Neural dynamics in primate cortex during exposure to subanesthetic concentrations of nitrous oxide

Abstract

Nitrous oxide (N2O) is a hypnotic gas with antidepressant and psychedelic properties at subanesthetic con-centrations. Despite long-standing clinical use, there is insufficient understanding of its effect on neural dynamics and cortical processing, which is important for mechanistic understanding of its therapeutic effects. We administered subanesthetic (70%), inhaled N2 O and studied the dynamic changes of spiking rate, spectral content, and somatosensory information representation in primary motor cortex (M1) in two male rhesus mac-aques implanted with Utah microelectrode arrays in the hand area of M1. The average sorted multiunit spiking rate in M1 increased from 8.1 6 0.99 to 10.6 6 1.3 Hz in Monkey W (p, 0.001) and from 5.6 6 0.87 to 7.0 6 1.1 Hz in Monkey N (p = 0.003). Power spectral densities increased in beta-and gamma-band power. To evaluate somatosensory content in M1 as a surrogate of information transfer, fingers were lightly brushed and classified using a naive Bayes classifier. In both monkeys, the proportion of correctly classified fingers dropped from 0.50 6 0.06 before N2 O inhalation to 0.34 6 0.03 during N2 O inhalation (p = 0.018), although some fingers continued to be correctly classified (p = 0.005). The decrease in correct classifications corre-sponded to decreased modulation depth for the population (p = 0.005) and fewer modulated units (p = 0.046). However, the increased single-unit firing rate was not correlated with its modulation depth (R2, 0.001, p = 0.93). These data suggest that N2 O degrades information transfer, although no clear relationship was found between neuronal tuning and N2O-induced changes in firing rate.