[Detection of novel sounds. Multiple manifestations of the same phenomenon?]

Detection of novel sounds must be a basic function of the auditory system, but the underlying neuronal mechanisms are largely unknown.

During repetitive stimulation or a monotonous auditory scene, many auditory neurons show a decrease in their response, presumably due to adaptation. However, these neurons are able to recover and respond again any time there is a change in the stimuli. This process is known as stimulus-specific adaptation (SSA), and could be the basis of the neuronal mechanism for change detection. Neurons showing SSA have been reported both in auditory cortex and subcortical regions, such as the inferior colliculus. Neurons that experience SSA at all levels could be involved in a change detection circuit, but the relationship between neurons in different areas is still unclear. SSA, as found in these neurons, shares a number of characteristics with mismatch negativity (MMN), a component of evoked potentials related to the detection of context novelty, and linked to some processes that involve memory and attention.

The responses to changes in sounds can be observed in multiple ways, ranging from the activity of single neurons to evoked potential recordings. The phenomena observed using these different approaches appear to be manifestations of the same underlying sensory process, which would involve both cortical and subcortical auditory nuclei, and could have its basis in stimulus-specific neuronal adaptation.