Distinct neural manifolds and critical roles of primate caudate nucleus in multimodal decision-making

Representational redundancy is ubiquitous in the brain with distributed networks encode task variables in a similar way, which may mask the unique roles of each region. Using a multisensory decision paradigm, here we showed that primate caudate nucleus (CN) dramatically differed from decision-related cortices in the reduced low-dimensional neural subspace, although possessing similar choice representations. Specifically, bimodal neural trajectories evolved towards nonvisual (vestibular) in CN, rather than towards visual as in frontal/parietal cortices. This challenges previous hypothesis that striatum mainly reflects cortical decision signals. Following recurrent neural networks simulations suggested that the cortico-subcortical distinction might be due to different intensities of single-modality inputs. We furtherly demonstrated that CN population responses represented the multisensory behavior strategy animal employed within the generalized drift-diffusion framework. Importantly, neural manipulations by unilateral drug injection and microstimulation confirmed CN's causal contributions to multisensory decisions. Overall, our results indicate beyond relay-station in cortico-striatal circuitry, CN plays distinct and critical roles in perceptual decision-making.