The temporal representation of the delay of iterated rippled noise in the ventral cochlear nucleus of the guinea-pig

1. We have examined the temporal discharge patterns of single units from th e ventral cochlear nucleus (VCN) of anaesthetized guinea-pigs in response t o iterated rippled noise (IRN). The pitch range evoked by the stimuli was f rom 32 to 1000 Hz. 2. Single units were classified into four groups using existing classificat ion schemes: primary-like (PL), onset (O), sustained chopper (CS) and trans ient chopper (CT). For all unit types the delay of the IRN stimuli was well represented in the all-order interspike interval histograms (ISIHs). 3. A subset of the onset units (onset-chopper, OC) showed a clear preferenc e for some delays of the IRN in their first-order interval statistics. We d escribe this delay preference as 'periodicity tuning'. The delay at which t he pitch estimate was at its maximum was designated its best periodicity. T he range of best periodicities for OC units was 3.75-13 ms (between 77 and 267 Hz). 4. The other unit types also showed enhancement of the first-order interval statistics at the delay of the MIN. The range of best periodicities was 1. 4-8.8 ms (113-714 Hz) for the CT group, 2.25-10.8 ms (93-444 Hz) for the CS group and 0.5-4.6 ms (217-2000 Hz) for the PL group. 5. The correlation between the maximum interval enhancement observed in res ponse to the IRN stimuli and the peak in the first-order ISM in response to white noise was 0.81 for OC units, 0.72 for CS units, 0.44 for CT units an d -0.15 for PL units. 6. These results demonstrate that all unit types in the VCN can enhance the representation of the delay of MIN using first-order interspike intervals (ISIs) over a range of periodicities. CS and OC units show the greatest ran ge of best periodicities and they are well-suited to encode the delay of IR NT in their first-order ISIs for a wide range of pitches.