Though typically seen as a cognitive disorder, Alzheimer’s disease can throw emotions off kilter, making people unusually sensitive to others’ feelings and moods. New research suggests biological underpinnings for such changes. A report in the May 28 Proceedings of the National Academy of Sciences online suggests that emotional hypersensitivity in people with AD and mild cognitive impairment correlates with reductions in brain structures that normally dampen emotional responses. Atrophy also showed up in brain areas important for understanding complex social cues, which might explain why people with AD often give simple emotional responses, said first author Virginia Sturm, who led the research with senior investigator Katherine Rankin at the University of California, San Francisco.

Besides robbing people of memory and cognition, AD can shift a person's mood and behavior in ways that are as debilitating but less studied. “The goal of this research was to see if we could home in on a simpler, more specific emotional change that might be increasing in AD,” Sturm told Alzforum. Her team focused on “emotional contagion”—an automatic mirroring of people's moods that some scientists consider a rudimentary form of empathy. The phenomenon exists across species—from babies who cry upon seeing other infants in distress, to birds that fly off together when a single member of the flock is threatened. Clinical and neuroimaging evidence gave Sturm and colleagues a hunch that emotional contagion may intensify in people with AD.

First, they noticed that some AD patients, curiously, retain social graces and relationships in the face of huge cognitive losses. “Their marriages and friendships persist despite their memory getting worse,” Sturm said. Meanwhile, functional magnetic resonance imaging (fMRI) shows that as AD patients lose activity in the default-mode network, which fires during sleep or daydreaming, their connectivity actually goes up in the salience network, which helps people respond appropriately to environmental stimuli (Zhou et al., 2010). “If your salience network is hyperactive, you may be more sensitive to social cues and be more emotional,” Sturm said. Salience network connectivity breaks down in people with frontotemporal dementia, a degenerative disorder characterized by lack of both social judgment and empathy.

In the current study, the UCSF researchers measured emotional contagion in 64 AD patients, 62 people with mild cognitive impairment, and 11 healthy controls. They used a portion of the Interpersonal Reactivity Index that asks caregivers or spouses to gauge the participant’s anxiety and unease in tense social situations. Measured this way, emotional contagion was higher in MCI patients than in controls, and still higher in the AD group. Consistent with past research, MCI and AD patients were also more depressed, though that correlated weakly with emotional contagion, suggesting that the two measures are somewhat independent.

Participants also underwent structural magnetic resonance brain imaging (MRI). Compared to controls, people with higher emotional contagion had smaller right temporal lobes, including smaller hippocampi. The hippocampus is known to dampen responses to stress and emotional stimuli. "As the hippocampus deteriorates, there may be increased emotion resulting from that loss of inhibition,” speculated Sturm. There was no correlation between brain volume and depression.

Other scientists found the results consistent with clinical observations. “People with Alzheimer’s are more emotionally labile. They can get angry and cry more easily,” said Cynthia Munro of Johns Hopkins University School of Medicine, Baltimore. She said the new work calls attention to the cognition-emotion balance in AD by highlighting how neurodegeneration may affect emotion.

The authors propose that measures of emotional contagion may be useful for assessing mood and behavioral changes in animal models of AD and other brain disorders. Fernando Cendes of the University of Campinas, Brazil, noted that measuring high emotional reactivity may help identify AD patients early (see full comment below).—Esther Landhuis.

Reference:
Sturm VE, Yokoyama JS, Seeley WW, Kramer JH, Miller BL, Rankin KP. Heightened emotional contagion in mild cognitive impairment and Alzheimer’s disease is associated with temporal lobe degeneration. PNAS Early Edition. 28 May 2013. Abstract

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  1. People with AD are very affected by their surroundings. They get agitated when they need to be hospitalized, or when going to crowded and unfamiliar places. The new data in this paper provide insight into the biological substrate for these symptoms. The authors show that atrophy of temporal lobe structures may be a basis for the heightened emotionality observed in AD patients.

    The symptoms are consistent with disrupted connectivity of the default-mode network and increased connectivity of the salience network, which are commonly seen in MCI and AD and occur in parallel to cognitive decline. The findings suggest that high "emotional contagion" could help with early diagnosis of AD and may be a useful measure for studies in AD animal models, both for evaluating disease mechanisms and testing new therapeutic agents.

    View all comments by Fernando Cendes

References

Paper Citations

  1. . Divergent network connectivity changes in behavioural variant frontotemporal dementia and Alzheimer's disease. Brain. 2010 May;133(Pt 5):1352-67. PubMed.
  2. . Heightened emotional contagion in mild cognitive impairment and Alzheimer's disease is associated with temporal lobe degeneration. Proc Natl Acad Sci U S A. 2013 Jun 11;110(24):9944-9. PubMed.

Further Reading

Papers

  1. . Heightened emotional contagion in mild cognitive impairment and Alzheimer's disease is associated with temporal lobe degeneration. Proc Natl Acad Sci U S A. 2013 Jun 11;110(24):9944-9. PubMed.
  2. . Divergent network connectivity changes in behavioural variant frontotemporal dementia and Alzheimer's disease. Brain. 2010 May;133(Pt 5):1352-67. PubMed.

Primary Papers

  1. . Heightened emotional contagion in mild cognitive impairment and Alzheimer's disease is associated with temporal lobe degeneration. Proc Natl Acad Sci U S A. 2013 Jun 11;110(24):9944-9. PubMed.