2019 May 6 – Along with their primary implication in emotional processing and related functions, the amygdala nuclei have been reported to process associatively learned values, economic decisions and certain social information. In a novel work led by Fabian Grabenhorst from the University of Cambridge, UK, single-neuron recordings in the amygdala of awake, behaving rhesus monkeys (Macaca mulatta) were found to underlie observational learning and mental simulation. In addition to standard electrophysiological techniques, researchers made extensive use of modeling to assign specific functions to registered codes and propose plausible interpretations of data. As monkeys learned the value of different visual cues in a behavioral test, either from the observation of social partners making reward-oriented choices or from own experience, value-coding neurons were prominently active in the lateral nucleus of the amygdala, a key region for associative learning. Such a shared code for others’ and own experiences is typical of mental simulation and prompted further insights: neurons in the amygdala were shown to simulate the partner’s decision making via value comparisons and consequent anticipation of choices. Comparison was suggested to emerge from mutual-inhibitory activity of value-coding neurons. On the other hand, partner’s forthcoming choices were anticipated by the firing activity of so-called simulation neurons, prevalently (but not exclusively) localized in the basomedial nucleus of the amygdala of the observer and separate from analogous own decision circuits. Thus, distinctive single-unit activity in the amygdala of monkeys mark the representation of others’ mental states, with conceivable relevance for the understanding of social interactions.