Distinct population dimensions separate sensory adaptation and expectation-related signals in visual cortex.

Mismatch negativity is conventionally quantified as a scalar response-amplitude difference between rare deviant and repeated standard stimuli, leaving its organization at the neuronal population level unresolved. We recorded population activity in mouse primary visual cortex (V1) during visual oddball and control paradigms while testing contributions from anterior cingulate cortex (ACC) input using optogenetic inhibition. Mismatch modulated firing rates bidirectionally, and these changes largely canceled out on average, yet produced robustly separable population activity patterns. On the stimulus-encoding manifold, repeated standard exposure produced standard-specific response attenuation and a shared rotation of standard and deviant representations, revealing a component not isolated by conventional stimulus-specific adaptation and deviance-detection contrasts. Off the manifold, standards and deviants occupied opposing positions along an ACC-modulated axis consistent with expectation confirmation and violation. Thus, visual mismatch responses engage separable transformations of stimulus representations and expectation-related population activity, with ACC input selectively contributing to the latter while not significantly affecting stimulus encoding or on-manifold adaptation.