VTA-IC dopaminergic inputs enhances the salience to consolidate aversive but not appetitive taste recognition memory via D1 receptors

Taste memory involves storing information through plasticity changes in the neural network of taste, including the insular cortex (IC) and ventral tegmental area (VTA), a critical provider of dopamine. Although a VTA-IC dopaminergic pathway has been demonstrated, its role to consolidate taste recognition memory remains poorly understood. We found that photostimulation of dopaminergic neurons in the VTA or VTA-IC dopaminergic terminals of TH-Cre mice increases the salience to facilitate consolidation of a novel taste stimulus regardless of its hedonic value, without altering their taste palatability. Importantly, the inhibition of the D1-like receptor into the IC impairs the salience to facilitate consolidation of an aversive taste recognition memory. Finally, our results showed that VTA photostimulation improves the salience to facilitate consolidation of a conditioned taste aversion memory through the D1-like receptor into the IC. It is concluded that the dopamine activity from the VTA into IC is required to increase the salience to facilitate consolidation of a taste recognition memory. Notably, the D1-like receptor activity into the IC is required to consolidate both innate and learned aversive taste memories but not appetitive taste memory.

Impact of hedonic value of stimuli on sampling dynamics during a preference test

The decision of whether to continue with a current action or to stop and consider alternatives is ever present in the life of an animal. Such continuous-time decision making lies at the heart of food preference tests whose outcomes are typically quantified by a single variable, the total amount consumed. However, the dynamics that give rise to such a quantity in terms of durations of bouts of sampling at a stimulus before pauses, and the impact of alternative stimuli on those bout durations and subsequent actions following a pause, can contain a richness of behavior that is not captured in a single palatability measure. Here we carry out multiple analyses of these dynamics, with a particular focus on assessing how the hedonic value of one taste stimulus impacts the behavior of a rat sampling a second taste stimulus during a preference test. We find evidence for an explicit competitive interaction between bout durations, such that the more palatable a stimulus the longer the bout durations when the rat samples the stimulus and the shorter the bout durations at the alternative. Such competition is reproduced in a model of a neural circuit that could underlie the continuous decision of when to end a sampling bout. We find that the competitive impact on bout durations is relatively short-lived whereas a competitive impact on the choice of which stimulus to approach following a pause persists. Such a discrepancy in the timescales for the decay of the impact of the alternative stimulus suggests different neural processes are involved in the choice of which stimulus to approach versus the choice of how long to sample from it. Since these two choices together combine to determine net consumption and therefore the inferred palatability or preference of a gustatory stimulus, our results suggest that palatability is not a unitary quantity but the result of at least two distinct, context-dependent neural processes.

LTD at amygdalocortical synapses as a novel mechanism for hedonic learning

A novel, pleasant taste stimulus becomes aversive if associated with gastric malaise, a form of learning known as conditioned taste aversion (CTA). CTA is common to vertebrates and invertebrates and is an important survival response: eating the wrong food may be deadly. CTA depends on the gustatory portion of the insular cortex (GC) and the basolateral nucleus of the amygdala (BLA) however, its synaptic underpinnings are unknown. Here we report that CTA was associated with decreased expression of immediate early genes in rat GC of both sexes, and with reduced amplitude of BLA-GC synaptic responses, pointing to long-term depression (LTD) as a mechanism for learning. Indeed, association of a novel tastant with induction of LTD at the BLA-GC input in vivo was sufficient to change the hedonic value of a taste stimulus. Our results demonstrate a direct role for amygdalocortical LTD in taste aversion learning.

LTD at amygdalocortical synapses as a novel mechanism for hedonic learning

A novel, pleasant taste stimulus becomes aversive if associated with gastric malaise, a form of learning known as conditioned taste aversion (CTA). CTA is common to vertebrates and invertebrates and is an important survival response: eating the wrong food may be deadly. CTA depends on the gustatory portion of the insular cortex (GC) and the basolateral nucleus of the amygdala (BLA) however, its synaptic underpinnings are unknown. Here we report that CTA was associated with decreased expression of immediate early genes in rat GC of both sexes, and with reduced amplitude of BLA-GC synaptic responses, pointing to long term depression (LTD) as a mechanism for learning. Indeed, association of a novel tastant with induction of LTD at the BLA-GC input in vivo was sufficient to change the hedonic value of a taste stimulus. Our results demonstrate a direct role for amygdalocortical LTD in taste aversion learning.

Taste Perception and Water Swallow Screen Results in Old-Old Women

Changes in both swallowing and taste commonly occur in advanced age, though the relationship between the two is unknown. This study examined the association between a water swallow screen test and taste identification and intensity rating. Participants included 47 community-dwelling women aged 85–94 years. Participants completed three trials of a water swallow screen and were observed for signs of aspiration, which, if present, indicated failure. Four pure taste stimuli at low and high concentrations and water were presented, and participants selected one of five taste labels and rated their intensity on the generalized Labeled Magnitude Scale. Ratios of intensity ratings were computed for each taste stimulus to compare the perception of low and high concentrations. The association between water swallow screen failure, correct taste identification, and taste intensity ratio was evaluated with logistic regression modeling, with mediating factors of frailty and number of comorbidities. Failure of three water swallow screen trials was associated with a higher taste intensity ratio for caffeine (bitter) and a lower taste intensity ratio for sucrose (sweet). Correct identification of taste, frailty, and number of comorbidities were not associated with failure of any number of water swallow screen trials. Intensity ratings of certain tastes may be associated with swallowing in old-old women. Heightened vigilance in this population may be necessary to prevent complications related to dietary intake.

Toward Improving Medication Adherence: The Suppression of Bitter Taste in Edible Taste Films

Bitter taste is aversive to humans, and many oral medications exhibit a bitter taste. Bitter taste can be suppressed by the use of inhibitors or by masking agents such as sucralose. Another approach is to encapsulate bitter tasting compounds in order to delay their release. This delayed release can permit the prior release of bitter masking agents. Suppression of bitter taste was accomplished by encapsulating a bitter taste stimulus in erodible stearic acid microspheres, and embedding these 5 µmeter diameter microspheres in pullulan films that contain sucralose and peppermint oil as masking agents, along with an encapsulated masking agent (sucralose). Psychophysical tests demonstrated that films which encapsulated both quinine and sucralose produced a significant and continuous sweet percept when compared to films without sucralose microspheres. Films with both quinine and sucralose microspheres also produced positive hedonic scores that did not differ from control films that contained only sucralose microspheres or only empty (blank) microspheres. The encapsulation of bitter taste stimuli in lipid microspheres, and embedding these microspheres in rapidly dissolving edible taste films that contain masking agents in both the film base and in microspheres, is a promising approach for diminishing the bitter taste of drugs and related compounds.

Madeleine cake and neurophysiological basis of memory

The article attempts to understand one of the most famous episodes of Marcel Proust's novel "Toward Svan" from the scientific point of view, an episode devoted to the process of extracting memories of life in Combray from the depths of the memory of the hero, which was caused by the taste stimulus of the cake Madlen. This process is considered in the psychological and neurophysiological aspect, and the phenomenon described by the artist of the word acquires new facets in this key and allows one to look deeper into its nature.