Casually, in a decade, the Internet revolution has metamorphosed us. Between e-mails, social networks and search engines that lead us to billions of sites and other blogs, Homo numericus does not know where to turn.

In the office, at home, in transport and even during holidays, we surf, chat, play or shop online in front of a screen. Around us, everywhere, computers, Wi-Fi, Bluetooth, smartphones and tablets through which we connect tirelessly. Nearly 90% of French people thus daily join the Web, where they spend an average of two and a half hours per day *.

A craze that some equate to a disaster, like the American essayist Nicholas Carr, author of the book "Internet makes it stupid?" (Robert Laffont ed.) And that others, on the contrary, perceive positively, as an accelerator of decision making and creativity. Given our lack of perspective, it is difficult today to decide the question.

The fact that new technology is raising fears is not new. The telephone, the television or the trains, from the steam locomotive to the TGV also generated in their time of the fear and the distrust. Except that this time, the doubts do not come from old conservatives restive to all modernity, but from tech savvy seasoned to 2.0.

To unravel the true from the false, neuroscience researchers have seized the subject.

The brain, an organ in constant reorganization

Any activity practiced regularly has an impact on the brain, says Professor Alain Lieury **, former director of the laboratory of experimental psychology of Rennes. "This body is eminently plastic, it reorganizes itself and creates new connections according to the stimulations and learning to which it is subjected."

When a child learns to read, for example, his brain reshapes. The visual zones hitherto exercised for the recognition of objects regress in favor of those dedicated to the recognition of letters.

The same applies to musicians: after years of piano or violin, the areas controlling the motor skills and the independence of the fingers develop considerably to the detriment of others, less solicited. This adaptation can be made not only at any age but also very quickly.

Neurons, champions of adaptation

Israeli biologists have demonstrated this through a small experiment conducted on forty-seven adult volunteers, who, in the dark, have undergone an intensive Braille training program.

At the end of five days, the MRI images of their brains already revealed notable transformations: their visual cortex began to encroach on that of the touch. Proof of the extreme malleability of our brain, which is therefore necessarily expressed also with the intensive use of digital tools.

In convicts on the Web, the wiring of some neural networks seems to be changing. The prefrontal cortex - the seat of personal synthesis and abstraction - would lose density, while the posterior cerebral regions would be strengthened. An evolution likely to blunt in the long run the capacities of reflection and intellectual analysis.

"As the brain is eager for novelty, the deluge of information poured over the Internet also affects the ability to pay attention," notes Jean-Philippe Lachaux ***, research director at the cerebral dynamic laboratory of Inserm (Lyon).

In the space of a few years, e-mail has for example been imposed in professional life. It has become the first means of communication, in front of the telephone and the mail.

"The untimely surge of messages on the screen is a source of distraction that the brain can not resist," he continues. Our concentration thus takes a big hit.

Concentration put to the test

According to a study by specialist firm Sciforma, it seems impossible to work for more than twelve minutes in a row without being interrupted. It's even worse for teenagers who are doing their homework with an eye on their Facebook profile or mobile phone: they will not be able to stabilize their attention for more than five minutes on the same exercise.

Result: the spirit is dispersed. Reasoning, "hanging on" to solve a problem is more difficult. In addition, by zapping from one page to another via hyperlinks, juggling between multiple windows open on the same screen, reading tweets or posts of a hundred signs, our brain dispels now claims short, fragmented.

He grabs more than he explores. He butins more than it deepens. For many of us, the linear reading of a long text becomes so difficult that publishers begin to break up books into small interactive text boxes, searchable in any order, just like the Internet.

Forgotten memorization efforts in favor of search engines

And who says deficit of concentration says lack of memorization, so difficulties in term to treat the information gleaned and to integrate them in a reasoning pushed.

"To memorize, it takes time," says Jean-Philippe Lachaux, "the mental representation must be able to stabilize and enrich itself in order to be well recorded." However, in the era of digital galloping encyclopedic knowledge is gradually giving way to swarming ideas, knowledge "fan".

Why get tired of remembering a poem by Baudelaire in extenso, the classification of chemical elements or the name of capitals of the Baltic countries since these data are just a click away via the search engines? And why remember the title and lyrics of a song while you can find it through the application Shazam® humming notes in the microphone of his smartphone?

