by Virginia Hughes
When you hear Alzheimer’s, you probably think of memory loss, language problems, and general confusion. These cognitive symptoms of the degenerative brain disease are devastating, and so it makes sense that they get the most attention in the media and scientific community.
Of course, the disease has emotional consequences, too. Some of these aren’t the least bit surprising: Depression, irritability, and agitation are expected as memory wanes and daily life becomes more difficult.
But Alzheimer’s brings other kinds of emotional changes that aren’t as easily explained, as I learned from a study published yesterday in the Proceedings of the National Academy of Sciences. Researchers found for the first time that individuals with Alzheimer’s show a high level of ‘emotional contagion’, the unconscious ability to mimic another person’s emotions. And as the disease progresses, destroying more brain cells and cognitive skills, this emotional empathy gets stronger, allowing patients to become more sensitive — and more vulnerable — to the feelings, words, and behaviors of other people.
“Patients with Alzheimer’s can become very sweet and nice and warm, and we all just fall in love with them a lot of the time,” says lead investigatorVirginia Sturm, an assistant professor at the University of California, San Francisco’s Memory and Aging Center. That might be because they’re picking up on emotional cues of the people around them, she says. “A caregiver’s emotional state can really influence the patient.”
This aspect of Alzheimer’s hasn’t been studied much, partly because complex social cognition is difficult to measure in people with declining intellectual capacity. That’s why Sturm was interested in emotional contagion. It’s a rudimentary imitation skill, present not only in adults but newborn babies, who cry in response to cries of other babies, as well as monkeys, rodents, and birds. “It’s a building block for more complicated forms of empathy,” she says.
Sturm’s team scanned the brains of 237 older people: 62 with mild cognitive impairment (a precursor to Alzheimer’s), 64 with Alzheimer’s disease, and 111 healthy controls. The researchers gave participants’ caretakers a questionnaire called the Interpersonal Reactivity Index, which measures emotional contagion (for instance, caretakers rated the accuracy of statements such as, “Being in a tense emotional state scares him/her”). The researchers also measured the participants’ depressive symptoms with the Geriatric Depression Scale.
Both emotional contagion scores and depressive symptoms rise as Alzheimer’s progresses, the study found. But only emotional contagion correlates with changes in the brain. The greater the loss of brain tissue from the temporal lobe — a region important for memory and emotional processing, and the first area to degrade in Alzheimer’s — the higher the emotional contagion.
Emotional connectedness doesn’t happen in every type of dementia. In fact, people with frontotemporal dementia (FTD), caused by degeneration in the brain’s frontal lobe, seem to change in the opposite direction, becoming more aloof as the disease progresses. “They’re just really oblivious to social cues,” says Sturm, who has spent a lot of time doing psychological testing on FTD patients. “With them I have a really different feeling. I know that they don’t really care if I make small talk, so I won’t.”
How could these two similar forms of neurodegeneration lead to such different emotional outcomes? The answer probably lies somewhere in the yin and yang of the brain’s emotional and cognitive networks.
Several years ago, Sturm’s colleagues began scanning the brains of people with Alzheimer’s disease and with FTD using a technique called resting-state functional connectivity. Unlike the typical brain scan, which captures the brain’s firing patterns while it’s involved in some specific task, such as looking at a picture or hearing words, this method scans the brain while the person is lying quietly, focused on nothing in particular. Even at rest, certain brain regions are known to synchronize their activity, ramping up or down at the same time, implying that they’re part of the same “functional” network.
Sturm’s colleagues showed that people with Alzheimer’s have weak connections (that is, out-of-sync activity) in the default mode network, which has hubs in the temporal lobe and the frontal cortex and seems to be important for episodic memory (and has been linked to a wide variety of other behaviors). Intriguingly, though, as this default mode network breaks down, another circuit, the so-called salience network, gets stronger. The salience network has hubs in part of the insula and part of the anterior cingulate cortex, both of which are involved in emotion and perception.
Perhaps most interesting of all: The opposite pattern happens in FTD. With that disease, Sturm’s colleagues found, the default mode network actuallygets stronger and the salience network gets weaker.
Nobody understands yet why the default mode network and the salience network have these reciprocal interactions, Sturm says. In the paper, she notes a similar relationship between emotional and cognitive circuits in post-traumatic stress disorder. In PTSD, emotional circuits get stuck in an over-active state, and this leads to shrinkage of the hippocampus, a region important for memory and cognitive control. Over time, the more cognitive, “rational” brain networks seem to lose their ability to dial down the emotional ones, leading to a positive feedback loop that can make PTSD worse. (I wrote about these stress circuits in a Nature story last year.)
The same kind of thing could be happening in Alzheimer’s disease, Sturm says, though for now that’s pure speculation. She plans to continue this line of research by taking a more thorough look at emotional contagion in dementia patients — by measuring how much their faces mimic other people’s emotions, for example. Because emotional contagion is exhibited by rodents, it might also be a good way to measure emotions in animal models of Alzheimer’s.
In any case, Sturm hopes that more researchers will consider the emotional side of the disease. “There’s been a lot about the memory problems in Alzheimer’s, but no one looks at the opposite side of the coin,” she says.