Perturbation of amygdala-cortical projections reduces ensemble coherence of palatability coding in gustatory cortex

Abstract

Taste palatability is centrally involved in consumption decisions—we ingest foods that taste good and reject those that don’t. Gustatory cortex (GC) and basolateral amygdala (BLA) almost certainly work together to mediate palatability-driven behavior, but the precise nature of their interplay during taste decision-making is still unknown. Here, we take a step toward filling this gap in our knowledge, by investigating the specific role that activity in the BLA→GC pathway plays in the emergence of palatability-related firing in GC response dynamics (which influence consumption decisions). We implanted electrode/optical-fiber probes in virally-prepared female Long-Evans rats, such that we could optogenetically hyperpolarize BLA→GC axons, perturbing activity in these axons without affecting BLA and GC somas, while recording GC neural responses to intra-oral presentations of a diverse taste battery. This inter-regional axonal perturbation strongly altered GC taste responses, but despite the laser illumination being tonic for the first 2s that the taste was on the tongue, the alterations were far from monolithic: rather than changing all moments of the response equally, or causing a simple exponential decay of changes, the perturbation was most strongly felt at the onset times of previously-described response epochs; furthermore, the effect was epoch-specific—perturbations had little impact on the amount of taste identity information in the “middle epoch” of the responses, but reduced evidence of palatability-related activity in the “late-epoch.” Finally, BLA→GC axon inhibition affected the nature of the epochal dynamics themselves, such that the normal abruptness of the behaviorally-relevant ensemble transitions into the palatability-related epoch was greatly diminished. These results suggest that BLA “organizes” behavior-related GC taste dynamics.

Loss of Stk11 in basolateral amygdalar projection neurons impairs taste aversion learning by altering the temporal pattern of taste response plasticity in gustatory cortex

“…This small discrepancy between these data and our prior results is likely due to our increased sample of Stk11 KO neurons and the fact that our current taste battery lacked sucrose, the reliable high palatability of which may have overwhelmed subtle between-group differences (see Discussion). Regardless, the slight, general enhancement in GC palatability-related firing makes sense: since a portion of palatability information in GC appears to come from BLA projections (Lin et al, 2021;Piette et al, 2012), a larger than normal contribution of BLA to GC taste responses might be expected resultant from the increased BLA excitability in the Stk11 knockout (Levitan et al, 2020).…”