I recently asked myself if I’ll still have a healthy brain as I get older. I hold a professorship at a neurology department. Nevertheless, it is difficult for me to judge if a particular brain, including my own, suffers from early neurodegeneration.
My new study, however, shows that part of your brain increases in size with age rather than degenerating.
The reason it’s so hard to measure neurodegeneration is because of how complicated it is to measure small structures in our brain.
Modern neuroimaging technology allows us to detect a brain tumour or to identify an epileptic lesion. These abnormalities are several millimetres in size and can be depicted by a magnetic resonance imaging (MRI) scanner, which operates at around 30,000-60,000 times stronger than the natural magnetic field of the Earth. The problem is that human thinking and perception operate at an even smaller scale.
Our thinking and perception happens in the neocortex. This outer part of our brain consists of six layers. When you feel touch to your body, layer four of your sensory cortex gets activated. This layer is the width of a grain of sand – much smaller than what MRI scanners at hospitals can usually depict. When you modulate your body sensation, for example by trying to read this text rather than feeling the pain from your bad back, layers five and six of your sensory cortex get activated – which are even smaller than layer four.
For my study, published in the journal Nature Neuroscience, I had access to a 7 Tesla MRI scanner which offers five times better image resolution than standard MRI scanners. It makes snapshots of the fine-scale brain networks during perception and thought visible.
Using a 7 Tesla scanner, my team and I investigated the sensory cortex in healthy younger adults (around 25 years old) and healthy older adults (around 65 years old) to better understand brain ageing. We found that only layers five and six, which modulate body perception, showed signs of age-related degeneration.
Layer four, needed to feel touch to your body, was enlarged in healthy older adults in my study. We also did a comparative study with mice. We found similar results in the older mice, in that they also had a more pronounced layer four than the younger mice. However evidence from our study of mice, which included a third group of very old mice, showed this part of the brain may degenerate in more advanced old age.
Current theories assume our brain gets smaller as we grow older. But my team’s findings contradict these theories in part. It is the first evidence that some parts of the brain get bigger with age in normal older adults.
Older adults with a thicker layer four would be expected to be more sensitive to touch and pain, and (due to the reduced deep layers) have difficulties modulating such sensations.
To understand this effect better, we studied a middle-aged patient who was born without one arm. This patient had a smaller layer four. This suggests their brain received fewer impulses in comparison to a person with two arms and therefore developed less mass in layer four. Parts of the brain that are used more develop more synapses, hence more mass.
Rather than systematically degenerating, older adults’ brains seem to preserve what they use, at least in part. Brain ageing may be compared with a complex machinery in which some often used parts are well oiled, while others less frequently used get roasted. From that perspective, brain ageing is individual, shaped by our lifestyle, including our sensory experiences, reading habits, and cognitive challenges that we take on in everyday life.
In addition, it shows that the brains of healthy older adults preserve their capacity to stay in tune with their surroundings.
A lifetime of experiences
There is another interesting aspect about the results. The pattern of brain changes that we found in older adults – a stronger sensory processing region and a reduced modulatory region – shows similarities to neurodivergent disorders such as the autism spectrum disorder or attention deficit hyperactivity disorder.
Neurodivergent disorders are characterised by enhanced sensory sensitivity and reduced filtering abilities, leading to problems in concentration and cognitive flexibility.
Do our findings indicate that ageing drives the brain in the direction of neurodivergent disorders? Older adults brains have been formed by a lifetime of experiences whereas neurodivergent people are born with these brain patterns. So it would be hard to know what other effects building brain mass with age might have.
Yet, our findings give us some us clues about why older adults sometimes have difficulties adapting to new sensory environments. In such situations, for example being confronted with a new technical device or visiting a new city, the reduced modulatory abilities of layers five and six may become particularly evident, and may increase the likelihood for disorientation or confusion. It may also explain reduced abilities for multitasking with age, such as using a mobile phone while walking. Sensory information needs to be modulated to avoid interference when you’re doing more than one thing.
Both the middle and the deep layers had more myelin, a fatty protective layer that is crucial for nerve function and communication, in the older mice as well as humans. This suggests that in people over the age of 65, there is a compensatory mechanism for the loss of modulatory function. This effect seemed to be breaking down in the very old mice though.
Our results provide evidence for the power of a person’s lifestyle for shaping the ageing brain.
A new study provides evidence that the human brain constructs our seamless experience of the world by first breaking it down into separate predictive models. These distinct models, which forecast different aspects of reality like context, people’s intentions, and potential actions, are then unified in a central hub to create our coherent, ongoing subjective experience. The research was published in the journal Nature Communications.
