A new study published in the journal Neuroscience has found that long-term exposure to high-altitude conditions can slow down the way people recognize faces and change the way their brains process emotions. The research compared young adults living at high altitudes with those living at lower altitudes and found that the high-altitude group not only took longer to recognize emotional faces but also showed distinct changes in their brain activity.

Long-term residence in high-altitude environments has been linked to a greater occurrence of mental health challenges, such as anxiety and depression. Statistics show that depression is significantly more common in high-altitude regions compared to lower areas. Studies focusing on people who migrate to or work in high-altitude places, like those in Tibet or the Himalayas, have consistently shown that the reduced oxygen levels at these elevations can negatively impact emotional well-being. Moving to high altitude regions has been reported to increase the chances of experiencing depression, anxiety, and even suicidal thoughts.

Depression is known to be closely related to negative patterns in how we think and process information. A strong connection exists between depression and a tendency towards negative thinking, fixating on negative thoughts, and difficulty controlling impulsive behaviors. This relationship has been observed in soldiers stationed in high-altitude areas; those with poorer mental health tend to exhibit stronger negative biases in their thinking. This negative thinking bias can also influence how we perceive facial expressions, which is important for social interactions. For instance, individuals with depression tend to show heightened brain responses to negative facial expressions and take longer to shift their attention away from them. Brain activity patterns, measured through electroencephalography, can even be used to detect depression based on how the brain reacts to emotional stimuli.

Previous research has indicated that high altitude exposure specifically affects the ability to recognize facial expressions. People at high altitudes have been found to struggle with correctly identifying happy expressions and are more likely to incorrectly identify neutral expressions as showing emotion compared to individuals at sea level. However, it has remained unclear how the brain changes caused by reduced oxygen at high altitudes contribute to these difficulties in emotional recognition and potentially lead to mental health issues like depression and anxiety.

It is understood that prolonged exposure to high altitudes can affect the frontal lobe and other areas of the brain, leading to a decline in cognitive abilities. The reduced oxygen levels at high altitudes can disrupt how brain cells use energy and can damage their structure and function, particularly in areas like the frontal, parietal, and temporal lobes. Since processing facial expressions heavily relies on the activity of the frontal lobe and visual cortex, it is plausible that people living at high altitudes might have reduced emotional recognition abilities compared to those at lower altitudes.

The researchers believed that these impairments would likely be reflected in unusual patterns in brainwave components related to facial processing. Specifically, they focused on two brainwave components: P1, which is associated with the early stages of visual perception, and N170, which reflects the brain’s structural encoding of facial features.

To investigate these questions, the researchers compared two groups of college students. One group consisted of 22 students from Tibet University, located at a high altitude of 3,658 meters (approximately 12,000 feet) above sea level. These students had all grown up at lower altitudes and had lived at the high-altitude university for more than two years after reaching adulthood. The second group, serving as a comparison, was made up of 24 students from universities in Beijing, a city at a low altitude of 52 meters (approximately 170 feet) above sea level. These students had never been to a high-altitude region. All participants had normal or corrected vision, were right-handed, had no history of neurological or psychiatric disorders, were not taking any drugs, and maintained regular lifestyles.

The study used a task where participants were shown pictures of faces displaying different emotions: happy, angry, and neutral. These faces were selected from a standardized system of Chinese facial expressions. Participants were asked to quickly and accurately identify the gender of the person in each picture by pressing a button. While participants performed this task, their brain activity was recorded using electroencephalography, a technique that measures electrical activity in the brain through sensors placed on the scalp. This method allowed researchers to track brainwaves associated with different stages of facial processing.

The researchers were particularly interested in two specific brainwave components: P1, occurring around 100 milliseconds after seeing a face, and N170, occurring around 170 milliseconds after seeing a face. These components are known to be related to early visual attention to faces and the structural encoding of facial features, respectively.

The results of the study revealed several key differences between the high-altitude and low-altitude groups. While both groups were equally accurate in identifying the gender of the faces, the high-altitude group was slower in their reaction times compared to the low-altitude group. This suggests that high altitude living slows down the process of recognizing facial features, even if it doesn’t impact accuracy.

The brainwave data provided further insights. The researchers found that the high-altitude group showed reduced amplitudes for both the P1 and N170 brainwave components compared to the low-altitude group. This means that the brain activity associated with both early visual attention to faces (P1) and the structural encoding of facial features (N170) was weaker in the high-altitude group. Furthermore, in the low-altitude group, there was a typical pattern of greater brain activity in the right hemisphere of the brain during the early stages of facial processing (P1 component). This is known as right hemispheric lateralization. However, this right hemisphere dominance was absent in the high-altitude group, suggesting that high altitude living alters the typical brain organization for facial processing.

Interestingly, when examining the N170 component in more detail, the researchers found a difference in how the two groups processed positive emotions. Typically, people show a “positive bias” in their brain activity when processing faces, particularly happy faces. This bias is reflected in a larger N170 response to happy faces compared to neutral faces. The low-altitude group showed this expected positive bias. However, this positive bias was significantly reduced in the high-altitude group. In other words, the brains of individuals at high altitude did not show as strong of a positive response to happy faces compared to neutral faces as those living at low altitude.

These findings suggest that long-term exposure to the reduced oxygen levels at high altitudes impacts both early and later stages of facial processing. The weaker P1 component indicates that high altitude affects the initial attention and visual processing of faces. The disappearance of right hemisphere lateralization might suggest that the brain adapts to high altitude by recruiting both hemispheres more equally, possibly due to limited cognitive resources under hypoxic conditions. The reduced N170 amplitude suggests that the encoding of facial features is also impaired by high altitude.

Most importantly, the decreased positive bias in the N170 response to happy faces may provide a neural explanation for the increased risk of depression at high altitudes. A reduced positive bias could mean that individuals at high altitude are less sensitive to positive emotional cues, which could contribute to a more negative emotional outlook and potentially increase vulnerability to depression.

However, the researchers acknowledged some limitations to their study. They did not directly measure depression or anxiety levels in the participants, so the direct link between the observed changes in brain activity and depression remains to be more fully established. The study was also cross-sectional, meaning it compared groups at one point in time rather than following individuals over time as they moved to high altitude. Future research should track individuals over time to see how their emotional processing changes after moving to high altitude.

The study, “Long-term high altitude exposure reduces positive bias of facial recognition: Evidence from event-related potential,” was authored by Yudian Cai, Xin An, Shan Dai, Hailin Ma, and Yan Wang.