Most researchers have a consensus on the key difference between human brains and those of other animals it is the size and complexity of our cerebral cortex, the brain's outer layer of neural tissue. Most of the research has been focussed on this area as it is believed that cerebral cortex is vital to our unique mental life. However, there are other interesting bits that are identical between humans and animals that are ignored – like tiny group of brain cells that use the chemical dopamine to communicate with other brain cells.
Dopamine, also known as the brain’s “pleasure chemical”, is actually involved in large number physical and mental processes. It is used by a cluster of neurons in the midbrain to transmit messages to other neurons. The dopamine neurons are small in number (~0.0006% of the neurons in the human brain) and found in all mammals and even “simple” animals such as turtles.
In an experiment during the 1950s, researchers discovered that rats seemed to enjoy the stimulation of the nerve bundle that links the dopamine neurons with their targets in the forebrain. On pressing a lever this stimulation was activated; the rats learned to do so and when left unchecked would do so thousands of times in a day. A similar experiment was performed in 1970 on a human patient where a patient learned to press a button to stimulate the dopamine nerve bundle. He pressed the button up 1500 times over the course of a three-hour session and reported experiencing feelings of pleasure during the stimulation. Subsequent studies have revealed that dopamine system can be activated by a wide range of pleasant experiences, like eating, having sex, winning games, listening to music, earning money, getting revenge, etc. it has also been found that addictive drugs, including opiates, alcohol and cocaine also activates the dopamine system and unlike natural ways, these drugs can evoke stronger activation and do not cause satiety.
In simple words, the dopamine system is a pleasure pathway in the brain. It explains why some drugs are so addictive the activation of the system by drugs is so strong that it makes drugs highly desirable. It must be noted that many mental events occur near the time of a reward, including changes in motivation, arousal, attention, emotion, and learning.
An important aspect of dopamine function is learning. Researchers believe that dopamine neurons change their activity when expectations about reward do not match the reality, signaling a ‘reward prediction error’ that supports learning. The events that result in an increase in dopamine levels are associated with reward, and those that are followed by decreases are linked with disappointment. It is unlikely that we have much awareness of the learning that dopamine activation induces, such as making us attached to things we unknowingly associate with dopamine activation. This lack of awareness might explain why people often make seemingly irrational choices.
The question now is can brain research be used to overcome the effects of dopamine in addiction? While Neuroscientists are actively pursuing the creation of drugs that block the learning induced by dopamine in addiction, there has been very limited success. The reason being – dopamine also has other roles to play – it is difficult to create a drug the blocks the learning without also blocking other functions of dopamine, such as feeling alert, motivated and happy.
Dopamine-induced learning is crucial but it is not the full story behind addiction. However, it does suggest that we should consider whether addiction is something that human reasoning on its own can overcome. Our special cerebral cortex can very well be in control of our actions, but the dopamine system may be its teacher.
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