Sensory basis of speech motor learning and memory

Changes to speech offer a quantifiable means to assess speech motor learning, and the resulting memory is thought to be motor in nature. Here, we evaluate this idea and show instead that memory for speech movements has a sensory basis. Speech motor learning, using altered auditory feedback, provides an experimental model to address this question as it involves auditory, somatosensory, and motor components to learning. Transcranial magnetic stimulation was used to disrupt auditory (superior temporal gyrus, STG), posterior somatosensory (S1), or motor (M1) cortex following speech motor learning. Retention tests were conducted 24 h later. It was found that following disruption of either STG or S1, motor memory retention was impaired whereas disruption of M1 led to retention that was no different than that of a no TMS control condition. The effects of disruption were specific to speech motor learning and did not interfere with speech production per se. Taken together, the findings support the notion that plasticity in the sensory cortex, both auditory and somatosensory, is necessary for speech motor learning and memory. In speech, changes to sensory systems enable the production of newly learned movements.