Correction for Ethier et al., Linear Summation of Cat Motor Cortex Outputs

Examples of displacement vectors. Individual displacement (A, B) obtained by stimulation of cortical points on their own are shown in green and blue. The resultant vectors (_res) were determined from the individual vectors by the rules of linear algebra and are shown in black. The vectors obtained by stimulation of two points simultaneously are shown in red (i.e., the experimentally obtained vectors). In C, we show a two-dimensional sagittal projection of the three-dimensional displacement vectors obtained by varying the stimulus intensities at two cortical points. The stimulus current (in microamperes) applied simultaneously at each cortical point is shown in the boxes. Except for the combination I₁ = 40 μA and I₂ = 14 μA, the direction of the movement is smoothly modulated as a function of the relative intensities of the two stimuli. The average ± SD angular separation between the experimental vectors and the resultants (i.e., predicted) in C was 11 ± 2.5°. Med-Lat, Mediolateral; Ant-Post, anteroposterior.