Every one needs to sleep. Many people may think that the purpose of sleep is a quiescent status with minimum level of brain activation to merely take a rest and passively remove fatigue accumulated during wakefulness. However, a growing body of evidence in neuroscience indicates that sleep plays much more active roles. One of the most important roles of sleep is to augment, or consolidate, learning and memory obtained during wakefulness. A better understanding of how sleep consolidates learning and memory would provide important knowledge of how students and adults can effectively learn and memorize. In the proposed research, we will specifically use visual perceptual learning (VPL), which refers to a long-term improvement of visual task performance by repetitive training on a particular visual task. By taking advantages of neural and behavioral characteristics of VPL and advanced non-invasive neuroimaging techniques, Dr. Sasaki and her team at Brown University will investigate detailed neural activation of the visual cortex during sleep. Investigations on how sleep functions to consolidate VPL may lead to better understanding of visual and brain plasticity (learning and memory) in human adults. Thus, the proposed activity will promote the progress of science in sleep and learning and advance the national health.
There has been a controversy whether consolidation of learning and memory during sleep occurs by reactivating what was learned or memorized during wakefulness (reactivation), or by removing unimportant information (downscaling). Based on our preliminary findings, we propose a two-process model of the sleep consolidation of VPL, in which both reactivation and downscaling occur in a serial and integrative fashion. In the first reactivation process, neural circuits only for the trained visual feature are reactivated for enhancement of learning where sigma activity is mainly involved. This reactivation process is followed by the downscaling process that occurs both with the circuits for the trained and an exposed but unlearned, therefore unimportant, feature. The validity of two-process model will be tested using psychophysics, and advanced neuroimaging techniques including concurrent measurements of polysomnography and magnetic resonance imaging, magnetic resonance spectroscopy and a decoding technique on blood-oxygen-level dependent signals as well as retinotopic mapping. Successful research results would verify the two-process model and provide invaluable information with which the quality of learning and memory will be enhanced.
