Different but complementary roles of NREM and REM sleep in facilitation of visual perceptual learning associated with neurotransmitters changes revealed by magnetic resonance spectroscopy.

While sleep is known to be beneficial to visual perceptual learning (VPL), the roles of NREM and REM sleep in facilitating VPL remain unclear (Sasaki, Nanez and Watanabe, 2010). It has been demonstrated that NREM sleep plays a role in performance enhancement, while REM sleep makes VPL more resilient to retrograde interference caused by training of a new and different task (Tamaki, Berard, Watanabe and Sasaki, 2018). These results suggest that plasticity of VPL increases for performance enhancement during NREM sleep, while it decreases for stabilization during REM sleep. To test this hypothesis, for the first time using magnetic resonance spectroscopy we measured the concentrations of excitatory (glutamate) and inhibitory (GABA) neurotransmitters in the early visual area (EVA), during NREM sleep and REM sleep. We previously found that the E/I ratio, the ratio of the concentrations of glutamate to GABA in EVA, represents the amount of plasticity of VPL. Thus, in the current experiment, we measured E/I ratios during NREM and REM sleep between two trainings on the texture discrimination tasks (TDT) with orthogonal background elements. Successive trainings on these stimuli are known to cause retrograde interference. The results replicated previous finding that performance on TDT trained before sleep increased without retrograde interference by new training after NREM and REM sleep. Importantly, the E/I ratio significantly increased during NREM sleep while it decreased during REM sleep. Furthermore, the E/I ratio during NREM sleep was correlated with performance enhancement over sleep (r=0.80), while the lower the E/I ratio during REM sleep, the more resilient to retrograde interference (r=−0.62). These results show that NREM sleep increases plasticity to enhance VPL, while REM sleep decreases plasticity to stabilize once enhanced VPL during NREM sleep. In conclusion, NREM and REM sleep play complementary roles for VPL, which are reflected by significantly different E/I ratios.