James, W. (1891) The Principles of Psychology (Henry Holt and Company). Miller, E. K. & Cohen, J. D. (2001) An integrative theory of prefrontal cortex function.
The other side of cognition: mind-wandering as spontaneous thought 1
‘A general view of the wonderful stream of our consciousness, what strikes us first is this different pace of its parts. Like a bird’s life, it seems to be made of an alternation of flights and perching’. William James Principles of Psychology, 1890. Cognitive experimental research has flourished for many years, reaching its apex in the 70ties. The reason of its success was twofold. It provided sound theoretical frameworks for analyzing higher cognition, as well as a systematic method for constructing tasks derived from those frameworks. An example is the 1977 model of Shiffrin and Schneider describing automatic and controlled components of human information processing. In their model all mental activity is under control of a cognitive task, typically a search task. Dependent on the conditions (‘varied or consistent mapping’) the task involves controlled or automatic processing. Both modes of processing are triggered by identical stimulus configurations, but in contrast with controlled processing automatic processing makes no demands on working memory. Later research using the dual task approach demonstrated a trade-off between two task that made similar demands on a shared ‘resource’. The trade off in performance occurred when experimenters varied either the priority or difficulty of the tasks. For example, a fully automated (‘easy’) task could be shared with a controlled (‘difficult’) task without affecting the quality of its output. In the decades that followed most cognitive researchers seemed to have accepted the idea of a limited capacity ‘resource’, at least for tasks that made an appeal on working memory. In line with Baddeley’s working memory model it was further assumed that control processes depended on central executive system that recruited more modular systems (e.g. visuospatial versus verbal). A step further was made by neuropsychologists who discovered that patients with damage of their frontal lobes performed poorly in tasks that relied on working memory. In particular the dorsolateral prefrontal cortex appeared to be a suitable candidate in directing or supervising control processes. Then cognitive experimental psychology gradually slipped into the domain of neuroscience, when researchers started using brain measures concurrently with behavioral measures. It started with measures taken from the scalp (ERPs), later followed by neuroimaging measures that provided a more direct window on what was going on inside the brain. It implied the birth of a new interdisciplinary approach called Cognitive Neuroscience. But to a certain extent is also meant the risk of opening ‘Pandora’s box’. The brain is not an easy organ to understand, certainly not from a functional perspective. A related problem of the new science of the brain was that it lacked theories to back up the the ever growing amount of data. Researchers also discovered that performance and brain activation measures could not always be nicely fit into a simple conceptual scheme. One of the interesting findings of the last decade was that energy expenditure in ‘easy’ tasks or even in a resting state did not match with a simple linear resource/effort model of the brain. For example, a rest period would logically imply zero involvement of working memory and its central executive. But neuroimaging data showed just the opposite: rest periods activated a network of the same brain regions as in memory and complex reasoning task. The network, later denoted as the default network was even consistently more active during baseline conditions than during experimental tasks. Varieties of task unrelated thought. Apparently, the mind freed of constraints of a cognitive task is free to ‘move hither and thither, or to scan its environment for interesting or 1
MInd wandering as spontaneous thought: a dynamic framework. Nature Reviews | Neuroscience volume 17 | November 2016 | 719
novel events. The new findings are reminiscent of William James’ famous sentences following his statement that ‘everyone knows what attention is’. James was not primarily interested in attention constrained by cognitive tasks. His central interest was the phenomenological side of attention: the wandering mind and ‘stream of consciousness’. The content of the mind unrelated to what a person does is also the focus of a recent review of Christoff et al. who formulated a novel and challenging framework for understanding spontaneous thought and mind-wandering. They first present a classification of task unrelated thoughts (see figure below). According to Christoff et al. the terms ‘task-unrelated’, ‘stimulusindependent’ and ‘spontaneous’ are sometimes used interchangeably in the cognitive and neuroimaging literature. This usage, however, is problematic because these terms designate separable dimensions. First, our thoughts or mental states may vary to the extent they are spontaneous, automatically constrained or deliberately constrained. A constraint is anything that ‘limits the free flow of contents of thought, and how these contents change over time’. Varieties of task-unrelated thought (adapted from Christoff et al. 2016). Task irrelevant states involve three subvarieties (Modes) of thoughts, each of which may be internally or externally oriented. (Orientation). Task relevant states are derived from Shiffrin & Schneiders (1977) framework. See text.
