Neuronal representation of conditioned taste in the basolateral amygdala of rats

Animals develop robust learning and long lasting taste aversion memory once they experience a new taste that is followed by visceral discomfort. A large body of literature has supported the hypothesis that basolateral amygdala (BLA) plays a critical role in the acquisition and extinction of such conditioned taste aversions (CTA). Despite the evidence that BLA is crucially engaged during CTA training, it is unclear how BLA neural activity represents the conditioned tastes. Here, we incorporated a modified behavioral paradigm suitable for single unit study, one which utilizes a sequence of pulsed saccharin and water infusion via intraoral cannulae. After conditioning, we investigated BLA unit activity while animals experience the conditioned taste (saccharin). Behavioral tests of taste reactivity confirmed that the utilized training procedure produced reliable acquisition and expression of the aversion throughout test sessions. When neural activity was compared between saccharin and water trials, half of the recorded BLA units (77/149) showed differential activity according to the types of solution. 76% of those cells (29/38) in the conditioned group showed suppressed activity, while only 44% of taste reactive cells (17/39) in controls showed suppressed activity during saccharin trials (relative to water trials). In addition, the overall excitability of BLA units was increased as shown by altered characteristics of burst activity after conditioning. The changes in BLA activity as a consequence of CTA were maintained throughout test sessions, consistent with the behavioral study. The current study suggests that the neuronal activity evoked by a sweet taste is altered as a consequence of CTA learning, and that the overall change might be related to the learning induced negative affect.     

A preference for genuine smiles following social exclusion

Research indicates that rejected individuals are better than others at discriminating between genuine (Duchenne) and deceptive (non-Duchenne) smiles (i.e., true versus false signals of affiliative opportunity). We hypothesized that rejected individuals would show a greater preference to work with individuals displaying Duchenne versus non-Duchenne smiles. To test this, participants wrote essays about experiences of inclusion, exclusion, or mundane events. They then saw a series of 20 videos of smiling individuals (10 with Duchenne and 10 with non-Duchenne smiles). Participants then indicated how much they would like to work with each target. Analyses revealed that compared to included and control participants, excluded individuals showed a greater preference to work with individuals displaying “real” as opposed to “fake” smiles. This effect was partially mediated by threats to “relational needs” (Williams, 2007) and fully mediated by threats to self-esteem. These results suggest that exclusion yields adaptive responses that could facilitate reconnection with others.     

Performance enhancement in a semi-autonomous confined microsociety

Research in a continuously programmed human experimental laboratory has been directed toward identifying, defining, and expanding generalized knowledge concerning motivational factorswithin the structure of human behavioral repertoires that maintain and enhance performance. Participants (in groups of three) engaged in a series of repetitive work activities (e.g., word sorting and rug-hooking) for extended periods each day, while living continuously in a residential laboratory. Other parts of the day were spent either interacting socially with other participants or engaging in individual recreational activities. The percentage of time devoted to the various work tasks provided the basis for selecting one activity that occurred with high frequency and one with low frequency. Performance of the low-frequency activity was then required in order to gain access to the high-frequency activity. Under such contingencies, time devoted to the original low-frequency activity increased greatly, and the participants consistently did more than the required amount of the low-frequency work than was necessary to restore access to the restricted work activity. The theoretical significance of these findings resides in the clear demonstration that a time-based model of value applies as well to the enhancement of work-like performance as it does to voluntarily selected or preferred recreational activities. Supported by Grant NASA (NAG 2-139) from the National Aeronautics and Space Administration.