Processing of binaural stimuli by cat superior olivary complex neurons

Abstract

A method was developed to record sterotactically from the cat Superior Olivary Complex (SOC) using glass micropipettes. Sound stimulation was given through a closed system that permitted independent variation of interaural time (delta time) and intensity (delta int) differences. The most common binaural units found (n = 34) were ipsilateral excitatory, contralateral inhibitory (EI1), cells of the Lateral Superior Olive (LSO). Some Medial Superior Olive (MSO) cells and presumed MSO ascending afferents were found but, as noted by other authors, we found it difficult to obtain single unit recordings from this nucleus. The LSO EI cells were mostly sensitive to higher frequencies and showed Peristimulus Time Histograms (PSTHs) consisting of a sharp "On" response followed by a plateau when stimulated with Best Frequency (BF) tone bursts or noise bursts. This "On" response was sensitive to delta time and delta int such that ipsilateral time lead or intensity increase resulted in a stronger response. The response reached a minimum around zero delta time or delta int. No sharp peaks or dips were seen in the physiological range needed for localization, instead the response increased with increasing ipsilateral lead or intensity to the maximum values tested (2048 microseconds delta time, 30 dB delta int). In the physiological range the delta time and delta int response were complementary (both increasing response as ipsilaterality was increased). Provided enough sound energy in the unit's sensitive region was present, the same delta time curves were produced when BF tone bursts, masked tone bursts, "sharp onset" tone bursts or noise bursts were used. Changing the delta time of the carrier of the tone burst alone had no effect (except for one cell with a BF of 560 Hz), only the relative time of arrival of the stimulus envelope seemed to be important. In contrast to these LSO EI cells MSO-type units showed EI or EE predominantly low frequency phase-locked responses. When stimulated with interaurally phase shifted (delta pha) BF tones the unit response was a cyclic function of delta pha. Some cells (all that were tested, n = 6 including the 560 Hz LSO EI cell) showed these cyclic responses when stimulated with noise bursts or non-BF tones. However, these "characteristic delays" were not necessarily in the physiological range, i.e. we could find no evidence that these units were responding to delta time/delta pha values corresponding to a particular sound source direction.(ABSTRACT TRUNCATED AT 400 WORDS)

Auditory time-intensity cues in the binaural interaction component of the auditory evoked potentials

“…According to Caird and Klinke (1983) the medial superior olive cells are sensitive to interaural time differences while the lateral superior olive cells are sensitive to both interaural time differences and interaural intensity differences. Levine et al (1993) suggests that dT is abnormal in lesions affecting the medial superior olivary bodies, and dI is abnormal in lesions affecting the ventral acoustic stria.…”

Anatomy and projection patterns of the superior olivary comlex in the mexican free‐tailed bat, Tadarida brasiliensis mexicana

“…The classic view of the MSO is that it is a nucleus whose neurons code for interaural time differences (ITDs) of low frequency signals (Masterton and Diamond, 1967;Goldberg and Brown, 1969;Guinan et al, 197213;Caird and Klinke, 1983;Langford, 1984;Yin and Chan, 1990). These signals generate discharges in the auditory nerve and cochlear nucleus that are phase-locked to the cycle-by-cycle action of the stimulus (Galambos and Davis, 1943;Rose et al 1967;Johnson, 1980).…”

Dynamic changes in level influence spatial coding in the lateral superior olive

“…Sensitivity to ITDs and ILDs is first established in the medial superior olive (MSO) and lateral superior olive (LSO), respectively (Boudreau and Tsuchitani, 1968;Caird and Klinke, 1983;Brown, 1968,1969). The response properties established in the superior olive are then reiterated in auditory centres along the ascending neuraxis.…”