Cortex-wide circuits for multisensory evidence accumulation and choice formation

Accurate decisions in natural environments require integrating sensory information across modalities. To determine where and when multisensory signals are integrated within the cortical hierarchy, we trained mice in a visuotactile evidence-accumulation task and used widefield and two-photon calcium imaging together with optogenetic perturbations to map cortical circuits. Mice showed enhanced performance in multisensory trials that matched an additive combination of the total unisensory evidence. Cortical imaging also revealed superadditive multisensory responses in parietal and frontal regions, but visual and tactile evidence was accumulated in distinct regions, with the rostrolateral visual area (RL) being more selective for visual and the frontal medial motor cortex (MM) for tactile inputs. This modality-specific segregation persisted beyond stimulus presentation with convergence into a modality-independent choice emerging only late in the trial in the anterolateral motor cortex (ALM). Two-photon imaging confirmed that ALM neurons predominantly encoded modality-independent choices with few neurons responding to specific sensory stimuli. Optogenetic inactivation of RL and frontal cortex during the stimulus or choice period further validated their respective roles in sensory evidence accumulation and choice formation. These findings reveal a hierarchical organization in which modality-specific evidence is maintained until late in the decision process, with frontal cortex turning multisensory signals into unified choices.