The title question might seem like a strange one but it is vitally important if we are to interpret neuroscience correctly and if we are to understand the mind–brain relationship. In my view, the capacity for thought does not depend on consciousness. The term “consciousness” is at best meaningless and at worst an impediment to understanding the mind.
“Consciousness” is a very vague term and, ultimately, I don’t think it has any useful meaning at all, apart from other categories such as sensation, perception, imagination, reason etc. Aristotle had no distinct term for it. Nor do I think did any of the ancient or medieval philosophers. Consciousness is a modern term that seems to subsume all of the sensate powers of the soul — sensation, perception, sensus communis, imagination, memory, sensory appetite, etc.
What we usually mean when we use the term “consciousness” is arousal, which is a perceptual ability — the state of being able to perceive. Arousal does indeed have a basis in neurophysiology — it arises from activation of the reticular activating system deep in the brain. But arousal is merely increased potency for sensory perception, movement, memory, etc. We don’t actually know what arousal means with regard to intellect, as distinct from memory and from behavioral markers. I will explain that in more detail below.
Of course, when you have impaired perception and memory, you have an impaired mental state. But what does that mean for other modalities like reason, will, etc.? It’s a rather devilish and profound question: If you can’t remember reasoning, does that mean that you didn’t reason, or does it merely mean that you were simply unable to form memories while you were reasoning?
The difficulty in defining “consciousness” is well recognized in medicine. For example, I ask medical students and residents who report to me that a patient is “unconscious” to explain exactly what they mean. Do they mean “sleeping,” “not moving,” “eyes are closed,” or “not answering questions”? After all, patients who are in coma often move and even brain-dead patients usually have reflexes. If a patient is unconscious while sleeping, he may still be dreaming, in which case he is quite aware of his dream, and thus “unconscious while asleep” doesn’t really mean unaware of everything, it just means unaware of some things.
This perennial problem with defining consciousness led to the development of the Glasgow Coma Scale (GCS) several decades ago. It has become the routine way that doctors describe “consciousness.” Patients are tested for three things: motor responses to stimuli, eye opening, and verbal responses, and they are assigned a numeral score according to a rubric. Full alertness (follows commands, opens eyes spontaneously, is verbally oriented to date and place) is 15. Brain death is 3. Mental status is always described in these terms — a ‘GCS of 8 (E2M4V2)’, for example, refers to a patient who opens his eyes only to noxious stimuli, moves in a non-purposeful way, and only makes grunting sounds. The GCS score is a meaningful and reproducible metric, whereas “unconsciousness,” because of its inherent ambiguity, is meaningless.
In medicine, the use of the terms “conscious” and “unconscious” is actually dangerous, because the vague meanings associated with these terms leads to miscommunication between physicians. A patient who is initially non-verbal and moves only by reflex who over time becomes quiet and unresponsive may be described in both states as “unconscious.” But the change may be a sign of impending catastrophe, and this change is not communicated unless specific details of the patient’s mental state are described. An “unconscious” patient in one bed may be sleeping. An “unconscious” patient in the next bed may be near brain death. The diagnosis of “unconscious” for both patients doesn’t capture that difference.
When we speak of mental states, clarity and specificity are essential.
Another example will make the point even more clear. When I was a medical student, my anesthesiology professor said that the fundamental goals of good anesthesia are “analgesia and amnesia.” This shocked me: I asked him, “What about unconsciousness? Doesn’t anesthesia make patients unconscious during surgery?” He replied that “unconscious” really has no medical meaning, and inability to feel pain and amnesia for the surgery are the only real measurable effects of anesthesia. We don’t know — and can’t know — if patients are “conscious” during surgery. We only know what behavior tells us: they show no physiological signs of pain and they have no memory of the event. The science of anesthesiology has nothing corresponding to “unconscious” — it merely monitors and strives for analgesia and amnesia.
Here is a personal example: I had spinal anesthesia for ankle surgery a decade ago. I did not have general anesthesia. I was awake and speaking with the anesthesiologist throughout the operation but I felt no pain (from the spinal anesthetic) and I had no memory whatsoever of the procedure (from the sedative they gave me, which has strong amnestic effects). As far as I was concerned, it was the same as a general anesthetic — I felt nothing and remember nothing. It was the same as being unconscious, which I was not. I was wide awake and conversing with the anesthesiologist (who is a friend of mine and reassured me that I said nothing embarrassing!). Without pain or memory, I was, for his purposes, unconscious, even though I was (they tell me) awake and talking the whole time. Subjectively I couldn’t distinguish analgesia and amnesia from unconsciousness. So what does “consciousness” mean?
This has implications for our understanding of Adrian Owen’s remarkable research on persistent vegetative state. Owen took patients who had such severe brain damage that they were diagnosed as having no mental state at all — they were “vegetative” — and using MRI technology demonstrated that many of these patients are capable of quite complex thought, despite being in the deepest level of “unconsciousness” known to medicine, just one step above brain death.
There is nothing in psychology that corresponds to “unconsciousness” as a distinct state. There is unawareness of sensations, inability to form perceptions, inability to remember, etc. “Consciousness” per se is superfluous to the description of mental states, and actually obfuscates things.
I’ve also had general anesthesia myself several times, and if you ask me whether I could reason and do mathematics and think about philosophy during general anesthesia, my only honest answer is “I don’t know.” I don’t remember doing those things, but then I don’t remember talking to the anesthesiologist when I had spinal anesthesia. When you erase memory and erase behavioral response to stimulation, what basis is there for asserting extinction of the intellect?
“Consciousness is just a proxy for a spectrum of mental states, and particularly implies a state of sensory arousal, capacity for memory, and capacity to move purposefully. The difficulty with using “consciousness” in philosophy and neuroscience is that impaired new memory formation, impaired perception and impaired behavior (i.e. impaired “consciousness”) does not preclude other mental states, such as the ability to recall old memories, to think abstractly, to experience emotions, etc. The ubiquitous example of this ‘consciousness while unconscious’ is dreaming, in which very high levels of thought occur during deep sleep, which is what we would ordinarily call a state of deep unconsciousness.
When we describe mental states, we can only meaningfully use the terms that Aristotle applied to powers of the soul — we need to ask about perceptual ability (can the patient see light, or hear sound), imagination (can the patient form mental images), memory, emotions, movement, or the use of reason. These are meaningful terms, and if we are in a state in which behavior and acquisition of new memories are extinguished, we have no basis for asserting that we have no other mental states during that time. As dreaming and the remarkable capacity for high-level thought in patients in persistent vegetative state demonstrate, “unconscious” people can have very complex mental states.
“Consciousness” adds nothing to the description of mental states. It is a meaningless term that too often misleads us, and it shouldn’t be used in medicine, neuroscience, or philosophy.