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Think about the background noise in an office. With phones ringing, people talking, coffee percolating, computers restarting, and keyboards clacking, how can anyone concentrate?
There’s a brain app for that. Can you even imagine paying attention to everything you heard, saw, touched, or smelled? Habituation is how we filter out all that junk noise so you can pay attention to the important things in your environment, like the quarterly report due in three hours. Humans aren’t the only creatures capable of habituation. So are fruit flies, which is why they are able to seek out food or a mate without the buzzing of other insects throwing them off.
Brains were on the mind of researcher Runa Hamid of the CSIR Center for Cellular and Molecular Biology in Hyderabad, India. She and her team went inside the heads of fruit flies and finally found the transporter protein which makes habituation possible. Without it, we wouldn’t be able to safely filter out every random stimulus to stay focused on what we need to. Messing with fly brains showed that this could lead to upgraded treatments for autism and ADHD.
“We show hypersensitivity towards an attractive odour [sic] is a direct corollary of habituation defects,” she said in a study recently published in PLOS Genetics.
How exactly habituation works still needs more demystifying, but observing scans of how fruit flies ignored a certain smell showed that it does involve chemical messages being zapped to the brain. Choline is at the center of all this. While it is a super-nutrient (produced in the liver and acquired through diet in humans) that can take on many tasks in the body, it is especially necessary for metabolic and nervous functions. The choline transporter protein in a neuronal membrane transfers choline to that neuron so it is morphed into the neurotransmitter acetylcholine.
Neurotransmitters are like chemical emails. They are released by the ends of neurons and zapped across a synapse, kind of like electronic messages shoot back and forth through wires, to reach another cell. Acetylcholine oversees habituation to smells. Hamid’s team also found that fruit flies which had choline transporters taken out of certain parts of the brain suddenly became hypersensitive to the smell they were exposed to, though the other flies continued to pay no attention to it. This has amazing implications for humans.
Even though more about habituation needs to be investigated, Hamid has an idea of what might be going on with the choline transporter. It might have been controlling stimuli that aren’t worth paying attention to by regulating feedback from the fly’s memory processing region, and it is possible for that feedback regulation to have happened backwards or forwards. There was a cavity in the insect’s brain which was identified as particularly important for managing the smell stimulus, which was necessary for the fly to be able to habituate, but all this is still hypothetical.
Symptoms of autism and ADHD have been found to be extremely similar to those exhibited by the flies whose modified brains did not allow them to just brush off the pervasive smell. Previous studies have also shown that there is a connection between ADHD and lowered levels of choline transporters. Trouble paying attention to something can result from the brain being unable to tune out enough extraneous stimuli.
Any neurological condition that might be related to habituation could benefit from this research, for which only a few flies had to suffer.