Many studies have shown that followers of the Net solicit less their deep memory, so-called long-term memory, thanks to which for example one of the Fables of La Fontaine can be recited more than thirty years after being learned by heart.

An American experiment conducted at Columbia University in New York and published in the journal Science in 2011 has proven that students retain much less information when they know that it is available ad vitam aeternam. The little they remember is not the information as such, but the place where it is stored (digital file, website ...).

Conclusion of the researchers: the computer does not serve them just crutch, but rather external memory supposed to provide theirs.

Digital technologies, sources of stress and anxiety

Chronophagous and stressful. This is how the majority of employees perceive the ubiquity of digital technologies in the world of work.

Of course, these new tools make it possible to share information in real time and make faster decisions. But, according to a survey conducted by the BVA institute at the end of September 2012, the excess of e-mails received during the day is a permanent stressor. Their surge requires a reactivity that is not necessarily productive: 86% of respondents treated e-mails immediately or at the latest in the hours that followed, often at the expense of real priorities.

This tyranny of the moment extends to the home since 61% of executives who have access to their professional email out of the office consulted at night, 47% at the weekend and 43% during the holidays. This inability to disconnect is a source of anxiety and in this case, beware of burnout.

The dangers of cyberdependence

By dint of receiving permanent alerts, our brain begs for more. He watches for the SMS, the e-mail that is late to arrive or any other digital stimulus that serves as a reward.

A state of lack that can become invasive and result in irritability and a need to consult his smartphone or computer quite compulsively.

In the opinion of some psychiatrists, this dependence not on content but on the tools themselves is of the same order as smoking. Fragile people can switch to addiction and become so-called cyber-addicts.

Recharging batteries (not those of their devices)

Our faculties of analysis and learning are conditioned by the quality of our sleep.

It is indeed during the night that are memorized the achievements of the day and that a sorting between essential and subordinate information takes place.

Conversely, not getting enough sleep "increases the risk of developing a chronic illness (diabetes, hypertension ...) that can alter cognitive functions," warns Professor Damien Léger, head of the Sleep and Vigilance Center. (Hospital Hotel-Dieu AP-HP).

To keep neurons alert, so we turn off our screens (computers, tablets ...) at least an hour before slipping under the duvet, because the blue light they emit keeps the brain in a state of vigilance and delays the sleep.

Oxygenate your neurons to avoid overheating

If the deep memory is little used, the short-term memory - working memory which manages the immediate memories - is, as for it, extremely solicited.

"She is often overheated," says Jean-Philippe Lachaux. To the point that it reaches saturation with some geeks who pass from the computer to the smartphone and never disconnect. Digital natives, those under 30 who are almost born with a mouse in their hand, may be faster to the point.

But, contrary to popular belief, they are not more multitasking than their parents and grandparents. The brain can carry out two tasks head-on when automatisms are put in place - like turning the wheel while changing gears when driving - but, beyond that, it loses efficiency.

This is why phoning by car reduces alertness and increases the risk of an accident. Less than three percent of us would seem to be really multitasking. The others juggle, somehow, with large margins of error and brain fatigue.

So as not to lose the pedals, we must "sequentialize" things, "to make monotech very short focusing on one activity at least for a few minutes before moving to the next," advises Jean-Philippe Lachaux. In short, give breaks to his brain.

Google and Facebook are not incompatible with Proust and Tolstoy. Authorize weekends and holidays without Internet to find the smell of printed paper, do a part of Scrabble® or a real sudoku and no longer virtual rebalancing the different functions of the brain. To function to the best of his abilities, "our brain needs global and varied stimulations," says Professor Alain Lieury.

You can also do physical exercise to oxygenate your neurons, listen to music, go to museums, learn a foreign language, meet new people ... Diversity, the unexpected and social relations are a real bath of youth for the brain.

No, the internet does not make silly

" On the contrary, this tool can develop our intelligence if we manage to stay the course, to escape the traps of interference (shock images that catch the eye, flashing sentences ...), so as to continue our search on the Web without leaving bending our attention, "said Jean-Philippe Lachaux

It is we who must master the tool and not he who must lead the dance by dragging us into his infinite mazes.

* According to the TNS Sofres Web Usage Study, the GFK Institute Internet Barometer and the 2012 Olfeo Study.
** Author of All the secrets of your brain (Dunod ed).
* Author of the Mindful Brain (Edited Odile Jacob).