Recent research findings are changing the way we think about brain plasticity. Brain plasticity is the ability of the brain to adapt to environmental changes. By transferring adult mice into social isolation, researchers at the University of Buffalo and Mt Sinai School of Medicine have found that brain plasticity is not specific to neurons. The stress of social isolation created specific changes in the brains of the adult mice, suggesting that brain plasticity also occurs actively in glial cells.
It has previously been discovered that abnormal social experience in neonatal or juvenile animals results in defective developmental myelination. Glial cells, oligodendrocytes specifically, produce myelin. Researchers at the previously named institutions wanted to know if this form of plasticity seen in young animals persists in the adult animal brain. This curiosity prompted several experiments with adult mice to observe changes in oligodendrocytes and myelination.
Adult mice, both males and females, were separated into a control group or an experimental group. The control mice were placed with other mice in a “group house.” Each mouse in the experimental group was placed in social isolation for eight weeks.
The socially deprived mice, both male and females, showed a decrease in myelin thickness, compared to the control group. This difference was statistically significant. Also, these myelin changes were specific to the prefrontal cortex, a brain region involved in complex emotional and cognitive behaviors. Myelin in other regions of the brain was of normal thickness.
It has previously been discovered that abnormal social experience in neonatal or juvenile animals results in defective developmental myelination. Glial cells, oligodendrocytes specifically, produce myelin. Researchers at the previously named institutions wanted to know if this form of plasticity seen in young animals persists in the adult animal brain. This curiosity prompted several experiments with adult mice to observe changes in oligodendrocytes and myelination.
Adult mice, both males and females, were separated into a control group or an experimental group. The control mice were placed with other mice in a “group house.” Each mouse in the experimental group was placed in social isolation for eight weeks.
The socially deprived mice, both male and females, showed a decrease in myelin thickness, compared to the control group. This difference was statistically significant. Also, these myelin changes were specific to the prefrontal cortex, a brain region involved in complex emotional and cognitive behaviors. Myelin in other regions of the brain was of normal thickness.
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| Electron micrograph of myelinated fibers in prefrontal cortex |
Further analysis found that axons with thinner myelin sheaths were associated with the presence of oligodendrocytes with immature nuclear chromatin. From this, the researchers concluded that the stress of social isolation caused a disruption of oligodendrocyte formation, resulting in less myelin production.
White matter in the brain is composed of myelin, produced by oligodendrocytes. In humans, it has been previously discovered that white matter abnormalities occur in psychiatric conditions such as depression. These conditions are characterized by social isolation and withdrawal. Also, demyelinating disorders, such as multiple sclerosis, show correlation with depression.
Brain plasticity is the ability of the brain to adapt to changes. Thus, in a separate experiment, when the previously socially isolated mice were re-integrated into the group house, oligodendrocytes returned to normal control levels and social behavior normalized.
Not only did this study reveal the involvement of glial cells in brain plasticity, it suggests a new correlation: Do myelin disorders and mood disorders interact with one another? And if so, how? Also, could social interaction enhance recovery from myelin disorder symptoms?
Sources:
University at Buffalo (2012, November 11). New form of brain plasticity: How social isolation disrupts myelin production. ScienceDaily.
http://www.nature.com/neuro/journal/vaop/ncurrent/full/nn.3263.html (data and picture)
I found an interesting study that links loneliness with left posterior superior temporal sulcus. After conducting a test that involved lonely people and a control group to determine if the the faces that they were presented with had misaligned eyes and identify what direction the eyes were looking at, lonely people found it harder to do the latter. Also, the full brain scans of lonely people showed less gray matter in the left posterior superior temporal sulcus, an area known for its implication in basic social and speech perception. The researchers confirmed the link between loneliness, left posterior superior temporal sulcus and the perception of eye gaze. They concluded that individuals who struggle with reading social cues are more prone to isolate themselves, thus increasing their chance of getting depression.
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The ramifications of social isolation on the brain are quite fascinating. To think that merely being cut off from social situations can actually alter the functionality of cells within the brain is extraordinary. When you think about the interactions between environment and heredity, a lot of different implications for this research come to mind. Are the people who experience a significant degree of social isolation born with a temperament that makes them adverse to social situations or are they raised in a socially-isolated environment? If we have someone who is say born with a high-reactivity temperament, the same people who usually grow up to be what we would call introverts, is their aversion to novelty, in this situation of the social nature, going to cause their oligodendrocytes to become malfunctional and contribute to a sense of depression that is going to lead to further social isolation in a seemingly infinite loop? Perhaps. I think a longitudinal study of high-reactivity infant's white matter density would be sufficiently illuminating and help to figure out how the two factors play off each other, is the brain causing depression which causes social isolation or is social isolation causing the brain to change and then experience depression?
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