Why it’s so hard to know how the brain rests

A mind at rest can provide inner peace and insight. But, from the perspective of neuroscience, we can never truly figure out what it means for the brain to “rest” this way.

Are you too preoccupied with work or other stress in life right now? Let’s practice a bit of mindfulness for a moment: close your eyes and become more in-tune with your breathing. Focus your attention on your chest, shoulders, and the rest of your body and how they feel as you relax. When you finally come to a state of rest, it may be easy to recognize what your body feels like — through your heartbeat adjusting to a new norm and the tension in your arms and legs going away — but what’s going on in the brain? For neuroscientists, studying the brain when it’s in this state of “rest” would help us understand what this peace of mind is like. But, taking a closer look, the brain never truly “rests” the same way the mind and body do.

When researchers began analyzing what went on in the brain using functional magnetic resonance imaging (fMRI), they focused on how neural circuits would respond when people were exposed to different stimuli, whether it was examining brain electrical activity when watching a video or when saying different words and phrases. Since then, they’ve studied the brain’s activity through the connectivity patterns that emerged when brain areas that were connected to each other were involved in these activities. Scientists gained much-needed insight into the underlying brain science of these everyday activities. As interesting as the results may have been, sometimes the most fascinating findings can come about from simply nothing. Ever since Bharat Biswal, then a graduate student at the Medical College of Wisconsin chose to sit inside an fMRI scanner and do nothing, his seminal 1995 manuscript on “resting” human brain activity would be the first in an area of research on “resting-state connectivity.”1

And so it began. Researchers pried into the default mode network (DMN), parts of the brain remained active when the brain was at rest, including the medial prefrontal cortex, the posterior cingulate cortex, the hippocampus, the precuneus, the inferior parietal lobe, and the temporal lobe, as they’re heavily involved in mental disorders like schizophrenia and depression and areas that would benefit from therapeutic techniques like mindfulness meditation. The resting-state’s correlation with behavioral performance and emotional measures has proven its usefulness in neuropsychiatry.2 By studying the functional organization of this network closely, we could get a better understanding of what this kind of “resting-state” would look like from a functional perspective, one that characterizes how parts of the brain relate to each other in their roles as they work together. It’d prove particularly useful for collecting brain data from individuals such as children or patients with Alzheimer’s who couldn’t complete particular cognitive tasks so easily. Since the detection of the DMN, scientists have also discovered at least five other resting-state networks involved in vision, hearing, movement, attention, and memory.3 The brain at rest remains involved in other responsibilities, too. Aside from integrating information within itself, devoting important facts or pieces of information to memory, and going over tasks that it might’ve recently learned when the brain sleeps, the resting-state networks can activate even in the blink of an eye. So, these resting-state networks describe brain activity regardless of whether we’re actually resting.

Using the statistical dependencies between various regions of the brain the underlying DMN could then be studied as it‘s involved in high-level cognitive processes like self-awareness and memory. Since then, it’s been shown that the disruption of the DMN, for example, has been associated with Alzheimer’s disease, depression, autism, and schizophrenia.4 For the neuroimaging community, the “resting-state” of the brain would provide a standard for data sharing between patients of different cohorts and populations when performing these experiments that depend on fMRI and EEG data.5 Through techniques such as mindfulness and yoga that activate and strengthen these parts of the brain when we put our minds to rest, we can even help these individuals dealing with diseases like Alzheimer’s and anxiety.

If there’s so much potential behind studying the resting state of the brain from both neurophysiological and mathematical perspectives, what’s preventing us from reaching it? First, there are many ways researchers can define “resting state.” Among different perspectives, we can characterize the “resting state” of a brain as what goes on when we have only spontaneous thoughts popping into our heads. Even when letting our minds wander or daydream, the brain is still active in some ways.6 Could we use this to describe a brain at rest?

