Brain Science of Aspergers and Autism Pt. 1: Sensory Overload
August 26, 2011 3 Comments
In this first post on the brain science of Aspergers I want to talk about the theory of neuroscientist Michael Merzenich. Merzenich is one of the world’s leading experts on brain plasticity, and his studies into the causes of Autism and his work on the Fast ForWord software program has revolutionised the lives of many young autistics.
Merzenich discovered that early in a child’s life when the brain is making its early connections, what neuroscientists call the “critical period”, a nerve growth factor (a protein called BDNF or Brain Derived Neurotropic Factor, which is responsible for growing nerve fibres in the brain) is released.
This turns on a part of the brain called the Nucleus Basalis, which is the area in the brain that allows us to focus our attention. This part of the brain stays on for the whole of the critical period, which lasts until a child is around 3-5 years of age. This helps the child to pay attention, but also to remember what the child is experiencing, and it is key to strengthening the connections in the brain. BDNF also is the protein responsible for closing down the critical period. After this period, the Nucleus Basalis only fires when something new or important happens, or while we are actively paying attention.
Merzenich discovered that in children genetically predisposed to autism, some situations may over-excite their neurons (nerve cells) in their brains and this in turn causes their brains to release large amounts of BDNF prematurely, which turns off the critical period. So instead of only the important connections being reinforced, all the connections in the brain are reinforced. This has the consequence that the child is left with a hypersensitivity to a great many sensory stimuli, with the inability to turn off the unimportant connections. This leaves them with “undifferentiated brain maps”. To quote Norman Doidge MD in his book The Brain that Changes Itself: “so many connections in the brainhave been indiscriminately reinforced, once a few neurons start firing, the whole brain can be set off. It also explains why autistic children have bigger brains – the substance [BDNF] increases the fatty coating around the neurons”. The result of this is the child is less able to filter the unimportant stimuli. This means it requires so much more effort for them to concentrate on the important stimuli, and consequently they get easily distracted and mentally exhausted.
The fact that their brains can get so easily over-stimulated for the brain to turn of the critical period prematurely, suggests to me that these children are born with slightly heightened sensory sensitivities, and with my own son, I certainly believe this to be the case. It is possible that this in some cases could be caused by Fragile X Syndrome, which is a genetic disorder that is sometimes linked to the causes of Autism and affects more boys than girls.