Controlling a single brain chemical expands window for learning language, music in animal model.
Learning language or music is usually a breeze for children, however, as even young adults know, that capacity declines dramatically with age. Now, a study from researchers at St. Jude Children’s Research Hospital shows that restricting a key chemical messenger in the brain helps extend efficient auditory learning much later in life. The team state that their data shows that limiting the supply or the function 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 that 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. Adenosine was known to reduce glutamate levels by inhibiting this neurotransmitter’s release. Circuits in the auditory cortex are highly susceptible to acoustic influences during an early postnatal critical period. The auditory cortex selectively expands neural representations of enriched acoustic stimuli, a process important for human language acquisition. Adults lack this plasticity. The current study shows that juvenile plasticity can be reestablished in adulthood if acoustic stimuli are paired with disruption of adenosine production in the auditory thalamus.
The current study utilises a variety of methods to demonstrate that reducing adenosine or blocking the A1 adenosine receptor that is essential to the chemical messenger’s function changes how adult mice responded to sound. Results show that when adenosine is reduced or the A1 receptor blocked in the auditory thalamus, adult mice passively exposed to a tone responded to the same tone stronger when it was played weeks or months later. Data findings show that these adult mice also gain an ability to distinguish between very close tones; mice usually lack this ‘perfect pitch’ ability.
Results show that the experimental mice retained the improved tone discrimination for weeks. Data findings show that the window for effective auditory learning re-opened in the mice and they retained the information. The team state they also observed that by disrupting adenosine signaling in the auditory thalamus, they extended 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 surmise their data shows that in adult mice, disrupting adenosine signaling in the thalamus rejuvenates plasticity in the auditory cortex and improves auditory perception. For the future, the researchers state that their results offer a promising strategy to extend the same window in humans to acquire language or musical ability by restoring plasticity in critical regions of the brain, possibly by developing drugs that selectively block adenosine activity.