Over-representation of speech in older adults originates from early response in higher order auditory cortex

Abstract

Previous research has found that, paradoxically, while older adults have more difficulty comprehending speech in challenging circumstances than younger adults, their brain responses track the envelope of the acoustic signal more robustly. Here we investigate this puzzle by using magnetoencephalography (MEG) source localization to determine the anatomical origin of this difference. Our results indicate that this robust tracking in older adults does not arise merely from having the same responses as younger adults but with larger amplitudes; instead, they recruit additional regions, inferior to core auditory cortex, with a short latency of ~30 ms relative to the acoustic signal.

Figure 1:

Model fit, expressed as Fisher z-transformed Pearson correlation between predicted and measured (source transformed) responses. A) Significantly better predicted brain responses in older adults than younger adults, in a region below left core auditory cortex (p ≤ .05 corrected within indicated bilateral temporal lobe). Outlines indicate Heschl’s gyrus (core auditory cortex, green) and superior temporal gyrus (blue). B) Average model prediction quality for each group separately.

Figure 2:

Response function in the region of difference. A) Mean absolute response function in the ROI based on significant difference in model fit (cf. Figure 1), with standard error. Older adults had significantly higher amplitude in the earliest response peak. B) Anatomical distribution of the difference in the absolute response strength during the window defined based on the first peak (10-40 ms). The anatomical distribution closely resembles the region of the difference in model fit.