The scientists behind the new study proposed that our world model is fragmented into at least three core domains. The first is a “State” model, which represents the abstract context or situation we are in. The second is an “Agent” model, which handles our understanding of other people, their beliefs, their goals, and their perspectives. The third is an “Action” model, which predicts the flow of events and possible paths through a situation.
“There’s a long-held tradition, and with good evidence that the mind is composed of many, different modules specialized for distinct computations. This is obvious in perception with modules dedicated to faces and places. This is not obvious in higher-order, more abstract domains which drives our subjective experience. The problem with this is non-trivial. If it does have multiple modules, how can we have our experience seemingly unified?” explained study author Fahd Yazin, a medical doctor who’s currently a doctoral candidate at the University of Edinburgh.
“In learning theories, there are distinct computations needed to form what is called a world model. We need to infer from sensory observations what state we are in (context). For e.g. if you go to a coffee shop, the state is that you’re about to get a coffee. But if you find that the machine is out-of- order, then the current state is you’re not going to get it. Similarly, you need to have a frame of reference (frame) to put these states in. For instance, you want to go to the next shop but your friend had a bad experience there previously, you need to take their perspective (or frame) into account. You possibly had a plan of getting a coffee and chat, but now you’re willing to adapt a new plan (action transitions) of getting a matcha drink instead.”
“You’re able to do all these things in a deceptively simple way because various modules can coordinate their output, or predictions together. And switch between various predictions effortlessly. So, if we disrupt their ongoing predictions in a natural and targeted way, you can get two things. The brain regions dedicated to these predictions, and how they influence our subjective experience.”
To explore this, the research team conducted a series of experiments using functional magnetic resonance imaging, a technique that measures brain activity by detecting changes in blood flow. In the main experiment, a group of 111 young adults watched an eight-minute suspenseful excerpt from an Alfred Hitchcock film, “Bang! You’re Dead!” while inside a scanner. They were given no specific instructions other than to watch the movie, allowing the scientists to observe brain activity during a naturalistic experience.
To understand when participants’ predictions were being challenged and updated, the researchers collected data from separate groups of people who watched the same film online. These participants were asked to press a key whenever their understanding of the movie’s context (State), a character’s beliefs (Agent), or the likely course of events (Action) suddenly changed. By combining the responses from many individuals, the scientists created timelines showing the precise moments when each type of belief was most likely to be updated.
Analyzing the brain scans from the movie-watching group, the scientists found a clear division of labor in the midline prefrontal cortex, a brain area associated with higher-level thought. When the online raters indicated a change in the movie’s context, the ventromedial prefrontal cortex became more active in the scanned participants. When a character’s perspective or intentions became clearer, the anteromedial prefrontal cortex showed more activity. And when the plot took a turn that changed the likely sequence of future events, the dorsomedial prefrontal cortex was engaged.
The researchers also found that these moments of belief updating corresponded to significant shifts in the brain’s underlying neural patterns. Using a computational method called a Hidden Markov Model, they identified moments when the stable patterns of activity in each prefrontal region abruptly transitioned. These neural transitions in the ventromedial prefrontal cortex aligned closely with updates to “State” beliefs.
Similarly, transitions in the anteromedial prefrontal cortex coincided with “Agent” updates, and those in the dorsomedial prefrontal cortex matched “Action” updates. This provides evidence that when our predictions about the world are proven wrong, it triggers not just a momentary spike in activity, but a more sustained shift in the neural processing of that specific brain region.
Having established that predictions are handled by separate modules, the researchers next sought to identify where these fragmented predictions come together. They focused on the precuneus, a region located toward the back of the brain that is known to be a major hub within the default mode network, a large-scale brain network involved in internal thought.
By analyzing the functional connectivity, or the degree to which different brain regions activate in sync, they found that during belief updates, each specialized prefrontal region showed increased communication with the precuneus. This suggests the precuneus acts as an integration center, receiving the updated information from each predictive module.
To further investigate this integration, the team examined the similarity of multivoxel activity patterns between brain regions. They discovered a dynamic process they call “multithreaded integration.” When participants’ beliefs about the movie’s context were being updated, the activity patterns in the precuneus became more similar to the patterns in the “State” region of the prefrontal cortex.
When beliefs about characters were changing, the precuneus’s patterns aligned more with the “Agent” region. This indicates that the precuneus flexibly syncs up with whichever predictive module is most relevant at a given moment, effectively weaving the separate threads of prediction into a single, coherent representation.
