Expectation of Tactile Signals in Human Motor Cortex

Somatosensory feedback and attention are critical for the execution of dexterous behaviors. Indeed, tactile and proprioceptive signals are sent to motor cortex such that they can be integrated into the motor plan while the expectation of feedback can shape motor responses. One downside to many of the studies that have found these interactions is that motor cortex has always been studied within the framework of a motor task, potentially squashing many of the smaller signals present and making others hard to disentangle. In this study we specifically investigate the presence of sensory expectations in human motor cortex in the absence of a motor task using two participants implanted with electrode arrays in both sensory and motor cortices, allowing us to identify signals corresponding to sensory expectation with fewer confounds. We found that the deployment of attention to individual fingers results in digit-specific activation of motor cortex while sensory cortex remains unperturbed. Moreover, we observed that, compared to an imagined movement task, the expectation signal in motor cortex existed in a distinct subspace that does not represent pure motor intent. Finally, we found that the expectation signals existed along a somatotopic axis that matched the somatotopic axis revealed by movement intent. This work highlights the fact that many signals are multiplexed in motor cortex.