Mice make complex reaching and grasping movements to retrieve water rewards during head-fixation (A) Task setup: a head-fixed animal mid-reach with representative markerless tracking. (B) Task timeline, with representative 3D triangulated forelimb “skeletons”. (C) Distal digit centroid trajectories from 100 ms before lift to 100 ms after contact, left and right trials offset for visualization. One example session. (D) Lift reaction time distributions, left and right trials depicted separately. (E) Time from lift to paw centroid arriving within 5 mm of the spout target tip. (F) Time between lift and spout contact. Box plots in D-F show the quartiles (box and central line), whiskers extend 1.5 times the interquartile range past the quartile boundary, and more distant points (outliers) are plotted individually. (G) Number of contact events within 1 second of the water cue per trial. Data were pooled across sessions for D-G. (H) Time between cue and spout contact during optogenetic experiments. (I) Representative digit centroid trajectories for a subset of right trials during optogenetic experiments, from −100 ms before lift to 1000 ms after lift. Data from one example session.

Paw aperture reveals stereotyped kinematics across idiosyncratic single trial reach-to-grasp movements (A) Paw aperture was computed from the paw markers using a simple geometric measure. (B) Aperture time series overlaid on the Z velocity of the paw centroid. The collect and extend events are defined by the aperture minimum and its subsequent local maximum. Representative trial. (C) Histograms of collect and extend event times for all trials, left and right trials separated. (D) Lift, collect and extend event times depicted on digit centroid trajectories for one example mouse. (E) Median over trials of aperture time series aligned to the moment of maximum centroid Z velocity.

Mouse reaching and grasping movements involve coordination across proximal and distal joints (A) Schematic of Euler angle inverse kinematics procedure, depicting 7 joint angles over the proximal joints; 17 distal angles not shown. (B) Time series of 5 representative joints, shown from −100 ms to +400 ms around lift onset (vertical dashed line). Left (blue) and right (red) trials shown separately. Horizontal scale bar is 100 ms. Vertical scale bar is 30 degrees. Dashed horizontal lines are 0 degrees. (C) Correlation matrices of joint angles over all recorded time points. Rows are ordered descending from proximal (shoulder) to distal (metacarpal phalanges, MCP, proximal interphalanges, PIP). (D) Example loss curve of the cross-validated principal component analysis performed on joint angle and joint velocity time series. (E) Estimated dimensionalities of joint angle and velocity kinematics across mice.

CFA and fS1 cells are heterogeneously tuned to specific movement features (A) 2-photon imaging fields of view for all mice aligned to the Allen Atlas common coordinate framework (CCF). fS1 corresponds to SSp-ul and M1 to MOp in the CCF. The dashed gray line indicates the outline of the forelimb primary motor cortex (MOp-ul, referred to here as CFA) as described in Muñoz-Castañeda et al 2021. See Figure 4S1 and Methods for field of view alignment details. Right, example max-projection images for CFA and fS1 for mouse 1 with magnified insets. M1 and fS1 correspond to MOp and SSp-fl in the Allen CCF nomenclature. (B) Modulation metric (see Methods) of cue-locked data for individual cells in CFA and fS1. Values displayed are the logarithm of the computed p-value, where each point represents a cell. All cells with p-values < 0.025 are shown colored: left-only modulated cells are blue, right-only modulated cells are red, and cells modulated to both conditions are purple. (C) Peri-event histograms and rasters of single trial activity from individual cells in CFA. Each column displays two cells locked to each trial event: cue, lift and first-spout-contact. Trials grouped within each condition by time-in-reach. Vertical scale bar: 10 events per second (arbitrary units). Horizontal scale bar: 100 ms. (D) As in C but for fS1.

Vibration mapping for each individual mouse. Each image shows the widefield calcium response +250 ms after a vibrational stimulus applied to the contralateral paw. Each image was aligned with the underlying Allen CCF by placing the broad fS1 (SSp-fl in the Allen nomenclature) shaped activity profile within the corresponding region. Placement was then verified against veridical injection coordinates obtained during surgery (not shown). The dashed line in each map indicates the outline of the forelimb primary motor cortex (MOp-ul) as described in Muñoz-Castañeda et al 2021. Each grey box indicates the placement of the imaging fields of view in CFA and fS1 for each animal. Note that the window for mouse 1 was tilted anterior-posterior during widefield imaging, reducing the measured response in the anterior half of the window. This was accounted for in estimating atlas alignment.

Kinematic details of proximal and distal joints during reaching and grasping can be decoded from CFA and fS1 population activity (A) Performance of decoding models predicting joint angle kinematics from RADICaL-inferred CFA rates. Violins depict the distribution of variance explained over cross-validation folds for each individual joint angle. (f: flexion, a: abduction/adduction, r: rotation, d: deviation, o: opposition, s: splay, MCP: metacarpal-phalanges, PIP: proximal-interphalanges; digits indicated by number). (B) Reconstructed joint angle time series for 5 representative joint angles. Black traces are original and colored are reconstructed; left trials are blue and right trials are red. Vertical dashed line indicates lift time, horizontal line indicates 0 degrees. Vertical scale bar is 30 degrees, horizontal scale bar is 100 ms. (C) Forelimb skeletal postures reconstructed from decoded joint angles for representative left and right trials (trials having median variance explained). 7 representative time points from lift time to grab time are shown. Gray postures are original data, colored postures are reconstructed as in B. Decoded joint angles in each time step were applied to the neutralized posture of the original data, preserving the original lengths of inter-marker links. (D). Performance of decoding models for all 5 mice. Each point is the median of the distribution of variance explained over cross validation folds, with proximal (magenta) and distal (goldenrod) angles considered separately. The black lines indicate the median variance explained over all proximal or distal joints for an individual mouse. (E-H) As in A-D but for fS1 data.

(A) Joint angle decoding as in Figure 5, but from CFA deconvolved calcium transients smoothed with a 35 ms Gaussian kernel. Data is presented as in Figure 5D and 5H. (B) as in A but for fS1. (C) Joint velocity decoding using RADICaL rates from CFA. (D) Same as C but for fS1.

(A) Joint angle decoding as in Figure 5 but with proximal joint angle time series regressed off of distal joints and distal joint angle time series regressed off of proximal joints. Decoding performed with RADICaL rates. Data is presented as in Figure 5D and 5H. (B) as in A but for fS1. (C) Joint angle decoding as in Figure 5 but with the distance to the spout of the paw centroid regressed off of all joint angles. (D) Same as C but for S1-fl. (E) Variance of joint angles and their variance explained when decoded using CFA RADICaL rates as in Figure 5. Each point has coordinates of the true kinematic variance and the variance explained for a single joint on a single cross-validation fold. (F) Same as E but for fS1.

CFA reflects target-specific information earlier and more persistently than fS1 (A) Projections of population activity from held-out single trials onto the target decoding dimension for CFA and fS1. Right trials are red and left trials are blue. Traces were normalized by the 90th percentile value across trials for left and right trials separately. (B) Distribution of threshold crossing times for projections shown in A. Black lines indicate medians. Star indicates significantly different medians at p < 0.05, Wilcoxon ranksum. (C) Performance of time-generalized target decoding analysis. Each heat map depicts the performance over all model training windows (columns) and test time points (rows). Time in trial runs vertically as in A. Both the training and testing epochs were −100 (leftmost column training, bottommost row test) to +1000 ms (rightmost column training, top row test) relative to cue. Training epochs were 100 ms non-overlapping windows and testing epochs were 10 ms bins.