Individuals with autism have “noisy” brains

Results of a research study conducted by Dr Elizabeth Milne, University of Sheffield

One of the goals of the Sheffield Autism Research Lab is to identify whether there are any differences in brain processes between individuals with autism and those who don’t have autism. If we are able to find clear differences, we hope that this will inform the diagnostic process in the future thus making diagnosis more reliable and also enabling earlier diagnoses to be made. One of the main ways we investigate this is by recording the electrical activity produced by the brain to discover whether there are any differences in the signal produced. The brain is extremely complex, containing approximately 100 billion neurons. Even small differences in how these neurons communicate can have profound effects on how individuals think and learn. To record electrical activity we use EEG equipment, which records brain activity up to 2,000 times each second. This means that even the smallest differences can be observed.

When we see something new, our brains start to process this information in a very regular, uniform way as we begin to identify what we are looking at. For example, within 0.2 seconds we start to process how bright or dark what we are looking at is. This initiation of processing generally happens with exactly the same strength of signal and with exactly the same timing if the same image is presented twice. However, a project, led by Dr Elizabeth Milne, found that something a bit different happens in the brains of people who have autism. Their signals aren’t quite as regular. Dr Milne found that when she compared the responses from one trial to the next, the point at which a signal started was more variable in those with autism compared to participants who didn’t have autism, and the strength of the signal was also more variable. These differences were observed in the visual cortex, at the back of the brain, the area which processes visual information. This variability is termed “neural noise” as there seems to be some interference influencing the regularity of signals. Experiencing these variable signals so early on in the visual processing system may have a knock-on effect on later processing. We don’t yet know what effect this finding of increased neural noise might have on behaviour but not having clear, regular signals is certainly likely to have an impact. It may make other aspects of information processing more challenging. Similar findings have also been observed by other groups using behavioural and fMRI techniques (Dr Hilde Geurts, University of Amsterdam; Prof Marlene Behrmann, Carnegie Mellon University in Pittsburgh) so this finding seems to be reliable. Following on from this work, we are now trying to understand how increased variability impacts on visual perception in those who have autism.

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