Hummos, A. | bioRxiv Science

bioRxiv2024

Episodic memory supports the acquisition of structured task representations

Generalization to new tasks requires learning of task representations that accurately reflect the similarity structure of the task space. Here, we argue that episodic memory (EM) plays an essential role in this process by stabilizing task representations, thereby supporting the accumulation of structured knowledge. We demonstrate this using a neural network model that infers task representations that minimize the current tasks objective function; crucially, the model can retrieve previously encoded task representations from EM and use these to initialize the task inference process. With EM, the model succeeds in learning the underlying task structure; without EM, task representations drift and the network fails to learn the structure. We further show that EM errors can support structure learning by promoting the activation of similar task representations in tasks with similar sensory inputs. Overall, this model provides a novel account of how EM supports the acquisition of structured task representations.

neuroscience↗

bioRxiv2023

Modulation of prefrontal couplings by prior belief-related responses in ventromedial prefrontal cortex

Humans and animals can maintain constant payoffs in an uncertain environment by steadily re-evaluating and flexibly adjusting current strategy, which largely depends on the interactions between the prefrontal cortex (PFC) and mediodorsal thalamus (MD). While the ventromedial PFC (vmPFC) represents the level of uncertainty (i.e., prior belief about external states), it remains unclear how the brain recruits the PFC-MD network to re-evaluate decision strategy based on the uncertainty. Here, we leverage nonlinear dynamic causal modeling on fMRI data to test how prior belief-dependent activity in vmPFC gates the information flow in the PFC-MD network when individuals switch their decision strategy. We show that the prior belief-related responses in vmPFC had a modulatory influence on the connections from dorsolateral PFC (dlPFC) to both, lateral orbitofrontal (lOFC) and MD. Bayesian parameter averaging revealed that only the connection from the dlPFC to lOFC surpassed the significant threshold, which indicates that the weaker the prior belief, the less was the inhibitory influence of the vmPFC on the strength of effective connections from dlPFC to lOFC. These findings suggest that the vmPFC acts as a gatekeeper for the recruitment of processing resources to re-evaluate the decision strategy in situations of high uncertainty. Author SummaryPrefrontal cortex (PFC) together with the mediodorsal thalamus (MD) jointly establish computations critical for behavioral adaptations. While the task uncertainty (i.e., prior belief) was represented by the ventromedial PFC (vmPFC), it remains unclear how the PFC-MD network reallocates the processing resources to re-evaluate decision strategy under uncertainty. Here we filled this gap by leveraging the Bayesian hierarchical modelling and nonlinear dynamic causal modelling in an associative learning task. We found that in situations of high uncertainty, the prior belief-related responses in vmPFC significantly strengthened effective connectivity from the dorsolateral PFC to the orbitofrontal cortex, but not to the MD. The findings provide evidence for the role of vmPFC in driving the re-evaluation of the decision strategy during behavioral adaptations in situations of uncertainty.

neuroscience↗