Last blog post, we dove a bit into the complexity of consciousness and an introduction to various topics of consciousness research. This week we will delve a bit more into the technical side of consciousness research. How can one measure and assess consciousness, specifically in people with disorders of consciousness? How does neuroimaging play a role in the field of consciousness research? And, most importantly, how can we even begin to conceptualize consciousness from a neurological standpoint?
Neural Bases of Consciousness:
Let’s begin our discussion by defining consciousness from a neurological standpoint. Last blog post, we defined consciousness via several philosophical standpoints, which was difficult in itself due to the abstract nature of consciousness. While you may think using hard science to define consciousness would therefore be easier, it is still difficult because there is controversy over how to neurologically pinpoint consciousness. Not only is there difficulty in neurologically defining consciousness, but there is also controversy over the best ways to research
consciousness and assess awareness, as we will discuss later. One of the most famous neurological theories of consciousness is Neural Correlates of Consciousness (NCC). This concept connects scientific observations of brain activity to the conscious experiences that participants report. Thus, consciousness is a property dependent on internal, complex neural processes.
For example, EEG is commonly used to study neuroscientific properties of consciousness, which are dependent on the brain’s patterns of neuronal firing and thus its overall electrical activity. When using EEG to study NCC, the main focus lies on the patterns of whole populations, rather than individual, neurons. The goal is to link activity between synchronized neuronal firings in different brain regions (ie - “neural oscillations”) and experiences of consciousness, which was an idea originally proposed by the famous scientists Crick and Kock in 1990. However, one of the first theories about the neurochemistry of consciousness developed a bit earlier in the 1980s. Christof von der Malsburg and Wolf Singer developed the idea that the brain processing and integrating information is linked to gamma oscillations in the brain, which are one of the highest-frequency brain waves. We will discuss in the next section how this principle was later used to connect specific mental states to specific brain wave frequencies.
Other theories for the neural bases of consciousness, besides NCC, are the Global Neuronal Workspace, Information Integration Theory, Recurrent Processing Theory, and Higher Order Theory. The prior two were discussed in the last blog post. As a bit of a recap, Global Neuronal Workspace considers a mental state conscious only when the information it holds is accessible in the “global neuronal workspace” to multiple neuronal systems including perceptual, long-term memory, evaluational, motor, and attentional systems. But how can you tell that this information is actually accessible to these various systems? The answer is simple: accessible information can be used by these systems to carry out their own processing and computations, thus designating that information as conscious information (as opposed to subliminal or preconscious information). Recently, cortical structures in the brain have been proposed as being composed of “workspace neurons” that specifically link neural systems through their long-ranging reach. To recap the second theory, which was also discussed in the previous blog post, Information Integration Theory (IIT) is when one’s neuronal activities and pathways must be able to integrate external sensory information and process it on multiple levels in order to be considered conscious. Finally, the two new neural theories of consciousness I will introduce today are Recurrent Processing Theory and Higher Order Theory. Recurrent Processing Theory
defines consciousness through specific interconnected sensory systems that provide each other feedback for later processing. Recurrent processing is a stage in this series of processing in which information returns from a stage of deeper processing and back to the original sensory area for further local processing. Lastly, Higher Order Theory postulates that someone must be aware of being in a certain mental state for it to be conscious. Thus, one must maintain a higher-order of self-awareness to qualify as conscious, which in this theory is neurologically linked to the prefrontal cortex. The prefrontal cortex, located in the frontal lobe, is linked to the complex logical and personality traits that are associated with being human. However, there are other brain regions linked with higher-level cognitive processing, such as the secondary somatosensory, insular, posterior parietal, and anterior cingulate cortices, which have also become focuses in studies of consciousness using neuroimaging.