Sensory contributions to control of human hand movements: digit representations in higher-order somatic loci and their neural interactions with primary motor cortex

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The proposed research will investigate the areas of the human brain that process both sensory and movement information related to the hand. The areas of interest include the primary and secondary somatosensory cortex and the medial superior parietal lobule. The goals are to understand how each of these cortical areas represent sensory input, and how their representations change when input becomes important to the task, or dictates an upcoming movement of the hand. The goals will be accomplished using two non-invasive techniques that provide complimentary information, functional magnetic resonance imaging (fMRI) and paired-pulse transcranial magnetic stimulation (TMS). For each area of interest, fMRI will be used to identify which digits occupy the most cortical territory, how intense responses are to specific types of sensory input, and if responses increase or decrease depending on how relevant the input is to the task, or movement. Using TMS, the interaction between each area of interest and the primary motor cortex, the largest contributor to the spinal path responsible for hand movements, will be probed. Each of the cortical areas of interest have direct projections with the primary motor cortex yet there are uncertainties about when the sensory area conveys its information to the primary motor cortex, and how this information is conveyed. For example, will the sensory projection reduce responses in primary motor cortex, or will it increase responses? Understanding the neural mechanisms that underpin sensory-guided hand movements is essential to developing therapies that aim to improve hand function in patients such as those have suffered stroke or with movement disorders such as dystonia. The proposed research program will investigate the cortical mechanisms of sensory-motor hand movement in healthy populations, a precursor to developing methods to assist clinical populations.