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 50-ms Gaussian kernel) corresponds to spiking activity during a 200 ms window for a specific range of tongue direction for feeding trials. Dashed lines indicate the 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).

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: rM1 - rostral M1, cM1 - caudal M1, SC(1/2) - area 1/2, and SC(3a/3b) - area 3a/3b. 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.

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(1/2) - area 1/2, and SC(3a/3b) - area 3a/3b. Error bars represent ±1 SE.

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.

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.

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: rM1 - rostral M1, cM1 - caudal M1, SC(1/2) - area 1/2, and SC(3a/3b) - area 3a/3b. 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.

Decoding accuracies from neuronal populations of equal size (N=28). Data shown separately for each subject, behavioral task, and condition. The dashed line signifies equal decoding performance for MIo and SIo. Chance level is 33.33%. Decoding accuracies from full populations are included in Supplementary file 1, Fig. 5.