Neuroscientists at New York University have found that a naturally occurring chemical in the brain can enhance visual processing and suggest that this chemical may represent part of the biological basis of visual attention. While the chemical, acetylcholine (ACh), had been known to increase the activity of individual neurons, it had not previously been shown that this activity enhancement leads to enhanced vision.
To examine the effect of ACh, the researchers looked at the brain's nicotinic acetylcholine receptors (nAChR), to which ACh binds to stimulate neural activity. Nicotinic receptors are named for the fact that they also bind nicotine--the addictive chemical in cigarettes.
ACh is a neurotransmitter--a chemical used to relay, amplify, and modulate signals between neurons and between neurons and other cells. Previous scholarship had shown that ACh enhances attention, in rodents, but the precise mechanisms behind these enhancements are not understood.
In this study, the researchers found that information that comes into the brain's visual cortex can be selectively enhanced by mimicking the effects of ACh with nicotine, resulting in the ability of neurons to detect, and to signal, stimuli that, without ACh's enhancement, were below detection threshold.
"That's what attention does--it strengthens the signal you're interested in and that strengthening helps you filter out other things" said Anita Disney of NYU, "Our findings show that acetylcholine has the ability to turn up the volume on visual activity, just like attention does."
Disney added that the study sheds additional light on the function of our cholinergic system--a system of nerve cells dependent on ACh as their neurotransmitters. In Alzheimer's patients, the cells in the cholinergic system have been damaged.
The findings appear in the latest issue of the journal Neuron. The study's lead author, Anita Disney, is a post-doctoral fellow at NYU's Center for Neural Science (CNS). The other authors are Chiye Aoki and Michael J. Hawken, both faculty members at CNS.
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