Fig. 2.

A: hidden state sequences detected by hidden Markov models in a single trial. Colored traces representing the probability of 4 hidden states [initial (blue), reaction (red), movement (green), and final (purple)] overlie the rastered activity of simultaneously recorded populations of premotor cortex (PM) mirror neurons (MNs; top) and PM non-MNs (bottom). Black markers below raster plots indicate the time of instruction onset (square), movement onset (circle), and object manipulation (triangle). Colored dashed and dotted vertical lines indicate the times at which the reaction, movement, and final states exceeded the 0.6 probability threshold (horizontal gray lines) used to define rise times for each population, with corresponding colored triangles indicating the duration between state transitions in the MN vs. non-MN population from PM. B: similar to A for primary motor cortex (M1) MNs (top) and M1 non-MNs (bottom). C: perievent histograms and multiple trial spike rasters for a single PM MN (left) and a single PM non-MN (right). Top frames show firing rates in 25-ms overlapping bins stepped at 5-ms intervals averaged across all trials involving each object separately (colored traces) and all trials together (solid black line); total number of trials (n_Trials) is indicated above frames. Modulation onset time, indicated by downward arrows, was defined when the firing rate averaged across all trials (black trace) crossed ±2 SD (dotted horizontal lines) from the mean baseline activity (horizontal gray lines) measured 500 ms preceding instruction onset). Bottom frames show spike rasters for 5 trials involving each object. Traces involving each object are colored differently [sphere (dark blue), button (orange), coaxial cylinder (teal), and perpendicular cylinder (pink)]. Black markers indicate the same behavioral events as in A and B, with inverted triangles indicating the end of the final hold period. D: similar to C for a single M1 MN (left) and a single M1 non-MN (right).