A multi-session simultaneous EEG-fMRI dataset with repeated experience sampling
This paper presents a multi-session simultaneous EEG-fMRI dataset from 24 healthy adults, organized in BIDS format, which combines continuous behavioral data, mental health surveys, and repeated experience sampling to investigate the neural correlates of spontaneous thought and the reliability of brain-behavior relationships across sessions.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of a preprint that has not been peer-reviewed. It is not medical advice. Do not make health decisions based on this content. Read full disclaimer
The human mind is rarely still. Even when we are sitting quietly, eyes open but not focused on anything in particular, our thoughts are busy. They drift to memories of the past, plans for the future, worries about the day, or the simple feeling of being alive in a body. Scientists call this state "mind-wandering," and it takes up nearly half of our waking hours. For a long time, researchers could only guess what was happening inside the brain during these moments of drifting thought. They could ask people to report what they were thinking, or they could take a picture of the brain's activity, but they could not do both at the same time with enough detail to see how the two connect.
To understand the brain, scientists often use two different tools. One tool, called functional magnetic resonance imaging, or fMRI, acts like a slow-motion camera that shows which parts of the brain are active in a specific area. It is excellent at showing location but moves too slowly to catch the rapid flickering of electrical signals. The other tool, electroencephalography, or EEG, uses sensors on the scalp to record the brain's electrical activity as it happens, capturing the speed of thought but struggling to pinpoint exactly where in the brain that activity is coming from. When researchers try to use both tools together, the powerful magnetic field of the scanner creates massive electrical noise that drowns out the delicate brain signals, making the data look like static on a radio.
A team of researchers has now overcome these hurdles to create a new, detailed record of the mind at rest. They gathered a group of twenty-four healthy adults and asked them to lie inside a powerful MRI scanner while wearing a special cap filled with sensors. The goal was to watch the brain's electrical and chemical activity unfold in real time while the participants let their minds wander. To make sure they were capturing genuine thoughts and not just random noise, the researchers used a clever method. Every minute or so, a gentle prompt would appear on a screen, asking the participants to rate their current state of mind. They were asked to describe whether their thoughts were about themselves or others, if they felt energetic or tired, and whether their mind was moving freely or stuck in one place. This process, repeated dozens of times, allowed the scientists to link specific moments of conscious experience directly to the brain activity happening at that exact second.
The study involved two main parts. First, the participants performed a task designed to test their focus. They watched a stream of images, mostly of city scenes, with a few mountain scenes mixed in. They were told to press a button for the cities and hold back for the mountains. This task revealed how the brain handles attention and how it slips up when the mind starts to drift. Second, and more importantly for understanding the wandering mind, the participants simply stared at a cross on the screen and let their thoughts go wherever they wanted. During these quiet moments, the researchers used a special technique involving tiny wire loops built into the sensor cap. These loops acted like a reference signal, measuring the electrical interference caused by the scanner itself. By mathematically subtracting this interference, the team was able to clean the data and see the true brain signals underneath. This allowed them to capture the brain's electrical rhythm with high precision, even while the machine was humming and vibrating around them.
The results offer a clear picture of what happens when we stop focusing on the outside world. When the participants were successfully holding back their button presses during the attention task, specific networks in the brain lit up, particularly areas involved in noticing important changes and controlling movement. However, when they made mistakes or their reaction times became erratic, the brain showed a different pattern, with activity shifting in ways that suggested a loss of control. During the resting periods, the data showed that the brain does not simply shut down when we are not doing a task. Instead, it remains highly active, cycling through different states of thought. The researchers found that the way people rated their thoughts—whether they felt focused on the past, the future, or themselves—correlated with distinct patterns of brain activity. For instance, thoughts about the self and the future tended to group together, while thoughts about other people and the past formed their own cluster.
One of the most significant findings is the reliability of these connections. The researchers scanned each participant on two separate days, sometimes weeks apart. They found that the relationship between the brain's electrical signals and the participants' reported thoughts was consistent from one session to the next. This suggests that the way our brains support our inner experiences is a stable trait, not just a random fluctuation. The study also confirmed that the brain's activity during these wandering moments is not chaotic; it follows organized patterns that can be measured and understood. By providing a massive, high-quality dataset that includes both the electrical and chemical views of the brain, along with detailed reports of what the participants were thinking, this work opens a new door for understanding the human mind. It gives scientists a powerful map to explore how our brains generate the rich, continuous stream of consciousness that defines our daily lives, even when we are doing nothing at all.
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