The effects of inhibitory postsynaptic potential (IPSP) barrages on coding of sinusoidal length inputs were investigated in slowly and rapidly adapting stretch receptors of crayfish (RM1 and RM2, respectively). To examine the contribution of postsynaptic firings, a description was obtained of the temporal correlations between sensory stimuli, pre- and postsynaptic spikes, plus the relative position of the latter. In this analysis, the times between an IPSP and the closest spike preceding or following it are known, respectively, as phase (phi) and cophase (theta). 2. Interactions were similar in RM1 and RM2. The usual effect was the expected increased postsynaptic interval durations, but special consequences were also evoked. With regular IPSPs there were epochs including inhibitory (S) and postsynaptic (R) spikes and fixed "alternations" at S/R times the IPSP rate. S/R ratios were usually 1:1 and 1:2, more rarely 2:1. There were sudden postsynaptic interval duration changes, or "jumps," between successive alternation ratios where inhibitory effects increased or decreased. With 1:1 and 1:2 ratios there was a gradual "sliding," or phi increase-theta decrease, at the pull and the opposite at the release. The theta and phi roughly paralleled the control postsynaptic intervals and the inhibited-minus-control differences, respectively, when sliding was present. Sliding disappeared, and phi and theta tended to become invariant, with 2:1 ratio. 3. Irregular IPSP increased postsynaptic interval irregularities and eliminated alternations. Phase values were irregularly distributed, but theta and control postsynaptic intervals were similar irrespective of pattern.(ABSTRACT TRUNCATED AT 250 WORDS)
