The globus pallidus is a major output station for the basal ganglia, a subcortical region of the brain that is heavilyimplicated in action selection and decision making. A subpopulation of neurons in the internal segment (GPi) projects tothe laternal habenula (LHb), often associated with the limbic system and known to encode for negative motivational value.Dysfunction in these structures have been implicated in neurological diseases, such as depression and schizophrenia,which are ultimately disruptions in the ability to evaluate environmental cues and regulate motor output. In order togain more information about the neurons which encode for this behavior, we conducted extracellular recordings whilethe mice are carrying out a set of reward learning tasks and analyzed the collected spike trains. We detail here themethods of information extraction from the neuronal populations that we have classified. We also present preliminaryresults of their activity profile for various outcomes as well as for reward history and prediction error. With collection ofinformation from a larger set of cells, we might be able to more definitively gain an understanding of the methods bywhich these neurons encode motivation, action selection and outcome evaluation.

The basal ganglia, a group of subcortical nuclei, play a crucial role in decision-making by selecting actions and evaluating their outcomes. While much is known about the function of the basal ganglia circuitry in selection, how these nuclei contribute to outcome evaluation is less clear. Here we show that neurons in the habenula-projecting globus pallidus (GPh) in mice are essential for evaluating action outcomes and are regulated by a specific set of inputs from the basal ganglia. We find in a classical conditioning task that individual mouse GPh neurons bidirectionally encode whether an outcome is better or worse than expected. Mimicking these evaluation signals with optogenetic inhibition or excitation is sufficient to reinforce or discourage actions in a decision-making task. Moreover, cell-type-specific synaptic manipulations reveal that the inhibitory and excitatory inputs to the GPh are necessary for mice to appropriately evaluate positive and negative feedback, respectively. Finally, using rabies-virus-assisted monosynaptic tracing, we show that the GPh is embedded in a basal ganglia circuit wherein it receives inhibitory input from both striosomal and matrix compartments of the striatum, and excitatory input from the 'limbic' regions of the subthalamic nucleus. Our results provide evidence that information about the selection and evaluation of actions is channelled through distinct sets of basal ganglia circuits, with the GPh representing a key locus in which information of opposing valence is integrated to determine whether action outcomes are better or worse than expected.