Physiological measures of auditory temporal integration in chinchillas and humans

Abstract

Temporal integration is a phenomenon in which signal detection improves with increasing signal duration. The magnitude of threshold improvement has been shown to vary as a function of signal frequency and is often diminished in the presence of hearing loss. In studies of chinchilla auditory nerve fibers and cochlear nucleus (CN) neurons, we have shown that single neuron thresholds improve with increasing duration in a manner similar to data from psychophysical studies. Moreover, it appears that a critical feature of duration coding in the CN is the pattern of spike activity rather than the total number of spikes over time. Thresholds measured in evoked-potential studies with chinchillas at the level of the inferior colliculus and with humans at the level of the cortex also reflect physiological evidence of temporal integration, with comparable frequency effects and degradation with hearing loss like that observed psychophysically. Although frequency effects that show greater threshold improvement for low versus high frequencies have been reported in the literature for decades, the underlying mechanism remains unclear and is under further investigation psychophysically and physiologically in our laboratories. The results of these investigations will be discussed along with potential underlying mechanisms.