Stimulus-choice (mis)alignment in primate area MT

For stimuli near perceptual threshold, the trial-by-trial activity of single neurons in many sensory areas is correlated with the animal's perceptual report.<br>This phenomenon has often been attributed to feedforward readout of the neural activity by the downstream decision-making circuits.<br>The interpretation of choice-correlated activity is quite ambiguous, but its meaning can be better understood in the light of population-wide correlations among sensory neurons.<br>Using a statistical nonlinear dimensionality reduction technique on single-trial ensemble recordings from the middle temporal (MT) area during perceptual-decision-making, we extracted low-dimensional latent factors that captured the population-wide fluctuations. <br>We dissected the particular contributions of sensory-driven versus choice-correlated activity in the low-dimensional population code.<br>We found that the latent factors strongly encoded the direction of the stimulus in single dimension with a temporal signature similar to that of single MT neurons.<br>If the downstream circuit were optimally utilizing this information, choice-correlated signals should be aligned with this stimulus encoding dimension.<br>Surprisingly, we found that a large component of the choice information resides in the subspace orthogonal to the stimulus representation inconsistent with the optimal readout view.<br>This misaligned choice information allows the feedforward sensory information to coexist with the decision-making process.<br>The time course of these signals suggest that this misaligned contribution likely is feedback from the downstream areas.<br>We hypothesize that this non-corrupting choice-correlated feedback might be related to learning or reinforcing sensory-motor relations in the sensory population. <br>