Disorder of consciousness (DOC) encompass brain death, coma, unresponsive wakefulness syndrome (UWS) and minimally conscious state (MCS). Investigation of these disorders are clinically relevant and are an opportunity to investigate the neural correlates of consciousness. The default mode network is one of the key networks that support consciousness. A lot of studies have focused on DOCs, but alongside the growing number of studies, the number of regions involved in consciousness has soared, making it highly challenging to identify the key regions and networks.
The aim of the present study is to summarize the brain regions and connectivity impaired in patients with a DOC and to enlighten the most important ones.
We selected articles that cited regions of interest (ROIs) impaired in DOCs, grouped the data in an adjacency matrix and did some mathematical processing to identify the most important ROIs and connections.
We found that the posterior cingulate cortex (PCC), the precuneus (PCU) and the medial prefrontal cortex (mPFC) are, accordingly with many studies, key regions underlying consciousness. The anterior cingulate (ACC), the inferior parietal lobule (IPL), the temporo-parietal junction (TPJ), the thalamus and the brainstem are also relatively frequently cited regions in impairment of consciousness.
Our study shows that DOCs and consciousness cannot be simplified as an impairment of one network or few regions but is the complex integration of key regions and networks.
Because all these regions are very heterogenous and are most of the time further divided in subregions, it will be increasingly important to use a clear and precise nomenclature to help further studies.
The accuracy of diagnosis for DOCs has recently improved a lot with the use of clinical and imaging tools, but the rate of misdiagnosis is still high; cognitive motor disorders (CMD) are probably in cause. Indeed, the regions that we found are linked with language, attention, praxis, and motivation. Lesions of these areas can cause clinical conditions that lead to CMD, thus inducing misdiagnosis.
A lot of regions leading to DOCs can probably lead to CMD. Because they can be further divided, a precise description of their subregions will become increasingly important.
Finally, it is important to keep in mind that the definition of consciousness is still very unclear and has been simplified as the combination of the wakefulness and the awareness for practical needs.