In cases of familial depression, changes in tissue thickness in key
brain structures in the right half of the brain may increase a person's
risk for developing depression, according to NIMH-funded researchers.
Similar changes in the left half of the brain were linked to the
severity of a person's existing depression or anxiety symptoms. Based
on their findings, the researchers proposed a possible mechanism for
how these brain changes affect depression risk in the April 14, 2009,
issue of the Proceedings of the National Academy of Sciences.
Background
Some
types of depression run in families, and certain changes in brain
structure and function have been observed in people with the disorder.
However, until recently, scientists have been unclear on the exact
relationship between these brain changes and depression.
Building
on previous research with a three-generation study population, Myrna
Weissman, Ph.D., and Bradley Peterson, M.D., both of Columbia
University College of Physicians & Surgeons and New York State
Psychiatric Institute, and colleagues used magnetic resonance imaging
(MRI) to assess brain changes in 131 people, ages 6-54. Roughly half of
these participants were considered at high risk for major depressive disorder (MDD),
due to having at least one parent or grandparent in the study diagnosed
with the illness. The other half, considered at low risk, had no family
history of the illness.
Results of the Study
From
pre-scanning interviews, the researchers found that people in the
high-risk group were more likely than those in the low-risk group to
report having MDD or an anxiety disorder
at some point in their lives. MRI scans showed that, on average, those
in the high-risk group had 28 percent thinner brain tissue across a
broad range of brain structures in the right half of the brain. These
changes were observed in young children in the high-risk group and in
older high-risk individuals who had never suffered from MDD or an
anxiety disorder themselves.
The brain areas most affected by
this thinning govern attention and the ability to process emotional or
social cues (such as faces or family pictures). In tests involving
these right-brain tasks, the researchers found that thinner tissue in
these areas was linked to greater inattention and poorer performance in
immediate and delayed visual memory.
Similar patterns of tissue
thinning in the left half of the brain appeared to be related to the
severity of a person's existing MDD or anxiety disorder symptoms in
both the high- and low-risk groups. This thinning was not as pronounced
as the thinning in the right half of the brain, and the difference in
tissue thickness between the high- and low-risk groups was not
statistically significant.
Significance
The findings
strongly suggest that changes in tissue thickness in the right half of
the brain directly affect a person's inherited risk for developing MDD.
The pattern of tissue thinning appears to be related to problems with
attention and processing of emotional or social signals. Such problems
may increase a person's vulnerability to developing mood or anxiety
disorders, according to the researchers.
That the thinning was
present in people at high risk, but who had never had MDD or an anxiety
disorder, as well as in high-risk children who had not been diagnosed
with depression, shows that these brain changes likely come before
illness onset and that they occur very early in life, possibly before
birth, say the researchers. Furthermore, while thinning in the right
half of the brain contributes to risk, thinning in the left half of the
brain appears to be required in order for a person to show symptoms of
these illnesses.
What's Next
More research is needed to
determine if the inherited risk for MDD is purely genetic, if there are
specific environmental factors necessary for triggering genetic risk,
or whether there is a combination of factors involved. Increased
understanding of how risk translates into developing MDD or other
mental disorders may lead to new methods of diagnosing, treating, or
preventing these illnesses.
Top:
Color coded MRI brain maps of differences in tissue thickness between
study participants at high- vs. low-risk for familial depression. Left
half of brain is shown on the left and right half on the right. Cool
colors (blue and purple) denote thinner areas in the high-risk group;
warm colors (yellow, orange, and red) are significantly thicker areas;
green areas show little to no difference in tissue thickness.
Bottom:
Flowchart represents a proposed model for how some MDD or anxiety
disorders develop. Double-headed arrows indicate factors that may
influence each other and jointly contribute to disease risk. Block
arrows show the hypothetical progression from inherited risk to
development of symptoms.
Source: Bradley Peterson, M.D., Columbia
University College of Physicians & Surgeons and New York State
Psychiatric Institute
Reference
Peterson BS, Warner V, Bansal R, Zhu H, Hao X, Liu J, Durkin K, Adams PB, Wickramaratne P, Weissman MM. Cortical thinning in persons at increased familial risk for major depression. Proc Natl Acad Sci U S A. 2009 Apr 14;106(15):6273-8. PMID: 19329490
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Dr. Jeffrey SpellerDr. Tanya Korkosz
Psychopharmacology Associates of New England
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