Posts tagged major depression
Articles and news from the latest research reports.
Optogenetics illuminates pathways of motivation through brain
Whether you are an apple tree or an antelope, survival depends on using your energy efficiently. In a difficult or dangerous situation, the key question is whether exerting effort — sending out roots in search of nutrients in a drought or running at top speed from a predator — will be worth the energy.
In a paper published online Nov. 18 in Nature, Karl Deisseroth, MD, PhD, a professor of bioengineering and of psychiatry and behavioral sciences at Stanford University, and postdoctoral scholar Melissa Warden, PhD, describe how they have isolated the neurons that carry these split-second decisions to act from the higher brain to the brain stem. In doing so, they have provided insight into the causes of severe brain disorders such as depression.
In organisms as complex as humans, the neural mechanisms that help answer the question, “Is it worth my effort?” can fail, leading to debilitating mental illnesses. Major depressive disorder, for instance, which affects nearly 20 percent of people at some point in life, is correlated with underperformance in the parts of the brain involved in motivation. But researchers have struggled to work out the exact cause and effect.
“It’s challenging because we do not have a fundamental understanding of the circuitry that controls this sort of behavioral pattern selection. We don’t understand what the brain is doing wrong when these behaviors become dysfunctional, or even what the brain is supposed to be doing when things are working right,” Deisseroth said. “This is the level of the mystery we face in this field.”
Clinicians refer to this slowing down of motivation in depressed patients as “psychomotor retardation.” According to Deisseroth, who is also a practicing psychiatrist, patients may experience this symptom mentally, finding it hard to envision the positive results of an action, or, he said, they may feel physically heavy, like their limbs just do not want to move.
“This is one of the most debilitating aspects of depression, and motivation to take action is something that we can model in animals. That’s the exciting opportunity for us as researchers,” said Deisseroth, who also holds the D.H. Chen Professorship.
Genes, depression and life satisfaction
Vulnerability to major depression is linked with how satisfied we are with our lives. This association is largely due to genes.
This is the main finding of a new twin study from the Norwegian Institute of Public Health in collaboration with the University of Oslo. The researchers compared longitudinal information from identical and fraternal twins to determine how vulnerability to major depression is associated with dispositional (overall) lifetime satisfaction.
Previous studies have systematically shown that life satisfaction is considerably stable over time. People who are satisfied at any one point in life are often also satisfied at other times in their lives. This stability—the dispositional life satisfaction—is often said to reflect an underlying positive mood or a positive disposition. Previous studies have also shown that people with such a positive disposition are less depressed, but very few studies have examined the mechanisms behind this relationship.
Results
• Both men and women who met the criteria for lifetime major depression (15.8% and 11.1% respectively) reported lower life satisfaction.
• 74% of the relationship between major depression and life satisfaction could be explained by genes.
• The remaining association (26%) could be explained by unique environmental factors.
• The researchers also calculated the heritability of dispositional life satisfaction and major depression separately. The heritability of dispositional life satisfaction, which has not previously been reported, was estimated to be 72%. In other words, it is largely genes that explain why we differ in our tendency to be satisfied and content with our lives.
• Major depression had a heritability of 34%, which is highly consistent with previous studies.
“The stable tendency to see the bright side of life is associated with lower risk of major depression because some genetic factors influence both conditions”, says researcher Ragnhild Bang Nes from the Division of Mental Health. Genes involved in satisfaction and positivity thus give protection against major depression. Nes is the main author of the study that was recently published in the Journal of Affective Disorders.
Susceptibility to both depression and overall life satisfaction is partly influenced by the same set of genes, but is also influenced by genes that are unique to each.
“The heritability figures mean that 72% of the individual differences in overall satisfaction, and 34% of the differences in depression, are caused by genes. These figures do not provide information on the importance of specific genes for an individual’s life satisfaction or risk of major depression. Traits and propensities like dispositional life satisfaction and vulnerability to major depression are not heritable in themselves. Heritability refers to the importance of genes for explaining the differences between people and the estimates may vary across time and place”, explains Nes.
Although the heritability of major depression was lower than that of life satisfaction, this does not necessarily mean that life satisfaction is far more heritable than depression. The researchers used questionnaire data from two time points to measure dispositional life satisfaction, and a single clinical interview to measure the prevalence of lifetime major depression. The use of only a single assessment to measure depression may partly explain why the heritability of depression is so much lower than life satisfaction.
Can we prevent depression by promoting life satisfaction?
“We found that depression and life satisfaction did not share as many environmental factors as genetic factors. This means that environmental factors of importance to life satisfaction (for example, activities and interventions that make you happy and content) only to a small extent protect against depression”, says Nes.
“Although our underlying disposition to life satisfaction and positivity appears to be relatively stable, small actions in our daily lives may provide temporary pleasures, and these are also important. How we spend our time is tremendously important for our happiness and well-being. It is therefore important to encourage and follow up on activities that make us happy”.
Nes adds:
“To some extent, positive experiences may also accumulate over time and create favorable conditions for our quality of life”.
(Source: fhi.no)