Figure 5.

Effect of movement direction on M1 unit activity. A, Two-dimensional representation of twitch direction in polar space. The x-dimension (medial–lateral) and the z-dimension (anterior–posterior) are shown. B, Top, Scatterplot showing the position of the right forelimb at peak twitch displacement for all twitches at P8 (left) and P12 (right). Bottom, Heatmap showing the most common position of the right forelimb at peak twitch displacement for all twitches at P8 and P12. C, Peristimulus time histograms of the mean (±SEM) firing rate of M1 units in relation to the onset time of anterior (blue), posterior (green), medial (orange), and lateral (yellow) forelimb twitches at P8 (left) and P12 (right). D, Mean (±SEM) response strength (Δfiring rate in relation to baseline) for anterior (blue) and posterior (green) twitches, and for medial (orange) and lateral (yellow) twitches at P8 (left) and P12 (right). The gray-shaded regions indicate 99% confidence intervals based on shuffled data. Asterisks indicate a significant difference between movement directions (p < 0.05). E, The slope (magnitude of the relationship between response strength and movement direction) for individual units is represented along the medial–lateral (x) and anterior–posterior (y) axes. The gray-shaded horizontal and vertical lines indicate 99% confidence intervals based on shuffled data. F, Top row, Stacked plots show the percentage of units tuned to anterior (blue) or posterior (green) twitches at P8 and P12. Bottom row, Stacked plots show the percentage of units tuned to medial (orange) or lateral (yellow) twitches at P8 and P12. The white regions indicate untuned units.