Advanced understanding of brain structure and function has improved the diagnosis and treatment of neurological disorders such as epilepsy, stroke, and spinal cord injury (SCI). Over half a century ago, Penfield used electrical stimulation of motor and sensory areas of cerebral cortex and revealed a distinct somatotopic organization of the brain. Today, 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 SCI 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. Challenges associated with brain mapping likely contribute to the varying reports regarding the extent of functional reorganization occurring in the brain following SCI. The goal of the proposed research is to develop novel covert paradigms for mapping sensorimotor brain activity. Visual or auditory cueing has been shown to improve the timing and vividness of motor imagery. Therefore, we expect that increasing sensory enrichment will strengthen the activation observed in the sensorimotor cortex during covert motor and sensory tasks. We will test multiple levels of sensory enrichment with the goal of enhancing sensorimotor activation. The four conditions that will be tested are: (1) simple imagery of a single- joint movement or sensory stimulus, (2) goal-directed imagery, (2) goal-directed imagery with auditory enrichment, (3) goal-directed imagery with auditory and somatosensory enrichment. Functional MRI will be used to measure motor, cutaneous, and proprioceptive cortical representations using the covert mapping paradigms described above. Able-bodied subjects will be recruited to allow for comparison of imagery-based cortical activation patterns to that measured during overt movement and sensory stimulation. We will also recruit participants with tetraplegia due to SCI allowing for confirmation that the covert mapping paradigms translate to the clinical population. We will test whether covert movement and stimuli activate the sensorimotor cortex in the expected manner based on published literature and overt mapping in able-bodied subjects. Enriched covert brain mapping will allow for measurement of cortical reorganization when overt techniques cannot be used. Through this study, we will gain an understanding of how imagined movement, cutaneous stimulation, and passive movement produce similar (or different) activation of the motor and somatosensory cortex. In future studies, we plan to use covert mapping to guide BCI electrode design and placement. Moreover, these advanced mapping procedures will provide new insights into the functional interactions between sensory and motor areas of the brain in able-bodied persons, and the effects of SCI on these functions. 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.
Functional neuroimaging can be used to map brain activity during movement or sensory stimulation. However, traditional methods cannot be applied to people with motor and sensory impairments such as those resulting from spinal cord injury (SCI). For Veterans with tetraplegia, restoration of upper limb function is a top priority. One possible way to restore upper limb function is to use brain-computer interface (BCI)-controlled motorized prostheses which enable natural upper limb movement and have advanced sensing capabilities. BCIs use implanted electrodes to record movement intention directly from the brain and it may be possible to convey sensory information back to the user through electrical stimulation of the brain. However, this requires accurate placement of electrodes. In the proposed research we propose to use enriched covert techniques (imagery) to map the motor and sensory areas of the brain in able-bodied subjects and people with tetraplegia. Covert brain mapping also enables the study of cortical changes that occur after injury or rehabilitation intervention.
