Nervous System And Reward Pathway

It is believed that certain individuals are predisposed or vulnerable to addiction based on biological, psychological and social influences. The euphoric high produced by many addictive substances is the result of overstimulation of the “pleasure center” of the brain. This is the same area that controls emotions, fear, self-control and overall feelings of wellness. The presence of these foreign chemicals creates a response that the brain will crave as soon as it fades. The brain’s chemistry works against its own health, as it rewires its decision making faculties around the primary goal of finding and taking more of the drug” (1). Many people mistakenly believe that psychological addiction is somehow less serious or real than physical addiction. The psychological aspects of addiction are much more challenging to repair and recover from than the physical addiction. Psychological addiction can last for years or even a lifetime.

This research paper will evaluate the biological aspects of addictive substance or behavior and how it affects the brain and organs. Biological aspects include dopamine levels that are replaced in the brain due to the reward system being overtaken and the absorption rate of the drug once it is ingested will be discussed. The biological aspects are extensive and permanent if the individual does not get the help they need. Furthermore the clinical issues of addictive substance or behavior will be discussed along with medical treatments and ethical issues. This includes treatments such as counseling

According to the biological perspective, drug use may start off as casual, but through continued use, it produces changes in the brain that influences the onset and maintenance of drug addiction. (Horvath et al., 2013). Drugs have their most prominent effects on the function of neurotransmitters. Almost all major drugs of abuse activate the reward system and cause a flood in the levels of dopamine which is a neurotransmitter that is involved in pleasure. As a result, not only do people learn to associate drug use with pleasure, but the brain also starts to reduce its own natural dopamine production in adjustment to the levels of dopamine produced by the drugs. This is called tolerance, and the consequences of tolerance are highly influential

When activated at normal levels, this system rewards our natural behaviors. Overstimulating the system with drugs, however, produces euphoric effects, which strongly reinforce the behavior of drug use—teaching the user to repeat it. (1)

Some dopaminergic (i.e., dopamine-releasing) neurons run from the substantia nigra to the corpus striatum; their loss gives rise to the clinical manifestations of Parkinson's Disease (Korczyn 1994); others, involved in the rewarding effects of drugs and natural stimuli, run from the mesencephalon to the nucleunucleus accumbens.

Addiction is like all behaviours “the business of the brain”. Addictions are compulsive physical and psychological needs from habit-forming sustenances like nicotine, alcohol, and drugs. Being occupied with or involved in such activities, leads a person who uses them again and again to become tolerant and dependent eventually experiencing withdrawal. (Molintas, 2006).

Among the numerous definitions for addiction, there lies yet another to define it from a biochemical perspective. Milkman (1983) defines it as “self-induced changes in neurotransmission that result in social problem behaviors." This definition encompasses the psychological, biochemical and social aspects of addictive processes. It is not limited to substance abuse and can be applied to any activity characterized by compulsion, loss of control and continuation of the substance despite harm. This has helped investigators gain a better understanding of the nature of addiction.

This experiment showed that blood flow to the brain changed in ways similar to that seen in other experiments where an infusion of cocaine is given to cocaine addicts. Similar changes in blood flow to the brain occur when low doses of morphine are given to drug-free individuals. The changes varied in accordance with the amount of money involved, and a broadly distributed set of brain regions were involved in anticipating a win. The more money involved, the more excited the person became. The primary response to winning, or the prospect of winning, was seen in the right hemisphere of the brain, while the left hemisphere was more active in response to losing (3). This similarity suggests that common brain circuitry is used for various types of rewards (4). This study is also important because identifying regions of the brain and then mapping the neural pathways that process the anticipation and rewards could possibly lead to the development of medications or interventions that could block these circuits and provide other treatment approaches.