The scientists then connected this integration process to subjective experience. Using separate ratings of emotional arousal, a measure of how engaged and immersed viewers were in the film, they found that the activity of the precuneus closely tracked the emotional ups and downs of the movie. The individual prefrontal regions did not show this strong relationship.
What’s more, individuals whose brains showed stronger integration between the prefrontal cortex and the precuneus also had more similar overall brain responses to the movie. This suggests that the way our brain integrates these fragmented predictions directly shapes our shared subjective reality.
“At any given time, multiple predictions may compete or coexist, and our experience can shift depending on which predictions are integrated that best align with reality,” Yazin told PsyPost. “People whose brains make and integrate predictions in similar ways are likely to have more similar experiences, while differences in prediction patterns may explain why individuals perceive the same reality differently. This approach provides new insight into how shared realities and personal differences arise, offering a framework for understanding human cognition.”
To confirm these findings were not specific to one movie or to visual information, the team replicated the key analyses using a different dataset where participants listened to a humorous spoken-word story. They found the same modular system in the prefrontal cortex and the same integrative role for the Precuneus, demonstrating that this is a general mechanism for how the brain models the world, regardless of the sensory input.
“We replicated the main findings across a different cohort, sensory modality and emotional content (stimuli), making these findings robust to idiosyncratic factors,” Yazin said. “These results were observed when people were experiencing stimuli (movie/story) in a completely uninterrupted and uninstructed manner, meaning our experience is continuously rebuilt and adapted into a coherent unified stream despite it originating in a fragmented manner.”
“Our experience is not just a simple passive product of our sensory reality. It is actively driven by our predictions. And these come in different flavors; about our contexts we find ourselves in, about other people and about our plans of the immediate future. Each of these gets updated as the sensory reality agrees (or disagrees) with our predictions. And integrates with that reality to form our ‘current’ experience.”
“We have multiple such predictions internally, and at any given time our experience can toggle between these depending on how the reality fits them,” Yazin explained. “In other words, our original experience is a product of fragmented and distributed predictions integrated into a unified whole. And people with similar way of predicting and integrating, would have similar experiences from the reality than people who are dissimilar.”
“More importantly, it brings the default mode network, a core network in the human brain into the table as a central network driving our core phenomenal experience. It’s widely implicated in learning, inference, imagination, memory recall and in dysfunctions to these. Our results offer a framework to fractionate this network by computations of its core components.”
But as with all research, the study has some limitations. The analysis is correlational, meaning it shows associations between brain activity and belief updates but cannot definitively prove causation. Also, because the researchers used naturalistic stories, the different types of updates were not always completely independent; a single plot twist could sometimes cause a viewer to update their understanding of the context, a character, and the future plot all at once.
Still, the consistency of the findings across two very different naturalistic experiences provides strong support for a new model of human cognition. “Watching a suspenseful movie and listening to a comedic story feels like two very different experience but the fact that they have similar underlying regions with similar specialized processes for generating predictions was counterintuitive,” Yazin told PsyPost. “And that we could observe it in this data was something unexpected.”
Future research will use more controlled, artificially generated stimuli to better isolate the computations happening within each module.
“We’re currently exploring the nature of these computations in more depth,” Yazin said. “In naturalistic stimuli as we’ve used now, it is impossible to fully separate domains (the contributions of people and contexts are intertwined in such settings). It brings richness but you lose experimental control. Similarly, the fact that these prefrontal regions were sensitive regardless of content and sensory information means there is possibly an invariant computation going on within them. We’re currently investigating these using controlled stimuli and probabilistic models to answer these questions.”
“For the last decade or so, there’s been two cultures in cognitive neuroscience,” he added. “One is using highly controlled stimuli, and leveraging stimulus properties to ascertain regional involvement to that function to various degrees. Second is using full-on naturalistic stimuli (movies, narratives, games) to understand how humans experience the world with more ecological accuracy. Each has brought unique and incomparable insights.”
“We feel studies on subjective experience/phenomenal consciousness has focused more on the former because it is easier to control (perceptual features/changes), but there’s a rich tradition and methods in the latter school that may help uncover more intractable problems in novel ways. Episodic ,emory and semantic processing are two great examples of this, where using naturalistic stimuli opened up connections and findings that were completely new to each of those fields.”
A study has found that engaging with frightening entertainment, such as horror films, is associated with temporary changes in brain network activity common in depression. The research also found that individuals with moderate depressive symptoms may require a more intense scare to experience peak enjoyment, hinting at an intriguing interplay between fear, pleasure, and emotion regulation. These findings were published in the journal Psychology Research and Behavior Management.
