It is surprisingly difficult to prove the complete absence of consciousness.
Sleep can vary in arousability from moment to moment, much like vegetative states and general anesthesia. Some mentation is often reported even when subjects are awoken from slow-wave sleep. Coma scientists have made major progress in assessing different degrees of consciousness after brain damage, showing that waking-like functions can be preserved in “behavioral coma.”
One class of behaviorally inert patients are conscious but paralyzed, a condition called “locked-in” syndrome. Some locked-in patients have been trained to use voluntary eye fixations on a computer keyboard, allowing them to spell out messages in a nearly normal way. Since any voluntary response can be used, eye fixations can be as good as finger pointing or verbal report.
Even slow-wave sleep may not be entirely unconscious. Deep sleep is characterized by massive, spatially synchronized delta waves, <2 Hz, in the cortex and thalamus. The trough of each delta wave involves widespread pausing of neuronal firing, while the peak shows a waking-style range of oscillations and neuronal firing. Even deep sleep may therefore be intermittently conscious, during the peak of the repeating delta wave.
Deep sleep is the most unconscious natural state, but some waking-like mentation has been reported by subjects awoken from deep sleep.
Physiologically, deep sleep is an active state, needed for consolidation of experiential memory traces via hippocampal-neocortical theta-gamma signaling. We do not know the full set of functions of deep sleep, but more than 200 types of gene expression are known to correlate with the sleep-waking cycle. Deep sleep therefore does not mean the absence of active, biologically important brain activities.
There are different kinds of unconscious processes.
Features of unconscious sensory processes do not apply to other unconscious brain events, like highly practiced automatisms, cerebellar and striate activities, long-term synaptic memories, parietal representation of nearby space, autonomic activities, etc. Not all unconscious brain events are alike.
GENERAL CONCLUSIONS
Contrary to popular belief, scientists have gathered a substantial body of evidence about conscious experiences and their brain basis. In the centuries since Newton’s color experiments an immense body of facts has been gathered about perceptual consciousness, using accurate report measures to compare precisely defined stimuli to each other. The study of waking consciousness, sleep and pathological impairments of consciousness has also seen significant progress.
In addition, “contrastive analysis” experiments that compare conscious events to closely matched unconscious analogues have been very productive in recent decades.
With advances in brain recording, the evidence has expanded quickly, so that a database search for “consciousness” and “conscious brain” shows many thousands of peer reviewed articles. This wealth of evidence does not necessarily mean that we “know what consciousness is,” in the sense that physicists know what “heat” means in thermodynamic theory. Inductive science seldom leaps directly to high-level theory. Rather, we work inductively, using observational definitions.
In this more modest sense, a great deal is known about conscious states and contents. Current theoretical efforts aiming to make sense of this evidence are tightly constrained.
[Excerpted from Part I – Unconscious States from Bernie Baars’ latest book “On Consciousness: Science & Subjectivity.”]
Global Workspace Theory (GWT) began with this question: “How does a serial, integrated and very limited stream of consciousness emerge from a nervous system that is mostly unconscious, distributed, parallel and of enormous capacity?”
GWT is a widely used framework for the role of conscious and unconscious experiences in the functioning of the brain, as Baars first suggested in 1983.
A set of explicit assumptions that can be tested, as many of them have been. These updated works by Bernie Baars, the recipient of the 2019 Hermann von Helmholtz Life Contribution Award by International Neural Network Society form a coherent effort to organize a large and growing body of scientific evidence about conscious brains.
