Ever wondered why older adults find it difficult to follow a conversation in noisy places despite having perfectly normal hearing abilities? Scientists may have found the answer! Researchers have determined that something is going on in the brains of typical older adults that causes them to struggle to follow speech amidst background noise, even when their hearing would be considered normal on a clinical assessment. They found that adults aged 61-73 with normal hearing scored significantly worse on speech understanding in noisy environments than adults aged 18-30 with normal hearing. The subjects of the study underwent two different kinds of scans to measure their brain's electrical activity while they listened to people talk. The researchers from the University of Maryland in the US were able to see what the subject's brains were up to when asked what someone was saying, both in a quiet environment and amidst a level of noise. They studied two areas of the brain.
They looked at the more 'ancestral' mid-brain area, which most vertebrate animals - all the way down to fish - have, and which does basic processing of all sounds. They also looked at the cortex, which is particularly large in humans and part of which specialises in speech processing. In the younger subject group, the mid-brain generated a signal that matched its task in each case - looking like speech in the quiet environment, and speech clearly discernable against a noisy background in the noise environment. However, in the older subject group, the quality of the response to the speech signal was degraded even when in the quiet environment, and the response was even worse in the noisy environment. "For older listeners, even when there is not any noise, the brain is already having trouble processing the speech," said Jonathan Z Simon, associate professor at the Maryland. Neural signals recorded from cortex showed that younger adults could process speech well in a relatively short time. The auditory cortex of older test subjects took longer to represent the same amount of information. "Part of the comprehension problems experienced by older adults in both quiet and noise conditions could be linked to age-related imbalance between excitatory and inhibitory neural processes in the brain," said Alessandro Presacco, PhD student at Maryland. "This imbalance could impair the brain's ability to correctly process auditory stimuli and could be the main cause of the abnormally high cortical response observed in our study," Presacco said. "Older people need more time to figure out what a speaker is saying. They are dedicating more of their resources and exerting more effort than younger adults when they are listening to speech," Simon added. The study was published in the Journal of Neurophysiology.
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