In a study conducted by P.M. Winter et al. in 1975, the anesthetic effect of air at atmospheric pressure was compared to the effect of helium-oxygen. The study aimed to evaluate the impact of nitrogen in ambient air on human performance using a divided-attention task. The results showed a significant decrease in response time when subjects breathed helium-oxygen, suggesting that nitrogen in ambient air slightly impairs human performance compared to a non-anesthetic gas like helium. It is worth noting that no narcotic effect of helium has been demonstrated at any pressure, distinguishing it from nitrogen.
https://pubmed.ncbi.nlm.nih.gov/1130736/