representations of sensory stimuli serve multiple distinct purposes, from the rapid recognition of familiar environments, to the precise identification of individual salient cues. In the insect mushroom body (MB), odours are encoded by the activity of Kenyon cells (KCs). The random wiring of olfactory projection neurons (PNs) and KCs in the MB calyx is thought to enhance odour discrimination. Here, we examined the impact of deviations from random wiring and demonstrated their significant roles in shaping odour representations. We confirm that different KC types have distinct PN input biases correlated with the contextual relevance of the odour information delivered by the PNs. By recording the functional responses of different KC types to ethologically defined odour categories, we found that the {beta} and {beta} KCs produce segregated representations of relevant odour groups, potentially enhancing the categorisation of odours based on ethological relevance. Simultaneously, these same KC types displayed distinct representations for food-related odours, supporting precise discrimination. In contrast, {gamma} KCs lacked significant segregation of odour representations by ethological category. Computational simulations refined with our functional data indicated that the specific PN input connection pattern of individual KC types largely accounts for the observed representations. Taken together, we propose that individual KC types process odour information with distinct objectives, supporting both ethological categorisation and discrimination.

neuroscience↗

bioRxiv2020

Drifting Assemblies for Persistent Memory

Change is ubiquitous in living beings. In particular, the connectome and neural representations can change. Nevertheless behaviors and memories often persist over long times. In a standard model, memories are represented by assemblies of strongly interconnected neurons. For faithful storage these assemblies are assumed to consist of the same neurons over time. Here we propose a contrasting memory model with complete temporal remodeling of assemblies, based on experimentally observed changes of connections and neural representations. The assemblies drift freely as spontaneous synaptic turnover or random activity induce neuron exchange. The gradual exchange allows activity dependent and homeostatic plasticity to conserve the representational structure and keep inputs, outputs and assemblies consistent. This leads to persistent memory. Our findings explain recent experimental results on the temporal evolution of fear memory representations and suggest that memory systems need to be understood in their completeness as individual parts may constantly change.

neuroscience↗