New paper on autism29 Dec 2012
If there is one thing I have learned recently, it is that autism is a really, really complicated disorder. Autism is best known for causing repetitive behaviors and problems with social communication, but it is also known to cause issues in sensory perception. Many hypotheses for the underlying neurophysiological basis have been proposed. Among these is the excitation/inhibition (E/I) imbalance hypothesis, which states that levels of cortical excitation and inhibition are disrupted in autism. An imbalance like this could be caused by unusual levels of certain neurotransmitters, such as glutamate and GABA, or by an unusual distribution of synaptic connections. Together with my collaborators (David Heeger, Marlene Behrmann, Nancy Minshew, and Ryan Egan), we tested this theory and report the results in a new paper published in Vision Research.
We chose to test the theory in the visual system because vision is one of the better understood systems in neuroscience and because the E/I imbalance theory has been proposed to explain hypersensitivity to sensory stimuli in autism. Specifically, we conducted two experiments on binocular rivalry, a well-studied phenomenon that depends critically on excitation and inhibition levels in cortex. Using a very simple computational model (a schematic is shown above), we made predictions about how imbalances in excitation and inhibition would affect perception during rivalry. Contrary to our expectations, we found no significant differences between autistic individuals and controls, and no evidence for a relationship between these measurements and the severity of autism. Of course, these results do not conclusively rule out an E/I imbalance in the visual system of those with autism. There are many alternative explanations that we describe in the Discussion section. But these results do seem to suggest that an E/I imbalance, if it exists, is likely to be small in magnitude.