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, 56 (11 Pt 2), 2712-6

Multiple Types of Movement-Related Information Encoded in Hindlimb/Trunk Cortex in Rats and Potentially Available for Brain-Machine Interface Controls

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Multiple Types of Movement-Related Information Encoded in Hindlimb/Trunk Cortex in Rats and Potentially Available for Brain-Machine Interface Controls

Weiguo Song et al. IEEE Trans Biomed Eng.

Abstract

Brain-machine interface (BMI) systems hold the potential to return lost functions to patients with motor disorders. To date, most efforts in BMI have concentrated on decoding neural activity from forearm areas of cortex to operate a robotic arm or perform other manipulation tasks. Efforts have neglected the locomotion functions of hindlimb/trunk cortex. However, the role of cortex in hindlimb locomotion of intact rats, which are often model systems for BMI testing, is usually considered to be small. Thus, the quality of representations of locomotion available in this area was uncertain. We designed a new rodent BMI system, and tested decoding of the kinematics of trunk and hindlimbs during locomotion using linear regression. Recordings were made from the motor cortex of the hindlimb/trunk area in rats using arrays of six tetrodes (24 channels total). We found that multiple movement-related variables could be decoded simultaneously during locomotion, ranging from the proximal robot/pelvis attachment point, and the distal toe position, through hindlimb joint angles and limb endpoint in a polar coordinate system. Remarkably, the best reconstructed motion parameters were the more proximal kinematics, which might relate to global task variables. The pelvis motion was significantly better reconstructed than any other motion features.

Figures

Fig. 1
Fig. 1
Rats were trained to walk on treadmill. (a) Pelvic motion was recorded from the robot endpoint and hindlimb kinematics was recorded with a high speed camera (M1,M2,M4,M5 are reflection markers; M3 is a virtual marker). (b) Stick figure of the hindlimb plotted at 10ms intervals and the firing rate from the population of neurons in rat PICIN22 (color bar represents firing rate in Hz). (c) Electrode tract and the lesion / recording site from recording electrode. (d) Typical waveforms and ISI of two isolated units in single wire, red line indicates 2ms.
Fig. 2
Fig. 2
Segments of real (thick green) and neural regression estimated (thin black) kinematics during locomotion under normal condition (a) and under load condition (b) in a single rat, rat_PICIN22. std stands for stride-to-stride absolute standard deviation of each kinematic parameter in 67 step cycles.
Fig. 3
Fig. 3
The R-squared values of kinematics variables from the fitted datasets (a) and the prediction test datasets (b) in different (robot, polar and joint) coordinate frames during normal and load field locomotion in 4 rats across all sessions. (Ah:hip angle; Ak: knee angle; Aa: ankle angle; wx,wy stand for world-centered markers’ position; hx,hy stand for hip-centered markers’ position; 1 to 5 stand for iliac crest, hip, knee, ankle and toe marker, respectively; error baars represent 1 std; * indicates a statistically significant difference using a paired t-test, p<0.05). Reconstruction of video marker x components were generally superior to z, especially in world coordinates, broadly consistent with the polar coordinate reconstruction differences.

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