Figure 3.

Example histograms from a single unit depict peak firing rate and latency changes in response to bimanual stimulation on mirror locations. Histograms are shown for one neuron's responses (unit 074a from case A) when the locations on each hand were stimulated individually, then for both locations simultaneously, and finally for stimulus blocks in which the ipsilateral (left hand) stimulus was presented at intervals before the onset of the contralateral (right hand) stimulus. (Six out of eight stimulation conditions recorded are shown.) Stimulation was presented in blocks of 100 trials. Histograms were smoothed by a spike density function. Vertical dashed lines indicate when the latency was determined in Matlab using the criteria described in the Materials and Methods. The duration for each stimulus was 500 ms, as indicated by the line on the x-axis; therefore, paired stimulation overlapped in time for all stimulus onset delays tested except for 500 ms. The measures we examined in the present study were only the peak firing rate within 50 ms of the contralateral stimulus onset and the associated latency of that response. The peak firing rates were suppressed by bimanual stimulation in this example. Contralateral stimulation alone resulted in a peak firing rate (with baseline activity subtracted) of 27 spikes/s, while the firing rate response dropped to its lowest level of 8 spikes/s when the ipsilateral stimulus preceded the contralateral stimulus by 100 ms.