Tag Archives: neuromodulators

Motivation vs Pleasure

Research that I’m currently doing for the Weordan project has revived thoughts about the nature of motivation and how physiology relates to behavior. What motivates people to spend long hours working or elite athletes to push through grueling training regimens? Most are clearly motivated beyond the potential return. They aren’t just fixated on the benefits of success. They have to be attracted to the idea of accomplishment itself. They want it more than they will enjoy it when it occurs.

The foundation of motivation comes from the interoceptive system. This is the system in the body that communicates the body’s status to its higher order systems in the brain. This is accomplished through chemical and stretch sensitive neurons as well as hormone signaling through the circulatory system. Satisfying the internal needs of the body can be accomplished by physiological means such as shivering when one is cold or by behavioral means such as acquiring and putting on a coat.

Behaviorally, there are two distinctive aspects of motivation. There is “liking”, which is the derivation of pleasure from partaking in a particular activity. The experience of “liking” leads to future pursuit of the experience, which can in turn be defined as “wanting”. Motivation is essentially “wanting” rather than “liking”. Further, especially in the case of addictive drugs, there doesn’t have to be much “liking” for a strong “wanting” to occur. This is because the chemicals contained in the drug act directly upon the “wanting” system rather than through “liking”.

Physiologically, “liking” and “wanting” are somewhat interdependent. However, they are modulated by different neuromodulators. This coincides with a difference in how “liking” and “wanting” wax and wane.

“Liking” is generally modulated by the neurotransmitter serotonin. Serotonin doesn’t perform the actual signaling between neurons. Instead, it acts to enhance or dampen the excitability of neurons in the region it is deposited and is supplied by neurons that originate in central regulating bodies. “Liking” is also homeostatic, meaning there is negative feedback. When a normally functioning individual engages in a behavior that is governed by a homeostatic system, they become sated to the point that they avoid the behavior.

“Wanting” is generally modulated by the neurotransmitter dopamine, which operate similarly to serotonin in that it doesn’t perform explicit signaling, but instead stimulates or depresses signaling globally within a region. “Wanting” is an allostatic system, meaning that it can’t turn itself off through normal signaling. It requires a homeostatic process to regulate it. This can happen if it is stimulated by a homeostatic system, such as those that are regulated by serotonin. It can also happen if over-stimulation causes post-synaptic neurons to desensitize. However, it seems that this desensitization isn’t as strong as a normal homeostatic response, as it doesn’t cause a negative response such as aversion, only desensitization.

This is a simplified view of the system. Many factors are at play in these systems. However, these are the strongest players, at least according to the best of my understanding. Further, the simplicity of the system is well supported by the distribution in the population. I would contend that extremely driven individuals aren’t all that uncommon. Neither are extremely unmotivated people. The distribution is flat compared to something like intelligence or athletic ability. This implies that a smaller number of factors govern innate drive to “want” than those more complex systems.

The differentiation between “wanting” and “liking” is nothing new in neuroscience. However, interesting behavioral consequences and world views present themselves when one considers these two drives as separate dimensions. One might expect someone with a strong “liking” system to spend more time enjoying the fruits of their accomplishments. Such a person would be inclined to accomplish less than another person who is otherwise identical but has a weaker “liking” system. Likewise, one might expect someone with a strong “wanting” system to spend more time in pursuit of accomplishments that are important to them. Such a person might be inclined to take on more challenging tasks and spend more effort on them than someone who had a weaker “wanting” system. This model suggests that a combination of strong “wanting” and weak “liking” would result in an extremely driven individual, the type of person that starts their own business and works long hours to make it successful. At the other end, someone with a strong “liking” and weak “wanting” would result in an extremely unambitious individual, the type of person who lives in their parents’ basement and spends all of their time on a hobby.

Serotonin and dopamine also happen to be associated with two other behavioral phenomena, depression and addiction. People that are depressed have a tendency to have a poorly functioning serotonin signaling system. This is treated pharmacologically with drugs called Selective Serotonin Re-uptake Inhibitors(SSRI). Prozac was the first such drug on the market. SSRIs increase activity of neurons affected by serotonin by blocking the systems that remove serotonin from the synapse. Dopamine is instead involved in addiction. Drugs like cocaine and methamphetamine have a similar affect on dopamine sensitive neurons that SSRIs have on serotonin sensitive neurons. Ritalin is a time-released low dosage amphetamine pill that is used to treat ADHD. The definition of the attention deficit portion of ADHD is quite compatible with a lack of “wanting”. Presumably, someone with a well functioning system for “wanting” would be more vulnerable to addictive substances than someone that has less “wanting”.

If high achievers have a tendency toward high dopamine and low serotonin, it is likely they are more prone than average to depression and substance abuse. Professional athletes and actors work in an extremely competitive environment where talent is usually not enough to make it. By and large, they must be extremely driven. They have to really “want” it and can ill afford to be spending their time enjoying what they’ve accomplished to maintain their position. Anecdotally, this group of individuals has a high incidence of depression and substance abuse. It is likely that this is in some part due to the stresses of celebrity. However, it seems possible that they also are more prone to these conditions due to the physiology that helped them to succeed.