I recently received this question:

I heard Seth Shostak mention in one of the “Big Picture Science” podcasts, that we are unconscious when we sleep.

I disagree. This is an altered state of consciousness.

Then.. you go further…

What about a COMA? Still not truly unconscious. People have memories after they wake up of people talking to them. They just don’t know where they come from.

What about NDE’s?

C’mon… if you were truly unconscious (regardless of scientific unmeasurability of brainwave activity) , you are still either having thoughts or remembering the thoughts before you wake up.

I contend that TRUE unconsciousness is ACTUAL death. (not clinical death – a decision made by instruments) The inability to think AT ALL in any capacity as if you had never been born.

Please discuss this? Am I wrong?

I do not believe in dualism. I trust that as I lay dying, I may have experiences that feel like fantastic dreams… but when I actually die… I am dead.

If I were unconscious while sleeping… How did my alarm clock wake me up? How did my snoring wife rouse me from non REM sleep?

Michael Goff (Aka, Evil Eye)

Thanks for the question. In short – this is wrong, or at least overly simplistic to the point of effectively being wrong. The primary problem is in dealing with consciousness as a binary state, and therefore any flicker of consciousness is not “unconscious.”

Consciousness is more of a continuum, and there are various states of consciousness. To answer what is unconscious, however, we need to first ask what does it mean to be conscious.

We don’t fully know, because we have yet to fully identify the neuroanatomical correlates to consciousness. Phenomenologically we define being conscious as being awake and aware of one’s surrounding and oneself. This is a high energy state, and requires a certain critical amount of brain function to maintain (we’re not exactly sure how much this is, but of note one hemisphere of the brain is capable of being conscious by itself, without the other half).

There are two general types of alterations in consciousness – diminished consciousness, and altered states of consciousness. These are not mutually exclusive, and often occur together.

Diminished consciousness results when brain function is impaired. The entire brain may be functionally impaired, or pieces of the brain may be damaged and prevented from contributing to consciousness. There is also the special case of brainstem function, which is necessary to maintain wakefullness. If the brainstem is sufficiently damaged, then even if the rest of the brain is completely intact, coma may result.

Impairments in consciousness occur on a spectrum from a little drowsy all the way to brain death. “Coma” describes a condition of significant impairment in consciousness, but does not define an absolute demarcation along the spectrum. People with impaired consciousness may have some retained consciousness, may be in a minimally conscious state, or may have no discernible consciousness (let’s call this latter condition “deep coma”).

In deep coma, people do not form memories, do not have any experiences, and do not display any evidence of consciousness – even far short of brain death. This state can be induced with medication, as is often done with general anesthesia. Anyone who has had full general anesthesia is aware of how complete the absence of consciousness can be – there often isn’t even the perception of the passage of any time.

Altered states of consciousness are a bit trickier to define. Generally these emerge when the manner in which the brain constructs our perceptions of reality and our conscious selves is altered. This can occur when a part of the brain that is vital to this construction is damage or suppressed, leading to out-of-body experiences, hallucinations, feeling separated from oneself or from reality.

The e-mailer brings up sleep – sleep actually represents various different stages of consciousness, which are all part of the normal functioning of the brain. There are four recognized stages of sleep, each with deeper suppression of brain function. Stage 1 is simple drowsiness, while stages 2-4 are progressively deeper. In stage 4 sleep it can be very difficult to arouse someone.

In these stages of sleep the brain is still able to respond to external stimuli, but I don’t think it is valid to argue that the brain is therefore conscious. That argument assumes that all brain function contributes to consciousness, but we know that it doesn’t. Many brain processes are subconscious. The brain can process and even respond to stimuli without conscious awareness.

Dreaming, or REM sleep, is another stage of sleep that is perhaps better understood as altered, rather than diminished, consciousness. The brain is very active in REM sleep, and we experience dreaming in which we can feel fully conscious. However, not all brain regions are contributing to dreaming consciousness the way they are in wakeful consciousness. Reality testing, for example, is not very active while dreaming, which is why our dreaming self can accept fantastical events that would not be accepted by our waking self.

Consciousness is a very interesting phenomenon and is still an area of active research and debate. We know that it results from brain function, that it takes a lot of brain function to maintain consciousness, and that the brain also does a large amount of subconscious processing. There are various forms of diminished or altered consciousness, both normal and pathological.

Although consciousness is a continuum, there are many states short of death that can be meaningfully described as “unconscious.”