I think the explanation found in “The Parkinson’s Protocol” By Jodi Knapp might give us a clue. She says “Dopamine activates five different cell receptors:” I think my dopamine loss is predominantly in the D3. I will tell you why.
The theory is, a person has lost 80% of their dopamine before they are diagnosed. I have not had normal responses to events when others found great pleasure for a long time. I had blamed my inability to laugh on my father’s strict reactions to my laughter in my youth. But when I read the islands of Valleja and nucleus accumbens reinforce the effects of pleasure, and emotions such as joy and laughter, it gave me reason to reevaluate.
D1, found in the cardiovascular system, as well as the cortex, striatum and limbic system of the brain. The actions spurred by dopamine and D1 control the growth and development of brain cells, and behavioral responses. They also modulate the actions of the D2 receptor.
D2, found in the brain but mostly in the basal ganglia, where learning and motor control take place. Together with D1, it is implicated in behavioral reinforcement.
D3, found in two areas of the limbic brain called islands of Calleja and nucleus accumbens, which are involved with reinforcing the effects of pleasure, and emotions such as joy and laughter.
D4 is involved in exploratory behavior and motor coordination. Most medications for the treatment of Parkinson’s target this receptor.
D5 is also found primarily in the limbic brain, and has a role in emotions, behavior, long term memory and smell. D5 receptors have a higher affinity for dopamine, meaning they bind to it more easily.
Going to the internet to learn more about D3 “The most important function of nucleus accumbens is to process and analyze the rewarding and reinforcing stimuli… It is also important in spatial and instrumental learning.” “The islands of Calleja are a group of neural granule cells located, where it aids in the reinforcing effects of reward-like activities.
Case in point: I allowed my son to throw me out of a perfectly good airplane attached to him for a skydiving experience as a reward for his successfully ceasing smoking.
If you watch the video, you will perhaps note I am so relaxed as we exit the plane.. like a rag doll. I had no fear or high expectations, and although I tried to smile for my sons, I felt no joy or excitement. Just a little confusion, about what I should do with my hands.
By way of explanation, there are a couple blank spaces on the video. All the divers had cameras on their heads and the dive was photographed from different angles. When he pulls the first chute it is to slow us down so we are falling the same rate as the photographers. When he pulls the second chute and it looks like it jerks us up, it is because the cameras continue falling at the faster rate, creating the illusion.
I ‘fibbed’ when I said it was fun… because I didn’t want to dampen their excitement. I feel more pleasure in watching the video than I did the day it was taken.
At the end My son, Stephen, who took me (because Tom and I didn’t have enough combined weight) made a comment about my calm.