Neurosurgeons can operate on brain tissue itself while a patient stays awake and talking, without the patient feeling pain in the brain. What makes this possible?
- Brain tissue itself contains no pain receptors (nociceptors)
- The brain is naturally numbed by its own high fat content
- Anesthetic applied to the scalp also numbs the brain underneath
- The brain cannot form new pain memories during surgery
Why A? And why not the others?
Correct answer: A. Brain tissue itself contains no pain receptors (nociceptors)
Awake craniotomy works because brain tissue itself, along with the skull's bony calvarium and the innermost membrane covering the brain, contains no nociceptors at all, so once a neurosurgeon is past the scalp there is nothing there capable of registering pain in the first place. The genuinely painful stages, the scalp incision, drilling through bone, and opening the outer membrane covering the brain, are all richly supplied with pain receptors and are numbed with local anesthesia and sedation; once past that boundary, the surgeon can stimulate and remove brain tissue while the patient stays awake, talking, and moving on command, which helps protect areas controlling speech and movement. It is true that the brain is unusually rich in fat, but that composition has nothing to do with pain sensation. Numbing agents applied to the scalp act only on the tissue they contact and cannot reach or protect deeper brain tissue, which needs no such protection since it has no pain receptors to block.
Source: NIH StatPearls: Anesthesia for Awake Craniotomy; BrainFacts.org (Society for Neuroscience): Why Doesn't the Brain Have Nociceptors?