1.How do we become addicted? The decision to first use an addictive substance is a choice, but if we become addicted (we don’t always), the addiction is a brain disease. Brain systems involved in positive and negative reinforcement get hijacked by the action of addictive drugs. It’s normal to crave things that we like, but in addiction our craving becomes out of our control. Addiction might be our normal craving system gone awry. This is the view of Nora Volkow, currently the National Institute of Drug Abuse (NIDA) director. You can hear her discuss addiction here. In lab animals, craving is investigated by watching the reinstatement of a learned behavior -- see this video for how this is done.
To make matters more complicated, there may be a genetic predisposition for addiction. Think about how a genetic predisposition may interact with our environment to produce addiction.
In the brain, addiction involves the dopaminergic reward system – the ventral tegmental area (VTA) and nucleus accumbens (NAC). But other neurotransmitter systems besides dopamine are involved, such as endogenous opioids and cannabinoids. Other brain areas besides the VTA and NAC are also implicated, such as the insula and the prefrontal cortex.
Have any of you struggled with smoking? See this video on what happens when nicotine enters the brain. Other drugs work in similar ways, as depicted this video on methamphetamine. For more animations on the effect of drugs on neural communication (and a good review of Week 2 course concepts) see the list on this link.
An overview of addiction research is here: http://www.well.com/user/woa/
This site has several resources for drug addiction information: http://www.thirteen.org/closetohome/science/index.html Also, click on “Home” on the left in the upper blue bar for more good information about addiction.
If you’re interested in a specific drug, you can find information on any of them here: http://www.drugtext.org/Table/Articles/
Here is the question:
Why is addiction considered a brain disorder and not just a bad habit? What is the difference between an addiction and a habit? In what ways are addiction and habit related? To get you started on this question, think about some of the course concepts we’ve had so far: How does classical/Pavlovian conditioning or instrumental/operant conditioning fit into the addiction puzzle? What are rewards, punishers, reinforcers,? How does craving and tolerance relate to addiction? (Hint: see the NOBA “Psychopharmacology” and “Conditioning and Learning” chapters.)
2. Schizophrenia is a brain disorder, and is not related to dissociative identity disorder (used to be called multiple personality disorder), which is thought to be caused by traumatic life experiences.
The negative symptoms (loss of normal behaviors) and positive symptoms (additions to cognition) in schizophrenia originate from different brain areas with opposite dopamine activity. The positive symptoms may be due to too much dopamine in the nucleus accumbens (the dopamine hypothesis). On the other hand, the negative symptoms are due to too little dopamine in the prefrontal cortex (the dorsolateral PFC, or DLPFC, more specifically). After understanding the function of our PFC (see Dr. Suzuki’s Lecture 23, “Executive Functions of the Frontal Lobe” for this week), you may see how an underactive PFC could result in schizophrenia’s negative and cognitive symptoms.
In current thinking, schizophrenia is caused by a combination of genetics and environment. Researchers have found that prenatal development is particularly vulnerable time, as long as there is a hereditable predisposition for schizophrenia. There are various factors, such as cold weather and high population density , which are related to viral or other infections in the pregnant mother. Also, lack of sun, and related vitamin D deficiencies might also be implicated.
Toxoplasmosis is an infection that may be related to schizophrenia -- yet another reason to get out of changing the kitty litter when you’re pregnant. Toxoplasmosis may also produce changes in otherwise normal humans. You can listen to Robert Sapolsky, one of the primary investigators on this topic, discuss it here. You can also read more about it at this site.
People with Schizophrenia
Many schizophrenics are brilliant, such as John Nash (remember the movie"A Beautiful Mind" ), Nathaniel Ayers (subject of movie "The Soloist" ) and Dr. Elyn Saks. You can see Dr. Saks talk about living with her illness, along with Kay Redfield Jamison, who is bipolar in this episode of the Charlie Rose series.
For an overview and more information on schizophrenia, see this site.
Like schizophrenia, depression can have both genetic and environmental causes that are related to differences in the brain structure and activity and to specific neurotransmitters (the monoamine hypothesis). The brain areas implicated in depression include an overactive amygdala and a hypoactive prefrontal cortex and anterior cingulate cortex, ACC. Stress can result in shrinking the hippocampus, from suppressed neurogenesis, which may be related to major depressive disorder symptoms. For further reading about neurogenesis and depression, you can read the following articles:
Much of the focus on the psychopharmacology of depression has been on serotonin – that too little exists in the brain of depressed patients. The amount of serotonin isn’t the whole story. Also, SSRIs are getting bad press. For some reason, dopamine reuptake inhibitors, such as Wellbutrin (buproprion), don’t get as much attention, although they are another popular and effective treatment for depression. Shock treatment, or electroconvulsive therapy (ECT), is making a comeback. Deep brain stimulation of the anterior cingulate cortex has been getting more common; you can hear Dr. Helen Mayberg talk about this here: http://www.dailymotion.com/video/x9vgvq_treating-depression-deep-brain-stim_tech
And then there’s sleep deprivation and exercise as possible alleviators for depression.
Here is the question:
Schizophrenia and depression are very different disorders, and this is reflected in different potential causes and effects on the brain. What is the most compelling evidence for you that schizophrenia and depression are disorders of the brain? What treatment for these disorders do you feel most hopeful about, and how does this treatment address the physiological causes?
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||09/24/2015 12:00 am