Yuka Sasaki - US grants

A growing body of evidence suggests that sleep plays an important role in strengthening what is learned before sleep and making the learning persist for a long time. This is called consolidation. Although consolidation in sleep is a key function in learning, the detailed mechanism is not clear. In this project, Dr. Yuka Sasaki of the Massachusetts General Hospital aims to clarify consolidation in sleep by combining cutting-edge brain imaging technologies such as magnetic resonance imaging (MRI), electroencephalography (EEG), magnetoencephalography (MEG), and functional MRI (fMRI). Particularly, the focus of the project is on examining the mechanism for sleep consolidation of learning of a visual task (perceptual learning) that is known to be associated with changes in a highly localized region in the visual cerebral cortex. Researchers are measuring spatio-temporal activation changes in the localized region during the initial period of sleep (non-REM sleep) after training on the visual task. Brain activity with high spatial resolution is obtained using MRI along with high temporal resolution brain signals obtained with EEG and MEG. By combining these signals with both temporally and spatially high resolution, the detailed mechanisms of sleep consolidation are being clarified. How such brain activity changes during sleep is related to improvement in performance on the visual task (the amount of perceptual learning) is being examined. The results from this project will contribute to a deeper understanding of the mechanism of sleep consolidation of perceptual learning.

This project provides rare opportunities of training and educating undergraduate and graduate students. Students learn cutting-edge neuroimaging techniques, such as the use of multimodal combinations of EEG/MEG/MRI, as well as functional MRI technique applied to retinotopic mapping. They also learn the theoretical backgrounds of the techniques. In addition, students learn how to analyze behavioral data through psychophysical experiments. Moreover, understanding of the consolidation process of memory and learning during sleep can help to improve education, by informing us how what is learned can be more efficiently and firmly memorized. In addition, therapeutic methods can be developed to eliminate or weaken bad and undesirable memory and learned habits, including traumatic memories, smoking, and obsessive behaviors.

DESCRIPTION (provided by applicant): A growing body of evidence suggests that sleep facilitates and is beneficial to perceptual learning. However, the underlying mechanism of this facilitatory action is largely unknown. There are two possible types of processing during sleep that may account for the facilitatory action: use-dependent processing and learning- consolidation processing. The use-dependent processing occurs during sleep in the brain mechanisms that are generally used during wakefulness prior to sleep. This processing leads to general changes of neural processing and does not occur specifically for the sake of learning. On the other hand, the learning- consolidation processing works specifically for learning. It is highly controversial concerning whether the use- dependent processing is sufficient for the facilitatory action or whether learning-consolidation processing is necessary for the facilitatory action. It is fundamentally important to know which type of processing occurs during sleep to clarify the mechanism of sleep facilitating perceptual learning, since it has not been directly tested which model is valid. We address this question in the present proposal. Sleep consists of different dynamics, such as those reflected by a multitude of frequency bands in spontaneous brain oscillations in each rapid eye movement (REM) and non-REM (NREM) sleep. This raises the possibility that only one type of processing does not necessarily occur consistently throughout the whole sleep period: the learning-consolidation processing might occur for some frequency bands in some cortical areas, while use-dependent processing might occur for others. Thus, we will systematically examine whether learning-consolidation processing or use-dependent processing occurs in each band in each REM and NREM sleep, and in different brain area(s). To test whether the learning-consolidation processing is necessary for facilitating perceptual learning during sleep, we will compare the spatio-temporal brain activation patterns during sleep that follows task performance that causes learning (learning paradigm) with those during sleep that follows task performance that does not cause learning (interference paradigm). For this purpose, we must obtain highly localized spatio- temporal information about brain activation during sleep;we will use a cutting-edge neuroimaging technique that combines fine temporal information from magnetoencephalography (MEG) and electroencephalography (EEG) with fine spatial information from magnetic resonance imaging (MRI) as well as individual retinotopic mapping in the early visual areas, to estimate the power and phase information of spontaneous oscillatory activities in the precisely localized cortical regions. Imaging will be conducted with concurrent polysomnography measurement to objectively identify sleep stages. Successful research results would provide significant knowledge to clarify how improvement of perceptual learning of a visual task and visual plasticity occurs during sleep after training of the task. PUBLIC HEALTH RELEVANCE: The primary goal of the proposed research is to investigate how learning is strengthened during sleep in young adults using advanced neuroimaging techniques. Successful research results may be used to improve our vision and enhance our learning ability.