Fig. 2: Neural geometry of single-finger movements.

A Peristimulus time histograms of recorded neural activity from 3 example channels during attempted flexion and extension of individual fingers on the contralateral (right) hand (lines show the average for different conditions, shaded regions show standard error). B Cumulative fraction of variance explained by the principal components of the trial and time-averaged neural activity. The top five components captured > 90% of the variance (ambient dimensionality 576 resulting from concatenation of 192 channels across three sessions), suggesting a low dimensional representation. C Schematic description of two metrics for characterizing the geometry of different movements in neural state space, where each axis corresponds to the activity of a particular neuron. Representational dissimilarity matrix (RDM) is estimated by measuring Euclidean distance (d_ij) between pairs of movements. Relative arrangement of the direction along which each finger modulates the activity in the neural state space is given by the cosine of angle (θ) between lines joining flexion-extension movements of a given finger. D RDM for neural activity during the hold period, averaged across three sessions for participant T5. Black indicates higher similarity. Off-diagonal elements were significantly larger than zero (p < 0.001). Significance level was computed by comparing the observed distances with a null distribution of 1000 distances. These null distribution distances were calculated by permuting neural activity across the two movements. E Similarity of the modulation directions for pairs of fingers. Nearby fingers have similar modulation direction, except for the thumb. F, G Visualization of neural activity using cross validated Targeted Dimensionality Reduction (TDR) followed by PCA. TDR directions identified by regressing from the kinematic variables (five dimensions, one for each finger, +1 for flexion/ −1 for extension, and 0 for rest) to trial & time-averaged neural activity in the last 0.4 s of each trial. Colors indicate fingers, line style indicates different movements (flexion/extension) and black dots indicate the ‘go’ cue. Arrows indicate the evolution of neural activity during the course of the trial. Two views of the 3D geometry are shown. Source data are provided in the Source Data file.