The study, “Persistent Angiogenesis in the Autism Brain: An Immunocytochemical Study of Postmortem Cortex, Brainstem and Cerebellum”, appears in the Journal of Autism and Developmental Disorders. “This is the first time, in humans, that a neurotransmitter in the brain has been linked to autistic behavior – full stop”, Robertson said.
Other recent brain-imaging studies have found differences in functional connectivity between autistic and non-autistic brains, and have also linked impaired brain activity with the inability to regulate emotions in individuals with autism. For the study, the researchers asked a group of participants – half of whom had autism, and half of whom did not – to complete a visual task that required brain inhibition.
Robertson mentioned that autism is generally defined as a disorder where in all the sensory input comes flooding in at the same time. “In addition, people with autism often have seizures – there is a 20 to 25 percent co-morbidity between autism and epilepsy – and we think seizures are runaway excitation in the brain”. The two human eyes take in two different images that the brain synchronizes into one which represents what is actually seen, but under the binocular rivalry condition, the brain produces the dual images that each eye takes in.
“Individuals with autism are known to have detail-oriented visual perception – exhibiting remarkable attention to small details in the sensory environment and difficulty filtering out or suppressing irrelevant sensory information”, Robertson said in a press release.
‘So if I show you a picture of a horse and an apple, the horse will entirely go away and you will just see the apple. To make out one image or the other, the brain must inhibit neural signals to push one out of visual awareness. “It just takes them longer to switch between them, and the second image is not as deeply suppressed”.
“It’s clear that there are changes in brain vascularisation in autistic individuals from two to 20 years that are not seen in normally developing individuals past the age of two years”, says Azmitia. In most cases, people suppress a visual image from awareness for many seconds at a time. “Where the average person might rock back and forth between the two images every three seconds, an autistic person might take twice as long“, she said. “They spend the same amount of time in the steady state, where they see only one image, as the average person”.
She said: ‘It’s not that there’s no GABA in the brain…it’s that there’s some step along that pathway that’s broken’.She explained the new findings lend support to the notion that the greater attention to detail might have something to do with GABA and neurotransmitters in general since many others play important roles in autism symptoms.
“It’s very diverse,” Robertson said. “There are two forms of GABA receptors, A and B, and the GABA A receptor can take multiple forms. We may be able to use this test to look at the effectiveness of drugs to give us a better idea about which of those receptors isn’t working properly. But it’s very complex
“If these findings hold true in children as well as adults … right now we cannot diagnose autism in children who cannot speak, but that’s when early intervention would be most effective,” she continued. “But before children can talk, they can see, so we may be able to use this type of visual task to screen children and see if there’s something imbalanced in their brains.”
Robertson warned, however, that understanding the signaling pathway for GABA won’t be a cure-all for autism.
“I’m excited about this study, but there are many other molecules in the brain, and many of them may be associated with autism in some form,” she said. “We were looking at the GABA story, but we’re not done screening the autistic brain for other possible pathways that may play a role. But this is one, and we feel good about this one.
NEO Web Desk