The article “Linear Summation of Cat Motor Cortex Outputs,” by Christian Ethier, Laurent Brizzi, Warren G. Darling, and Charles Capaday, which appeared on pages 5574–5581 of the May 17, 2006 issue, the incorrect version of Figure 7 printed. The correct version of the figure and legend are printed here.
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.
