How Last Week’s Workout or Restless Night Still Affects Your Brain

According to research from Aalto University, your workout or restless night last week could still affect your brain well into the following week. The study, published in PLOS Biology, revealed that external factors like sleep, physical activity and mood can influence brain connectivity over various time scales.

Cross-sectional design studies do not record data over time

It is crucial to explore how external factors like sleep, physical activity and social interactions influence brain activity over time, to understand how our brain responds to the world around us. Our flexible brain dynamics can shift rapidly within milliseconds, or gently fluctuate over longer periods as seen in major psychiatric disorders.

Studying how neural activity varies over different time scales furthers our understanding of how certain brain areas and networks are engaged and interact in response to external factors. Functional brain connectivity patterns can accurately track daily fluctuations in mood and certain neural networks alter their activity over time when performing a specific task.

Existing research typically uses cross-sectional designs that often only image individuals at a single time point. Although these studies have greatly contributed to our understanding of brain network activity, they lack data that concerns how this activity changes over time.

“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,” said lead author Dr. Ana Triana, a researcher at Aalto University.

External factors influence brain activity in two phases

The team collected 133 days of behavioral data, using smartphones and wearables, on one subject. They additionally took 30 functional magnetic resonance imaging (fMRI) scans assessing attention, memory, resting state and the effects of naturalistic stimuli. The data from the devices and scans were complemented with daily surveys that collected information on mood, sleep quality, social interactions, exercise and alcohol, caffeine and theine consumption.

“The use of wearable technology was crucial. Brain scans are useful tools, but a snapshot of someone lying still for half an hour can only show so much. Our brains do not work in isolation,” said Triana.

The study carried an added layer of complexity, as Triana herself served as the subject of the research.

“At the beginning, it was exciting and a bit stressful. Then, routine settles in and you forget,” she said.

During the study, the team identified that changes in brain connectivity were influenced by external factors such as sleep, physical activity, mood and autonomic nervous system activity. They also discovered these influences impacted brain connectivity via two distinct response patterns:  

• A short-term wave that lasted less than 7 days
• A long-term wave that lasted up to 15 days

The short-term wave indicated rapid adaptations, such as heart rate variability, which altered brain activity in shorter timeframes. The long-term wave implied gradual and longer-lasting effects, including the impact of mood and sleep duration, found to affect areas associated with attention and memory.

The effects on brain activity influenced by sleep duration were also delayed in some cases, suggesting that the impact of sleep may not be felt immediately but can build up over time, affecting subsequent brain states.

The level of estradiol, which varies throughout the menstrual cycle, may also mediate the observed lags in connectivity changes as sex hormones influence sleep patterns, heart rate variability and brain connectivity.

The data also highlighted individual variability across different tasks and sessions, supporting the notion that while neural networks are generally stable, they can exhibit significant day-to-day changes influenced by various behavioral and physiological factors.

Aiding in the early detection of neurological disorders

The person-centered approach emphasizes how understanding the dynamics of brain connectivity over time provides a more conclusive perspective on the intricate relationships between behavioral, physiological and environmental factors.

“We must bring data from daily life into the lab to see the full picture of how our habits shape the brain, but surveys can be tiring and inaccurate. Combining concurrent physiology with repeated brain scans in one person is crucial. Our approach gives context to neuroscience and delivers very fine detail to our understanding of the brain,” said co-author Dr. Nick Hayward, a neuroscientist at the University of Cambridge and Imperial College London medical doctor.

The study also serves as a proof of concept for patient research, demonstrating that real-time monitoring of brain changes can aid the early detection of neurological disorders.

“Linking brain activity with physiological and environmental data could revolutionize personalized healthcare, opening doors for earlier interventions and better outcomes,” said Triana.

Reference: Triana AM, Salmi J, Hayward NMEA, Saramäki J, Glerean E. Longitudinal single-subject neuroimaging study reveals effects of daily environmental, physiological, and lifestyle factors on functional brain connectivity. PLOS Biology. 2024. doi: 10.1371/journal.pbio.3002797

This article is a rework of a press release issued by Aalto University. Material has been edited for length and content.