Taking a look further, in a study of five volunteers under fMRI scans, the authors found “very large individual differences in inner phenomena, suggesting that the resting-state itself may differ substantially from one participant to the next.”7 There are many “resting states,” not just a single one. During the descriptive experience sampling (DES) of the experiment, in which the subjects were told to write down what they were experiencing when their brains were at rest when they heard random “beeps,” their responses included awareness, introspection, and emotions and feelings. Still, the authors didn’t report any correlations between the experience and the brain activity itself. So, what’s going on in the brain doesn’t necessarily match what our minds and bodies experience when at rest.

And how does one know when their mind is truly at rest? People who practice mindfulness meditation may recognize the feelings of relaxation or being so in-tune with their bodies that they’re only living in the present moment. For some, meditation can be about coinciding one’s experience with the Buddhist idea of trying to experience everything as if it’s the first time. Even after releasing all of one’s trains of thought and then taking note of what it feels like, the “resting state” can also differ between what subjects report at the moment and what it felt like in hindsight, the authors reported. For the purpose of research, this raises issues in how an individual who takes note of what their “resting state” experience is in figuring out themselves what the “resting state” means and feels like for them.

Then, take note of what it feels like. But, wait! When you jot down what your brain in a “resting state” feels like, you’re no longer in a state of rest. You’re taking note of your state of rest after it’s over. Does remembering the experience of a “resting state” when you take note of it afterward differ from the experience itself? (Imagine asking yourself “what was I just thinking, a moment ago?”) The researchers noted that, when the subjects noted what the resting state felt like in retrospect, it did, indeed, differ from how it felt in the moment. The difference between understanding what one’s resting state feels like at the moment when it’s resting and what it feels like afterward also presents a challenge to defining and describing the brain’s resting state. In ideas dating back to French Philosopher Auguste Comte in 1830, when one reflects on an experience in retrospect, the experience itself doesn’t interfere with the act of reflecting on it.8

And, given the differences in understanding experiences in retrospect, the feelings of the “resting state” can be difficult to describe, as one participant noted:

2. (Lara, participant 2, sample 7.7) Lara is looking at the edges of the scanner mirror — left bottom corner, and sees two of them, layering. Simultaneously she is hearing herself say, to no one in particular, “I really want to talk to you.” The voice is recognized to be her own, expressed in her own natural way; however, the vocal characteristics are not of her own voice but of some female voice that she doesn’t recognize. The wrongness of the vocal characteristics was noted only retrospectively — at the moment of the beep, experientially, Lara simply hears herself talking. She knows who the “you” is in this sentence, but the sentence is not directed to that person. She is also seeing her hands. (Sensory awareness and inner hearing with idiosyncratic characteristics).

On top of the variations in the type of activity present in the brain when at rest and the difficulty discerning resting state from experimental results, we also have to look deeper into what’s going on at the level of single neurons in the brain to figure out what this activity is. We can use the dynamic behaviors that a neuronal population can perform as it’s close to its equilibrium state at which the signals sent from one neuron to the other balance out.9 This brings differences in mathematical formulations of what’s called a “dynamic repertoire” of brain function. From there, the individual’s cognitive and perceptual states that make up resting-state experience can be studied.10 Is the resting state a fixed point on a graph where sets of data diverge from each other?11 Other methods involve looking for random changes in these local brain dynamics and global network structures that are used in creating these more dynamic patterns of the resting state.12

Some researchers have even advocated putting the idea of a “resting state” brain to rest. In this sense, a brain at rest is never truly “resting.” Letting individuals watch movies has proven more valuable than letting the brain rest in some cases12 while the “special status” of the resting-state itself being the absolute baseline against which all other signals must be compared has been challenged.14

Regardless, the resting state has still proven useful provides a method of the resting-state activity of a brain can further improve techniques meant to help strengthen our nervous systems such as mindfulness as well as provide more thorough results for research on neuropsychiatric disorders such as Alzheimer’s and dementia. Despite the difficulties studying the resting state of the brain, overcoming them to find its benefits could give us greater peace of mind.

Sources

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4. Poline, Jean-Baptiste, et al. “Data sharing in neuroimaging research.” Frontiers in neuroinformatics 6 (2012): 9.
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