The Practicing Brain
Practice makes perfect. You’ve probably had the phrase drilled into your head for quite some time – and grown to believe that there’s some merit to it – that the longer you work on a particular skill, the better you’ll be – just by doing it over and over again. It might surprise you to learn, however, that humans are hardly the only species that has fully embraced this aphorism. Male zebra finches, for example, spend most of their wakeful hours practicing slight variations of courtship songs throughout the day – hardly any different than the star quarterback perfecting throws or the concert pianist who dedicates an hour or two a day to practice.
When it comes down to the wire, the zebra finch is able to make the moment count – executing his song with the right agility and precision when there’s an attractive potential mate nearby. Researchers have decided to investigate further – looking into why this is the case, but it was only recently that the technology became available to observe the brain circuitry at work within these birds.
Now, thanks to several new tools, including the ability to monitor a hundred neurons at once and some powerful machine learning analyses, neuroscientists at Duke University have seen the circuitry of the brain that controls the bird’s practice sessions and his performance.
So what did their findings suggest? When it comes to the day of the grand recital, the finch’s basal ganglia receives a drop of a neurotransmitter called noradrenaline. This is a region within the forebrain which is responsible for the nuances of complex movement in every vertebrate animal. Noradrenaline acts a bit like an adjuster switch – controlling the variability levels within the song, actively making it hold as close to the desirable deal as possible. Their findings were described in the journal Nature during the week of Oct. 20.
When the birds are singing by themselves, simply to hear how each note sounds in their vocal cords, then the basal ganglia’s neurons permit a slight degree of variation within their songs. These variations are what the researchers have found are critical when it comes to ‘mapping’ out the intricate circuitry of the brain and determining the most efficient way to go about producing a song.
“To figure out how to move, it needs to first try out many different movements, to try out different ways of accomplishing a goal of moving their body,” says researcher Jonna Singh Alvarado, the leader of this project that he conducted as his Ph.D. dissertation at Duke University. “They need to learn, ‘If I think this, how am I about to move? How will that move my body?’ and it needs to do that in many variations.”
Just by doing an arbitrary task, however menial, a number of times creates what we ourselves like to call “muscle memory.” Over time, according to Alvarado, who is now conducting post-doctoral research at Harvard: “You’ve established this kind of brain-to-movement dictionary, where you’ve explored all these different ways that you can give commands and they can move your body.” After you’ve tried a number of variations on the same theme, you’ve added some new pathways to the brain – and you’ve likely committed to memory how the variations on performing that particular task have played out – how slight alterations can change the outcome, and your brain has a mental encyclopedia of how to proceed at the right moment.
Just like a physical copy of an encyclopedia on printed pages, these don’t hold up forever, and can quickly be paved over for newer circuitry that the brain may need more urgently in the spur of the moment. This is why having lots of practice, even after that piano recital, is crucial to keeping the neural circuitry up to speed. Says Alvarado: “If they don’t keep polishing these circuits with constant activity, they slowly drift and degrade. Practicing and continuing to explore this vocal space and keeping your dictionary updated is very important to keep the performance at tip top shape.”
To the untrained observer, the slight differences between the zebra finches’ practice rhythms and the subsequent courtship performances when a potential mate is within hearing range are highly nuanced to most human observers, barely even detectable, according to Richard Mooney, who is the George Barth Geller professor of neurobiology at Duke’s School of Medicine and served as Alvarado’s thesis advisor. The female zebra finches, however, can pick up on that difference, and they tend to prefer a fast performance. To understand this, Alvarado’s team recorded the finches’ practice songs and played them over a speaker. They failed to capture the attention of the female finches, but swift and precise songs played for them made the captive finches curious to search for the source of the pleasant sounds.
“Songbirds have made this problem more simple for us,” Alvarado remarks. Their basal ganglia is surprisingly complex – with each of its neurons serving a single job in a rather complex array of specialized song circuitry.
Bird brains might not be all that large, but this left a sizable computational problem that the researchers needed to figure out.
“One of the things that’s been really hard in other animals is to figure out what the link is between the variability you’re producing, and the variability you want to produce,” said John Pearson, an assistant professor of biostatistics and bioinformatics at Duke – a subdiscipline that uses navigational software tools to look at and disseminate genetic data. Pearson was the lead researcher on the neurons’ statistical analysis: “This is the first time that people have gotten a real sizable population of these cells, and we can begin to try to link the variability in vocal performance to the variability in neural activity.”
Mooney, who considers himself to be a longtime fan of legendary guitarist Jimi Hendrix, recalls that he had recognized a similar style of rehearsal when listening to Hendrix’s informal four-track living room tapes. “It kind of goes everywhere, there’s the kernel of one song, but then it sort of morphs. It’s like free jazz or something. And, you know, I think he was just really, really good at exploring when he was alone.”
The same motor rehearsals on those tapes are applicable with just about any learned skill that you perfect over time through practice, says Alvarado. “But then, there’s a moment in which you have to execute in a high-stakes situation—that can be something like predation, either escaping predator or catching prey, and it can be courtship: it’s time to perform and we need to do it in a very specific way that we know the other party is listening.”
Mooney, who has spent decades studying bird songs, said that the researchers’ work draws from data using a number of different fields of scientific expertise, even incorporating the work of their colleagues at UC Berkeley and the University of Oregon. “It took a lot of different people to get all these parts worked out. It’s a big, very complex story.”
You may wonder why the work is important beyond simply explaining an age-old maxim in scientific terms – but their work goes beyond that. While this study focuses on the basal ganglia of birds – it offers researchers a window into understanding more about motor disorders that affect humans, including Parkinson’s and Huntington’s diseases, Tourette’s syndrome, and others.
“In Parkinson’s, motor variability is dysfunctional and completely dysregulated and that is through the degeneration of these same basal ganglia circuits,” says Alvarado. “Understanding how (basal ganglia neurons) function normally and how their activity gets changed and rewired to produce completely different patterns of movement is pretty paramount to understanding just how to fix these problems in the future,” he says with some optimism about the shape of things to come.
