Direction of tongue motion in each behavioral task.

(A) Schematic of the location of three spouts, left (L), middle (M), and right (R), for the drinking task. Tongue direction was categorized based on spout location. (B) Calculation of 3D tongue direction during feeding. θ is the instantaneous 3D direction of the tongue tip over a 100 ms interval between its positions at t1 and t2, where t1 = 0 and t2 = t1 + 100. The dotted line shows the actual trajectory during this interval.

Examples of single neuron activity in relation to tongue direction.

(A) Each peri-event time histogram (PETH and ±1 SE, smoothed by a 25-ms Gaussian kernel) corresponds to spiking activity for a specific range of tongue direction for feeding trials. Dashed lines indicate 100-ms interval used for calculating the tongue direction. (B) PETHs for drinking trials with the same spout, centered at the point of minimum protrusion of the tongue (0-s). Percent tongue displacement along the anterior-posterior axis is shown in grey, with shaded area representing ±1 SD. Vertical lines indicate 500-ms interval used for tuning analysis.

Directional tuning of neurons during control tasks.

(A) 3D firing rate map of a neuron in MIo during feeding. Smaller inset plots are 1D tuning curves across each axis. (B) Percentage of neurons tuned to direction, combined for both subjects. Recordings were taken from four areas of the OSMCx: rMIo - rostral M1, cMIo - caudal M1, SIo(3a/3b) - area 3a/3b, and SIo(1/2) - area 1/2. Error bars represent ±1 SE.

Directional tuning to yaw and pitch during feeding.

(A) Firing rate maps of a neuron in MIo and in SIo across yaw and pitch angles. Firing rates were averaged across all 100 ms feeding intervals within a 10° range. (B) Proportion of neurons tuned to yaw and pitch, combined for both subjects. Recordings were taken from four areas of the OSMCx: rM1 - rostral M1, cM1 - caudal M1, SC(3a/3b) - area 3a/3b, and SC(1/2) - area 1/2. Error bars represent ±1 SE.

Cosine tuning of MIo and SIo neurons.

(A) Distribution of 3D preferred directions in unit sphere for neurons that fit the tuning function during feeding, combined for both subjects. The origin represents the start of a movement. Color bar represents posterior-anterior axis. (B) Distribution of the index for the depth of directional tuning, combined for both subjects.

Distribution of PDs in MIo (yellow) and SIo (purple) neurons during control feeding (A) and drinking (B).

For the feeding task, polar plots are split into 10° bins with thick colored lines representing the mean PD. For the drinking task, error bars represent ±1 SE.

Neural population trajectories vary across directions.

Trial-averaged trajectories of MIo and SIo population activity along the first three latent factors for Monkey R, grouped by direction. Axes for SIo are 1/4 scale of MIo. Arrows indicate the end of the trajectory. Percentages denote the sum of the variance explained by the first three factors. Inset plots show the difference between the average inter-trajectory distances of MIo and SIo over time for both feeding and drinking.

Effect of nerve block on direction of tongue movement.

(A) Distribution of tongue directions during feeding. (B) Variance in 3D trajectory endpoints during drinking (Posterior-Anterior, Inferior-Superior, Left-Right) for each direction: left (L), middle (M), right (R). (C) Variation in the distance of drinking endpoint positions from the mean endpoint. Left halves of hemi-violins (black) are control and right halves (red) are nerve block for an individual. Horizontal black lines represent the mean and horizontal red lines the median. Results of two-tailed t-test and f-test are indicated by asterisks and crosses, respectively: *,† p < 0.05; **,†† p < 0.01; ***,††† p < 0.001. Smaller inset plots show that there was no effect in the sham nerve block condition, for reference. The sham procedure was identical to the nerve block, except the anesthetic was substituted with saline solution

Effect of nerve block on drinking kinematics in Monkey R.

(A) Tongue tip trajectories from starting position to one of three drinking spouts in the control and nerve block conditions. (B) Drinking trajectory endpoints, where the black dot represents the mean endpoint position.

Effects of nerve block on directional tuning of OSMCx neurons during feeding and drinking tasks.

(A) Percentage of directionally tuned neurons in four areas: rMIo - rostral M1, cMIo - caudal M1, SIo(3a/3b) -area 3a/3b, and SIo(1/2) -area 1/2. Filled in bars represent control while empty bars represent nerve block. Error bars represent ±1 SE. (B) Percentage of MIo and SIo neurons which gained or lost directionality with the addition of nerve block.

Effects of nerve block on the distribution of PDs of MIo (yellow) and SIo (purple) neurons.

(A) For the feeding task, polar plots are split into 10° bins with thick colored lines representing the mean PD. Significant circular concentration test (k-test) comparing control and nerve block are indicated by asterisks: *p < 0.05; **p < 0.01; ***p < 0.001. (B) For the drinking task, error bars represent ±1 SE. Filled in bars represent control while empty bars represent nerve block.

Effect of nerve block on population trajectories.

Trial-averaged trajectories of MIo and SIo population activity for Monkey R’s feeding and drinking sessions, grouped by direction. Axes represent the latent factors from control data, with the x-axis chosen as the factor with the highest degree of separation between directions. Lighter, dotted lines represent superimposed population trajectories in the nerve block condition. Insets show the difference between the average inter-trajectory distances for control and nerve block conditions.

Accuracies of two different decoding algorithms from MIo and SIo populations of equal size (N=28).

(A) Comparison between average decoding accuracy of KNN classifier. Chance level is 33.33%. (B) Comparison between average decoding accuracy by LSTM network. Data shown separately for each subject, behavioral task, and condition. The dashed line signifies equal decoding performance for MIo and SIo. Decoding accuracies from full populations are included in Figure 13 – figure supplement 2.