The role of the gustatory cortex in incidental experience-evoked enhancement of later taste learning

Abstract

The strength of learned associations between pairs of stimuli is affected by multiple factors, the most extensively studied of which is prior experience with the stimuli themselves. In contrast, little data is available regarding how experience with incidental stimuli (independent of any conditioning situation) impacts later learning. This lack of research is striking given the importance of incidental experience to survival. We have recently begun to fill this void using conditioned taste aversion (CTA), wherein an animal learns to avoid a taste that has been associated with malaise. We previously demonstrated that incidental exposure to salty and sour tastes (taste pre-exposure-TPE) enhances aversions learned later to sucrose.Here, we investigate the neurobiology underlying this phenomenon. First, we use immediate early gene (c-Fos) expression to identify gustatory cortex (GC) as a site at which TPE specifically increases the neural activation caused by taste-malaise pairing (i.e., TPE did not change c-Fos induced by either stimulus in isolation). Next, we use site-specific infection with the optical silencer Archaerhodopsin-T to show that GC inactivation during TPE inhibits the expected enhancements of both learning and CTA-related c-Fos expression, a full day later. Thus, we conclude that GC is almost certainly a vital part of the circuit that integrates incidental experience into later associative learning.

Strong Aversive Conditioning Triggers a Long-Lasting Generalized Aversion

“…But what these elementary features are with respect to tastants and CTA is unknown. In addition to basic taste modality (sweet, sour, salty, etc..) the GC has been shown to encode other taste features such as identity, palatability, and novelty/familiarity, all of which are elements to potentially evaluate taste stimuli by (Gallo, Roldan, & Bures, 1992; Lin et al, 2012; Flores et al, 2018; Mukherjee, Wachutka, & Katz, 2019). In our study, what elementary features are shared by salt, the generalized tastant, and saccharin, the conditioned stimulus, remain to be identified.…”

LiCl-induced sickness modulates spontaneous activity and response dynamics in rat gustatory cortex

“…Discussion. Nutritional requirements, environmental conditions, and experience work together to guide consummatory behavior [2,11,13], in cooperation with an animal's internal state (e.g., hunger, illness) [1]. This necessitates the study of how physiological states impact perception, as this relationship intrinsically shapes the likelihood of survival.…”

“…One such region is gustatory cortex (GC), which is involved both in processing of palatability and illness-related learning [13, 14]. As of now, however, little is known about the cortical processing of malaise.…”

The impact of familiarity on cortical taste coding

“…This enhancement has been shown to be dependent on the GC (Flores et al, 2018). Future experiments might focus on the effect of taste familiarization on specific subpopulations of GC (which was not certified by peer review) is the author/funder.…”

“…For example, animals become familiar with novel tastes over successive encounters. This process of familiarization is important to the animal both in driving future ingestive decisions (Domjan, 1976; Harder et al, 1989; Mura et al, 2018) as well as impacting subsequent learning (Lubow, 2009; Flores et al, 2016; Flores et al, 2018; Flores et al, 2022).…”