Abstract
In search of a solution to the long standing problems encountered in traditional brain computer interfaces (BCI), the lateral descending tracts of the spinal cord present an alternative site for taping into the volitional motor signals. Due to the convergence of the cortical outputs into a final common pathway in the descending tracts of the spinal cord, neural interfaces with the spinal cord can potentially acquire signals richer with volitional information in a smaller anatomical region. The main objective of this study was to evaluate the feasibility of extracting motor control signals from the corticospinal tract (CST) of the rat spinal cord. Flexible substrate, multi-electrode arrays (MEA) were implanted in the CST of rats trained for a lever pressing task. This novel use of flexible substrate MEAs allowed recording of CST activity in behaving animals for up to three weeks with the current implantation technique. Time-frequency and principal component analyses (PCA) were applied to the neural signals to reconstruct isometric forelimb forces. Computed regression coefficients were then used to predict isometric forces in additional trials. The correlation between measured and predicted forces in the vertical direction averaged across six animals was 0.67 and R2 value was 0.44. Force regression in the horizontal directions was less successful, possibly due to the small amplitude of forces. Neural signals above and near the high gamma band made the largest contributions to prediction of forces. The results of this study support the feasibility of a spinal cord computer interface (SCCI) for generation of command signals in paralyzed individuals.
Highlights
Severe injuries at the cervical spinal cord can result in quadriplegia due to extensive paralysis of the body below shoulders
Braincomputer interfacing (BCI) is a technique to substitute for the lost command signals in these severely paralyzed individuals, using neural signals recorded from the brain
If we look at the big picture, the final pathway for all the motor control information processed in the brain is the descending tracts of the spinal cord before the signals reach the skeletal muscle
Summary
Severe injuries at the cervical spinal cord can result in quadriplegia due to extensive paralysis of the body below shoulders. Braincomputer interfacing (BCI) is a technique to substitute for the lost command signals in these severely paralyzed individuals, using neural signals recorded from the brain. Brain-computer interfaces attempt to “read” the volitional information from various cerebral cortices, primarily those involved in planning and execution of the motor function. A large number of microelectrodes implanted in the brain parenchyma record single spike activity of local neurons to extract the volitional information. Attempts have been made to characterize the local field potentials and cortical surface recordings with non-penetrating electrodes as a source of volitional information (Schalk et al, 2008; Kubanek et al, 2009)
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