Sleep patterns, physical activity, mood, and heart rate can affect brain connectivity in the short and longer term, results of a unique precision brain mapping study suggested.
Investigators found even small changes in heart rate and mood or a single restless night affected brain networks involved in attention, memory, and cognition up to 2 weeks later.
The study is unusual in that the single participant was the lead investigator. The findings, which included data collected over nearly 5 months from cognitive and psychological tests and 30 functional MRI (fMRI) scans, offer rare insight into how daily activities and physical factors affect brain networks over the course of days and weeks.
Ana Maria Triana, PhD
The results underscore the importance of monitoring patients over time in a natural environment, and not just relying on patient consultations, lead investigator Ana Maria Triana, PhD, Departments of Computer Science and Neuroscience and Biomedical Engineering, School of Science, Aalto University, Espoo, Finland, told Medscape Medical News.
Such monitoring could take advantage of modern technologies like smartphones that can track a person’s sleep, physical activity, and other patterns over time, she said.
“Our behavior and mental states are constantly shaped by our environment and experiences. Yet we know little about the response of brain functional connectivity to environmental, physiological, and behavioral changes on different timescales, from days to months,” Triana added in a release.
The findings were published online on October 8, 2024, in PLOS Biology .
The Power of One
Mental states are affected by numerous external factors. Triana’s team is keen to learn how behavior and brain activity “co-fluctuate” over time in individuals with psychiatric disorders.
The relationship between behavior and brain activity has traditionally been studied with cross-sectional designs that sample many individuals at a specific timepoint. But such studies may not translate into similar findings within single individuals.
A growing area of research, known as precision functional mapping, uses brain activity data collected from fMRI. This approach has shown that individual-specific functional connectivity differs from group-averaged connectivity.
There’s a clear need for more longitudinal studies with frequent measurement points outside the lab to study brain-behavior relationships, said Triana.
“Brains are not isolated organs. They react to stimuli; they react to the environment,” she noted.
‘Good Data’ Collection
The current study included just one participant — Triana, an active 33-year-old with no history of severe psychiatric or neurologic disorders or of chronic medical conditions.
Triana completed a battery of questionnaires at baseline to assess personality traits (Big Five Inventory), stress (Perceived Stress Scale [PSS]), mood (Patient Health Questionnaire-9 [PHQ-9]), anxiety (Generalized Anxiety Disorder 7-Item Scale), and sleep (Pittsburgh Sleep Quality Index).
Researchers collected responses to the PHQ-9 and PSS at regular intervals throughout the study.
Triana also underwent 30 fMRI scans over 15 weeks to measure functional brain connectivity.
While in the scanner, Triana performed four tasks: The cognitive tests Psychomotor Vigilance Test and dual n-back test, which measure attention and working memory; freely writing down her thoughts; and movie-watching (part 2 from “The Grand Budapest Hotel”). Researchers also measured eye-tracking, heart rate, and breathing rate.
Throughout the study, which spanned 133 days, sensors and a smartphone and smart “ring” collected daily information on sleep, physical activity, autonomic nervous system activity, and mood. She also answered questionnaires at random times asking about stress and pain levels as well as mood.
Initially, the constant monitoring felt intrusive, but Triana soon adapted, making the testing a part of her daily routine. She emphasized her determination to gather “good data.”
The Impact of Restless Sleep
The study focused on variations in task performance as reflected in functional brain connectivity. Researchers examined correlations between the averaged blood oxygen level–dependent signals across regions of interest, along with other connectivity measures.
The investigators used two models for analysis. The first accounted for factors from the previous day, while the second included longer lags, examining how external factors influenced functional connectivity over a period of up to 15 days.
The study revealed significant relationships between restless sleep from the prior night and the brain’s default mode network, frontoparietal network (FPN), and somatomotor network. Sleep interruptions were linked to a decrease in connectivity across most network connections.
“However, the effect of sleep duration on working memory does not seem to occur immediately but is observed after a 2-week delay,” investigators noted. In addition, awake time in bed emerged as a significant predictor of brain connectivity.
“In other words, spending more time in bed without sleeping increased the connectivity in selected links,” the investigators noted.
The results suggest “multiple factors involved in the sleep quality, and not only the sleep duration, are important for the efficiency of node communication within and between networks,” they added.
These findings are crucial, as sleep has a profound impact on nearly all mental disorders, Triana noted.
Regular Physical Activity ‘Crucial’
Other analyses showed the previous day’s inactive time was the key factor influencing changes in the between-network integration of the FPN.
“Our results suggest that physical activity plays an important role in influencing changes in functional connectivity related to working memory over time,” wrote the authors. “In particular, reduced physical activity on the day before relates to diminished FPN integration.”
Investigators also found associations between brain connectivity not only for recent physical activity but also for activity over several previous days.
“These findings suggest that physical activity levels have both immediate and delayed effects on brain networks, which supports the idea that regular physical activity might be crucial for maintaining optimal brain network integration and communication over time,” the authors noted.
Additional results supported the notion that associations between brain connectivity and external factors extend beyond just the previous day, suggesting a more prolonged and sustained relationship between external influences and neural processes.
The study also showed that prior heart rate variability (HRV) was linked to resting-state functional connectivity.
“Our results suggest that recent HRV (<5 days) correlates with regional functional connectivity at rest. Specifically, FPN was predicted by the previous day’s resting HRV, an association not previously reported in group-based studies,” the authors observed.
In addition, past mood was associated with brain connectivity at rest and during movie-watching.
‘A Unique Opportunity’
These experimental data “offer a unique opportunity” to develop new methods for analyzing multivariate brain and sensor data, including longitudinal studies that combine data from fMRI, smartphones, and wearables.
Triana’s own research team aims to run the experiments again, this time with a patient diagnosed with a mental health disorder.
“The next step is to actually understand how these fluctuations happen in people who have been diagnosed with a disorder and see if these changes have a correlation with their symptoms,” she said.
This should provide a deeper understanding of the disorder, which could eventually lead to better treatments, she added.
The study included data from a single individual, which limited the generalizability of the findings. Also, the second model analyzed variables and time lags independently, so there was no assessment of the interplay between variables.
It’s unknown if the influence of external factors on functional connectivity extends beyond the studied 2-week timeframe. Another possible limitation is that researchersdidn’t explore whether current connectivity may shape responses to future events.
Commenting on the research for Medscape Medical News, Monica Rosenberg, PhD, associate professor, Department of Psychology, The University of Chicago, Chicago, said this “impactful” paper is an “important illustration” that many aspects of daily life affect functional brain organization.
“Although we often use single snapshots of brain data to make inferences about a person’s unique pattern of brain connectivity pattern and behavior, we need to consider how changes withinindividuals across different timescales impact our measures,” she said.
The study enables future work in this area “by sharing a unique densely sampled dataset,” Rosenberg added.
Study authors received support from The Ella and Georg Ehrnrooth Foundation; Aalto Brain Centre, Aalto University; and the Research Council of Finland. The authors reported no relevant disclosures related conflicts of interest.
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