Figure 3.

Neuronal activity representing forthcoming movement, action, or arm use. A, An SMA neuron showing enhanced selective activity when right arm supination was the forthcoming first movement in the behavioral task. The rasters show neuronal discharges aligned at the onset of the first movement (vertical lines), and the perievent histograms indicate the sum of discharges with a 40 ms bin width. Rasters and histograms are displayed in a matrix arranged with respect to the first movement (columns) and second movement (rows). The thick horizontal line at the bottom represents 500 ms. The thick vertical line at the bottom right indicates the 40 spikes/s firing rate. For the time period during which the category of representation of neuronal activity corresponded to the model matrix shown at the top right (for this example, the first movement model), histograms are color coded according to the model matrix. For the remaining period, histograms are colored gray. The display format of the rasters and histograms in B and C is the same as that in A. B, Action-selective activity in a pre-SMA neuron observed before initiation of the first motor element. In this example, neuronal activity is preferential for the impending selection and initiation of supination, regardless of the laterality of arm use. C, Arm-use-selective activity in an SMA neuron. In this example, neuronal activity is preferential for the impending use of the left arm, regardless of whether the selected action is supination or pronation. D, Distribution of neurons exhibiting selectivity for the arm-use, action, or individual movements performed as the first motor element in the behavioral task. LS, Left supination; RS, right supination; LP, left pronation; RP, right pronation.