Tuesday, September 23, 2008
The Neuroscience of Reward
The thrill is gone? Blame your brain, says a little blurb by Eric Nagourney in today's Science Times. A study by Dr. Karen Faith Berman and colleagues in The Proceedings of the National Academy of Sciences compared brain scans of people in their 20s and their 60s while playing a slot-machine-like-game on a computer in two conditions - one when they anticipated winning money and the second in which they actually won. In the anticipation condition, the people in their 20s showed three brain areas associated with reward activated and it sounds like dopamine levels were also elevated, whereas the people in their 60s showed increased activity in only one of those three reward areas and produced less dopamine. Now I became curious about the methods and although the PNAS would not let me read the article without paying a fee, I could read the abstract. There I learned that two measures were employed - a special kind of Positron Emission Tomography (PET) scan that sounds like it can stain for dopamine - getting a measure of its production in the midbrain, and fMRI which measures comparitive increases in metabolism of oxygen (a measure said to be associated with increased "activation") in prefrontal areas. In the younger people increased dopamine production was positively correlated with activity in the prefrontal areas which in other studies have been activated in conditions associated with "reward." However, the older group (whom the abstract indicated were healthy) showed a negative correlation, which the Times indicates means that less dopamine produced less reward, although a negative correlation would mean that more dopamine produced less reward. I can't tell without reading the article which is the case, but suffice it to say that the association between dopamine and reward was different for the older group. I also cannot tell from the abstract if the two levels of dopamine levels produced by each group were compared outright, i.e. the younger people produced more than the older, or if each group had a baseline level of dopamine measured and if the difference in production was compared to that baseline in the 'anticipation of reward' condition. My biggest question had to do with the experimental conditions themselves. Are the experimenters sure that the money acted as an equally rewarding influence on both groups? And most importantly are they sure that a randomly selected group of people in their sixties would respond with the same 'reward' to a computer game as people in their twenties? Anecdotally, I could report a very different relationship between computers and people in their 20s versus people in their 60s. Just wondering.