Awake brain surgery keeps coming up in lectures as evidence that the brain has no pain receptors, which sounds like a contradiction given that the brain is where pain is experienced.
If the brain generates the sensation, why does cutting it produce nothing?
Accepted Answer
Because generating a sensation and detecting a stimulus are different jobs, done by different tissue.
Pain begins at nociceptors, free nerve endings in skin, muscle, joints and viscera. The brain parenchyma has none. So there is nothing there to fire when it is cut, and no signal to interpret.
The brain is the interpreter, not the sensor. Asking why it does not hurt when cut is a bit like asking why a camera lens does not appear in its own photographs.
Worth adding that the skull, scalp, and especially the meninges are richly innervated. That is why awake craniotomy still needs local anaesthetic to open the head, and why meningitis hurts so much.
One correction to a claim that usually follows this, because it comes up every time.
People often conclude that headaches therefore cannot come from the brain, so they must be imagined or psychological. That does not follow. Headache is generated by structures that do have nociceptors: meninges, blood vessels, muscles, nerves.
The absence of receptors in the parenchyma says nothing about whether head pain is real. It only says where it starts.
It is also what makes awake mapping possible at all. The surgeon can stimulate regions and ask the patient to speak or move, locating eloquent cortex before removing anything near it.
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