Role of the supplementary motor area in auditory sensory attenuation.

Self-generated tones elicit smaller brain responses as compared to externally generated tones. This phenomenon known as sensory attenuation has been explained in terms of an internal forward model in which the brain predicts the upcoming events and thereby attenuates the sensory processing. Such prediction processes have been suggested to occur via an efference copy of the motor command that is sent from the motor system to the lower order sensory cortex. However, little is known about how the prediction is implemented in the brain's network organization. Because the supplementary motor area (SMA) is a primary brain structure of the motor system, we attributed the implementation of the prediction to the SMA. To address this question, we examined generative network models for auditory ERPs. ERPs were evoked by either a self-generated or externally generated tone, while subjects were paying attention to their motor action or to the tone. The tone itself was the same throughout all conditions. The network models consisted of three subsets embedding alternative hypotheses of the hierarchical structures: (1) auditory fields of the temporal lobe, (2) adding connections to the SMA, and (3) adding prediction signal to the SMA. The model comparison revealed that all ERP responses were mediated by the network connections across the auditory cortex and the SMA. Importantly, the prediction signal to the SMA was required when the tone was self-generated irrespective of the attention factor, whereas the externally generated tone did not require the prediction. We discussed these results in the context of the predictive coding framework.