How age influences the perception of ambiguous facial expressions

Do you find it easy to perceive people you meet as happy and positive? Or are you vigilant and look for signs of dissatisfaction and anger in their facial expressions?

Your perceptions may be related to how old you are. A new study from the Norwegian University of Science and Technology (NTNU) shows that older people tend to interpret ambiguous facial expressions as positive to a greater extent than younger people.

We know little about how the brain interprets signals that are ambiguous. At the same time, we know that uncertainty affects people's mental well-being. Being able to interpret ambiguous signals we receive from our surroundings is crucial for our well-being."

Maryam Ziaei, researcher at NTNU's Kavli Institute for Systems Neuroscience

Fight or flight center

Zianei studies how a small organ at the bottom of our brain, called the locus coeruleus, works when we try to understand other people's emotions.

The name Locus coeruleus is Latin and can be translated as "the blue spot" or "the blue area". The body plays an important role when we focus on solving tasks. It helps to capture our attention when we are inattentive, such as when we are walking on the street engrossed in our own thoughts and a car suddenly comes up behind us.

The "blue spot" is no more than one-and-a-half centimeters high and only a few millimeters wide, but plays an important role in our response to stress and panic as it produces norepinephrine, the body's "fight-or-flight" hormone.

"This structure regulates how alert and attentive we are. At very low activity, we will be sleepy and lethargic, while increased activity makes us awake and focused. But we can also get too much activity in the locus coeruleus, then we become distracted and experience stress," Ziaei said.

Adapting to cognitive impairment

Perceiving another person's emotional signals can be challenging if these signals are contradictory. If you are talking to a person who is both smiling and looking angry at the same time, you have to be alert and pay attention to understand whether the person is friendly or not. This means that the small blue-coloured organ in the brain must function optimally.

At the same time, our cognitive skills tend to deteriorate with age. Now it seems that the Locus coeruleus is able to adapt and compensate for this weakening.

To learn more about this, researchers at the Kavli Institute have had people of different ages study images of faces with different expressions, while measuring brain activity.

A total of 75 people aged 21 to 30 years, and 69 people aged 67 to 75 years participated in the study, half divided between women and men in both age groups.

The pictures they were to interpret showed faces that went from being clearly happy, more or less ambiguous to clearly angry.

"We saw that the participants took longer to interpret the ambiguous expressions, while the older participants interpreted these as happy to a greater extent," Ziaei said.

More active among the elderly

"It may be that the younger we are, the more we tend to interpret these ambiguous signals negatively, as if they pose a threat. In people with good mental health, this will change with age," she said.

The researchers measured brain activity and took pictures of the brain while the participants assessed the images. They found that the oldest participants showed activity than the younger ones in the Locus coeruleus when the images were completely ambiguous.

The researchers also saw that the oldest participants had greater activity in the connection between the locus coeruleus and the frontal lobe, more specifically  the dorsolateral prefrontal cortex. This part of the frontal lobe is particularly related to cognitive control, memory and attention.

Prior to the study, the participants in the study were thoroughly surveyed using questionnaires. They were asked a number of questions related to mental health, such as the occurrence of anxiety or depression, regulation of emotions and empathy. This allowed the researchers to create a profile of each participant's state of mental well-being.

"We also see a correlation between how much this connection between the LC and the dorsolateral prefrontal cortex is activated, and how well the person feels. We found that the older participants who had increased activity in the connection between the locus coeruleus and the dorsolateral prefrontal cortex also had better well-being," sas Ziaei.

Protects against cognitive impairment

The researchers believe this shows that the locus coeruleus adapts as we age, so that it compensates for reduced cognitive abilities.

The function of the dorsolateral prefrontal cortex, or weaknesses in its functioning, is also associated with diseases such as Parkinson's disease and Alzheimer's. This makes the findings extra interesting, according to the researchers.

Identifying this signalling pathway can bring researchers one step closer to targeted treatment of emotional difficulties in depression in old age, or in neurodegenerative diseases.

The fact that the locus coeruleus responds more actively to sensory impressions that arouse attention has a protective effect against cognitive impairment as people age.

An example is when you suddenly hear the sound of a car behind you, even though you are totally absorbed in your own thoughts, a phenomenon that has been shown by other research.

"If we can make changes here, either with stimulation, with medication or with exercise, we may be able to affect the function of this part of the brain. Not only in people with illness, but for people as a whole. What we want to understand here is the connection between our ability to process social information, and how it is related to feeling good mentally," says Ziaei.

The researchers worked in close collaboration with Heidi Jacob from Harvard Medical School, Boston, USA.