It is broadly agreed that consciousness is an emergent property of complex nervous systems. But there is no granular understanding of which circuits are implicated. There is progress here, however. Researchers have developed diagnostic indices based on EEG activity, such as multivariate classifiers8 and EEG reactivity, such as the Perturbational Complexity Index (PCI)9,10, to reliably tell whether someone is in a vegetative state or a (more reversible) minimally conscious state. There appears to be good agreement between these methods. Therapeutic neuromodulation (precisely targeted noninvasive technology like transcranial Direct Current Stimulation, or tDCS) has successfully brought minimally conscious patients back.11 Closed-loop neuromodulation is already able to act on, and sense, brain state based on feedback, though this is limited for now to epilepsy.
If deployed in line with a set of internationally validated guidelines to diagnose the presence or absence of consciousness, in future a combination of these technologies can be standardised to wake people from comas. Such guidelines could also identify areas of interest for probing the neural correlates of consciousness. Chinese Academy of Sciences researchers are looking at neural circuits associated with specific aspects of consciousness — notably self-awareness — in macaque brains.12 Manipulating these parts of the brain may help people with Alzheimer’s, or other disorders of consciousness. An understanding of the circuit basis of consciousness could also help quantify specific aspects lacking, and thereby point to the best intervention, e.g. thalamic stimulation. Such investigations and analysis may help us back into a working definition of consciousness.
Whether machines and animals have consciousness,13,14 and most recently understanding of whether organoids and other synthetic biological organisms are capable of developing a kind of consciousness remains a big scientific question.15