Thesis defense Christian Utzerath (Donders series 415)
9 January 2020
Promotor: prof. dr. J. Buitelaar, co-promotor: prof. dr. F. de Lange
Hypopriors in autism spectrum disorder
Humans do not perceive the world like a camera. We do not perceive the world through factual sensory impressions. Rather, what we perceive is what we believe the world to be like, enriched by purposefully sought out sensory information. This actually crucial to humans, since it enables us to rapidly understand and interact with our environment much faster than otherwise. We only notice the influence our expectations have over us if we get startled by something unexpected. Collectively, the beliefs about the world that we entertain are called priors.
A recent hypothesis states that individuals diagnosed with autism spectrum disorder (ASD) use their priors to a lesser degree than most people. This would cause them to perceive the world more ‘real’ than other people. At the same time, it would also lead these individuals to experience a world that is more volatile and surprising. This might be an explanation why everyday activities can be much more stressful for someone with ASD. However, there is little evidence yet for or against this hypothesis, particularly at the level of the brain.
This project addressed the question whether, at the level of the brain, individuals with autism use their priors to a lesser degree than others. We did so by scanning individuals with and without ASD while they were performing simple visual tasks, using functional magnetic resonance imaging (fMRI) and magnetoencephalography (MEG). These tasks exposed the participants to images that were sometimes more and sometimes less surprising. In most people, expected images are processed using less brain activity and with a more focused neural response, which can be seen as neural markers of priors. Thus, if individuals with ASD underused their priors, we expected to see differences in these brain markers.
In one of these experiments we found a differing brain response in the ASD group compared to the control group. This concerned a task in which images followed one another in predictable sequences that could be learned by observation, thus creating expectations about the images on screen. The control group showed increased brain activity when these expectations were violated by images that did not conform to the learned sequence. This was not so in the ASD group. In other tasks, were the priors were did not require learning, there was no difference between the group. This suggests that underuse of priors in ASD might occur only in situations were these priors have to be recalled from memory and applied.