The Synaptic Bases of Mental Diseases

The brain is fighting against autism


Eye-tracking experience
Each dot indicates the position of the gaze while viewing a video showing a child playing.
Left : the blue dots are the areas targeted by a child with typical cerebral development.
Right : the red dots are targeted by a child suffering from autistic disorders.


Highlight from the Schaer’s Lab

The “social brains” of children with autism spectrum disorder are impaired, some compensating with a hyperconnectivity of the neural networks.

The difficulties experienced by people with autism spectrum disorder (ASD) are characterized by communication and social interaction problems as well as restricted and repetitive behaviors. Experts believe that the origins of these symptoms are due in part to a dysfunction in brain development. Researchers are trying to gain a better understanding of what lies behind the dysfunction in the hope of one day being able to treat the illness. Their strategy is based on studying brain function at an early developmental stage when the first symptoms appear and neuronal plasticity is at its crisis point.

Social learning disorders

Newborns are attracted by voices, faces and signs of sociability. This interest forms the basis for their social learning –in other words, their interactions with others. From the cellular point of view, it is reflected in the formation of a neural network of connections between different areas of the brain. These networks constitute the so-called “social brain”. Researchers know that infants who later develop ASD already pay less attention to social cues in their first year of life. “Some children with ASD are less attracted to ‘social’ stimuli. But we don’t know what happens in their brains at this very young age”, says Holger Sperdin, research associate in the team of Synapsy researcher Marie Schaer. Although we know the brain areas involved in processing social information, scientists are unfamiliar with the reasons for this dysfunction in individuals with ASD. The team of Marie Schaer has managed to identify differences in the connectivity in the social brains of very young children with ASD. The study, which was led by Holger, was published in eLife in 2018.

In search of the neural correlates of autism

Synapsy researchers have set up a state-of-the-art, tailor-made experimental paradigm in an attempt to pinpoint these differences. This experiment records neural activity using electroencephalogram (EEG) and measures eye movements. 36 children aged two to four years –18 of whom with ASD– were shown videos containing social stimuli. “They were shown sequences of short films featuring social stimuli such as faces or children playing. It’s a passive observation, because their young age means we can’t ask them to perform more complex tasks”, explains Holger. These two techniques –EEG and eye tracking– were used to try to find out how ASD children see the world, what neural correlates are involved in the visual exploration of the social stimuli, and whether early differences are observable.

Innate or acquired hyperconnectivity?

The researchers noticed that the way young children with ASD explored the videos was very different to that of children with typical development. “We were struck at first by the differences in how stimuli were explored. When a face appeared, children with typical development all focused their eyes on it, while the explorations of ASD children were more scattered”, says Holger.
The team also observed a higher degree of connectivity in ASD children between certain areas of the social brain and increased activity in two specific brainwave frequencies (alpha and theta). “We know from other studies that theta frequency is an important part of the social brain, with alpha frequency playing a role in visual attention. Here we found that there was a hyperconnectivity in the waves and between certain cerebral regions of the social brain in young children with ASD compared to those with typical development,” continues Holger.

By correlating eye-tracking data with the EEG, Holger Sperdin and his colleagues have shown that among the very heterogeneous population of ASD children, those whose visual exploration is closest to that of children with typical development have the highest EEG hyperconnectivity. This seemingly counter-intuitive outcome suggests that neuronal hyperconnectivity is a compensatory mechanism. In other words, the data appears to indicate that some children manage to correct the dysfunction of the social brain via hyperconnectivity. This paves the way for early intervention therapies since nothing seems permanently fixed in the social brain of ASD children. Nevertheless, long-term studies are needed to find out how these correlates develop and whether early therapies can correct them.

Author : Yann Bernardinelli – Les Mots de la Science

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