New research sheds light on the mechanisms of consciousness in the human brain
To understand consciousness in the brain, we need to understand what different ways of losing consciousness have in common.
The drive to understand consciousness, and how mind arises from matter, is an ancient philosophical conundrum, popularised by philosophers such as Aristotle and Descartes. However, as our scientific understanding of the brain mechanisms of consciousness improves, it may also lead to improved clinical care for patients with disorders of consciousness, and patients who need general anaesthesia for surgery.
Thanks to advanced brain scanning technologies such as functional Magnetic Resonance Imaging (fMRI), we know that when an individual loses consciousness as a result of general anaesthesia or brain damage, their brain becomes less connected i.e. the ability of brain regions to exchange information becomes compromised. But do all these connections matter equally for consciousness?
New research published in the journal Nature Communications and based on Gates Cambridge Scholar Andrea Luppi's MPhil thesis provides some answers to this critical question. In the study, researchers used fMRI to scan the brains of healthy volunteers while they were undergoing anaesthesia with propofol, a drug widely used during surgical procedures. The team also scanned brain injured patients who had been diagnosed as being in vegetative or minimally conscious state.
The researchers found that a set of brain regions collectively known as the brain's default mode network (DMN) are especially affected by loss of consciousness, in both patients and anaesthetised volunteers. The DMN is well known for its role in creativity, imagination and thoughts about the self, as well as acting as the human brain's autopilot. Clinically, degradation of DMN activity has also been linked to Alzheimer's disease and several psychiatric conditions, highlighting its importance for cognitive function.
In this study, the neuroscientists found that when consciousness is lost, activity of the DMN becomes less diverse, more predictable, suggesting that less information may be exchanged and integrated with the rest of the brain. Crucially, these results were observed both in patients and in anaesthetised healthy volunteers, suggesting that they are not specific to either group, but rather may represent a general aspect of loss of consciousness. "To understand consciousness in the brain, we need to understand what different ways of losing consciousness have in common," says Andrea I Luppi , the lead author of the study who is currently doing a PhD in Clinical Neurosciences.
The study is the result of an international collaboration between three research groups. The University of Cambridge's (UK) Division of Anaesthesia, headed by Professor David K Menon, has a research programme aiming to elucidate the neural basis of consciousness and cognition in health and disease, led by the study's senior author Dr Emmanuel A Stamatakis. Professor Adrian M Owen's group at The Brain and Mind Institute, the University of Western Ontario (Canada) seeks to understand the effects of brain injury in order to improve diagnosis and early detection and to find possible new treatments. Dr Lorina Naci's lab at the Institute for Neuroscience, Trinity College, Dublin (Ireland) researches how functional organisation of the brain supports human cognition and consciousness. This study highlights the importance of international collaborations to advance the neuroscience of consciousness.
*Picture credit: This image shows main regions of the default mode network (yellow) and connectivity between the regions colour-coded by structural traversing direction (xyz -> rgb). Source: Wikimedia Commons. Author: Andreashorn.