Temporally-precise basolateral amygdala activation is required for the formation of taste memories in the gustatory cortex

Abstract

Learning to associate malaise with the intake of novel food is critical for survival. Since food poisoning may take hours to affect, animals developed brain circuits to transform the current novel taste experience into a taste memory trace (TMT) and bridge this time lag. Ample studies showed that the basolateral amygdala (BLA), the nucleus basalis magnocellularis (NBM) and the gustatory cortex (GC) are involved in TMT formation and taste-malaise association. However, how dynamic activity across these brain regions during novel taste experience promotes the formation of these memories is currently unknown. We used the conditioned taste aversion (CTA) learning paradigm in combination with short-term optogenetics and electrophysiological recording in rats to test the hypothesis that temporally specific activation of BLA projection neurons is essential for TMT formation in the GC, and consequently CTA. We found that late-epoch (LE, >800ms), but not the early epoch (EE, 200-700ms), BLA activation during novel taste experience is essential for normal CTA, for early c-Fos expression in the GC (a marker of TMT formation) and for the subsequent changes in GC ensemble palatability coding. Interestingly, BLA activity was not required for intact taste identity or palatability perceptions. We further show that BLA-LE information is transmitted to GC through the BLA[->]NBM pathway where it affects the formation of taste memories. These results expose the dependence of long-term memory formation on specific temporal windows during sensory responses and the distributed circuits supporting this dependence. SignificanceConsumption of a novel taste may result in malaise and poses a threat to animals. Since the effects of poisoning appear only hours after consumption, animals must store the novel tastes information in memory until they associate it with its value (nutritious or poisonous). Here we elucidate the neuronal activity patterns and circuits that support the processing and creation of novel-taste memories in rats. Our results show that specific patterns of temporal activation in the basolateral amygdala transmitted across brain areas are important for formation of taste memory and taste-malaise association. These findings may shed light on long-term activity-to-memory transformation in other sensory modalities.