Effects of aging on the neuromagnetic mismatch detection to speech sounds.

The ability to discriminate speech sounds is crucial for higher language functions in humans. However, it remains unclear whether physiological aging affects the functional integrity of pre-attentive phonological discrimination. The neuromagnetic cortical responses during automatic change detection of speech sounds (/ba/versus/da/) were recorded in 24 young and 21 aged male adults. We used minimum norm estimate of source reconstruction to characterize the spatiotemporal dynamics of magnetic mismatch responses (MMNm). Distributed activations to phonetic changes were identified in the temporal, frontal and parietal regions. Compared to younger participants, elderly volunteers exhibited a significant reduction of cortical responses to phonetic-MMNm, except for the left orbitofrontal cortex and anterior inferior temporal gyrus. However, among the identified regions of interest, we did not observe significant between-group differences in the hemispheric asymmetry of phonetic-MMNm. Conclusively, our results suggest an altered phonetic processing at the perceptual level during physiological aging.