Fig 4. Cortical activity fits well to the cosine tuning curve.

Average cortical activity (black, ± SD) of neurons controlling each of the 6 arm muscles fit to a cosinusoidal tuning curve (green curve). Four of the six cortical activities are strongly directionally tuned (coefficient of determination R² > 0.7). Error bars show standard errors across trials with randomly chosen motor strategy (see text for more details). Simulation results are in agreement with experimental studies (Georgopoulos, Kalaska et al. [2], Fu, Suarez et al. [13], Moran and Schwartz [19]).