04 December 2008

Thoughts on forks

Whenever there is purposeful, goal-directed behavior going on, dopamine is involved. Without dopamine, there is no purposeful behavior. At 1% of normal dopamine concentrations even feeding and drinking stops. In Parkinson's disease the parts of the brain most intimately involved with purposeful movement (as opposed to thinking) are deprived of dopamine, and at 20% of normal concentrations it becomes hard to move. Dopamine is key to organized behavior and motivation: it reinforces activity in brain tissue and strengthens synapses.

So whenever you see purposeful behavior going on you might ask yourself "where is the dopamine coming from?". Only rarely do we see humans engaged in behavior that directly activates dopamine neurons. Eating comes to mind: sensory neurons in the mouth detect the presence of good food and immediately activate dopamine neurons in an attempt, if you will, to reinforce whatever behavior brought the food there. But that behavior, the movement of the fork or the chop-sticks, was learnt at some point. Suckling is the only form of eating we know from the start. We suckled the breast and the milk was warm and sweet and we stopped crying. We suckled the twig and it was cold and hard and we cried. When suckling brought warmth and sugar, dopamine was released and the neuronal ensembles generating the behavior and remembering the context were reinforced. Later we learned a bottle works almost as well. We learned to hold the bottle. And a few years and millions of dopaminergic learning experiences later we learned to use the fork.
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