Beyond simplicity – the increasingly complex role of the Default Mode Network in goal-directed behaviour
“Twas brillig, and the slithy toves, Did gyre and gimble in the wabe;.”
― Lewis Carroll, Jabberwocky
Whilst sometimes simplicity is a desirable state of affairs when presenting elaborate concepts, the Occam’s Razor approach sometimes falls short of the real story. This is an issue I have always had with conveniently distilled principles, and systems of ‘thought’ which generalise such principles in appealing to human nature’s desire for answers! Life is rarely simple when one thinks carefully about it! Having said that a good starting point is to make things black and white, to get a fundamental idea across, accept it’s generality. Then once the penny has dropped, begin to dismantle it, and pick apart to get down to finer granularity and more specific meaning...
So far, the ‘anti-correlated’ networks model as espoused throughout my writings, serves as a useful concept for understanding how the brain’s machinery acts in apparent opposition. Much like a computer’s core components being in binary state of on/off, so the brain functions act antagonistically to subserve one need or another, but not holding both in action at once. Likewise with muscles that flex or extend, equilibrium doesn’t generate results, it’s the dynamic shift of balance that creates the impetus and overcomes inertia. (Quantum physics aside for now with respect to superposition, or the capacity to potentially be active in all possible states at once...)
Extending notions such as Occam’s Razor to cut through to the likely ‘truth’ of matters in fundamental understanding, I tend to adopt (and encourage others to do so) the tenet that, if something seems simple to understand, and makes perfect sense, it’s probably not actually accurate. It is far too convenient to be grasped as such. The notion of two networks that switch on and off falls into this category. It is an elegant idea, and nicely slots into a narrative of the universe that brings light and darkness into holistic unity, yin and yang, male and female. Opposing forces that balance and harmonise, creating energy and action in an eternal dance of momentum and interaction.
So for a while now, having established, and proclaimed this principle of brain mechanics, I yearn to dismantle the proposition, to find greater complexity in the simplistic idea, to begin to specify where the general principle holds true, and where it breaks down. Or provides further sub-divisions of principles that begin to be usable beyond the generic.
A paper in 2012 by Nathan Spreng questioned the ‘dismissal’ of the default mode network as ‘task negative’. That is, it has been by definition labelled as ‘default’ and associated with a resting state that has no bearing on task performance. In opposition with the so-called ‘task positive’ network (also known as Central Executive, and referenced in terms of ‘fronto-parietal’ functioning), it appears to ‘switch off’ when the CEN is ‘on’, and by my own hypothesising, represents a potential distracting influence on goal directed tasks that could be demonstrated measurably as negatively impacting on task performance. (Signature of poorer task performance being an indication that DMN activity/dynamic functional connectivity fluctuations are ‘encroaching’ on stable FC of Central Executive network activity facilitating focus on task.) Given that the DMN is said to be a key hub in which sense of ‘self’ is constructed, it stands to reason that certain elements of goal-directed functioning will require a self-referential perspective in order to perform successfully. This is particularly likely where performing a task requires drawing on prior experience: memories of what ‘I’ have encountered previously. This has indeed been shown to be true with respect to accessing autobiographical memories that help ‘solve’ a problem (Andrews-Hanna, 2012; Spreng et al., 2009; Buckner & Carroll, 2007). So the question then becomes one of narrowing down what is the role of the DMN in cases where this important integrative hub (with let’s remember a significantly high metabolic demand for resources) can contribute relevant processing power to performance on-task.
Elton and Gao (2015) began to address this question and stimulate further research impetus to unpack the flexible role of the default mode network in goal directed behaviour, and to disparage the notion that it is only involved in task-irrelevant thoughts and ‘meaningless’ distraction. As an integrative hub for multiple sources including multisensory information, and formulating a sense of ‘self’ clearly this is an important functional network that has much bearing on one’s capacity to successfully negotiate life’s challenges! My earlier piece indicated that it already will have an important role in consolidating information following task performance, and integrating experiences into an updated model of the world and where ‘I’ fit in. So we can already surmise that, whilst performance on a task ‘in the moment’ might be the key priority (for survival?) requiring DMN ‘as a whole’ to be ‘switched off’ and not interfere with the current priorities, a key component of any successful and evolutionarily prosperous system is to take stock of it’s achievements and failures, evaluate lessons learnt, and store this knowledge to enable future performance, efficiency and optimal operational capacity!
Research such as Elton and Gao (2015) describe indicates that the DMN does in fact show flexible functional connections even when performing ‘on task’, with increased connectivity with regions involved in executive control. This is task specific, and both involved in internally oriented as well as externally oriented tasks. (Despite general consensus that on externally-focused tasks the DMN shows a pattern of reduced gross activation.) Elton and Gao postulate that the DMN serves a dual purpose in ‘broadband’ monitoring both the internal and external worlds “to maintain self-consciousness and vigilance during this state (Gilbert et al., 2007; Raichle et al., 2001)”, but also to ‘uncouple’ regions not pertinent to external task-orientation where required. Given this monitoring function, a most consistently preserved coupling was observed to be with regions of the salience network, including the right inferior frontal gyrus – pertinent in detecting salient stimuli. Likewise, in emotional tasks with the anterior insula, where rapid response to task relevant features was facilitated.
So now we have a sense that this integrative hub can shift its processing power and capacity between task-specific coupling/uncoupling (particularly when the task becomes more externally oriented and therefore preferring disengagement with more ‘self-referential’ processes) and more ‘broadband’ monitoring of the world (both externally and internally) in order to facilitate flagging of salient stimuli in accordance with the salience attentional network that can enable switching between 'task positive' (CEN) and default mode networks ‘more generally’. As such this represents a window into how the brain seeks to optimise it’s capacity to switch functions ‘on and off’ as it were, or redistribute resources and be more selective in turning relevant aspects ‘off’ as necessary.
The question that falls upon my own research aspirations to address involves how these networks subserving aspects of ‘self’ in the context of adventurously challenging contexts can threaten to undermine efficiency/optimality of brain functioning and disrupt task performance. Particularly where performance on task may have life-threatening consequences! And likewise, how certain individuals are able to better make decisions and perform ‘on-task’ in the moment of requirement by virtue of this underlying capacity to turn the relevant regions ‘off’ whilst still actively monitoring the environment (both externally and internally). And from that how other individuals less capable of governing their functioning in this way, can learn to harness more control over this optimal state of being. Finally, with a deeper understanding of the functional role and connectivity between and within these key brain networks, we can begin to appreciate how concepts such as ‘self’ have basis in targetable/measurable neural activity, and how the system synthesises experiences and goal-directed behaviours into an updated and enhanced model of ‘self’ that is the basis for improved performance and sense of purpose in the future!
Andrews-Hanna, J. R. (2012). The brain’s default network and its adaptive role in internal mentation. Neuroscientist, 18, 251–270
Buckner, R. L., & Carroll, D. C. (2007). Self-projection and the brain. Trends in Cognitive Sciences, 11, 49–57.
Elton, A. and Gao, W. (2015). Task-positive Functional Connectivity of the Default Mode Network Transcends Task Domain. Journal of Cognitive Neuroscience 27:12, pp. 2369–2381
Spreng, R. N. (2012). The fallacy of a “task-negative” network. Frontiers in Psychology, 3, 145.
Spreng, R. N., Mar, R. A., & Kim, A. S. (2009). The common neural basis of autobiographical memory, prospection, navigation, theory of mind, and the default mode: A quantitative meta-analysis. Journal of Cognitive Neuroscience, 21, 489–510.
The science of cognition and perception in context
This is where I elaborate upon brain science relating to cognitive functioning dependent on environmental context.