Most people who have pulled an all-nighter are all too familiar with that 'tired and wired' feeling. Although the body is physically exhausted, the brain feels slap-happy, loopy and almost giddy. Now, neurobiologists have uncovered what produces this punch-drunk effect. In a new study, researchers induced mild, acute sleep deprivation in mice and then examined their behaviors and brain activity. Not only did dopamine release increase during the acute sleep loss period, synaptic plasticity also was enhanced -- literally rewiring the brain to maintain the bubbly mood for the next few days.