Changes in emotion and mood are common in people with Alzheimer’s Disease (AD) and in many cases of mild cognitive impairment (MCI). It remains unclear whether these emotional changes are a result of stress from loss of cognitive function, from co-occurring mood disorders such as depression or anxiety disorders, or from some other cause. A study recently published in the Proceedings of the National Academy of Sciences suggests that emotional changes in people with AD may result from neurodegeneration in the brain’s temporal lobe. Interestingly, these very structural changes can allow for enhanced emotional connectivity on the part of those with AD, because these changes increase the individual’s sensitivity to the perceived emotional states of those around them.
This sensitivity to the emotion displays of others is known as emotional contagion, a basic underlying emotional mechanism through which individuals orient their physiological and emotional states to those around them. Emotional contagion can occur outside of conscious awareness, and is hypothesized as an evolutionary and developmental root of empathy, one which can be observed in human infants and other mammals. A group of researchers at the University of California, San Francisco designed a study to see whether emotional contagion is higher in individuals with AD and MCI, and to assess its connection to the neural networks that pertain to emotion.
The investigators recruited 237 participants; 64 were patients with AD, 62 were diagnosed with MCI, and 111 were cognitively healthy participants used as a control group. Participants were given structural MRIs, and administered a questionnaire with a measure of emotional contagion and a measure of depression.
Emotional contagion was significantly higher among those with AD, and participants with MCI also scored higher than the control group. Participants with MCI and AD also had significantly higher levels of depressive symptoms than the control group, but were not significantly different from each other. There was a statistically significant but small correlation between emotional contagion and depressive symptoms.
MRI images found that higher levels of emotional contagion were associated with degeneration in parts of the brain’s temporal lobe, including the hippocampus, a region of the brain related to memory that is affected by AD, and three gyri (or ridges on the cerebral cortex) that are associated with several social and emotional functions. There were no associations between brain volume and depressive symptoms.
These findings suggest that emotional sensitivity and “contagion” in AD is not only related to distress and mood disorder, but results from specific changes in the structure of the brain that affect emotional reactions. While these changes limit the individual’s ability to regulate his or her emotions, they also may allow for greater emotion sharing and interpersonal connections for individuals who may otherwise struggle in social interactions.
This study may lead to research on the role of emotional reactivity in the development of AD progression, and might contribute to animal model laboratory research on AD that can use measures of emotional contagion to assess neurological changes.
Sturm VE, Yokoyama JS, Seeley WW, et al. Heightened emotional contagion in mild cognitive impairment and Alzheimer’s disease is associated with temporal lobe degeneration. PNAS (2013). DOI: 10.1073/pnas.1301119110