Auditory response properties of neurons in the tectal longitudinal column of the rat

Abstract

The newly-discovered tectal longitudinal column (TLC) spans the paramedian region of the mammalian tectum. It has connections with several nuclei of the auditory system. In this report, we provide the first detailed description of the responses of TLC neurons to auditory stimuli, including monaural and binaural tones and amplitude modulated tones. For comparison, responses in the inferior colliculus (IC) were also recorded. Neurons in the TLC were sensitive to similar ranges of frequency as IC neurons, could have comparably low thresholds, and showed primarily excitatory responses to stimulation of the contralateral ear with either phasic or sustained response patterns. Differences of TLC compared to IC neurons included broader frequency tuning, higher average threshold, longer response latencies, little synchronization or rate tuning to amplitude modulation frequency and a smaller degree of inhibition evoked by stimulation of the ipsilateral ear. These features of TLC neurons suggest a role for the TLC in descending auditory pathways.

Connections of the superior paraolivary nucleus of the rat: projections to the inferior colliculus

“…4, 6–8) which innervated the recently identified TLC (Saldaña et al, 2007; Marshall et al, 2008). We also noted the presence of labeled axons in the ipsilateral medial geniculate body.…”

Auditory System

“…The TLC is reciprocally interconnected with the the SPO and also received inputs from all IC subdivisions and (Saldaña et al, 2009;Aparicio et al, 2010;Viñuela et al, 2011) and may be a source of inhibitory inputs (Mugnaini and Oertel, 1985;Vetter and Mugnaini, 1985). The electrophysiological features of these neurons reveals that they possess broad frequency tuning, high threshold, long latencies, little synchronization or rate tuning to amplitude modulation frequency and a small degree of inhibition evoked by stimulation of the ipsilateral ear (Marshall et al, 2008). These responses features suggest that they play a role in processing background rather than foreground features of the auditory scene.…”

The organization of frequency and binaural cues in the gerbil inferior colliculus

“…If the frequency difference is small (usually 1 to a few Hz, but in some cases up to ∼100 Hz), neurons in the IC can follow this changing phase, because of the specialized circuits that collect and enhance the phase‐locking produced by hair cells and the auditory nerve. Sensitivity to the binaural beat can occur to the fine structure of low‐frequency sounds or to the envelopes of sounds including high‐frequency carriers, as has been shown in many species (Kuwada, Stanford, & Batra, ; Batra, Kuwada, & Stanford, ; Yin & Chan, ; McAlpine, Jiang, & Palmer, ; Marshall et al, ), including gerbils (Spitzer and Semple, ). We used the analytic procedures described by Yin & Kuwada () to quantify the responses of ITD‐sensitive neurons.…”