Later On

A blog written for those whose interests more or less match mine.

The Elastic Brain

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Rebecca Boyle writes in Aeon about some research that has promise for, among other things, treating autism:

Five years ago, in a new city and in search of a new hobby, I decided to try playing a musical instrument for the first time. I had never learned to read music; in my grade school, the optional orchestra class was offered at the same time as the optional robotics class, and I chose the latter. Understanding nothing about chords or music theory, I settled on the relatively simple mountain dulcimer, a three-stringed lap instrument from Appalachia.

I was proud of how quickly I picked it up. I could replicate many of the old-time fiddle tunes, Civil War ballads and Ozark folk songs my instructor played during demonstrations, and I learned to discern notes by ear. I was hardly a virtuoso, however, and after a few months I hit a plateau. I could hear how they were supposed to sound, but challenging, faster-tempo songs remained out of my grasp. Frustrated, I distinctly remember thinking: ‘If only I’d learned music as a kid, I might have been great at this.’

I haven’t played my dulcimer in several months, but the day might be coming when I could actually learn to play as I would had I learned during childhood. I might be able to swallow a pill that restores my brain to a more flexible, receptive state. This new, more childlike brain – rendered literally more ‘plastic’ because of its ability to forge many more connections between neurons – would enable me to learn far more readily each time I practised a tune.

Early childhood is characterised by a series of critical periods – circumscribed times when the brain opens up and changes profoundly in response to input from the environment as new skills are learned. During these times, the rapidly-morphing brain – an organ so malleable that neuroscientists call it ‘plastic’– sculpts itself into the perfect vehicle for navigating the world. During one critical period, for instance, children master specific visual skills. During another critical period, they master emotional control, and during another, language. When the brain opens up and becomes plastic too early or too late, circuits are laid down incorrectly and disorders like autism or schizophrenia may result, forever altering how we process the world. At no other point in our lives are we more primed to receive new information and put it to use than during the critical periods of early childhood. ‘Genius is no more than childhood recaptured at will,’ the French poet Charles Baudelaire wrote in 1863.

As we emerge from toddlerhood, our brains become less plastic and it becomes more difficult – sometimes even impossible – to learn new things, from movement to language to social behaviour. Even accented speech results from loss of plasticity in the brain; after adolescence, most people never lose an accent, no matter where they settle down in years to come.

It makes sense, of course, that the brain would ultimately settle down and put the brakes on its own, rapid-fire flux. If our minds were to keep changing at such frantic pace, we would never be able to perform the day-to-day business of survival: gathering food, sheltering from the elements, procreating and caring for our young.

There is an evolutionary reason for stabilising brain circuits after a period of rapid learning to adapt to the environment, notes Takao Hensch, a neuroscientist at Boston Children’s Hospital and Harvard University and an expert in brain plasticity. ‘If circuits are constantly changing in response to experience, then the brain becomes inefficient as a processing device.’ Stability is so important to the mature brain that it goes to great lengths to inhibit plasticity.

Yet learning in adulthood still occurs because the connections between neurons, called synapses, are still constantly adapting to the environment – though at a slower pace than before. With practice, adults can learn to play the dulcimer and speak many languages. And in times of need, the brain can ramp up plasticity: survivors of traumatic brain injury or stroke, for instance, can learn to walk and speak again as their brains fire up new synapses to replace the ones they lost. Rather than disappearing, it turns out, plasticity has merely been suppressed by a network of inhibitory neurons and the molecules that they use to communicate. Depending on circumstance, the brain can open up and become plastic again.

The possibility of reawakening our youthful, receptive brains has piqued a lot of interest among educators, therapists, and those in search of expanded experience or thought. I might be able to immerse myself in music lessons and absorb them more effectively. Others might disable the plasticity brakes before a trip abroad, quickly learning a new language. Still others might wish to tweak an imperfect golf swing. The implications are more profound for people with autism spectrum disorders, mental illness and physical disabilities: re‑opening critical periods could help us rebuild the physical structures of our brains, erasing bad connections and wiring them anew.

Among the first neuroscientists to track critical periods in the brain during the 1960s were David Hubel and Torsten Wiesel of Harvard. They knew that children born with cataracts could not see properly even after their cataracts were removed – but why?

To help answer the question, the researchers surgically altered newborn kittens by sewing one eye shut until the animals were fully grown. Without input from the closed eye, the cells in the visual cortex re-wired themselves to the open eye, endowing it with a property called ocular dominance; it was the eye that could see best. The eye that had been sewn shut, meanwhile, lost its ability to focus; it developed a permanent disability called amblyopia, or lazy eye.

The researchers later repeated a similar experiment with adult cats, getting different results: when sewn eyes were reopened, cells from the visual cortex went back to normal and responded to the eye they had been been dedicated to from birth. In these adult cats, both eyes ended up seeing equally well. They were different than children with cataracts and kittens with amblyopia, whose neural connections had been altered during a critical period of development, their brains forever changed. Since adult cats had their eyes sewn shut long past the point when brains were so plastic, their cells reverted to form.

Hubel and Wiesel, who collaborated for more than 25 years, won the 1981 Nobel Prize in Physiology or Medicine for their work and enormous insight. They also inspired the young Hensch, who changed his undergraduate major from computer science to neurobiology while a student at Harvard in the 1980s.

‘It was their work in the visual system that made this a biologically tractable question: how does experience shape the brain?’ Hensch says today. . .

Continue reading.

Written by LeisureGuy

27 March 2015 at 3:03 pm

Posted in Science

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