Bohm, C. | bioRxiv Science

bioRxiv2024

Reduced selection during sweeps lead to adaptive momentum on rugged landscapes

AbstractEvolutionary theory seeks to explain the remarkable diversity and adaptability of life on Earth. Current theory offers substantial explanatory power, but it overlooks important transient dynamics that are prominent only when populations are outside equilibrium, such as during selective sweeps. We identify a dynamic that we call "adaptive momentum" whereby lineages with a selective advantage can temporarily sustain more deleterious mutations. This reduction in the strength of purifying selection allows populations to explore fitness valleys that are usually too costly to enter, potentially leading to the discovery of otherwise inaccessible fitness peaks. Using mathematical and agent-based simulations, we demonstrate adaptive momentum and show how periods of disequilibrium become windows of enhanced adaptation. Genetic exploration can occur during these windows without requiring mechanisms such as changing environments or complex landscapes. Adaptive momentum provides a simple potential explanation for bursts of rapid evolution observed in nature, including in pathogens such as SARS-CoV-2 and cancers. (152 words)

evolutionary biology↗

bioRxiv2023

Functional specialization and structured representations for space and time in prefrontal cortex

Neurons in prefrontal cortex exhibit selectivity for a range of behaviorally relevant variables, such as sensory stimuli, place, time, choice, context, and category. At the population level, representations of these variables can be organized in various ways--for instance, geometrically or hierarchically. However, how selectivity for each feature is distributed across cells and how this gives rise to such population-level representational structure is unclear. To address these questions, we analyzed coding for space, time, and category in rats performing a navigational task featuring two behavioral categories, starts and goals, each consisting of multiple locations. Population activity was organized hierarchically, with neural distances between elements of a category being smaller than the distances between categories. At the single cell level, individual medial prefrontal cortex (mPFC) neurons were tuned to category and space independently, consistent with hierarchical population geometry emerging from random mixed selectivity, while neurons exhibited preferences for representing space or time across categories, consistent with functional specialization. These distinct selectivity rules across different levels of abstraction suggest that different aspects of prefrontal representations have disparate origins and may enable modularized computations across multiple behaviors and contexts.

neuroscience↗