Neurotransmitters and Neurons
The brain is made up of a large group of cells called neurons. Neurons are the functional unit of the brain and control all neurological processes, including thoughts and behavior. The nervous system is essentially a group of interconnected neurons. Neurons communicate with each other via small junctions called synapses. Neurons use special chemical messengers, called neurotransmitters, to communicate across these synapses. Neurotransmitters are released by one neuron into the synapse and then bind to the other neurons. These neurotransmitters can either activate other neurotransmitters or cause them to be less active. Dopamine is a neurotransmitter that can activate neurons in many different parts of the brain.
Dopamine and Schizophrenia
One of the functions of dopamine is to control thoughts and decision-making. Dopamine acts as a sort of a gatekeeper for which impulses and thoughts become conscious and can be acted upon. Neuron signals that result in high levels of dopamine are able to continue. A 2005 article in the "Journal of Computational Neurology" explains that dopamine is the driving force behind the generation of ideas and the creative drive.
Dr. Chudler at Washington University also explains how dopamine can be related to certain psychiatric disorders, such as schizophrenia. High levels of dopamine could, in theory, allow a flood of thoughts and impulses to flow throughout the brain, leading to the hallucinations and delusions that are a hallmark of schizophrenia. Many drugs that are used to treat schizophrenia (also known as antipsychotics) work by either lowering dopamine levels in the brain or blocking dopamine's effects.
Aside from its role in overseeing thoughts, actions and behavior, dopamine also has a very important role in motivation. In June 2009, "Nature" published an article that helps detail this other function of dopamine. Dopamine-sensitive neurons are highly concentrated in a part of the brain called the substantia nigrans. This part of the brain controls the sensation of pleasure and motivation. Pleasurable sensations cause dopamine to be released in the brain, causing these neurons to become active. This mechanism underlies the euphoria that is caused by addiction to stimulants (such as amphetamines), narcotics, and alcohol. Use of these substances causes a sudden burst of dopamine to be released into the substantia nigrans, which communicates to the brain that something very pleasurable is occurring. This dopamine surge is also responsible for generating the high motivation for the procurement of more drugs or alcohol.