Fig. 2.

Effects of tarsal forces on muscle synergies in front and hindlegs. A and B: stimulation of the tarsal campaniform sensilla of the front (A) and hind (B) legs produced activation of the muscles that generate substrate grip [tibial flexor (FLEX TIB) and retractor unguis (RETR UNG)], as previously found in the middle legs. However, activation of the trochanteral depressor (DEPR TROCH) was vigorous in hindlegs (B, right) but only weak or absent in the front legs (A, right). C and D: cumulative histograms of muscle responses to stimulation of tarsal receptors. These plots show firing during the force application (indicated by the half-sine waveform) as well as periods (50% stimulus duration) before and after mechanical stimuli were applied to the tarsus. Inputs from tarsal campaniform sensilla in front (C) and hind (D) legs strongly excited distal leg muscles but were only weakly coupled to proximal leg musculature in front legs, consistent with their flexible use in walking and climbing.