BMI Seminar // Randy Bruno: High-order thalamus in behavior

Each sensory modality has its own primary and secondary (“high-order”) thalamic nuclei. While the primary thalamic nuclei are well understood to relay sensory information from the periphery to the cortex, the role of high-order sensory nuclei is elusive. One theory has been that these collect reafferent motor signals and/or motor efference copy to disambiguate movements from environmental stimuli, but our results demonstrate poor encoding of motor information. Another theory has been that secondary nuclei may support feature-based attention. If true, one would also expect the activity in different nuclei to reflect the degree to which modalities are or are not behaviorally relevant in a task. We trained head-fixed mice to attend to one sensory modality while ignoring a second modality and simultaneously recorded from secondary somatosensory and visual thalamus. Training could switch the modality that maximally activated a secondary thalamic nucleus. Secondary nuclei appear to encode behaviorally relevant, reward-predicting stimuli regardless of stimulus modality. This does not produce multimodal encoding in sensory cortex, but may instead gate plasticity of apical dendrites in cortical layer 1 to enable them to acquire the behaviorally relevant task dimension.