Glutamate, Adenosine, and our critical period of learning – part 3

We are a bag of bio-chemicals mixed in with a lot of water and some other tissues and bone that give us structure.  My waste-line may be a slim 34” at sea level, but over 35” at the top of Aspen Mountain- we are held together by atmospheric pressure, bones and other tissues- but what makes us go round are the interactions of the various enzymes, proteins, amino acids, and a multitude of other chemical, bio-electrical, and mechanical processes.

What was colloquially referred to as the “mind/body connection” in the 1960s is now being investigated with tools that were just not available back in the bell-bottom era.  Although we are still just scratching the surface, we are learning about the long term effects of factors such as stress on our body.  We are beginning to understand the science behind phrases such as “stress is the big killer”.

In parts 1 and 2 of this blog series we reviewed a little of what we know about stress and even how negative emotions (through a stress mitigated system and glial excitotoxicity) can generate toxic levels of Glutamate that can make our cochlea and our auditory system function at less than an optimal level.

Adenosine is no more complicated than caffeine and too little or too much of either of them can have dramatic effects.

Recent research by Dr. Stanislav Zakharenko and his colleagues at the St.Jude Department of Developmental Neurobiology have uncovered what they think is another biochemical that may be implicated in the difference between how children and adults acquire language and music.

It is long thought that there is a “critical period” after which young adults lose their ability to absorb language and music to the same extent that children do.  In short, children are sponges and adults, at least in my case, are brick walls.  This is especially true with learning a second language and music.  But what is the reason behind this critical period?

Dr. Zakharenko’s group examined the neuromodulator “adenosine”- one of the genetic building blocks of life- that naturally occurs in the auditory thalamus and found that, at least in mice, limiting its concentration allows the adult mice to perform more like younger mice.

Age related critical period for learning a new language and for learning music

“By disrupting adenosine signaling in the auditory thalamus, we have extended the window for auditory learning for the longest period yet reported, well into adulthood and far beyond the usual critical period in mice,” said corresponding author Stanislav Zakharenko, M.D., Ph.D., a member of the St. Jude Department of Developmental Neurobiology. “These 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.”

Learning language or music is usually a breeze for children, but as even young adults know, that capacity declines dramatically with age. St. Jude Children’s Research Hospital scientists have evidence from mice that restricting a key chemical messenger in the brain helps extend efficient auditory learning much later in life.

“By disrupting adenosine signaling in the auditory thalamus, we have extended the window for auditory learning for the longest period yet reported, well into adulthood and far beyond the usual critical period in mice…. These 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.”

It turns out that changing the concentration of the neuromodulator adenosine (which limits the production of the neurotransmitter substance Glutamate) in some way is implicated in an extension or delay of the critical period of learning language and music.

Like Glutamate (and coffee, especially my first cup in the morning), too little is as bad as too much.  But it does look like there may be an optimal concentration of Adenosine that may allow adults to learn and discriminate as well as children. Stay tuned to this line of research. 

 

About Marshall Chasin

Marshall Chasin, AuD, is a clinical and research audiologist who has a special interest in the prevention of hearing loss for musicians, as well as the treatment of those who have hearing loss. I have other special interests such as clarinet and karate, but those may come out in the blog over time.