Drugs and the brain

  The organ systems of the human body are all very complex and unique, just as they are in any other vertebrate animal. The immune system has methods of combining immunoglobulin genes to create millions of types of antibodies, the cardiovascular system has countless capillaries and pathways for blood, and the abdomen is full of twists and turns of the digestive system’s fifteen feet of intestines. Without contest, however, the nervous system is the most intricate and evolved system of the human body. Our advanced nervous system is what sets humans apart from any other mammals or animals on Earth. We are the only species to communicate efficiently, invent things, and formulate cultures and identities. On a cellular level, what is different about the way our brains work? 

A question like this does not have a definitive answer, but there are some well-informed hypotheses that give good explanations. One suggests that humans have an especially high brain mass to body ratio. As our species evolved, our relative number of neurons for our body size grew and grew. A large number of neurons means a large number of synapses, allowing for more synaptic pathways to integrate a larger amount of information. Our body’s nervous system is comprised of 86 billion neurons, each with the important task of communicating signals to the next neuron. Within the central nervous system, neuron pathways process and integrate information received from the sensory/afferent division of the nervous system in order to “decide” what actions to take. Most of the body’s sensory information is autonomic, or received without the individual’s conscious thought. However, the somatic nervous system relates to anything that happens in the body due to intentional thought and movement.

The brain is responsible for so many body functions that things can easily go wrong. Many neurological, storage, personality/mood, developmental, and prion diseases can result when certain pathways are compromised. For example, multiple sclerosis is a very difficult disease which results from the myelinating cells of the brain and spinal cord (oligodendrocytes) being removed from multiple focal areas. Without myelination in the central nervous system (CNS), processing times can suffer and transmission of signals within the brain is compromised. Symptoms presented depend on locations and severity of demyelination in focal areas. Some early presenting symptoms include difficulty speaking, weakness in limbs, or visual disturbances. As things progress, symptoms worsen to difficulty moving, blindness, or severe neuropathic pain. Essentially, some issue in the brain results in chunks of the brain to be demyelinated. Without this myelination, function of  those nerves is diminished and symptoms are determined by location. Those suffering from this illness may experience periods of recovery while disease is in remission. Because cause is unknown, treatment is centered around treatment of symptoms rather than curing disease. 

Alternatively, issues within the brain can be caused by injury from outside the body. Impact or puncture can sever connections in the brain, resulting in a loss of function. A classic example is Phineas Gage, a 25 year old man who was struck with a tamping iron through the frontal lobe of the brain. After a miraculous recovery, his personality was very different. He was less kind and patient. Because the area of his brain responsible for impulse control and personality were damaged and healed differently before, his brain worked differently. 

Traumatic brain injuries can affect the sensitive frontal lobe of the brain, leading to impulsivity and aggression in those suffering. TBIs can be caused by concussions, infections, hypoxia, or tumors. Injuries heal differently for each individual, so recovery path is uncertain. For some, recovery is complete enough that only small personality and motor changes remain. For others, lifelong disability lingers. 1.4 million people experience a TBI a year, 50,000 of which are fatal.  60-80% of patients experience personality changes.

Aside from injury and disease causing issues, people also choose to exploit the brain’s pathways for a number of reasons. The brain uses pathways to “reward” the conscious brain and encourage behaviors that are evolutionarily determined as “good” for the individual’s fitness. This is why rich, fatty foods taste better than low calorie low impact foods, or why people get “runner’s high” after they exercise. 

Many of the body’s systems and pathways evolved in a drastically different lifestyle than what we accept today. This can lead to mismatch of what is culturally accepted as good and evolutionarily good. Many products and services offered to us seek to exploit this natural reward pathway in order to feel good for an artificial reason. Fatty foods activate the reward pathway because a high amount of calories means more fuel for the body. People exploit this by producing alcohol sugars which activate the reward pathway without the downside of a caloric surplus, something often viewed as undesirable in today’s society. 

Many drugs can exploit this reward pathway by mimicking the neurotransmitter responsible for activation. Additionally, these chemicals last far longer and activate more intensely than the body’s natural neurotransmitters. Other drugs artificially manipulate the natural release of neurotransmitters in order to affect the activation of the pathway. Interestingly, society has determined some drugs to be legal and widely available while others are criminalized and prohibited by governments. Legal drugs typically seek to manipulate this pathway in order to improve brain function, alter mood, or affect bodily functions. Prohibited drugs typically seek to cause a “high” that makes the user experience heightened emotions and diminished pain/negativity.

Repeated use of certain types of drugs can result in permanently altered brain chemistry and function, leading to addiction. Addiction is a disease that causes heavy withdrawal symptoms and can strip individuals of their ability to make decisions. While we know much more about addiction than ever before, treatment can be complicated and difficult. Even successful rehabilitation leaves people with permanent effects and psychological trauma.