Extended Data Figure 6: Additional analysis of population activity.

a, Cumulative distribution of fraction of sessions classified as movement-related for inhibitory (red) and excitatory (green) neurons, showing the relative invariance of inhibitory neurons and dynamism of excitatory neurons (P < 0.001, Kolmogorov–Smirnov test). b, Movement-related excitatory neuron populations in each session compared to the previous session. Grey, fraction of neurons classified in the previous session; white, not classified in the previous session. A large number of newly movement-related neurons were added in the first few sessions (P < 0.001, comparison between sessions 2–4 versus 10–14, Wilcoxon rank sum test). c, Fraction of excitatory neurons classified as movement-related in each session. Black, training (n = 7 mice, this is the data shown in Fig. 2b); red, no training (n = 6 mice). The expansion of movement-related neurons is specific to animals that underwent training (P = 0.74, sessions 1–2 combined; P < 0.001, sessions 3–7 combined; Wilcoxon rank sum test). d, Average population activity aligned to movement onset (black dotted line). Average activity (calcium event trace) of each movement-related excitatory neuron was averaged. The population activity diverged from baseline 105 ms before movement onset (red dotted line, Methods). e, Standard deviation of activity timing of individual movement-related excitatory neurons across sessions. Focusing on neurons that are classified as movement-related in three or more sessions, the standard deviation of activity onset timing relative to movement onset is plotted across sessions. Sessions were binned into one-third of the total number of sessions each neuron was classified. Activity timing became more stable on the neuron-by-neuron basis (r = −0.14, P < 0.001). f, Histogram of the time from movement onset that the activity of each movement-related neuron significantly diverged from baseline. 9.2% of movement-related excitatory neurons show significant pre-movement activity, a composition similar to a previous study¹⁴. 82.7% of activity of movement-related neurons occurred during the periods between 105 ms before movement onset and movement offset (Methods). g, The cumulative fraction plot of the timing of all activity onsets of movement-related excitatory neurons during rewarded movements. Each group of sessions is shown as a line, with different colours representing different sessions. The distribution of activity onset timing during later sessions shifts towards the movement onset (P < 0.001, Kolmogorov–Smirnov test for all three comparisons). All error bars are s.e.m.