In the November 12 issue of the journal Neuron, researchers reveal the first direct evidence of real-time dynamic plasticity in the aural processing areas of the brain; a mechanism for fine tuning aural pattern recognition and noise exclusion.
In a noisy environment the auditory system tracks the repeating pitch of a voice, suppressing the background sounds.
“Children who are diagnosed with developmental dyslexia can be particularly vulnerable to the deleterious effects of background noise,” says senior study author Dr. Nina Kraus, who directs the Auditory Neuroscience Laboratory at Northwestern University.
When Dr. Kraus and her team measured repeated responses in the auditory brainstem, children without dyslexia were better able to adapt to repeated audible signals than variable signals. Whereas brainstem encoding in the children with dyslexia did not adapt well to the repeating auditory signal.
This was further linked to the successful perception of speech in noise. “The ability to sharpen representation of repeating elements is crucial to speech perception in noise, since it allows superior tagging of voice pitch, an important cue for segregating sound streams in background noise,” offers Dr. Kraus. “The disruption of this mechanism contributes to a critical deficit in noise exclusion, a common symptom in developmental dyslexia.”
Dr. Kraus’s team also observed that, when compared with the children that did not have dyslexia, the dyslexic children showed enhanced brain activity in response to variable sound stimuli. “This may enable dyslexic children to represent their sensory environment in a broader and arguably more creative manner, although at the cost of the ability to exclude irrelevant signals,” speculates Dr. Kraus.