Abstract
Recent studies in posterior parietal cortex (PPC) have found multiple effectors and cognitive strategies represented within a shared neural substrate in a structure termed “partially mixed selectivity” (Zhang et al., 2017). In this study, we examine whether the structure of these representations are preserved across changes in task context and is thus a robust and generalizable property of the neural population. Specifically, we test whether the structure is conserved from an open-loop motor imagery task (training) to a closed-loop cortical control task (online), a change that has led to substantial changes in neural behavior in prior studies in motor cortex. Recording from a 4x4 mm electrode array implanted in PPC of a human tetraplegic patient participating in a brain-machine interface (BMI) clinical trial, we studied the representations of imagined/attempted movements of the left/right hand and compare their individual BMI control performance using a one dimensional cursor control task. We found that the structure of the representations is largely maintained between training and online control. Our results demonstrate for the first time that the structure observed in the context of an open-loop motor imagery task is maintained and accessible in the context of closed-loop BMI control. These results indicate that it is possible to decode the mixed variables found from a small patch of cortex in PPC and use them individually for BMI control. Furthermore, they show that the structure of the mixed representations is maintained and robust across changes in task context.
Significance Statement Multiple effectors and cognitive strategies are represented within a small patch of human posterior parietal cortex (Zhang et al., 2017). However, it is unknown to what degree the structure of the representations is maintained across different task contexts. Here, we focus on the task contexts of brain-machine interface (BMI) training and online control, different contexts that have led to substantial changes in neural behavior in prior studies in motor cortex. We find that the structure of the representation of different movement conditions is largely maintained between the two contexts and that the different representations can all be separately decoded and used for online BMI control.
Footnotes
Authors report no conflict of interest
This work was supported by the National Institute of Health (R01EY015545), the Tianqiao and Chrissy Chen Brain-machine Interface Center at Caltech, the Della Martin Foundation, the Conte Center for Social Decision Making at Caltech (P50MH094258), and the Boswell Foundation.
This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license, which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properly attributed.
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