Electrophysiological signatures of inequity-dependent reward encoding in the human OFC

Dorsal-Caudal and Ventral Hippocampi Target Different Cell Populations in the Medial Frontal Cortex in Rodents

Direct projections from the ventral hippocampus (vHPC) to the medial frontal cortex (MFC) play crucial roles in memory and emotional regulation. Using anterograde transsynaptic tracing and ex vivo electrophysiology in male mice, we document a previously unexplored pathway that parallels the established vHPC-MFC connectivity. This pathway connects the dorsal-caudal hippocampus (dcHPC) to specific subregions of the ventral MFC (vMFC), in particular the dorsal peduncular cortex. Notably, this pathway exerts a strong inhibitory influence on vMFC by targeting a substantial proportion of inhibitory neurons. Retrograde transsynaptic tracing in male rats indicated that vMFC subregions project disynaptically back to vHPC. These results, altogether, suggest the existence of a remarkable functional circuit connecting distinct functional areas: the cognition-related dcHPC with the emotion-related vMFC and vHPC. These findings further provide valuable insights in the cognitive and emotional abnormalities associated with the HPC-MFC connectivity in neurological and psychiatric disorders.

Simultaneous intracranial recordings of interacting brains reveal neurocognitive dynamics of human cooperation

Cooperative interactions profoundly shape individual and collective behaviors of social animals. Successful cooperation requires coordinated efforts by cooperators toward collective goals. However, the underlying behavioral dynamics and neuronal mechanisms within and between cooperating brains remain largely unknown. We recorded intracranial electrophysiological signals from human pairs engaged in a cooperation game. We show that teammate coordination and goal pursuit make distinct contributions to the behavioral cooperation dynamics. Increases and decreases in high-gamma activity in the temporoparietal junction (TPJ) and amygdala distinguish between establishing and maintaining cooperation and forecast transitions between these two states. High-gamma activity from distinct neuronal populations encodes teammate coordination and goal pursuit motives, with populations of TPJ neurons preferentially tracking dominant motives of different cooperation states. Across cooperating brains, high-gamma activity in the TPJ and amygdala synchronizes in a state-dependent manner that predicts how well cooperators coordinate. These findings provide fine-grained understandings of human cooperation dynamics as a state-dependent process with distinctive neurocognitive profiles of each state.

Human Substantia Nigra Neurons Encode Reward Expectations

Dopamine (DA) signals originating from substantia nigra (SN) neurons are centrally involved in the regulation of motor and reward processing. DA signals behaviorally relevant events where reward outcomes differ from expectations (reward prediction errors, RPEs). RPEs play a crucial role in learning optimal courses of action and in determining response vigor when an agent expects rewards. Nevertheless, how reward expectations, crucial for RPE calculations, are conveyed to and represented in the dopaminergic system is not fully understood, especially in the human brain where the activity of DA neurons is difficult to study. One possibility, suggested by evidence from animal models, is that DA neurons explicitly encode reward expectations. Alternatively, they may receive RPE information directly from upstream brain regions. To address whether SN neuron activity directly reflects reward expectation information, we directly examined the encoding of reward expectation signals in human putative DA neurons by performing single-unit recordings from the SN of patients undergoing neurosurgery. Patients played a two-armed bandit decision-making task in which they attempted to maximize reward. We show that neuronal firing rates (FR) of putative DA neurons during the reward expectation period explicitly encode reward expectations. First, activity in these neurons was modulated by previous trial outcomes, such that FR were greater after positive outcomes than after neutral or negative outcome trials. Second, this increase in FR was associated with shorter reaction times, consistent with an invigorating effect of DA neuron activity during expectation. These results suggest that human DA neurons explicitly encode reward expectations, providing a neurophysiological substrate for a signal critical for reward learning.