The phenomenon of human consciousness has captivated scientists for many years. Advances in brain imaging technologies have enabled researchers to make significant progress in uncovering the neural mechanisms that underlie conscious experience. Consciousness refers to an individual’s subjective awareness of their thoughts, feelings, and surroundings, and scientists have long been intrigued by the workings of the brain that give rise to this phenomenon.
The Dimensions of Consciousness
There are essentially three main dimensions of consciousness. The first is physiological arousal or wakefulness, the second is the ability and awareness to have conscious experiences and our feelings and thoughts, and the third is the sensory experience which deals with more abstract concepts and perceptions. Combined they form the overall state of consciousness.
Two of the most promising techniques for exploring the neural correlates of consciousness are functional magnetic resonance imaging (fMRI) and electroencephalography (EEG).
fMRI and EEG Reveal Neural Correlates
When patients are in different states of consciousness, scientists have found neural correlates that reveal a lot about human consciousness.
fMRI
fMRI uses changes in blood flow within the brain to infer changes in neural activity. This approach has been valuable in uncovering information about the neural networks involved in consciousness, including the default mode network that becomes active when the brain is in a state of rest and not engaging with the external environment.
EEG
EEG, on the other hand, measures the electrical activity of the brain through electrodes placed on the scalp. EEG offers real-time measurement of brain activity with a high level of temporal precision. It helps in studying the rapidly changing nature of conscious experience, including the timing and sequence of neural activity leading to perception.
Together, these techniques have revealed a lot about the neural mechanisms of consciousness and have paved the way for future studies to explore the neural basis of consciousness in greater detail. Scientists reveal that it’s not just one single region; a network of regions in our brain work together to create memory, thought, and attention.
A study that checked patients in REM sleep showed that by combining data from fMRI and EEG, activity within the thalamus, a deep part of the brain where information is processed, changes in coordination with activity in the default mode network, which is essentially a collection of regions within the cortex, during states of wakefulness. However, for those in non-REM sleep or those who were given anesthesia, researchers noticed a decrease in functional connectivity of the different regions of the brain. This shows how essential neural correlates are for us to be fully aware during the state of wakefulness.
What Happens When Patients Don’t Respond to Commands?
Scientists are still finding it difficult to find answers about the state of consciousness of patients who don’t respond to commands. Are they conscious and aware but can’t respond, are they conscious but detached from external stimuli, or are they completely unconscious? So, to find answers, they started studying gradients of activity in the brain rather than recording the activity in a particular region.
Dr Zirui Huang, research assistant professor at the University of Michigan Medical School Department of Anesthesiology, says that consciousness is complex, just like a Rubik’s cube. If you look at just a single surface, you may be confused by the way it is organized. You need to work on the puzzle by looking at all dimensions. He added, “We demonstrated that disruptions of human consciousness—due to pharmacological, neuropathological, or psychiatric causes—are associated with a degradation of one or more of the major cortical gradients depending on the state.”
