Some addiction research implicates problems with the common brain chemicals serotonin and norepinephrine. Dr. Robbins, for example, described experiments with amphetamine abusers showing signs of reduced serotonin activity in the frontal part of the cortex, the brain's wrinkled outer layer. The frontal cortex is the scene of the brain's higher-level thought processes, such as decision making. It is tied to other brain parts by numerous nerve cell circuits, including feedback loops that pass through the striatum, a region strongly affected by dopamine release from the midbrain. The striatum also receives signals from the brain's cortex, emotional and memory centers, and returns messages to the cortex via a series of brain structures serving as relay stations.
Addiction presumably disrupts the brain's ability to make sound choices.
But the decision-making process is complicated, notes Jonathan Cohen, a psychologist and psychiatrist affiliated with Princeton University and the University of Pittsburgh. Good decision-making requires control over competing possibilities, Dr. Cohen said at the neuroscience meeting. But it also requires monitoring choices to see whether they produce the desired result. Perhaps addiction involves problems with the monitoring system as well as the control system. Dr. Cohen described research implicating another part of the cortex, the anterior cingulate, in monitoring the brain's choices.