Representational geometry of perceptual decisions in the monkey parietal cortex.

Lateral intraparietal (LIP) neurons represent formation of perceptual decisions involving eye movements. In circuit models for these decisions, neural ensembles that encode actions compete to form decisions. Consequently, representation and readout of the decision variables (DVs) are implemented similarly for decisions with identical competing actions, irrespective of input and task context differences. Further, DVs are encoded as partially potentiated action plans through balance of activity of action-selective ensembles. Here, we test those core principles. We show that in a novel face-discrimination task, LIP firing rates decrease with supporting evidence, contrary to conventional motion-discrimination tasks. These opposite response patterns arise from similar mechanisms in which decisions form along curved population-response manifolds misaligned with action representations. These manifolds rotate in state space based on context, indicating distinct optimal readouts for different tasks. We show similar manifolds in lateral and medial prefrontal cortices, suggesting similar representational geometry across decision-making circuits. [Display omitted] • We examine parietal neural activity in motion and face discrimination tasks • Population neural response dynamics form a curved manifold during decision-making • Manifolds rotates across tasks, changing optimal readout of the decision variable • Circuit models of perceptual decisions need revision to include task dependency Comparison of neuronal activity during decision-making in face and motion discrimination tasks reveals task-dependent response geometry that shapes optimal readout of the decision variable. [ABSTRACT FROM AUTHOR]