"The brain is just so f---ing sexy right now."

That is the candid summation of Dr Jared Horvath​, an educational neuroscientist at the University of Melbourne, for why so many people are attaching gadgets to their skull for the purpose of stimulating (though not in the lowbrow way) that wobbly mass between their ears.

"The promise is so strong. Hey, congratulations, I can make you better, faster, stronger, by changing nothing in your life except putting on this device. Who doesn't want that? It's such a sexy promise," says Horvath.

It's a decade since Norman Doidge's book The Brain That Changes Itself popularised the concept of neuroplasticity – the brain's ability to form new connections in the process of learning.

There's since been an explosion of interest in brain stimulation as a way to beef up neuroplasticity, in the hope it will accelerate learning, memory and brain repair.

Transcranial direct current stimulation (tDCS), which passes a weak electric current across the brain with scalp electrodes, claims a small army of DIY adherents trying to boost alertness and concentration, as well as serious scientists aiming, among other things, to reverse cognitive impairment in older people.

A related method, transcranial magnetic stimulation, is an approved treatment for depression, but also has life-changing potential to ramp up emotional intelligence in autism, something eloquently described by John Elder Robison​ in his 2016 autobiography Switched On.

But the big recent news in brain-tickling comes from the slightly shadowy research arm of the US Department of Defence.

In April, the Defence Advanced Research Projects Agency (DARPA) announced the recipients of US$50 million funding into a technique it dubs "targeted neuroplasticity training" (TNT), something DARPA hopes will clip 30 per cent off the time it takes to learn a foreign language, and turbocharge training in related cloak-and-daggery such as code-breaking and intelligence-gathering.

With terror on the rise, mastery of foreign phrasebooks is front and centre for national security. But the push to exploit neuroplasticity is also gripping the wider education community, and will be the subject of a major international conference in Brisbane this September.

So there are plenty of folk with an interest in the nitty gritty on the DARPA research and, crucially, whether it can deliver.

The TNT program will centre on something called vagus nerve stimulation, a technique that's been researched for more than two decades as a potential fix for stroke, cognitive dysfunction and tinnitus.

The procedure delivers electric current to the vagus nerve as it runs through the neck with a device that, like a pacemaker, is implanted in the chest wall and has a wire that wraps around the nerve.

Vagus nerve stimulation is approved by the US Food and Drug Administration for the treatment of severe epilepsy and depression and, in April, a handheld device called gammaCore, which stimulates the vagus through the skin – no need for surgery – was authorised as a treatment for cluster headache.

But it is the intimate role played by the vagus in learning that has DARPA excited.

"The brain works on the principle of surprise," says Michael Kilgard​, a Professor in the School of Behavioural and Brain Sciences at the University of Texas, whose team received US$5.8 million of the DARPA funding.

"So when you're walking along and you stumble upon a snake it's surprising – 'Oh my god, something just happened, I need to pay attention, I need to learn this.'"

It is at this point, Kilgard explains, that the vagus nerve kicks in, sending an urgent telegraph to the brain that "this is important".

The brain is then flooded with neurotransmitters that enhance memory of the serpentine surprise by promoting neuroplasticity.

And the link to grasping a foreign patois?

"The idea is, with learning bunches of words, we could use the very same mechanisms that are engaged when you look down and see a snake, or teeter on the edge of a cliff, or you're fighting for your life," says Kilgard.

The problem for military recruits a thousand hours in to their Farsi course, and grappling with the subjunctive tense, is the absence of anything approaching the surprise factor. Tickling the vagus nerve, it is hoped, will bypass all that ennui and convince the brain that the grammar is "need to know".

Will it work?

Kilgard's team has some impressive research runs on the board suggesting it might. One study, published in 2015, highlights a problem familiar to anyone from the Orient struggling with the vagaries of English.  

"For native Japanese speakers, 'r' and 'l' are almost impossible," says Kilgard.

"Even after 30 years in the US, with flawless English and no problem having a conversation, if you test them they actually cannot tell 'r' from 'l'. It's a very subtle contrast ... and if you can't hear it, you then can't produce it."

That problem, at least in part, prompted Kilgard's team to have rats listen to the sounds "rad" and "lad" while having their vagus nerve stimulated.

"Now, for a rat, an English language word is like a foreign language, some new thing that means nothing to them. There's no reward, there's no task, there's no nothing," says Kilgard.

In other words, making a rat listen to "rad" and "lad" is the rodent equivalent of teaching a very bored kid something they don't want to know.

But the nerve tickle led to significantly stronger and faster responses in the rats' brains to those sounds.

"You can double the strength of the brain's response to these words and not change the response to other control words, which the animals have never heard," says Kilgard.

And that finding could translate to better speech perception in humans, something Kilgard is putting to the test in a human trial, just begun, to see whether vagus nerve stimulation can accelerate learning of words in Swahili. 

Despite the massive interest in brain stimulation, however, the reality thus far is cause for circumspection rather than breathless fervour.  

