FROM MODULES TO NETWORKS
Until the advent of brain imaging technologies, brain science was based on neuroanatomy and functional deficits caused by discrete brain injuries – this generated a view of the brain as being composed of specialised modules that have distinct functions. This representation of the brain still dominates most undergraduate neuroscience text books and has permeated popular science. Over time, this modular topography has become increasingly refined – dividing the brain into smaller and smaller parcels correlated with specific function.
On the other hand, brain imaging technologies have challenged the modularised representation of localised brain function. Positron emission tomography, functional magnetic resonance imaging and increasingly sophisticated EEG have enabled the study of embodied and embedded brains under a myriad of conditions and states. These technologies consistently reveal widespread activation of the brain – across areas of the brain previously represented as being anatomically and therefore functionally separate.
Brain activation occurs on various temporal scales and encompasses pathways of network connectivity through long-range synchronisation. This pattern of network activity and coherence was envisioned by Francisco Varela in 2001 in a seminal article entitled – ‘The brainweb: phase synchronisation and large-scale integration’.
The Human Connectome is a visualisation project that incorporates the outcomes of brain studies that have revealed or substantiated functional connectivity. The Human Connectome is a new vision of the brain as a network of interdependent networks – ‘a meshwork of selfless selves’. This functional connectivity, revealed through brain imaging, is now being fleshed out through detailed neuroanatomy – most notably the San Diego Brain Observatory where they are generating a 3D Atlas of a human brain. The Atlas is based on 2,401 serial tissue sections of the artist H.M’s brain correlated with his post-mortem MRI data.
WHAT IS A NEURAL NETWORK
Brain networks consist of collections of interconnected brain areas that act in concert. A large-scale functional network can therefore be defined as a collection of interconnected brain areas that interact to perform functions e.g. cognition. Distributed large-scale networks, organised and coordinated in a coherent manner, underpin healthy cognitive and emotional function.
The timing and rhythm of network dynamics is critical to all aspects of our mental life. Thankfully temporal dynamics of large-scale brain networks is not something we have to consciously attend to or regulate – we are packed full of internal metronomes and rhythmic generators that maintain network coherence.
Critical metronomes that contribute to brain coherence include the breath and underlying slow oscillators. Research shows that the cultivated or mindful mind is more coherent and agile – able to shift deftly from self-generated and amorphous default mode network activity to executive task-object focused attention, perceptual discrimination and conceptual problem solving. It has also been shown that mindfulness inoculates us against the negative aspects of mind wandering.
LAYERS OF BRAIN FUNCTION
Ninety percent of the energy used by the brain is devoted to intrinsic activity rather than activity evoked by stimuli. The majority of this energy can be attributed to DMN activity suggesting that DMN baseline activity supports and maintains other activity within the brain.
The sheer amount of neural energy utilised by the DMN and its activity at rest – make the DMN a likely candidate for maintaining the ‘neural framework’ on which other oscillatory activity arises. The DMN creates an active neural space occupied by higher processing. In addition, the energy utilised by the DMN is thought to create and maintain the framework for consciousness itself.
THE BRAIN & ORGANISM HUM AT 0.1HZ
Brain science tends to neglect the organism as a whole. Indeed much of the biological noise of the organism in fMRI studies is filtered out. Some of this oscillating noise turns out to be correlated with particular frequencies of brain activity and systemic oscillations related to cardio-respiratory regulation.
Of particular interest to our current discussion are the numerous EEG and fMRI studies that have identified intrinsic low frequency oscillations in cerebral activity at <0.1Hz. This intrinsic brain activity is generated by the DMN and is correlated with respiration, heart rate, arterial blood pressure and cerebrospinal fluid flow during resting states. It has been suggested that low frequency oscillations, underpin the coherence within the brains networks, as well as the physiological coherence between the brain and body.
It seems like no coincidence then that 0.1Hz equals 6 cycles/minute – roughly the rate of relaxed breathing which effortlessly arises during relaxation. In addition, infra slow (0.01–0.1Hz) oscillations have been shown to be prominent and significant during cognitive tasks, and also correlate with faster (1–40Hz) neuronal oscillations – suggesting a relationship between the slow DMN and fast cognitive oscillations.
This finding has led some researchers to suggest that DMN and cardiorespiratory oscillations underlie fast oscillations, including much faster alpha/beta oscillations within the resting brain. These slow oscillations are thought to modulate excitability in cortical areas. This observation suggests that effective cognition and task-evoked activities – depend on the coherence of the resting brain – which is cultivated through relaxation.
Perhaps the most radical suggestion to arise from this line of brain research is that low-frequency oscillations detected in the brain are intrinsic processes originating from respiration and/or haemodynamics – stated a little differently – intrinsic brain function within the DMN may not be neural in origin. Whatever the causal story, the integration between oscillations in the brain and body are more apparent during certain states of heightened cardiorespiratory synchronisation – such as slow-wave sleep, meditation and pranayama.
DMN – MUCH MORE THAN MIND WANDERING
Creativity is often portrayed as some sort of anarchic free for all. Research into creative and divergent thought indicates that the creative act is more about attention. The ‘controlled attention model’ of creative thought, regards spontaneous DMN activity as a generator of creative thought – encompassing a wide range of imaginative processes, mental simulations and rapid episodic spontaneous thought.
Divergent and creative thinking is not just about thought generation, it is about the evaluation of potentially novel solutions. This cognitive scrutiny of generative DMN flow, is achieved through strong functional connectivity with parts of the executive control network – specifically the inferior prefrontal cortex. This connection reflects a top-down (cortical) control of bottom-up DMN processes. In other words, cognitive control mechanisms may be responsible for directing and monitoring the spontaneous activity of the DMN.
Top-down control supports divergent thinking by inhibiting unoriginal ideas and shifting attention to fresh semantic spaces and solutions. In the absence of sufficient or coordinated cognitive control, divergent thinking can become compromised – reducing our capacity to be selective and move beyond habitual patterns and solutions.
FEATURED IMAGE:
Ravinder Jerath and Molly W.Crawford. Layers of brain activity: a functional model based on the default mode network and slow oscillations (2015).