Spontaneous thought as a mental state arises relatively freely without strong constraints on the contents of each state and on the transitions from one mental state to another. Dreaming is one example, creative thinking (demanding some deliberate constraints) another. Automatic constraints can be thought of as a ‘family of mechanisms that operate outside of cognitive control to hold attention on a restricted set of information’. For example, affective salience and sensory salience can both act as sources of automatic constraints. Finally deliberate constraints refer to goal directed mental states, equivalent with cognitive control. They refer to a flexible mechanism that can be freely allocated to various goals. For example, we can deliber ately maintain our attention on a dry and boring lecture, bringing our thoughts back to the lecture whenever they begin to stray . A second dimension is the orientation of thoughts. Within each of the three ‘modes’ the orientation of thoughts may be either internal (stimulus independent) or external (stimulus dependent). For example, in the automatically constraint mode a student that is trying to fall asleep, may find it hard not to ponder about the examination of next day. Or a person in a library may find it hard to ignore a buzzing fly. An example of an internally oriented deliberate constraint is the car driver who is already planning the multiple errands she wants to combine into a single car ride. Anxious and obsessive disorders are further clinical examples of mental states with strong automatic constraints. Clinically important deviations in spontaneous thought can be manifested in either excessive variability (like in ADHD) or excessive stability (like in depression) of thought contents over time Christoff et al. also present an interesting neural model suggesting how large-scale networks in the brain relate to the dynamics of thought, and they may interact in conditions of automatic and deliberate constraints. On top in the hierarchy is the fronto-parietal control network
interacting with parts of the default network, the dorsal attention network and the salience network. Declaring the dynamics of the wandering mind as the principal goal of investigation is certainly a great challenge that will present new methodological problems. The new approach is also not without risks, if investigators leave the relatively safe path of task-induced constraints. Traditional experimental design at least allows to focus on predefined mental states, in more tightly controlled conditions both with respect to what the subject ‘is doing’ as to the content and time flow of information in the brain. In contrast, Christoff et al. see promises in an approach that intends to combine ‘online experience sampling or first-person measures of ongoing thought dynamics with measures of neural act ivity’. Such a subject oriented neurophenomenological approach may easily strand in case-studies describing specific neurocognitive states of specific individuals. Another factor is the apparently unlimited ‘brain space’ in terms of interacting networks that may become co-activated in unconstrained conditions, as well as conditions where the source of constraint is difficult to control by the experimenter. Isn’t this very much like opening Pandora’s box?2
References Schneider,W.; Shiffrin, Richard M. (1977). Controlled and automatic human information processing: I. Detection, search, and attention. Psychological Review, Vol 84(1), Jan, 1-66 Baddeley, A.D., Hitch, G.J.L (1974). Working Memory, In G.A. Bower (Ed). Kok, A., K.R. Ridderinkhof, Ullsperger, M.(2006). The control of attention and actions: current research and future developments Brain Research pp. 1 – 6 James, W. (1891) The Principles of Psychology (Henry Holt and Company). Miller, E. K. & Cohen, J. D. (2001) An integrative theory of prefrontal cortex function. Annu. Rev. Neurosci. 24, 167–202. Christoff et al. (2016). Mind-wandering as spontaneous thought: a dynamic framework. Nature Reviews Neuroscience volume 17 | November 2016 | 719 Kane, M. J. et al. (2007) For whom the mind wanders, and when: an experience-sampling study of working memory and executive control in daily life. Psychol. Sci. 18, 614–621 Shulman, G. L. et al. (1997). Common blood flow changes across visual tasks: II. Decreases cerebral cortex. J. Cogn. Neurosci. 9, 648–663 Raichle, M. E. et al. (2001) A default mode of brain function. Proc. Natl Acad. Sci. USA 98, 676–682. Callard, F., Smallwood, J., Golchert, J. & Margulies, D. S. (2013) The era of the wandering mind? Twenty-first century research on self-generated mental activity. Front. Psychol. 4, 891 Fazelpour, S. & Thompson, E. (2015) The Kantian brain: brain dynamics from a neurophenomenological perspective. Curr. Opin. Neurobiol. 31, 223–229.
The expression ‘opening Pandora’s box’ is not used here in its original harsh sense namely, releasing evil and disease. But rather as a metaphor for ‘creating a maze’ or, ‘complicating matters without direct necessity’