I need to get this out there: I’m quite sick of a particular trend I’m noticing in various academic and social circles. The trend is this (and I myself am quite guilty of it): we seem to be in the habit of discussing neurotransmitters and the various neural systems they inhabit in terms of the sorts of mental tendencies they are associated with.
So, for instance, someone will talk about dopamine in terms of dopamine’s effect on concentration. I’ll frequently see something of the following sort in forums dedicated to discussing nootropics, for instance:
“I’m having difficulty concentrating, am I low on dopamine?”
First off, there are not many ways in which to know whether or not someone is “low on dopamine” absent significant cognitive and psychological deficits (think Alzheimers or Parkinson’s). That is, we have good evidence for characterizing Parkinsonian-like symptoms in terms of dopamine deficiency in the basal ganglia, for instance. That sort of talk is fine. But in everyday contexts, we really ought to NOT think about neurotransmitters in terms of mental states like concentrating, remembering, intending, et cetera. That is very dangerous if only because it masks a complex issue in overly reductive terms.
My take on the matter is this: a large portion of our “knowledge” concerning psychological effects of particular neurotransmitters comes from case studies of individuals with very debilitating cognitive deficits like Alzheimers and Parkinsons. These deficits form a sharp boundary around which theorists can characterize the neural systems relevant to the onset of the disease. That is, we’re understanding the function of a neural system only in virtue of its relevance to very significant but also very GENERAL deficits. It does not necessarily indicate something about the regular function of the neural system in and of itself: we can’t, so to speak, separate the neural system and ascribe a function to it absent this particular persons diagnosis.
So a person who is NOT presenting with these debilitating conditions but using similar language to describe his or her psychological difficulties may or may not be explainable in virtue of the same neural systems. Someone who says in an everyday context “Hey I can’t concentrate, why is that” may be intending that he cannot concentrate on certain sorts of tasks, like reading a philosophy book or doing math problems. And because the tasks are different, it is completely possible that the neural systems involved are different. The interplay between neural transmitters is EXTRMELY intricate and the exact function of an NT is also structurally differentiated (meaning that an NT may be relevant to function A in brain area X but may be relevant to function B in brain area Y).
Lastly, and I really want to stress this: we need to be externalists about mental states in the sense that we need to look to environment more to discuss various cognitive problems like attention deficit and/or memory issues and so forth. When someone says they are depressed, it cannot be evaluated at some level which is independent of the social contexts they tend to use that description within.