The investigation was conducted by researchers Yuting Zhan of Ningxia University and Xu Ding of Shandong First Medical University. Their work was motivated by a long-standing psychological puzzle known as the fear-pleasure paradox: why people voluntarily seek out and enjoy frightening experiences. While this phenomenon is common, little was known about how it functions in individuals with depression, a condition characterized by persistent low mood, difficulty experiencing pleasure, and altered emotional processing.
The researchers were particularly interested in specific brain network dysfunctions observed in depression. In many individuals with depression, the default mode network, a brain system active during self-referential thought and mind-wandering, is overly connected to the salience network, which detects important external and internal events. This hyperconnectivity is thought to contribute to rumination, where a person gets stuck in a cycle of negative thoughts about themselves. Zhan and Ding proposed that an intense, controlled fear experience might temporarily disrupt these patterns by demanding a person’s full attention, pulling their focus away from internal thoughts and onto the external environment.
To explore this, the researchers designed a two-part study. The first study aimed to understand the psychological and physiological reactions to recreational fear across a spectrum of depressive symptoms. It involved 216 adult participants who were grouped based on the severity of their depressive symptoms, ranging from minimal to severe. These participants were exposed to a professionally designed haunted attraction. Throughout the experience, their heart rate was monitored, and saliva samples were collected to measure cortisol, a hormone related to stress. After each scary scenario, participants rated their level of fear and enjoyment.
The results of this first study confirmed a pattern seen in previous research: the relationship between fear and enjoyment looked like an inverted “U”. This means that as fear intensity increased, enjoyment also increased, but only up to a certain point. After that “sweet spot” of optimal fear, more intense fear led to less enjoyment. The study revealed that the severity of a person’s depression significantly affected this relationship.
Individuals with moderate depression experienced their peak enjoyment at higher levels of fear compared to those with minimal depression. Their physiological data showed a similar pattern, with the moderate depression group showing the most pronounced cortisol stress response. In contrast, participants with the most severe depressive symptoms showed a much flatter response curve, indicating they experienced less differentiation in enjoyment across various fear levels.
The second study used neuroimaging to examine the brain mechanisms behind these responses. For this part, 84 participants with mild-to-moderate depression were recruited. While inside a functional magnetic resonance imaging scanner, which measures brain activity by detecting changes in blood flow, participants watched a series of short clips from horror films. They had resting-state scans taken before and after the film clips to compare their baseline brain activity with their activity after the fear exposure.
The neuroimaging data provided a window into the brain’s reaction. During the scary clips, participants showed increased activity in the ventromedial prefrontal cortex, a brain region critical for emotion regulation and processing safety signals. The analysis also revealed that after watching the horror clips, the previously observed hyperconnectivity between the default mode network and the salience network was temporarily reduced. For a short period after the fear exposure, the connectivity in the brains of these participants with depression more closely resembled patterns seen in individuals without depression. This change was temporary, beginning to revert to baseline by the end of the post-exposure scan.
Furthermore, the researchers found a direct link between these brain changes and the participants’ reported feelings. A greater reduction in the connectivity between the default mode network and salience network was correlated with higher ratings of enjoyment. Similarly, stronger activation in the ventromedial prefrontal cortex during the fear experience was associated with greater positive feelings after the experiment. These findings suggest that the controlled fear experience may have been engaging the brain’s emotion-regulation systems, momentarily shifting brain function away from patterns associated with rumination.
The authors acknowledge several limitations to their study. The research primarily included individuals with mild-to-moderate depression, so the findings may not apply to those with severe depression. The study was also unable to control for individual differences like prior exposure to horror media or co-occurring anxiety disorders, which could influence reactions. Another consideration is that a laboratory or controlled haunted house setting does not perfectly replicate how people experience recreational fear in the real world.
Additionally, the observed changes in brain connectivity were temporary, and the correlational design of the study means it cannot prove that the fear experience caused a change in mood, only that they are associated. The researchers also did not include a high-arousal, non-fearful control condition, such as watching thrilling action movie clips, making it difficult to say if the effects are specific to fear or to general emotional arousal.
Future research is needed to explore these findings further. Such studies could investigate a wider range of participants and fear stimuli, track individuals over a longer period to see if the neural changes have any lasting effects, and conduct randomized controlled trials to establish a causal link. Developing comprehensive safety protocols would be essential before any potential therapeutic application could be considered, as intense fear could be distressing for some vulnerable individuals.
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