NEURAL DYNAMICS OF CONTEXT, CUE AND RULE ENCODING: THE ROLE OF PV- AND SOM-INTERNEURONS IN THE MEDIAL PREFRONTAL CORTEX

The prefrontal cortex plays a key role in the representation of cognitive parameters, including task-relevant sensory cues, action selection and context. However, the contribution of specific inhibitory interneuron subtypes to the representation of these task features in active cell assemblies is incompletely understood.
Here we examine the role of parvalbumin (PVIs) and somatostatin (SOMIs) expressing interneurons within the prelimbic cortex (PL) of mice in a contextual-auditory decision task. In this task, mice initiate a trial by nosepoke and are presented with randomly chosen auditory cues and spatial contexts, followed by a decision between two lickspouts. While initially neither auditory nor contextual cues are task relevant, later in training a rule component is assigned to one of the two modalities. In these later stages, the correct choice depends on either spatial context or auditory cues. The design dissociates the representation of stimulus from rule relevance. We observe that acquiring spatial-context rules is easier for the mice than acquiring auditory-based rules.
To investigate the contribution of parvalbumin-expressing and somatostatin-expressing interneurons to cortical computation, we performed calcium imaging in freely moving mice, either panneuronally or selectively targeting PVIs or SOMIs. By comparing representations of tones and contexts across training and combining it with detailed movement tracking, we characterize task-variable representations across multiple cell types in the medial prefrontal cortex. Together, the results provide insights into how interneuron populations participate in neural computations in this brain area.