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Fig. 2. (A–D) Response characteristics of DBNi1-2 evoked by forced deflections of the second antennal joint between the scape and pedicel. (A) Compound excitatory postsynaptic potentials (EPSPs) elicited by imposed movements with ramps of amplitude 23° at an angular velocity of 300°s-1 during both adduction and abduction of the antenna. The positions of the antenna at the extreme positions of the deflection are indicated as insets. (B) Correlation between the increase in spike frequency and movement velocity up to 900°s-1 during abduction and adduction between 0 and 100°. Values are means ± S.E.M. of normalised data for 3–7 stimulus periods in five animals. (C) Directional sensitivity to imposed deflections of the scape–pedicel joint (range 0–80°; four steps of 20° each; 300°s-1 as in A). Curves indicate relative mean spike counts (± S.E.M.) per ramp (N=7 animals). The curves are discontinuous every 20°, corresponding to the pauses between two ramps at a constant angular position. Arrows indicate the direction of movement (the outer curves are for movements towards the back of the insect; abduction); the solid line at 30° indicates the antennal resting position. The radius of circles represents the percentage of the maximum response (outer circle, 100%). The shaded sector indicates the range of naturally occurring movements of the scape–pedicel joint. (D) Electrical stimulation of afferent antennal nerves during intracellular recording from DBNi1-2. The shortest latencies (2ms) resulted from stimulation of N1 in the scape (the arrow indicates spikes). Electrical stimulation of the flagellar N1 resulted only in EPSPs of small amplitude and long latency (7ms). Stimulation of N2B failed to elicit any responses. The downward shift in the intracellular trace after stimulation is due to the microelectrode capacitance and was also seen when the electrode tip was extracellular. sc, scape; pd, pedicel; fl1, first flagellar segment; fl6, sixth flagellar segment. Asterisks indicate transient stimulation artefacts. Each recording consists of five superimposed sweeps.