Response properties of neurons in the central nucleus and external and dorsal cortices of the inferior colliculus in guinea pig

Abstract

The inferior colliculus (IC) represents a mid-brain structure which integrates information from many ascending auditory pathways, descending corticotectal projections and intercollicular pathways. The processing of information is different in each of the three main subdivisions of the IC--the central nucleus (CNIC), the dorsal cortex (DCIC) and the external cortex (ECIC)--which may be distinguished morphologically as well as by different inputs and outputs. To assess the differences in information processing we compared the response properties of single neurons in individual subnuclei of the IC in anesthetized guinea pigs. In comparison with DCIC and ECIC neurons, the CNIC neurons as a group were characterized by a sharper frequency tuning (as expressed by Q10 values), a lower average threshold, a shorter average first-spike latency of response to tones at the characteristic frequency (CF), a higher occurrence of non-monotonic rate/level functions and a higher rate of spontaneous activity. CNIC neurons and DCIC neurons reacted to tones at the CF more frequently by a sustained type of response than did ECIC neurons. The difference between the parameters of DCIC neuronal activity and ECIC neuronal activity was found to be smaller. The frequency tuning (expressed in Q10 values), spontaneous activity and dominance of monotonic rate/level functions were very similar in both structures; ECIC neurons expressed a higher average threshold and a shorter average first-spike latency than did DCIC neurons. Responsiveness expressed as the average maximal firing rate to tones at the CF was significantly higher in the CNIC than in the ECIC. The results give additional support to the idea that the CNIC is a part of a fast, frequency-tuned, low threshold and intensity-sensitive ascending pathway, whereas the other two subdivisions are involved in additional processing of information that involves feedback loops and polysensory pathways.

Serotonin Shifts First-Spike Latencies of Inferior Colliculus Neurons

“…1 A). Such a wide range is typical of IC neurons in the free-tailed bat and in other species (Bodenhamer and Pollak, 1981;Klug et al, 2000, Syka et al, 2000. Latency varied with recording depth, such that neurons recorded at shallower depths along the dorsoventral axis of the IC had longer latencies (multiple regression, p Ͻ 0.01; r 2 ϭ 0.24) and also exhibited a greater range of latencies than neurons deeper in the dorsoventral axis (Fig.…”

Antidromic Activation Reveals Tonotopically Organized Projections From Primary Auditory Cortex to the Central Nucleus of the Inferior Colliculus in Guinea Pig

“…The driven spike rate was taken as the total spike rate minus the spontaneous spike rate and was calculated from the PSTHs for a set time window. This window was selected based on visual assessment of all the PSTHs (compared with the spontaneous PSTHs where no stimulus was presented) and what has been used for other ICC (Snyder et al 2004;Syka et al 2000) and A1 (Arenberg et al 2000;Bierer and Middlebrooks 2002) recording studies. For acoustic stimulation where the stimulus duration was 50 ms, we used FIG.…”

Inhibition Has Little Effect on Response Latencies in the Inferior Colliculus

“…In the rat, guinea pig, cat, and bats, the majority of IC neurons have response latencies between 5 and 50 ms (Kitzes et al 1978;Jen and Schlegel 1982;Harrison and Palmer 1984;Langner et al 1987;Park and Pollak 1993;Ehert and Romand 1992;Fitzpatrick et al 1995;Le Beau et al 1996;Lu et al 1997;Ferragamo et al 1998;Klug et al 2000;Syka et al 2000). This range is broader than observed in lower auditory brainstem nuclei (Halpea et al 1994;Klug et al 2000).…”