What is the physiological difference between sleep, unconsciousness and anaesthesia?

I suppose you could start with sleep being a state from which you are rousable, whereas unconsciousness and anaesthesia are not.

The physiological differences are probably better explained by a neurologist, but the EEG (brainwave) features of sleep are different to those in anaesthesia. Sleep has different wave findings depending on your stage – REM has quite an active EEG, deep sleep less active etc.

Anaesthesia (general) is a different beast. It’s a drug-induced reversible state of reduced consciousness, pain relief and (much of the time) muscle relaxation. It is not a rousable condition – the entire point of it is to stop you from feeling/being conscious of the goings ons in the operating theatre. Depth of anaesthesia can be measured by EEG, and the findings are characteristically less active. The anaesthetic drugs we use essentially switch off the neurones in the brain; this doesn’t happen in sleep. If you give enough of an anaesthetic drug you can even induce isoelectric EEG – i.e. no activity at all.

Unconsciousness – physiology depends on the cause. If it’s a brain bleed, you’ll have different brain activity to say, a seizure lasting 40 mins. They’re both unconscious states if you’re not rousable. General anaesthesia could also be described as controlled unconsciousness.

Source: anaesthetic/ICU doctor

Yet another computer analogy, here we go.

Sleep:

windows xp shutdown sound

windows xp startup sound

Although it’s more like the hibernate mode, really.

Unconsciousness: your system has encountered an error and needed to shut down

Technically unconscious refers to any time you are not fully awake and aware iirc, but traditional “knocked out” unconsciousness is basically a BSOD.

Anesthesia: Your brain is running normally but with no programs open. No (or very little) data is being written, recorded, or saved to any form of memory.

I really want an easy to understand explanation of this too. I’ve always had the feeling that I’m really just dying when I go under anesthesia, then being rebooted, like a clone or something, when I come to.

Lets try and relate this to how you might see it with a computer.

Sleep: Is an orderly process of shutting down. Buffers are flushed and processed are stopped in an orderly and predictable manner. And becoming awake is the reverse where things start back up in a similar orderly manner.

Anesthesia: Is more like a suspend or hibernate mode. There is no gradual shutdown, you are running like normal one moment and the next you are not running (so to speak). Aside from baseline processes everything is just stopped or suspended.

Unconsciousness: This ‘normally’ happens when something goes wrong. Going into shock, having a bad reaction, getting hit in the head, etc. It’s like your computer crashing and getting a BSOD. Notable is the loss of data (like in a blackout): one moment you might be fine and the next you are laying on the floor with no memory of anything in between the two.

I probably butchered this bad but you should get the point.

Oo! I recently read an article that elucidated a bit on this subject. Basically there are two neural systems (DMN and DAT) that when in complete balance results in unconsciousness and when out of balance leads to consciousness. The article has a great Spiegami explanation:

“Imagine you and a friend want to go out to dinner but you want Chinese food and your friend wants pizza. If both of your preferences carry equal weight, nobody gets to eat. Let’s say that’s like unconsciousness. But when one of you gives in, yum: Consciousness.”