My Rhymes Are So Dop… amine

February 18, 2007 at 2:31 am by in science
 

Dropping da neuroscience seems to have even gotten some street cred lately: a google search of “dopamine rap” pops up the hip hop artist Dopamine. His myspace profile boasts, “Dopamine is a neurochemical occuring naturally in the brain. It is responsible for movement and emotion, much like the music this artist creates.” Not exactly right, but I guess close enough for Myspace.

At least it’s a better description than the one Made With Molecules uses in describing their dopamine necklace: “love, passion & pleasure,” which annoyingly perpetuates the stereotype of dopamine as a pleasure chemical.

I can hear you all asking, “so if dopamine isn’t a pleasure chemical what is it? Cause dude I… I mean a friend of mine… once did some coke and said it was a blast!” The quick answer is that dopamine is involved in learning and the pleasure one feels is a secondary effect of the rewarding nature of the drug. The long answer is as overwhelmingly verbose as one would expect, and frankly no one really completely understands it yet. I can however give a slightly more informed yet still understandable version, which in the very least might help you seem smart at cocktail parties.

Dopamine “the slightly more informed” Primer

Let’s start by destroying a metaphor. You’re brain is not a bathtub with neuron spigots for neurochemicals labeled “happy” or “pleasure.” In fact, the chemicals themselves are valueless and are often used in rather unrelated sections of the brain and body. Dopamine is no different, but we’re just gonna focus on it’s function in the reward and learning system.

In the spirit of accessible and interesting approaches to science, I’ve constructed an little neuro-allegory entitled “The Shrine of Wa-King and the Dopa-monks”.

The Shrine of Wa-King and the Dopa-monks The Dry Version
In the mists on top of a high mountain stands the Shrine of Wa-King, the god of working memory. The Shrine of Wa-King is guarded from the rest of the world by a group of monks known as the Dopa-monks. Dopamine controls the flow of info into the prefrontal cortex where working memory resides.
Unfortunately, the Shrine is very small and can only hold about seven objects on it’s base at a time. Travelers come from all over the world to place their offerings, and it is the monks’ job to constantly update the offerings at the base of the shrine. Of course, not all offerings are worthy for the Shrine of Wa-King and the Dopa-monks’ most holy duty is to judge which offerings are the most eye-catching and relevant. Working memory space is limited to an average of seven chunks of info. Dopamine neurons are activated when a reward shows to be greater than expected, indicating the importance of the information. These neurons are also activated by aversive, novel, unexpected or intense stimuli, and cues associated with such events.
The Dopa-monks have two castes: the D1s who make the holy trek carrying the offerings up the mountain to the Shrine, and the D2s whose remain at the base of the mountain and keep an eye out for travelers with worthy offerings. Unimportant travelers with nothing to offer would be thwarted by the numerous rituals and “You No Go” bureaucratic nonsense. This system involves two types of receptors D1 and D2. The excitatory D1 receptors in the “Go” pathway act to update working memory by selecting salient info from the thalamus. The inhibitory D2 receptors act to stop the “NoGo” pathway from putting a break on the thalamus.
Sometimes a really eye-catching and sexy offering shows up causing a mass of monks to crowd around the base of the mountain. At times like this, the level of excitement rises causing everyone to zealously ferry multiple important offerings up the mountain. If this continues too long, the monks become overwhelmed and distracted, even bringing irrelevant items up to the Shrine. Eventually, the monks grow too tired to bring anything up and they go home. Once rested they return to finding new offerings for the Shrine. In this way, the balance between desirable and novel offerings is maintained. Highly salient info causes multiple “phasic” bursts of dopamine which ensures that this info and all related cues enter into working memory. If this continues too long, the overall “tonic” level of dopamine heightens causing the updating to become too frequent and thus less relevant. Continuous high tonic levels can overwhelm the receptors, and then only extremely potent info can elicit a response until the system resets itself.
Sometimes this system gets disrupted like when the Princess Coca cruise ship tourists surge forth with their bribe money and worthless trinkets. The tourists’ money is good, so invariably the all the monks end up frantically clamboring up the mountain with bags of baubles. The monks often continue this excited pace far past weariness until they fall over in exhaustion‚Äîyet still keeping an eye out for the next cruise ship. Amphetamines and other addictive drugs usurp this learning mechanism because the artificial dopamine increase is always greater then the expected award. This causes the brain to mark everything as an important cue for initiation of future drug seeking. The pleasure itself is secondary which is why people continue after the pleasure has abated.
The Dopa-monks also sometimes have problems with the ADHD bug which reduces the number of monks out on the grounds and interferes with them doing their job. As a result, they get distracted and fail to choose the most relevant offerings to bring up the mountain. Current theories of ADHD indicate that the lack of focus and lower response time is in a large part due to a disruption in this dopamine system causing low overall tonic levels of dopamine and making updating of working memory more difficult.
When Dopa-monks do their job well, finding the most salient offerings, the Shrine of Wa-King is a beautiful sight with a regularly changing assortment of highly desirable and important relics. The dopamine system finds what is most salient at any point resulting in a powerful and flexible process of awareness and learning.

Resources

  1. Developing Intelligence : Exploration, Reinforcement, and Updating in ADHD
  2. Developing Intelligence : Dopamine for Dummies
  3. Developing Intelligence : Exploration & Exploitation Balanced by Norepinephrine & Dopamine
  4. Picower Inst for Learning and Memory at MIT: Open Mind Series on Addiction
  5. Dopamine – Wikipedia
Tags: , , ,

3 Comments

  1. enjoyed yr novel teaching approach! ok so on the adhd front, how do you get the monks to keep their numbers & functions up to par?
    e

  2. ADHD treatment today consists mostly of the Dopmine reuptake inhibitor Ritalin or other amphetamine variants — basically upping your tonic dopamine levels. Norepinephrine reuptake inhibitors also help some people. I’m not sure exactly how NE works for this but I think it helps with focus somehow. This later class of drugs that work on the NE system has the issue that with some people it seems to work great for a while then just stop working.

    Non drug wise, there is some successful work with using brain feedback devices to help train people to focus.

  3. Ha ha ha. This is a very cute story about the DA system.

    I was getting anxious (because it’s getting way past my bedtime) about finding a simplified but to the point way to reviewing the DA system for my students. Then I saw Chris’ Dopamine for dummies and then your post! Now my memory about DA is refreshed and I’ll point the students to these two posts for the fun part, too.

    Thanks.