People diagnosed with major depressive disorder (MDD) experience a greater degree of negative emotion when remembering painful experiences than people without the disorder, a new study indicates. It is generally agreed that autobiographical memory dysfunction is one of the core features of this disorder.
But little is known about the neural mechanisms behind the emotional impact of negative autobiographical memories related to MDD.
The study found that people with major depressive disorder were able to control the negative emotions about as well as people unaffected by MDD, but used somewhat different brain circuits to do so. The study identifies brain differences in MDD related to processing of autobiographical memories, the memories of the events and knowledge of one’s life, that help us form our self-identity and guide our interactions with the world.
“This study provides new insights into the changes in brain function that are present in major depression. It shows differences in how memory systems are engaged during emotion processing in depression and how people with the disorder must regulate these systems in order to manage their emotions,”
said Cameron Carter, MD, Editor of Biological Psychiatry: Cognitive Neuroscience and Neuroimaging, which published the paper.
Amygdala And Hippocampus
Autobiographical memory consists of episodes recollected from an individual’s life. It is a combination of episodic (personal experiences and specific objects, people and events experienced at particular time and place) and semantic (general knowledge and facts about the world) memory.
In this study, the personal memories used to evoke emotion help tap into complex emotional situations that people with MDD experience in their daily lives. Previous studies mostly investigated responses to normative stimuli, like photos of facial expressions, loaded words, or images of distressing situations taken from standardized stimulus sets, and not personal memories.
The 29 men and women with MDD included in the study reported higher levels of negative emotions when bringing negative memories to mind than 23 healthy comparison people. Using functional magnetic resonance imaging, senior author Kevin Ochsner, PhD, of Columbia University and colleagues traced the elevated emotional responses to increased activity in an emotional hub of the brain, called the amygdala, and to interactions between the amygdala and the hippocampus – a brain region important for memory.
Reducing Negative Affect
People with major depressive disorder were able to tune these increased negative emotions down to normal levels when recalling the memory as a distant observer.
“When they were using this strategy, people with MDD showed a pattern of brain activity that was comparable to what was shown by the healthy controls, with one key difference – greater dampening of a region of posterior hippocampus that has been associated with recalling specific memory details,”
said lead author Bruce Doré, PhD, of University of Pennsylvania. The extent to which the posterior hippocampus was dampened in the MDD people also predicted how successful they were at reducing the negative affect.
These results suggest that although negative memories have a stronger impact on people with MDD, they may be able to regulate their emotional response by making it harder to remember specific details of the experience.
“This is generally consistent with a growing body of work suggesting that people with MDD are able to regulate their emotions when instructed to, but they may tend towards doing so in an abnormal manner, such as being more likely to use problematic strategies like distraction and rumination in daily life,”
said Dr. Doré. This kind of work, he said, is consistent with the notion that people with MDD could benefit from training that focuses on identifying and effectively using appropriate strategies for emotion regulation.
“It is possible that training could help to normalize the MDD-related functional brain differences that we observed here,”
said Dr. Doré.
Episodic Autobiographical Memory Differences
It may be worth noting that not everyone has the same memory style. A 2015 study even found that these different ways of experiencing the past are associated with distinct brain connectivity patterns that may be inherent to the individual and suggest a life-long ‘memory trait’.
“For decades, nearly all research on memory and brain function has treated people as the same, averaging across individuals. Yet as we know from experience and from comparing our recollection to others, peoples’ memory traits vary. Our study shows that these memory traits correspond to stable differences in brain function, even when we are not asking people to perform memory tasks while in the scanner,”
lead investigator Dr. Signy Sheldon, assistant professor of Psychology at McGill University, said.
Two brain slices show different memory traits. Credit: Rotman Research Institute
In the study, 66 healthy young adults (average age 24) completed an online questionnaire – the Survey of Autobiographical Memory (SAM) – describing how well they remember autobiographical events and facts.
Their responses fell between the extremes seen in people with Highly Superior Autobiographical Memory (HSAM) or Severely Deficient Autobiographical Memory (SDAM) recently described by memory researchers. This allowed researchers to study normal variation in autobiographical memory.
After filling out the online survey, the 66 participants had their brains scanned at Baycrest with resting state functional magnetic resonance imaging, a technique that maps patterns of brain connectivity, or how activity correlates across different brain regions.
Brain Connectivity Patterns
The researchers focused on connections between the brain’s medial temporal lobes and other brain regions. The medial temporal lobes are well known to be fundamentally involved with memory function.
Those who endorsed richly-detailed autobiographical memories had higher medial temporal lobe connectivity to regions at the back of the brain involved in visual processes, whereas those tending to recall the past in a factual manner (minus the rich details) showed higher medial temporal lobe connectivity to areas at the front of the brain involved in organization and reasoning.
The findings raise interesting questions for cognitive scientists, related to aging and brain health. One of the more provocative inquiries: could certain memory traits be protective, delaying the manifestation of age-related cognitive decline in later years? Could they perhaps also protect against depression?
This research was part of a new trend in focusing on differences in brain structure and function across healthy people. It is the first to relate such brain differences to differences in everyday autobiographical memory functioning.
Another twist to the story is that studies have shown culture can affect the point of view autobiographical memory is recalled in. People living in Eastern cultures are more likely to recall memories through an observer point of view than those living in Western cultures.
Also, in Eastern cultures, situation plays a larger role in determining the perspective of memory recall than in Western cultures. For example, Easterners are more likely than Westerners to use observer perspective when remembering events where they are at the center of attention (like giving a presentation, having a birthday party, etc.).
There are many reasons for these differences in autobiographical perspectives across cultures. Each culture has its own unique set of factors that affect the way people perceive the world around them, such as uncertainty avoidance, masculinity, and power distance.
While these various cultural factors contribute to shaping one’s memory perspective, the biggest factor in shaping memory perspective is individualism. One’s sense of self is important in influencing whether autobiographical memories are recalled in the observer or field point of view.
Western society has been found to be more individualistic, with people being more independent and stressing less importance on familial ties or the approval of others. On the other hand, Eastern cultures are thought of as less individualistic, focusing more on acceptance and maintaining family relationships while focusing less on the individual self.
The way people in different cultures perceive the emotions of the people around them also play a role in shaping the recall perspective of memories. Westerners are said to have a more “inside-out view” of the world, and unknowingly project their current emotions onto the world around them. This practice is called egocentric projection. For example, when a person is feeling guilty about something he did earlier, he will perceive the people around him as also feeling guilty.
On the other hand, Easterners have a more “outside-in view” of the world, perceiving the people around them as having complementary emotions to their own. With an outside-in view, someone who was feeling guilt would imagine the people around them looking upon them with scorn or disgust. These different perceptions across cultures of how one is viewed by others leads to different amounts of field or observer recall.
In situations where one’s physical appearance and actions are important (for example, giving a speech in front of an audience), the memory of that situation will likely be remembered in the observer perspective. This is due to the general trend that when the focus of attention in a person’s memory is on themselves, they will likely see themselves from someone else’s point of view.
This is because in “center-of-attention” memories, the person is conscious about the way they are presenting themselves and instinctively try to envision how others were perceiving them.
Since women feel more objectified than men, they tend to be put in center-of-attention situations more often, which results in recalling more memories from the observer perspective. Studies also show that events with greater social interaction and significance produce more observer memories in women than events with low or no social interaction or significance. Observer perspective in men was generally unaffected by the type of event.