Loss of less than half a night\'s sleep can impair memory and alter the normal behavior of brain cells, U.S. researchers say. A series of studies presented at Neuroscience 2012, the annual meeting of the Society for Neuroscience, in New Orleans, highlighted the important role sleep plays. One-in-5 U.S. adults show signs of chronic sleep deprivation, making the condition a widespread public health problem related to health issues such as obesity, cardiovascular problems and memory problems. Other studies presented included: -- Sleepiness disrupts the coordinated activity of an important network of brain regions; the impaired function of this network is also implicated in Alzheimer\'s disease. -- Sleeplessness plays havoc with communication between the hippocampus, which is vital for memory and the brain\'s \"default mode network.\" -- In a mouse model, fearful memories could be intentionally weakened during sleep, indicating new possibilities for treatment of post-traumatic stress disorder. \"As these research findings show, we cannot underestimate the importance of a good night\'s sleep,\" Dr. Clifford Saper of the Harvard Medical School and an expert on sleep and its deprivation, said in a statement. \"Brain imaging and behavioral studies are illuminating the brain pathways that are blocked or contorted by sleep deprivation, and the risks this poses to learning, memory and mental health.\"