Reach-to-grasp and hand manipulation will be studied in tetraplegic humans with neural recordings from multielectrode arrays (MEAs) and intracortical microstimulation (ICMS) of somatosensory cortex. Recordings will be performed within the cortical grasp circuit with MEAs implanted in two grasp-related areas, the ventral premotor cortex (PMv) and the anterior intraparietal area (AIP) of the posterior parietal cortex (PPC). ICMS will be delivered to Brodmann's area 1 (BA1) of somatosensory cortex.
Aim 1 will compare recordings from PMv and AIP to determine how grasping is processed by these two areas. We will test the hypothesis that AIP is more concerned with high-level goals and PMv more with motor trajectories. These results will be important for selecting areas for implantation for future neurosprosthetics development.
Aim 2 will examine the tactile cues that can be provided by ICMS. We hypothesize that detection, discrimination, and location of stimuli will be perceived by varying parameters of frequency, amplitude and location of the ICMS. These findings will be used for providing stimulation induced tactile feedback for brain-machine interface (BMI) applications.
In aim 3 we will use three tasks that combine decoding neural signals from AIP and PMv with ICMS for somesthetic feedback for a bidirectional BMI. The tasks will be used to test BMI performance (1) for frequency and amplitude discrimination of ICMS without visual feedback (?handbag task?), (2) for learning-based proprioception, and (3) a manipulandum task that implements force feedback for adjusting grasp. We hypothesize that the patients will successfully perform these tasks, indicating that bidirectional BMIs are feasible and can deliver tactile and proprioceptive information for grasp and hand manipulation. We have already developed artifact rejection techniques and demonstrated their application in a non-human primate (NHP) bidirectional BMI task. We also have all of the regulatory approvals for these studies and already have had success with BMI applications in tetraplegic patients using PPC recordings. Thus the outlook is good for successful completion of these aims within 3 years. The results of these aims will advance both the scientific understanding of grasp processing in human cortex and the development and implementation of bidirectional BMIs to assist patients with movement disorders.

Public Health Relevance

Tetraplegia is a particularly severe form of paralysis in which patients are paralyzed from the neck down. Tetraplegic patients lose partial or total function and sensation of all four limbs and are unable to perform even the most rudimentary activities of daily living on their own. According to the National Spinal Cord Injury Statistical Center approximately 160,000 people in the USA are living with complete or partial tetraplegia as of 2014. A majority of these patients still have sufficiently intact cortex to plan movements, but they are unable to execute them. Thus they are candidates for assistance using cortical brain-machine interfaces. Moreover, these prosthetics have applicability beyond spinal cord lesion and can also help patients with motor disabilities from stroke and neurodegenerative diseases. Better understanding of the cortical grasp pathway (aim 1), providing somatosensory feedback with intracortical microstimulation (aim 2), and combining intracortical stimulation feedback with brain control (aim 3) promise to greatly benefit patients.

National Institute of Health (NIH)
National Institute of Neurological Disorders and Stroke (NINDS)
Research Project--Cooperative Agreements (U01)
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Special Emphasis Panel (ZNS1)
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Gnadt, James W
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California Institute of Technology
Schools of Arts and Sciences
United States
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Armenta Salas, Michelle; Bashford, Luke; Kellis, Spencer et al. (2018) Proprioceptive and cutaneous sensations in humans elicited by intracortical microstimulation. Elife 7: