One type of memory we often take for granted is our working memory. This is a catch-all term for very short-term memory, over a few seconds up to a couple of minutes. It can include things such as like remembering the licence plate of your Uber just long enough for you to glance up from your smartphone screen and find the car. It could also refer to something a bit more challenging like doing metal arithmetic.
I have problems with my working memory all the time, and one phenomenon that often strikes me during a conversation is that I find myself asking, “What were we just talking about?” There’s usually a reason I lost my train of thought; for example I got distracted by someone else arriving or the conversation went off on a tangent.
A recent study showed that in the brain, the chemical acetylcholine might be responsible for keeping us on track in the face of distractions such as these. Acetylcholine is one of the major neurotransmitters in the brain, along with its more famous counterparts: dopamine and serotonin. It’s less well-known, though, because we don’t have such a good understanding of what exactly it does.
Quite a few studies now have shown that acetylcholine is important for working memory. It keeps neurons in the prefrontal cortex firing for periods of time. This allows them to bridge the gap between seeing something (like reading the licence plate of your Uber) and doing something about it (like realizing which Uber is yours and getting in). The prefrontal cortex is in a great position to do this. It receives inputs from brain areas that make sense of visual stimuli, and it has outputs to brain areas responsible for initiating actions. The study showed that acetylcholine was also important for keeping the prefrontal cortex neurons firing even when distracting things were occurring during the gap.
Another cool finding was that acetylcholine also was important for keeping the firing of “fixation cells” going throughout. This is important because we think these “fixation cells” are responsible for maintaining attention on the task at hand.
Acetylcholine is a pretty complex chemical, so the receptor that allows it to work has a lot of different subtypes. The important one was the alpha-4-beta-2-nicotinic type. Yes, that’s right, nicotine as in cigarettes. Acetylcholine is also involved in the effects of cigarettes on the brain. This type of acetylcholine receptor is also affected in Alzheimer’s disease. This new research shows that it may also be important for disorders such as Attention Deficit Hyperactivity Disorder (ADHD). Perhaps this will allow researchers to develop new, more specific, drugs for these two diseases - and others - based on this knowledge.
Sun, Y., Yang, Y., Galvin, V. C., Yang, S., Arnsten, A. F., & Wang, M. (2017) Nicotinic α4β2 Cholinergic Receptor Influences on Dorsolateral Prefrontal Cortical Neuronal Firing during a Working Memory Task. Journal of Neuroscience 37: 5366-5377