Distinct contributions of the nucleus reuniens, prefrontal cortex, and hippocampus to spatial working memory

Neunuebel, JoshuaMemory is an abstract concept referring to stored representations of previous experience that may prove relevant to future behavior. Working memory refers to the process by which those representations are put to use in a given context, with a necessary temporal component. Spatial working memory (SWM), in particular, refers to those working memory activities occurring within the context of spatial navigation behaviors. The process requires representations of learned experiences, current context, comparisons between the two, and rule-based decision making. Each of these has been previously shown to depend on some combination of three critical structures; the prefrontal cortex (PFC), the hippocampus (HC), and the midline thalamic nucleus reuniens (Re). However, it had not yet been demonstrated when during the SWM timeline the information flow across specific pathways linking the structures was necessary to support accurate goal-directed navigation. The current experiments use optogenetics to target pathway-specific activity during isolated portions of the SWM timeline. The results, suggesting high-degrees of selectivity to contributions necessary to SWM, are discussed within the context of how the brain supports the construction and application of critical neuronal representations for: learned experiences, current context, comparisons between the two, and rule-based decision making.University of Delaware, Department of Psychological and Brain SciencesM.S

Neural timescales reflect behavioral demands in freely moving rhesus macaques

Abstract Previous work demonstrated a highly reproducible cortical hierarchy of neural timescales at rest, with sensory areas displaying fast, and higher-order association areas displaying slower timescales. The question arises how such stable hierarchies give rise to adaptive behavior that requires flexible adjustment of temporal coding and integration demands. Potentially, this lack of variability in the hierarchical organization of neural timescales could reflect the structure of the laboratory contexts. We posit that unconstrained paradigms are ideal to test whether the dynamics of neural timescales reflect behavioral demands. Here we measured timescales of local field potential activity while male rhesus macaques foraged in an open space. We found a hierarchy of neural timescales that differs from previous work. Importantly, although the magnitude of neural timescales expanded with task engagement, the brain areas’ relative position in the hierarchy was stable. Next, we demonstrated that the change in neural timescales is dynamic and contains functionally-relevant information, differentiating between similar events in terms of motor demands and associated reward. Finally, we demonstrated that brain areas are differentially affected by these behavioral demands. These results demonstrate that while the space of neural timescales is anatomically constrained, the observed hierarchical organization and magnitude is dependent on behavioral demands

Making Sense of the Multiplicity and Dynamics of Navigational Codes in the Brain.

Since the discovery of conspicuously spatially tuned neurons in the hippocampal formation over 50 years ago, characterizing which, where, and how neurons encode navigationally relevant variables has been a major thrust of navigational neuroscience. While much of this effort has centered on the hippocampal formation and functionally-adjacent structures, recent work suggests that spatial codes, in some form or another, can be found throughout the brain, even in areas traditionally associated with sensation, movement, and executive function. In this review, we highlight these unexpected results, draw insights from comparison of these codes across contexts, regions, and species, and finally suggest an avenue for future work to make sense of these diverse and dynamic navigational codes