Learning a language or recognizing music is usually a breeze for children, however, this capacity dramatically declines with age.  Now, a study from researchers at St. Jude Children’s Research Hospital shows the restriction of a key chemical messenger in the brain helps extend efficient auditory learning much later in life.  The team states limiting the supply of the neuromodulator adenosine in a brain structure called the auditory thalamus preserved the ability of adult mice to learn from passive exposure to sound. The study is published in the journal Science.

Previous studies show the auditory thalamus is the brain’s relay station where sound is collected and sent to the auditory cortex for processing. The auditory thalamus and cortex rely on the neurotransmitter glutamate to communicate, with adenosine also shown to reduce glutamate levels. Circuits in the auditory cortex are highly susceptible to acoustic influences during the early postnatal period, with the auditory cortex selectively expanding neural representations of enriched acoustic stimuli, a process important for human language acquisition.  The current study shows juvenile plasticity can be reestablished in adulthood if acoustic stimuli are paired with disruption of adenosine production in the auditory thalamus.

The current study utilizes a variety of methods to demonstrate reducing adenosine or blocking the A1 adenosine receptor changes how adult mice respond to sound.  Results show when adenosine is reduced or the A1 receptor blocked in the auditory thalamus, adult mice passively exposed to a tone exhibit a stronger response to the same tone played weeks or months later. Data findings show these adult mice are able to distinguish between very close tones, an ability mice usually lack.

Results show the mice retain the improved tone discrimination for weeks.  Data findings show the window for effective auditory learning re-opened in the mice and they retain the information.  The team states they also observed disrupting adenosine signaling in the auditory thalamus extends the window for auditory learning for the longest period yet reported, well into adulthood, and far beyond the usual critical period in mice.

The team surmises their data shows disrupting adenosine signaling in the thalamus rejuvenates plasticity in the auditory cortex and improves auditory perception in mice.  For the future, the researchers state their results offer a promising strategy to extend the same window in humans to acquire language or musical ability.

Source: St. Jude Children’s Research Hospital

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