Learning orthogonalizes visual cortical population codes

Training in behavioral tasks can alter visual cortical stimulus coding, but the precise form of this plasticity is unclear. We measured orientation tuning in 4,000-neuron populations of mouse V1 before and after training on a visuomotor task. Changes to single-cell tuning curves were apparently complex, including appearance of asymmetric and multi-peaked tuning curves. Nevertheless, these changes reflected a simple mathematical transformation of population activity, suppressing responses to motor-associated stimuli specifically in cells responding at intermediate levels. The strength of the transformation varied across trials, suggesting a dynamic circuit mechanism rather than static synaptic plasticity. This transformation resulted in sparsening and orthogonalization of population codes for motor-associated stimuli. Training did not improve the performance of an optimal stimulus decoder, which was already perfect even for naive codes, but the resulting orthogonalization improved the performance of a suboptimal decoder model with inductive bias as might be found in downstream readout circuits.