Substance addiction can hugely impact on a person’s thinking, functioning and behaviour. Whilst depressant drugs such as alcohol and opioids slow down your central nervous system (CNS), stimulants such as cocaine or amphetamine increase the activity of the CNS, leading to higher blood pressure, heart rate and increased alertness. Repeated abuse of the substance leads to tolerance and withdrawal, in turn this leads to the user showing signs of irrational behaviour. Another form of substance abuse is hallucinogens; they can cause powerful changes in sensory perceptions. It works by binding to the serotonin receptors, these neurons control visual information and emotions, and this can lead to various effects on the user. Neurobiology can help us understand the reasons for addiction and the effects they have on us. Groman and Jentsch (2012) discuss key issues of differentiating the causes and consequences of addiction through neuroimaging and behavioural research on monkeys, they found that the dysfunction of the dopamine

Robinson and Berridge postulate that repeated exposure to drugs of abuse, persistently changes the brain circuits involved in attributing incentive salience. In accordance with that theory are several studies that have demonstrated that exposure to certain drugs such as cocaine enhances the motivation to seek or self-administer these drugs in the future (Horger, Shelton & Schenk, 1990; Deroche, LeMoal & Piazza, 1999). For a detailed discussion of this theory please refer to Robinson and Berridge (1993;

The central nervous system consists of the brain and spinal cord. The brain is involved with thinking, learning, memory, body movement, emotion, and even the immune system activity, however there is so much more that the brain is involved

The central nervous system and the peripheral nervous system work together to collect information from within the body and from the environment outside it. The systems process all the collected information and send instructions to the body; to obtain an appropriate response. Once the data arrives, the brain will sort and file it before sending out any commands on what to do. The central system is the main command center of the body that contains the brain as well as the spinal cord. The peripheral nervous system contains a network of nerves that connect the rest of the body to the central nervous system.

The complexity of the human brain creates mystery when determining the influence of neurophysiological factors and their role in the process of addiction. There is a proposed relationship between drug addiction and the mesolimbic dopamine system, with the mesolimbic pathway from the ventral tegmental area to the nucleus accumbens considered the ‘reward centre’ of the human brain (Alcohol Rehab, 2011). A release of dopamine is necessary for ‘reward’ which is hypothesised to initiate the addiction cycle by providing positive reinforcement for drug self-administration (Feltenstein & See, 2009). Methamphetamine triggers the release of dopamine from synaptic vesicles which flood the synaptic cleft activating feelings of euphoria, well-being

From a biological perspective, brain structures play a significant role in sensitivity to reward. The ventral tegmental area is involved in the production of the neurotransmitter dopamine. Dopamine is important, (Dreher, Meyer-Lindenberg, Kohn & Berman, 2008) as it influences the Amygdala, the function which regulates emotion and produces feelings of euphoria when one is rewarded. The Hippocampus plays a role in enhancing SR (Kelley & Mittleman, 1999) and will commit this euphoric feeling into memory and recall the connection between reward and happiness later on. Motor function also plays a role as an individual is required to consciously move around in order to find and obtain a reward, and the pre frontal cortex is involved in attention and planning when it comes to reward.

“The overstimulation of this reward system, which normally responds to natural behaviors linked to survival (eating, spending time with loved ones, etc.), produces euphoric effects in response to psychoactive drugs. This reaction sets in motion a reinforcing pattern that “teaches” people to repeat the rewarding behavior of abusing drugs ”(“Understanding Drug Abuse). Using addictive drugs floods the limbic brain with dopamine, taking it up to as much as five or ten times the normal level. A person with elevated dopamine levels now has a brain that begins to associate the substance with an outside neurochemical reward (“Your Brain on Drugs”). As a person continues to abuse drugs, the brain adapts to the overwhelming surges in dopamine by producing less dopamine or by reducing the number of dopamine receptors in the reward circuit. The result is a lessening of dopamine’s impact on the reward circuit, which reduces the abuser’s ability to enjoy the drugs, as well as the events in life that previously brought pleasure. The decrease in normal dopamine levels encourages the addict to keep abusing drugs in an attempt to bring the dopamine function back to normal, except now larger amounts of the drug are required to achieve the same dopamine high, an effect known as tolerance (“Understanding Drug Abuse ). That is what leads to the state of addiction, which leaves the person in a cycle of craving, using, withdrawal, and relapse.