Dopamine, a chemical signaler of the brain, has important roles in the control of learning and attention and is also involved with motor functioning, or movement. When substances interfere, the amount of dopamine present in the brain is altered and the ability for brain circuits to take up dopamine is decreased.
Causes
Antipsychotic agents are known to block the re-uptake of dopamine. Specifically, both amphetamine and cocaine are two known dopamine-blocking substances. A dopamine receptor called the D2 receptor is one area that dopamine blockers are said to affect, according to Brayn Kolb and Ian Q. Whishaw in the book "Fundamentals of Human Neuropsychology." Apormorphine, is another substance that works against dopamine. Amorphine was found to increase blood flow in parts of the brain linked to dopamine-controlled functions in a study conducted by P. Grasby and colleagues, published in 1993 in "Psychological Medicine."
Outcomes
The blockage of dopamine is problematic since dopamine is involved with reinforcement learning, according to Diane L. Santesso and colleagues in 2009 in "Human Brain Mapping." In addition, dopamine blockage is linked to Parkinson's disease, a disease categorized by muscle rigidity which causes difficulties with movement, according to Kolb and Whishaw. Mental disease, specifically schizophrenia, is thought to be caused by excessive amounts of dopamine at dopamine receptor sites, researchers note.
Location
Blocked dopamine is thought to affect the anterior cingulate cortex, a center of the brain involved with reward-related learning, according to Santesso and Colleagues. This area is also involved with attention, particularly in the context of sensory input type, according to Kolb and Whishaw. The basal ganglia is an area thought to be involved with movement, according to Kolb and Whishaw and has also been linked to dopaminergic functioning.
Theory
When dopamine is blocked, predictions about the outcome of a behavior are more likely to be incorrect. A positive error occurs when a behavior is learned because it produced a reward when it theoretically should not have, according to Santesso and colleagues. The incorrect behavior is continued as a result of this experience. A negative error occurs when a behavior is not attached to a reward when it should have been. As a result, the behavior is terminated, as the authors explain.
Process
A dopamine antagonist is anything that decreases the biochemical effect of dopamine. Drugs like amphetamines and cocaine interfere with the transfer of dopamine at an area referred to as the synaptic cleft, according to Kolb and Whishaw. They also cause excessive amounts of dopamine to be released from the presynaptic membrane-the area of dopamine release.
References
- "Human Brain Mapping"; Single Dose of a Dopamine Agonist Impairs Reinforcement Learning in Humans: Evidence from Event-Related Potentials and Computational Modeling of Striatal-Cortical Function; Diane L. Santesso et al.; 2009
- "Psychological Medicine"; The Effect of the Dopamine Agonist, Apomorphine, on Regional Cerebral Blood Flow in Normal Volunteers; P.M. Grasby et al.; 1993
- "Fundamentals of Human Neuropsychology"; Bryan Kolb & Ian Q. Whishaw; 2003
