were tested using a tapping task, where they used their fingers to tap a specific sequence of numbers on a keyboard, and their performances were measured by accuracy and speed. This finger-tapping task was used to simulate learning a motor skill. The first group was tested, retested 12 hours later while awake, and finally tested another 12 hours later with sleep in between. The other group was tested, retested 12 hours later with sleep in between, and then retested 12 hours later while awake. The results showed that in both groups, there was only a slight improvement after a 12-hour wake session, but a significant increase in performance after each group slept. This study gives evidence that REM sleep is a significant factor in consolidating motor skill procedural memories, therefore sleep deprivation can impair performance on a motor learning task. This memory decrement results specifically from the loss of stage 2, REM sleep. Declarative memory has also been shown to benefit from sleep, but not in the same way as procedural memory. Declarative memories benefit from the slow-waves nREM sleep. A study was conducted where the subjects learned word pairs, and the results showed that sleep not only prevents the decay of memory, but also actively fixates declarative memories. Two of the groups learned word pairs, then either slept or stayed awake, and were tested again. The other two groups did the same thing, except they also learned interference pairs right before being retested to try to disrupt the previously learned word pairs. The results showed that sleep was of some help in retaining the word pair associations, while against the interference pair, sleep helped significantly. After sleep, there is increased insight. This is because sleep helps people to reanalyze their memories. The same patterns of brain activity that occur during learning have been found to occur again during sleep, only faster. One way that sleep strengthens memories is by weeding out the less successful connections between neurons in the brain. This weeding out is essential to prevent overactivity. The brain compensates for strengthening some synapses (connections) between neurons, by weakening others. The weakening process occurs mostly during sleep. This weakening during sleep allows for strengthening of other connections while we are awake. Learning is the process of strengthening connections, therefore this process could be a major explanation for the benefits that sleep has on memory. Research has shown that