Subanesthetic concentration of nitrous oxide and human memory

• 1.

  1. Subanesthetic concentrations of nitrous oxide are used for analgesia and are occasionally abused. The effects of 30% nitrous oxide on human learning and memory, facility for solving mathematical problems and subjective feelings were investigated.

• 2.

  2. There were 40 normal volunteers; two drugs; 30% nitrous oxide in oxygen (N) and 100% oxygen (P, placebo); and two experimental sessions. Subjects were divided into four groups according to the drug which they inhaled in the two sessions: PP, PN, NP and NN.

• 3.

  3. “N” produced a marked decrease in learning; mean number of words recalled was 22.9 vs. 50.2 for “P” (P < .001).

• 4.

  4. On the digit span test, the percent correct under “N” was 63.0 vs. 76.8 under “P” (p< .01), indicating an impairment of short-term memory. “N” also reduced the number of mathematical problems attempted; mean number was 39.0 vs. 52.8 for “P” (p < .002) and reduced the accuracy: 75.5% for “N” vs. 94.8% for “P” (p < .001).

• 5.

  5. Computation of the difference scores between the number of words learned in Session I and the number recalled in Session II indicated impairment of retrieval under “N”. There was no evidence of state-dependent learning.