Important Components of Substance Use Disorder
The scope of this paper in regard to physiology of brain mechanisms will detail changes that occur as a result of the use of substances of abuse in substance use disorder. In addition, some studies point to genetic and social influences that may play a role in the use of substances of abuse.
In a 2009 study by (Bevilacqua & Goldman, 2009) genetic components of substance use disorder were studied. The results showed that although there is some type of genetic component and that substance use disorder were moderate to highly heritable, there was also a social component that could not be ruled out. The issue at hand is that in twin studies for heritability, many of the populations shared similar social and environmental factors that also played a role in the use of substances. The likelihood that a substance was available was a factor in the use of the substance. It appears that this plays a role in earlier use but the genetic factor plays a greater role in later use. The exact mechanism in genetic factors could not be determined but the highest heritability occurred under specific social conditions so that the genetic component of the disorder became relevant. It was determined that a combination of environment and genes played a role in initial use and with the development of a substance use disorder.
There have been many studies regarding the changes that occur in the brain as a result of substance use. The hypothesis in this case is that changes begin from the initial voluntary intake of a substance and move the brain through a series of changes that impair cognitive function and bring the user to a state of persistent and irresistible drug use (Everitt & Robbins, 2013). The discovery of long term synaptic potentiation, a type of strengthening of synaptic transmission, was first described in the early 1970’s. These changes are physiological changes in the brain that occur as a result of input from external sources. In this way it is believed that memories are formed (Purves D, Augustine, & Fitzpatrick, 2001; Volkow, Wang, Fowler, Tomasi, & Telang, 2011).
The idea that these known changes might be the basis for alterations in other areas of the brain paved the way for studies directly related to transformations that occur as a result of substance use. In (Volkow, Wang, Fowler, Tomasi, & Telang, 2011) we can see that all synapses in the brain have the ability to change from sensory and chemical input. This is known as neural plasticity.
In the case of substances of abuse there is a clear path that leads to these changes. The idea that many drugs of abuse directly influence the production of dopamine in the dopamine rich neural pathways of the mesolimbic cortex is well studied (Daglish et al., 2008). In some cases this is likened to hijacking. Part of this disorders process is like that of storing memories. Synaptic changes occur in the ventral tegmental area (VTA) and in the nucleus accumbens (NAc) directly from the continuous use of substances of abuse (Volkow, Wang, Fowler, Tomasi, & Telang, 2011).
The process of substance use disorder does not happen instantaneously. These changes happen in some type of order and begin in the VTA. Dopamine weakens the VTA and begins to create initial behavioral changes in response to introduction of drugs of abuse (Volkow, Wang, Fowler, Tomasi, & Telang, 2011). This is a type of stimulus–reward learning attributable to dopamine (Flagel et al., 2011). The initial reaction to the drug is the increased production of dopamine which is so powerful that the person is motivated to take it again. This would make it appear that the addiction is an immediate response. This does not begin to explain the continued use after pathological problems start to occur (APA, 2015).