Researchers from the GIGA CRC In vivo Imaging at the University of Liège (Belgium), the EPF Lausanne and the University of Geneva publish a study that shows that the phenomenology of “mind blanking” challenges the belief that the human mind is always thinking.
We generally consider that our mind is full of thoughts when we are awake. Like a river stream always running, similarly we entertain our own dynamic mental stream: a thought can lead to another, relevant to what we do or not, ebbing between our inner life and the outer environment. How can the brain sustain such a thought-related mode constantly, though?
A study just published in the Proceedings of the National Academy of Sciences indicates that it actually cannot, and that our brains also need to “go offline” for some moments, which we can experience as blanks in the mind.
Researchers from the University of Liège and EPF Lausanne & University of Geneva re-analyzed a previously collected dataset where healthy participants were reporting their mental state as this was before hearing an auditory probe (beep) while resting in the MRI scanner. The choices were among perceptions of the environment, stimulus-dependent thoughts, stimulus-independent thoughts, and mental absences.
Functional images were being collected during this experience-sampling method. The researchers found that mind blanking episodes were reported quite rarely compared to the other states, and that they were re-appearing also scarcely across time.
Using machine learning, the researchers further found that our brains during mind-blanking episodes organized in a way where all brain regions were communicating with each other at the same time. This ultra-connected brain pattern was further characterized by high amplitude of the fMRI global signal, which is a proxy of low cortical arousal.
In other words, when reporting mind blanking our brains seem to be in a mode similar to that of deep sleep, only that we are awake.
“Mind blanking is a relatively new mental state within the study of spontaneous cognition. It opens exciting avenues about the underlying biological mechanisms that happen during waking life. It might be that the boundaries of sleep and wakefulness might not be that discrete as they appear to be after all”, says the principal investigator Dr. Demertzi Athena, FNRS researcher at GIGA ULiège.
“The continuously and rapidly changing brain activity requires robust analysis methods to confirm the specific signature of mind blanking”, continues Dr. Van De Ville Dimitri.
The researchers claim that the rigid neurofunctional profile of mind blanking could account for the inability to report mental content due to the brain’s inability to differentiate signals in an informative way.
While waiting for the underlying mechanisms to be illuminated, this work suggests that instantaneous non-reportable mental events can happen during wakefulness, setting mind blanks as a prominent mental state during ongoing experience.
During ongoing task-free conditions, spontaneous experience is ongoing, dynamic, and rich in mental content (1), taking the form of mental states. Mental states are transient cognitive or emotional occurrences that are described in terms of particular content (what the state is ‘about’) and the relation we bear to this content (e.g. imagining, remembering, fearing).
Thoughts, in that sense, are sequences of mental states (2). Ongoing experience can also show moments of mind blanking (MB) during which there is a failure to report the content of thoughts, often accompanied by a post-hoc realization that our mind “went away” (3). Behavioral studies indicate that MB happens scarcely during task performance, yet with a considerable frequency.
For example, it has been shown that, during focused tasks, MB was reported on average 14.5%of the times whenever subjects evaluated their mental state upon request (3), and 18% of the time when participants reported MB by self-catching (4). In terms of neural correlates, instructing participants to “think of nothing” as compared to “let your mind wander” led to lower fMRI functional connectivity between the default mode network (DMN) and frontal, visual, and salience networks.
On the one hand, this is indicative of how pre-scan instructions influence connectivity results (5), and how MB might exhibit a distinct neural profile on the other. Indeed, MB has also been associated with deactivation of Broca’s area and parts of the hippocampus, as well as with activation of the anterior cingulate cortex, which has been interpreted as evidence for reduced inner speech (6).
Decreased functional connectivity in the posterior regions of the DMN and increased connectivity in the dorsal attentional network has also been found in an experienced meditator practicing content-minimized awareness, which can be considered as a phenomenological proxy to MB (7).
Collectively, these studies indicate that, although the investigation of MB is rising over the years, its neurobehavioral characterization remains inconclusive. This might be due to several reasons. First, MB has been studied after deliberately inducing it or in highly-trained individuals, therefore its spontaneous occurrences are not generalisable. Second, in some cases MB has been studied in isolation from other mental states, therefore its inter-state dynamics are lacking.
Third, current MB’s neural correlates concern a limited number of brain regions, leaving the whole-brain functional connectome uncharted. In this study, we aimed at delineating the neurofunctional profile of MB in a comprehensive way. For this purpose, we used fMRI-based experiencesampling in typical individuals (8) in order to: a) account for the behavioral quantification of spontaneous (no induction) MB occurrences, b) determine MB’s inter-mental-state dynamics, and c) estimate the MB’s functional fine-grained connectome at the whole-brain level.
reference link :https://www.biorxiv.org/content/10.1101/2021.05.10.443428v2.full
Original Research: Closed access.
“Mind blanking is a distinct mental state linked to a recurrent brain profile of globally positive connectivity during ongoing mentation” by Demertzi, A et al. PNAS