Human posterior auditory cortex gates novel sounds to consciousness

Abstract

Life or death in hostile environments depends crucially on one's ability to detect and gate novel sounds to awareness, such as that of a twig cracking under the paw of a stalking predator in a noisy jungle. Two distinct auditory cortex processes have been thought to underlie this phenomenon: (i) attenuation of the so-called N1 response with repeated stimulation and (ii) elicitation of a mismatch negativity response (MMN) by changes in repetitive aspects of auditory stimulation. This division has been based on previous studies suggesting that, unlike for the N1, repetitive ''standard'' stimuli preceding a physically different ''novel'' stimulus constitute a prerequisite to MMN elicitation, and that the source loci of MMN and N1 are different. Contradicting these findings, our combined electromagnetic, hemodynamic, and psychophysical data indicate that the MMN is generated as a result of differential adaptation of anterior and posterior auditory cortex N1 sources by preceding auditory stimulation. Early (Ϸ85 ms) neural activity within posterior auditory cortex is adapted as sound novelty decreases. This alters the center of gravity of electromagnetic N1 source activity, creating an illusory difference between N1 and MMN source loci when estimated by using equivalent current dipole fits. Further, our electroencephalography data show a robust MMN after a single standard event when the interval between two consecutive novel sounds is kept invariant. Our converging findings suggest that transient adaptation of feature-specific neurons within human posterior auditory cortex filters superfluous sounds from entering one's awareness.

From sounds to words: A neurocomputational model of adaptation, inhibition and memory processes in auditory change detection

“…3). Thus, the results of our simulations are in line with (and integrate) two previous accounts which explained the emergence of an MMN to frequency change either on the basis of release of tonic inhibition (Näätänen, 1990) or neuronal adaptation (Jääskeläinen et al, 2004).…”

“…To account for the stronger anterior superior-temporal sources observed for the MMN response compared with N1 responses, previous adaptation models (Jääskeläinen et al, 2004;May & Tiitinen, 2010) assumed different frequency tuning of neuronal responses for anterior and posterior areas of the superior-temporal cortex (non-specific in posterior parts, sharply tuned in anterior parts). However, these assumptions are difficult to maintain in view of current knowledge about adaptation in the auditory system.…”

“…While these different explanations highlight the relevance of different processes, they converge on the importance of short-term mechanisms acting upon, or being driven by, the most recent sensory input. Mechanisms previously hypothesized to underlie the MMN response include cortical inhibition (Näätänen's (1990) "release of tonic inhibition" model), neuronal adaptation (Jääskeläinen et al's (2004) differential adaptation model), short-term synaptic plasticity (model-adjustment hypothesis (Winkler et al, 1996)) or a combination of these mechanisms. For example, the predictive coding model takes into account both synaptic plasticity and neuronal adaptation (Friston, 2005), whereas models described by May and colleagues (1999; focus on adaptation and lateral inhibition.…”

Enhancement of brain event-related potentials to speech sounds is associated with compensated reading skills in dyslexic children with familial risk for dyslexia

“…Although the current view of the mechanism-generating MMN is that the divergence of sensory input (deviant stimuli) with the memory trace created by the repetition (standard stimuli) elicits MMN. An alternative explanation claims that the deviant stimulus merely activates new afferent neuronal populations causing the diverging response, and thus the detection of change (Jääskeläinen et al, 2004;May & Tiitinen, 2010;Näätänen, 1992;Paavilainen, Alho, Reinikainen, Sams, & Näätänen, 1991).…”

Neuromagnetic responses to chords are modified by preceding musical scale

“…Furthermore, VI maj was presented at an equal frequency with the other conditions for I maj , I min and VI min . Therefore, the mechanism underlying the augmentation of N1m activity for VI maj may be distinct from sensory adaptation and gating effect of the feature-specific auditory neurons (Hari et al, 1982), which is partly associated with the classical mismatch negativity (MMN) generation mechanism (Jaaskelainen et al, 2004).…”