if they just want to improve reaction time, they could simply do meth like more normal people instead of squandering nonrenewable, industrially critical helium on wanking off to yudkovsky

argon is heavier than nitrogen, meaning that narcotic effect would be even stronger. if you go down periodic table, xenon is almost potent enough to be used on its own as anesthetic

how this all actually works is one of bigger open problems in medicine, but i'm pretty sure that simplified hypothesis of lipid solubility, recalled by some orange posters is mostly wrong. my guess is that because 1. chiral anesthetics exist and have different potencies while having exactly the same physical properties, 2. there are compounds that look like anesthetics, but have opposite activity, and 3. this very neat paper ~~that i can't find right now~~ https://www.jneurosci.org/content/jneuro/21/6/RC136.full.pdf where authors identified pocket on membrane side ( = greasy) of GABA receptor that when filled just the right way with anesthetic will open this channel, meaning narcosis if you put enough of it. they found it through directed mutagenesis study ie when that pocket was artificially filled with bigger aminoacid side chains no change was observed. we know that similar effects appear in other channels, for example NMDA