By studying what is called fragile X syndrome, Roberto Araya’s team has found that sensory signals that come from the outside world are underrepresented in the brain, whereas it was previously believed that they were overrepresented.
In other words, it would seem that these signals do not take up enough space in the brain, whereas it was assumed until now that they took up too much.
“It was quite a surprise for us, because generally we talk regarding autism as a situation of sensory hypersensitivity,” said Mr. Araya, who is a neuroscientist, biophysicist and researcher at the CHU Sainte – Justine.
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Even more precisely, the researchers succeeded in distinguishing the way in which the brain interprets the signals which arrive to it from outside (sound, light, touch and others) from the way in which it interprets its internal signals (those , for example, which allow it to recognize an object or a parent).
These internal cues remain overrepresented in patients with fragile X syndrome, Araya explained, but it now appears that external cues are underrepresented, which he says is a complete paradigm shift.
“This combination of issues is what generates this very difficult behavioral change for people with autism,” he said. I think it’s a piece of the puzzle that will completely change the understanding of autism.”
Previous work concluded that fragile X syndrome was characterized by a hyperexcitable cortex. Experiments on mice indicate instead that it would be the reverse, hence the “under-representation of signals” described by the researchers.
This explains why autistic mice are “very lost” in their interpretation of the outside world, Araya said.
“Their internal signals are overrepresented,” he explained. But at the same time, their external signals, those that should not be distorted because it is reality, are under-represented. Antennas that are turned to the outside world do not represent things correctly.
This is what makes the lives of autistic people so “difficult”, added the researcher: they struggle to distinguish relevant signals from insignificant signals, and everything ends up feeling important to them.
This under-representation of external signals might be attributed to the absence, in the brains of people with fragile X syndrome, of the FMRP protein. A member of the team, Soledad Miranda-Rottmann, then demonstrated that it is possible to correct the problem.
This opens the door to the development of new therapies that might help patients with fragile X syndrome correctly perceive signals from the outside world, Araya said.
“We have found the mechanism and we can correct the interpretation of the sensory information,” assured the researcher. This is a very important first step in solving the disease.”
We can then tackle the processing of internal information, he concluded, but only if necessary, since we cannot exclude that the only correction of the representation of external signals is sufficient.
The conclusions of this study were published earlier this year by the prestigious American journal Proceedings of the National Academy of Sciences.