Figure 3: Fine-temporal scale refinement of firing-motor output relationship in a subpopulation of L5b PNs.

(a) Three examples of L5b PNs’ peri-event time histograms, aligned by the ‘orient’ position (time ‘0’, white dots). Fifty-six consecutive first reach success and 80 consecutive first reach failure trials are stacked. White arrows indicate the time when food pellets were provided. The correspondent forelimb velocity, are shown overlaid on the top. Neural activities were normalized and expressed as Z score. Neuron A’s firing highly correlated with forelimb action but remained unchanged with training. Neuron B’s firing became correlated with forelimb action after training. Neuron C’s firing did not correlate with forelimb reaching action irrespective of training. (b) Averaged neural activities of the three L5b PNs shown in a during first reach success (red, mean±s.e.m.) and first reach failure (blue, mean±s.e.m.) trials on days 1 and 7. Arrows indicate the time when the neural activity began to diverge (TUD, time until divergence, see Methods). (c) Hierarchical clustering of 131 L5b PNs (recorded from five rats) based on single neuron I_M during motor learning. The dendrogram (upper half) depicts Euclidean distance of single PN I_M vectors across 7 training days, with major subgroups indicated by different colours in the dendrogram. (d) Twenty-seven L5b INs (recorded from five rats) were classified into subgroups by applying the same method of hierarchical clustering of single neuron I_M as shown in c. (e) Summary of training-dependent changes of the optimal time lag of I_M (τ_opt. for the three major types of L5b PNs (recorded from five rats) classified by hierarchical clustering. Frequency histograms of individual neuron τ_opt. at days 1 and 7 are shown on the top and the right respectively. Sixty out of sixty-one of type 2 neurons exhibit a decrease in τ_opt., which are distributed below the dashed line with unit slope.