, discussed the neuroscience of chronic drug use at the 2015 meeting of the Society of Biological Psychiatry. His basic message was that chronic drug use is associated with A) loss of the reward value of the drug and B) a progressive increase in dysphoria and stress when off the drug. Both factors drive craving and drug seeking.
Access to high as opposed to moderate doses of a drug lead to an escalation in drug intake, and associated persistent increases in withdrawal dysphoria, which Koob called “the dark side.”
Koob explained that a month of detoxification is not sufficient, and that people quitting a drug need more time to let dopamine increase and to let levels of corticotropin releasing factor (CRF), which drives the anxiety and dysphoria of withdrawal, normalize. He stressed that for people addicted to opiates, it is important to taper levels of the drug to minimize withdrawal symptoms.
In addition to CRF, dynorphin also plays a role in chronic drug abuse. This opiate peptide acts at kappa opiate receptors and is associated with anxiety, dysphoria, and psychosis as opposed to morphine, which acts at mu opiate receptors and is associated with euphoria and decreased pain. Koob found that administration of the kappa opiate antagonist norbinaltorphimine (nor-BNI) blocks dose escalation of methamphetamine and brings abstinence-related compulsive drug seeking back to baseline.
At the 2015 meeting of the Society of Biological Psychiatry, Bruce McEwen, professor of neuroscience at Rockefeller University, gave an overview of stress’s effect on the brain. He explained that “chronic stress makes you stupid,” and said that while one can compensate for the effects of chronic stress, one cannot reverse them.
Short-term stress can be helpful, increasing cortisol, with generally positive effects. When stress lasts longer, the chronic increase in cortisol starts to cause problems: impaired memory, endangered neurons, decreased bone and muscle, and metabolic abnormalities.
McEwen said that chronic stress shrinks the dendrites in the medial prefrontal cortex and the hippocampus. A healthy prefrontal cortex is necessary for new learning and memory.
Chronic stress also enlarges the orbital frontal cortex and the amygdala. An oversized orbital frontal cortex can induce habits, making a person susceptible to repetitive thinking and obsessions, addictions, or other compulsive behavior. An oversized amygdala can provoke fear and anxiety.
Editor’s Note: Stress can make people more susceptible to substance abuse, which in turn leads to losses in cortical control.
Many people suffer problems with mental functioning after an apparent concussion (otherwise known as mild traumatic brain injury, or mTBI) that does not show abnormalities on traditional brain imaging measures such as the MRI. New technology called diffusion tensor imaging (DTI) shows that the integrity of white matter tracts may be disturbed by concussions. White matter comprises parts of the brain where myelin wraps around axons, as opposed to grey matter, which reflects the presence of neuronal cell bodies.
In a longitudinal study published in the Journal of Neurotrauma, Vigneswaran Veeramuthu and colleagues compared 61 people with an mTBI to 19 healthy controls. The mTBI participants had their neuropsychological faculties assessed an average of 4.35 hours after their trauma, and participated in DTI scans an average of 10 hours after the trauma. Both the neuropsychological assessment and the DTI scan were repeated six months later. When the acute and follow-up assessments were compared to the same assessments in control participants, the two groups showed differences in numerous white matter tracts at the six-month mark. There was also an association between the degree of abnormality observed on the DTI scans and decrements in performance on the tests of neuropsychological functioning both immediately after the trauma and six months later.
The researchers concluded that their results “provide new evidence for the use of DTI as an imaging biomarker and indicator of [white matter] 