Joiner, W. M. | bioRxiv Science

bioRxiv2018

Proprioceptive Sonomyographic Control: A novel method of intuitive proportional control of multiple degrees of freedom for upper-extremity amputees

Technological advances in multi-articulated prosthetic hands have outpaced the methods available to amputees to intuitively control these devices. Amputees often cite difficulty of use as a key contributing factor for abandoning their prosthesis, creating a pressing need for improved control technology. A major challenge of traditional myoelectric control strategies using surface electromyography electrodes has been the difficulty in achieving intuitive and robust proportional control of multiple degrees of freedom. In this paper, we describe a new control method, proprioceptive sonomyographic control that overcomes several limitations of myoelectric control. In sonomyography, muscle mechanical deformation is sensed using ultrasound, as compared to electrical activation, and therefore the resulting control signals can directly control the position of the end effector. Compared to myoelectric control which controls the velocity of the end-effector device, sonomyographic control is more congruent with residual proprioception in the residual limb. We tested our approach with 5 upper-extremity amputees and able-bodied subjects using a virtual target achievement and holding task. Amputees and able-bodied participants demonstrated the ability to achieve positional control for 5 degrees of freedom with an hour of training. Our results demonstrate the potential of proprioceptive sonomyographic control for intuitive dexterous control of multiarticulated prostheses.

bioengineering↗

bioRxiv2018

Reduced transfer of visuomotor adaptation is associated with aberrant sense of agency in Schizophrenia

One deficit associated with schizophrenia (SZ) is the reduced ability to distinguish sensations resulting from self-caused actions from those due to external sources. This reduced sense of agency (SoA, awareness of ownership over self-generated actions) is hypothesized to result from a diminished utilization of internal monitoring signals of self-movement (i.e., efferent copy) which subsequently impairs forming and utilizing sensory prediction errors (differences between the predicted and actual sensory consequences resulting from movement). Here, we investigated the connections between clinical SZ symptoms and motor adaptation, a process that uses sensory prediction errors to update motor output. Schizophrenia patients (SZP, N=30) and non-psychiatric healthy control subjects (HC, N=31) adapted to altered movement visual feedback, and then applied the motor recalibration to untested contexts (i.e., the spatial generalization to untrained targets). Although adaptation was similar for SZP and controls, the extent of generalization was significantly less for SZP; movement trajectories made by patients to the furthest untrained target (135{degrees}) before and after adaptation were largely indistinguishable. Interestingly, deficits in the generalization were correlated to positive symptoms of psychosis (e.g., hallucinations), but not negative symptoms. Generalization was also associated with subjective measures of SoA across both SZP and HC, emphasizing the major role action awareness plays in motor behavior, and suggesting that tendencies to misattribute agency, even in HC, manifest in abnormal motor performance. We discuss the possible link of these findings to cerebellar circuit abnormalities that may be a common source for deficits in the utilization of sensory prediction errors and aberrant SoA.

neuroscience↗