Extended Data Fig. 1 |. Additional information for task design, recording sites and behavioural performance.

a, Spatial arrangements of the 12 reaching targets. The target density near the trained target (down, up or right) was higher in order to sample more neural states for reaches that were more likely to be altered by learning, for the purpose of studying generalization of learning³. Ideally, one would like to have equally-spaced reach targets as dense as possible, but because monkeys could perform a limited number of trials each day, a compromise solution was to increase the density of targets near the trained target. Note that the curl field can be either clockwise (CW) or counterclockwise (CCW). Here we show CW fields as an example. b, Utah-array implant locations in monkey U and recording sites in monkey V. Recordings were performed in PMd and M1 in the hemisphere contralateral to the reaching arm. Top panel: an intraoperative photo of three Utah-array implants in monkey U. Bottom panel: a schematic map illustrating the approximate locations of recording sites in monkey V based on stereotactic coordinates; data in this work included units recorded from multi-electrode V-probes and Neuropixels probes. Histology has not yet been done on either monkey. Using the cortical landmarks, we estimated that the recording sites in monkey V largely overlapped with the lateral half of the area covered by the three Utah arrays in monkey U. AS: Spur of arcuate. CS: central sulcus. PCD: precentral dimple. c, We computed behavioural (top panel) and neural generalization (bottom panel) with the sign of the effects flipped for CCW fields to match the effects of CW fields, compared to Fig. 1d and Fig. 2c. We found a spatial asymmetry in behavioural and neural generalization, with more learning in the ‘push’ direction (i.e., the direction to oppose the curl field). Error bars, s.e.m. across sessions (monkey U, n = 4, 3; monkey V, n = 5, 3). d, Top panel: trial-averaged hand speed in different blocks over multiple learning sessions. Shaded area, s.e.m. across sessions (monkey U, n = 4; monkey V, n = 5). Bottom panel: compensatory hand force perpendicular to the reach direction in one example session. Hand force in late-learning trials (dark red) showed a more stereotypical, less variable temporal pattern with an earlier onset than in early-learning trials (light red). Time zero, movement onset.