"Motivation": Cortex vs. Limbic System

I speculate that dopamine affects how easy or hard it is to initiate activities. This particularly seems to affect activities requiring significant energy, like exercise, and/or decision making, like planning a trip or moving. I introduced this idea a little bit in an earlier blog post.

I found that when I was dopamine deficient, I couldn't initiate exercise myself. I could tag along if someone else initiated it though, and feel better during and after. A woman from my church invited me to go walk with her on Tuesday mornings, and I could do that. My husband and I joined a twice weekly yoga class, and I could go to that.

It seemed silly to me that I couldn't initiate these sorts of things myself. In the past I treated this as a moral failing, and beat myself up about it. That made me feel awful, but I still mostly wouldn't be able to do it. This most recent time I was more accepting about it. I still tried to convince myself to go exercise, but was more gentle about it. Sometimes I would succeed in going and exercising by myself, but mostly I wouldn't. Instead of treating it as a moral failing, I treated it as a science experiment. What was different about the times when I was able to go and exercise?

Once I got the dopamine increased enough I could mostly initiate exercise by myself no problem. It wasn't that I was trying harder, or being more morally upright. It just felt like a road block that had been there was just gone.

When I studied more about dopamine, and what affects it, I realized that dopamine levels seemed to correspond to how easy or hard it was to initiate that sort of activity. When dopamine levels were mostly low, I would only be able to do it as a follower or after some sort of experience that sufficiently increased dopamine. Now that dopamine levels are mostly ok (got the bupropion working right), I can initiate exercise myself most of the time, except after experiences that sufficiently decrease dopamine.

All this made me realize that the concept we call "motivation" really has more facets than I'd realized before. What you think about how much you "should" do something, how much you want to do it, and what you think about where it ranks in your priority and value schemes are one set of factors. How you feel when your think about doing something -- how your biochemistry reacts to the idea -- is another. They're controlled by different parts of your brain (cortex vs. limbic system), and are not always in sync.

I suspect that the latter part is the one that's more tied into physiological state -- how much dopamine, energy, etc. you've got to start with and how those change in reaction to your proposed activity, like exercise. It can agree and reward you with an added burst of dopamine, which makes it real easy and appealing to go off and initiate the activity. It can also disagree and make you feel uneasy about it (not sure if this is it decreasing dopamine, increasing stress chemicals, or both), and make it real hard.

It seems to me that in some cases the meaning of "motivation" is pretty clear:

• Motivated = cortex decides to do it, limbic system agrees, you do it
• Unmotivated = cortex decides not to do it
  

However, what do we say about the case where the cortex decides to do it but the limbic system disagrees? Generally this is where things gets tough and we are prone to beat ourselves up. I bet we end up in this state more often when dopamine is low. I also bet that when dopamine is low and we end up in this state, we're much less likely to be able to force ourselves to initiate the activity anyway. Here's the trap: the way we think about failing to initiate activities like this can further decrease dopamine, making it even harder next time.

I certainly find myself in that state much less often now. For a few months, before using the bupropion to increase dopamine tone, I was in that state almost all the time. I exercise much more often now than I did then. I don't actually decide to exercise any more often -- likely I decide to do it less frequently. The difference is that now it's much easier to follow through on that decision. Does that reflect a difference in "motivation" or not?

Dopamine deficiency, Parkinson's, and CIS

I have been reading the 23andme forums quite a bit, on the lookout for things related to the whole cholinesterase inhibitor sensitivity issue. 23andme is working with the Michael J. Fox foundation to make it easy for Parkinson's sufferers to use the service in return for their participation on surveys (see article here). As a result, a lot of people with Parkinson's Disease are active participants. One such participant asked about excess salivation, which I recognized as a symptom of cholinergic excess. So, off I went on a new research tangent... It turns out that there is a significant overlap between the symptoms of Parkinson's and the symptoms of cholinergic excess. According to the book "Handbook of Parkinson's Disease" (see Fifth Edition, p. 383, "Mechanisms of Action" section), decrease in the level of dopamine, as is seen in Parkinson's, can cause the symptoms of cholinergic excess. It says this happens because it's the ratio of acetylcholine activity relative to dopamine activity that's significant. So, I went out and read about dopamine, and dopamine deficiency. I found all sorts of exciting stuff in that quest -- enough to fill a huge number of future blog posts, so watch out. Click here for a good web page describing the basic neurophysiology of dopamine, and here for a list of the effects of dopamine deficiency. Here are some highlights:

