If a medical provider uses local anesthesia on say the nose or ears (a location near the brain), could it extend to the brain and put part of the brain to "sleep"?
Would the patient be able to stay awake or could the anesthetic render him unconscious?
If the patient is able to stay awake, would he instead lose the function of the affected region of the brain? I realize this could depend on the exact region of the brain, but just in general, is it possible?
Local anesthetics like lidocaine work by blocking voltage-gated sodium channels; these channels are the biological basis of action potentials and therefore neurotransmission. Exposure to any typical axons in sufficient dose will completely block all neurotransmission down those axons, whether in the CNS or peripherally.
Although it's common to talk of local anesthesia "putting to sleep" some body part, there's very little in common with sleep (unlike general anesthesia, which, depending on the anesthetic agent, can sometimes share some features with sleep). Brain neurons are not merely "disconnected" from each other during sleep, instead, brain networks are in a different state of function, for example with cortical neurons sharing periods of activity and quiescence that produces the "slow waves" of slow-wave sleep.
Local anesthesics "leaking" into the brain is potentially a big problem when it happens. Hamilton, 1992, discusses the specific issue of local anesthetics ending up in the brain stem during eye surgery. Since the brain stem controls important things like breathing, stopping neural activity there is an emergency situation.
That said, when done properly, local anesthesia in the head is common and generally safe. Medical personnel performing local anesthesia need to be aware of the local anatomy where they are working to avoid off-target effects.
Local anesthetics as well as regional cooling have been used in neuroscience experiments (for example see Boehnke & Rasmusson 2001), in both animal models and humans, to create "temporary lesions" in the brain and investigate function of brain region. So, yes, if used in a targeted manner, local anesthetics can be used to temporarily interfere with local brain function without necessarily causing loss of consciousness.
