Researchers have found that a subtle measure of brain activity can give insight into personal feelings of depression, without even asking people directly about it.
Down the line, that might lead to earlier diagnosis and treatment of depression.
The findings were published in the journal Biological Psychiatry: Cognitive Neuroscience and Neuroimaging.
Gina Kuperberg, a professor of cognitive science and professor of psychology at Tufts University, postdoctoral researcher Victoria Sharpe, and graduate student Apoorva Vallampati set up an experiment to measure the brain’s response to depression-related words in context. They wondered if people with low levels of depression would react differently to reading information about it compared to people without those feelings.
The researchers measure event-related potentials, which are types of brain activity that can be monitored noninvasively at the surface of the scalp. Subjects wear what looks like a bathing cap equipped with sensors that record electrical activity as their brains process information, including language.
The team was interested in whether information is expected or not depending on the context set up by words that came before.
“We all evaluate the context in the light of our beliefs, our thoughts, our knowledge that we store in long-term memory,” says Kuperberg, who is also a psychiatrist at Massachusetts General Hospital.
Between 300 to 500 milliseconds after hearing or seeing a word, words that are more unpredictable produce a larger event-related potential, like a spike in brain activity.
“That event-related potential peaks at around 400 milliseconds after word onset and it’s called an N400,” says Kuperberg. “Essentially, the larger the N400, the more unpredictable your brain finds that incoming word.”
Conversely, the smaller the N400, the more predictable the brain finds that incoming word and the reaction effect is graduated, like a slope. Measuring the N400 “can give you a neural measure of how much the brain is expecting any incoming word in the light of your beliefs and knowledge, as well as what came before it.”
They also studied a neural response that comes later, called late positive potentials, which occur at 600-900 milliseconds after first seeing or hearing a word. The higher the spike for the LPP, the more attention is focused on that word.
These effects are happening all the time for us all, so Sharpe and Kuperberg had to devise a very tightly controlled environment to measure the specific effect they were interested in.
“We ended up spending a year making these stimuli really clinically relevant by drawing upon clinically well-validated rating scales and DSM-5,” the latest Diagnostic and Statistical Manual of Mental Disorders, a standard reference in mental health field.
For the study, the researchers worked with 39 undergraduate volunteers, some of whom had low levels of depression (and none were on medication). Students read various statements, including some related to depression, on a screen. Certain sentences came on the screen word by word.
“We wanted the sentences—the little vignettes—to sound as natural as possible; we didn’t want people to struggle to read them,” says Kuperberg.
Some of the statements were about other people, while some were phrased as first-person statements, such as “Most days I feel very sad.”
“We wanted to see the degree to which these particular depression-relevant words, referring specifically to yourself, were expected versus unexpected,” says Kuperberg.
What they found was that people with a predisposition to depression had a smaller N400 response to statements about self and depression, indicating that line of thought was expected—that it resonated with them. For non-self-relevant statements about the same topics, there was the usual N400 reaction to a new word, the same as those for people without any depressive tendencies.
Likewise, the late positive potentials, which indicate more focused attention on a word, keyed in on depressive-related words in the people with a tendency toward depression.
Why these effects occur is straightforward. “Anyone who’s got depression or is susceptible to depression can have intrusive thoughts, like rumination,” she says. “They’re classically called negative automatic thoughts and are very implicit and not necessarily under your control.” They become habitual, so that in this case, first-person statements about depression are naturally expected in thought processes.
The monitoring of brain activity taps into these more implicit neural mechanisms and correlates with overt depression, says Kuperberg. “You can detect this really quickly in the brain activity.”
That says, she emphasizes that this is not a screening tool, but “it shows in principle that you can detect these neural patterns, which I think has implications for both understanding mechanisms and in the more distant future, implications for screening,” she says. “A lot more work needs to be done—this research is in the earlier stages of development.”
Source: Tufts University