• High/increasing dopamine levels make you feel good: the "high" caused by many drugs of abuse like cocaine, heroin, and amphetamines work by temporarily greatly increasing dopamine release
• Low/decreasing dopamine levels make you feel bad: the "low" after such drugs wear off, the plunging feeling when something you did that you expected to be praised for instead results in scorn or abuse, etc. are caused by your dopamine levels decreasing
• People feel motivated to seek experiences which are expected to increase dopamine, and to avoid experiences which are expected to decrease dopamine.
• Dopamine is involved in reinforcement training: if you expect a positive outcome of an intended action, you get an increase in dopamine. If you get a positive outcome, you get even more dopamine. If you get a negative outcome, your dopamine drops precipitously.
• Dopamine is involved in social dominance: successful assertion of social dominance increases dopamine; being the target of someone else's assertion of social dominance decreases dopamine
• Dopamine is involved in behaviors related to food: eating increases dopamine; chronic overeating decreases dopamine receptors so you have to eat more to get the same "high" (see article on role in obesity here); but, paradoxically, low dopamine decreases motivation for and willingness to expend effort to gt food (in a paper on Regulation of Effort in Food-Seeking Behavior rats are less inclined to press a lever to get food if you suppress their dopamine).
• Dopamine is involved in sexual behavior: a good description of this role of dopamine is here.
• Dopamine is related to motivation and perception of one's ability to effect change (empowerment) in general: many of the symptoms of dopamine deficiency relate to lack of motivation and enthusiasm; high dopamine leads to a feeling of "social potency" and the feeling that you can take action that leads to success (and higher dopamine); success at such attempts leads to even more dopamine; failure leads to less dopamine, and makes it harder to try again.
• Dopamine may be related to subjective experience of temperature: high dopamine makes you feel warmer, low dopamine makes you feel colder. I need to research this more, but I certainly notice this effect correlating with other indicators of dopamine level. I have found some other places that mention this, for example this paper abstract says increased dopamine increases heat dissipation (skin is hotter, but core gets colder).

Anyway, reading about all this I realized that the state I have been in after getting the cholinesterase inhibitors far enough out of my system looked just like what I'd learned about dopamine deficiency. Sure enough, dopamine reuptake inhibitors, which increase the effect of dopamine by making it spend more time in the synapse, had a huge impact. I've been feeling a strange inability to initiate action, even for stuff I wanted to do, like make dinner, or start this blog. I could eat plenty if it were put in front of me, but seldom ever felt hungry, and had difficulty making myself prepare food -- particularly anything at all complicated -- even though I know how important it is to eat. (In the old days, I would have just grabbed a snack or microwavable convenience food, but that's incompatible with my efforts to avoid cholinesterase inhibitors, so it's a lot more of a problem now.) I didn't really feel enthusiastic about anything, even stuff I know I would normally be excited about, like the Yuri's Night celebration or seeing old friends I hadn't seen in a long time. Dopamine reuptake inhibitors, specifically bupropion, made all these effects go away within a few hours. Now, the typical way this would be interpreted in our culture is "oh, that's an antidepressant, so if it helped it means you must have been depressed." I could get into a semantic argument about this, and maybe I should in a future post. (Interestingly, it's also used to relieve smoking addiction -- another condition relating to dopamine and cholinergic receptors.) For now, leave that aside and consider this as a Human System Debugging experiment which confirms that dopamine is likely playing a role here. The fact that the success of that experiment allows me to finally get on with writing this stuff down is a happy side effect. :) So, putting all that together with the insights from the Parkinson's book leads to an interesting hypothesis: maybe low dopamine increases sensitivity to the effects of cholinesterase inhibitors. If so, then people with conditions which cause low dopamine, such as Parkinson's, or who are deficient in dopamine either by genetic predisposition, current circumstance, or nutritional insufficiency of dopamine precursors may be at greater risk for suffering symptoms of cholinergic excess from ingestion of cholinesterase inhibitors. If they also have a compromised ability to detoxify cholinesterase inhibitors, such as the BCHE, ACHE, and PON1 SNPs described by Dr. Soreq, this could be a bad combination. This is my current favorite hypothesis for conditions which could lead to what I'm calling Cholinesterase Inhibitor Sensitivity (CIS).