Motor and somatosensory cortex are know to have a distinct somatotopic organization. This and additional knowledge of neuronal coding functions are being used to develop brain-computer interfaces (BCIs) that establish functional connections between cortical neurons and prosthetic and assistive devices. BCIs often use electrodes placed in brain areas responsible for volitional control and sensation of limb movements, particularly the arm and hand regions. Mapping brain regions is possible using functional magnetic resonance imaging (fMRI), although studies are difficult to perform in persons with motor and sensory impairments. People with spinal cord injury have disrupted efferent and afferent pathways between the cortex and the limbs making it necessary to rely on covert techniques, such as kinesthetic motor imagery, to map sensorimotor brain activity.
We are developing novel covert paradigms for mapping sensorimotor brain activity. Visual, auditory, and other sensory enrichments will be used to enhance traditional imagery paradigms. We expect that with increasing enrichment, we will improve cortical mapping as measured by increased peak activity and less overlap between adjacent cortical representations. In the future, we will use covert mapping to guide BCI electrode design and placement. Similarly, neurofeedback rehabilitation protocols could be designed to target abnormal cortical activity directly, or sensory enrichments could be incorporated into traditional rehabilitation paradigms to facilitate activation of dormant neural pathways.
Our BCI studies have used both fMRI and MEG-based presurgical planning to determine the location of the implanted arrays. The figure below shows motor-related activity in two individuals with chronic spinal cord injury. The expected somatotopic organization is observed in motor cortex. Hand activity (blue) is the most lateral starting at the hand knob (marked with Ω), followed by wrist flexion/extension (green), elbow flexion/extension (yellow), and the most medial shoulder shrug (orange).