ORIGINAL PAPER J. P. Walton á R. D. Frisina á J. R. Ison W. E. O'Neill Neural correlates of behavioral gap detection in the inferior colliculus of the young CBA mouse Accepted: 6 February 1997 Abstract The gap detection paradigm is frequently used in psychoacoustics to characterize the temporal acuity of the auditory system. Neural responses to silent gaps embedded in white-noise carriers, were obtained from mouse inferior colliculus (IC) neurons and the results compared to behavioral estimates of gap detection. Neural correlates of gap detection were obtained from 78 single neurons located in the central nucleus of the IC. Minimal gap thresholds (MGTs) were computed from single-unit gap functions and were found to be comparable, 1±2 ms, to the behavioral gap threshold (2 ms). There was no dierence in MGTs for units in which both carrier intensities were collected. Single unit responses were classi®ed based on temporal discharge patterns to steady-state noise bursts. Onset and primary- like units had the shortest mean MGTs (2.0 ms), fol- lowed by sustained units (4.0 ms) and phasic-o units (4.2 ms). The longest MGTs were obtained for inhibi- tory neurons  x  14 ms. Finally, the time-course of behavioral and neurophysiological gap functions were found to be in good agreement. The results of the present study indicate the neural code necessary for behavioral gap detection is present in the temporal dis- charge patterns of the majority of IC neurons. Key words Temporal resolution á Forward masking á Inferior colliculus á Startle inhibition á Mus musculus Abbreviations ASR acoustic startle response á BF best frequency á DAB diaminobenzidine á DW driven window á IC inferior colliculus á MGT minimal gap threshold á MT minimum threshold PSTH peri-stimulus time histogram á QW quiescent window á SNR signal-to-noise ratio á TMB tetramethylbenzidine á TW time window Introduction Discrimination of species-speci®c vocalizations is ac- complished, in part, by using temporal information carried in the amplitude ¯uctuations of the vocalization envelope (Katz and Berry 1971). Rapid changes in the temporal envelope of speech have been postulated by Rosen (1992) and others to be a key property for speech recognition (Assmann and Summer®eld 1989). De®ning the role of the central auditory system (CAS) in tem- poral processing is one key to uncovering the neural foundation of auditory perception (Phillips 1993). Fur- thermore, certain de®cits in temporal resolution may underlie speci®c developmental and acquired language disorders. Tallal and Stark (1985) reported that certain developmental de®cits in language and reading com- prehension, in normal hearing subjects, appear corre- lated with the inability to process rapid acoustic temporal events on the order of tens of milliseconds. Therefore, the neural mechanisms that underlie tempo- ral resolution in the peripheral and central auditory nervous systems are of great importance. The detection of brief silent intervals, or temporal gaps, in an ongoing sound is a simple, yet extremely ecient method used to assess temporal resolution (Plomp 1964; Shailer and Moore 1983; Fitzgibbons 1983; Green and Forrest 1989). Psychoacoustic evidence suggests that such fundamental processing as detection of silent gaps embedded in noise correlates with more J Comp Physiol A (1997) 181: 161±176 Ó Springer-Verlag 1997 J.P. Walton (&) á R.D. Frisina Otolaryngology Division of Department of Surgery, University of Rochester School of Medicine & Dentistry, Rochester NY 14642-8629, USA, Tel.: +1-716 275-4852; Fax: +1-716 244-4103 e-mail: jpw@mother.ent.rochester.edu J.R. Ison Department of Brain and Cognitive Sciences, University of Rochester, Rochester NY 14627, USA R.D. Frisina, W.E. O'Neill Department of Neurobiology and Anatomy, University of Rochester School of Medicine and Dentistry, Rochester NY 14642-8603, USA