In May, for example, Jonna Nilsson and colleagues from the Karolinska Institute and Stockholm University, reported that  tDCS had no perceptible effect on cognitive skills, including working memory, in a study of 123 older adults.

Horvath, who co-edited the 2017 book From the Laboratory to the Classroom: Translating Science of Learning for Teachers, is not surprised by the findings.

In 2015 he published a sweeping analysis of tDCS outcomes in the literature.

"Can we use tDCS to help people learn better, faster, become smarter? The short answer? Nope, can't do it. The long answer took me about five or six years of trawling through data and doing my own work to realise that the evidence is quite clear that we can't do it," says Horvath.

At the heart of this abject failure there is, according to Horvath, a fundamental flaw of logic.

"The argument ... is that learning is simply changes in the brain, which it totally is. But the mistake is then thinking, 'Well, cool, because learning leads to changes in the brain, if I then change the brain that will lead to learning'," says Horvath.

A 2016 study published in the journal Psychological Science, for example, found that activity in the brain's temporal gyrus is important for solving maths problems. On Horvath's view, such a finding doesn't mean stimulating the temporal gyrus will make you any better at maths.

"You can stimulate that part of the brain all you want to but if I don't engage with the learning, if I don't think about it, if I sleep through it, I'm still not going to learn a thing," he says. 

There is, however, a critical difference between tDCS and Kilgard's vagus nerve stimulation.

In most tDCS studies the stimulation is administered during the cognitive training.

"In our approach the stimulation occurs after the activity has already left the brain," says Kilgard. And it is the timing of the stimulation that, according to Kilgard, is critical.

All learning involves feedback to the brain about whether you got a task right or not, something that happens after you complete it.

"I hit the tennis ball, it travels through the air, and several seconds later I see I got an ace and I won the game," says Kilgard.

"I know, wow, that was a great tennis serve ... my neurons can go back and figure out which ones to strengthen to make that serve happen again and again and again."

Vagus nerve stimulation shortly after, say, a word is learned, can mimic the reward of a Scud-like ace, messaging the brain to lay down that pattern of activity in memory.

On the other hand, stimulating the brain during the learning task could simply disrupt it.

"If you deliver a big burst of current you've now distorted the relative timing of everything in the brain, and that is probably a bad thing," says Kilgard.

"If your auditory cortex is trying to learn a new musical suite on the violin, you probably don't want someone stimulating that very same area at exactly the time those neurons are trying to fire in some particular pattern. To make them all fire synchronously is probably a bad idea."

Horvath's research, however, also casts doubt on the usefulness of vagus nerve stimulation.

"The stimulation was no better than a kid that just wants to pay attention. Nerve stimulation did nothing more than if you were learning something you enjoy versus something you didn't enjoy," says Horvath.

Kilgard doesn't dispute this, but points out that attention is precisely what goes missing in action for many students slogging through the complex syntax, grammar and vocabulary of languages such as Farsi, Arabic or Russian.

And it is in this no man's land of study drudgery that an artificial boost from the vagus might just push candidates across the line.

Indeed, promoting neuroplasticity in the classroom has become something of a buzz topic in education.

Roberto Lent, Professor of Neuroscience at the Federal University of Rio de Janeiro, will be a keynote speaker at the  International Science of Learning Conference in Brisbane.

Lent has just co-authored a study with João Sato​ of Brazil's Federal University of ABC that deploys a hi-tech way to see if students are paying attention, the sine qua non for moulding youthful brains.

"Hyperscanning" uses a portable apparatus to image brain activity in two or more people at the same time. Sato and Lent's team hooked it up to a lecturer and four students.

"When there is synchronicity between two brains, and two brain regions, the hypothesis is that they are communicating," says Lent.

Sato and Lent recorded four eight-minute segments of a 40-minute lecture.

"Attention flies away from the teacher after the first 10 minutes of a spoken lecture," says Lent.

Of course, most experienced lecturers use more rudimentary measures, such as fidgeting and covert texting, to detect attention drift in students. Nonetheless, a formal device for measuring which techniques are truly engaging pupils has undoubted value.

But for parents and teachers keen to bump up Johnny's neuroplasticity, the Brazilian expert still plumps for the basics.

"Sleep is important for consolidation of memory, that's more or less well established," says Lent, who advocates naps in school for small children.

And exercise, says Lent, is shown to increase neuron production in the hippocampus, a brain area critical in memory formation.

"The hippocampus of people doing exercise frequently is larger  ... [and given] simple learning tasks ... they do better than the others who are sedentary," says Lent.

Horvath also champions the basics, suggesting parents get involved with their kids' learning and ensure that schools are using best practice teaching. On the educational promise of neuroscience he remains, however, gloomy.

"The one thing neuroscience will never teach teachers or students is what to do, how to learn. How do we improve our learning or teaching? Those answers come from the classroom, they don't come from the brain."

DARPA has just laid down 50 million bucks that says he's wrong.

@pbiegler