Long-Term Functional Changes in Multiple Cortical Areas

<div><p>(A) Color-coded (red shows high values; blue, low values) representation of individual contributions measured as the correlation coefficient (<i>R</i>) of neurons to linear model predictions of hand position for 42 training sessions. The average contribution steadily increased with training. The bar on the left indicates cortical location of the neurons.</p> <p>(B–E) Average contribution of neurons located in different cortical areas (PMd, M1, S1, and SMA, respectively) to hand position prediction during 42 recording sessions.</p> <p>(F) Average contribution for the whole ensemble to hand position prediction versus hand velocity predictions. A linear increase in contribution was observed only for predictions of hand position.</p></div

Directional Tuning in Frontoparietal Ensemble during Different Modes of Operation in Task 1

<div><p>(A–D) Directional tuning during pole control (A), brain control with arm movements (tuning assessed from cursor movements) (B), brain control without arm movements (tuning assessed from cursor movements) (C), and brain control with arm movements (tuning assessed from pole movements) (D). In each of the color-coded diagrams (red shows high values and blue low values; see color scale), the rows depict normalized directional tuning for individual cells. Because of the high directional tuning values of some cells (e.g., that shown in [H]), a color scale limit was set at 0.3 to allow color representation of the largest possible number of cells. Each tuning curve contains eight points that have been interpolated for visual clarity. Correspondence of tuning patterns under different conditions has been quantified using correlation coefficients (shown near lines connecting the diagrams). The highest correspondence was between tuning during pole control and brain control with arm movements. A much less similar pattern of direction tuning emerged during brain control without arm movements. Polar plots near each diagram show average directional tuning for the whole neural ensemble recorded. They indicate an average decrease in tuning strength and shifts in the preferred direction of tuning as the operation mode was switched from pole to brain control. Spread of preferred directions (90° corresponds to uniformly random distribution) is indicated near each polar plot.</p> <p>(E–G) Scatterplots comparing DTD (maximum minus minimum values of tuning curves) during pole control versus brain control with and without arm movements. DTD during brain control was consistently lower than during pole control. This effect was particularly evident during brain control without arm movements.</p> <p>(H–J) Changes in directional tuning for individual neurons under different conditions. Blue shows pole control; red, brain control with arm movements (tuning assessed from pole movements); and green, brain control without arm movements. The first illustrated cell (H) was tuned only when the monkey moved its arm, more so during pole control. The second cell (I) had similar tuning during all modes of operation, but tuning depth was the highest for pole control and the lowest for brain control without arm movements. The third cell (J) was better tuned during brain control.</p></div

Ensemble Encoding of Gripping Force, Plasticity of Directional Tuning, and Neuronal Contribution to Model Performance during Learning to Control the BMIc for Reaching and Grasping

<div><p>(A) Perievent time histograms (PETHs) in task 2 for the neuronal population sampled in monkey 1. The plots on top are color-coded (red shows high values; blue, low values). Each horizontal row represents a PETH for a single-neuron or multiunit activity. PETHs have been normalized by subtracting the mean and then dividing by the standard deviation. PETHs are aligned on the gripping force onset (crossing a threshold). Plots at the bottom show the corresponding average traces of gripping force. Note the general similarity of PETHs in pole (left) and brain (right) control in this relatively easy task. Cortical location of neurons is indicated by the bar on the top left. Note the distinct pattern of activation for different areas.</p> <p>(B) Changes in the mean contribution of neurons from different cortical areas to model predictions during training of monkey 1 in task 2.</p> <p>(C) Increases in directional tuning for six cortical areas during training in pole control in task 3.</p> <p>(D and E) Increases in neuronal contribution to linear models predicting hand position (blue), hand velocity (red), and gripping force (black) during learning task 3 in both monkeys.</p> <p>(F and G) Representative robot trajectories and gripping force profiles in an advanced stage of training in task 3 during both pole and brain control. The bottom graphs show trajectories and the amount of the gripping force developed during grasping each virtual object. The dotted vertical lines in the panels indicate the end of reach phase and the beginning of grasp phase. Note that during both modes of BMIc operation, the patterns of reaching and grasping movements (displacement followed by force increase) were preserved.</p></div