The effects of REM sleep deprivation (RSD) on neurotrophic factors, specifically nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF), were assessed in 2000 by Sie et el. Neurotrophins are proteins found in the brain and periphery that aid in the survival, functioning and generation of neurons; this is an important element in the synaptic plasticity process, the underlying neurochemical foundation in forming memories.[31] Sei et al., inserted electrodes into the skulls of seven pairs of rats to measure Electroencephalogram (EEG), and inserted wire into the neck muscles of the rats to measure Electromyogram (EMG), a technique used to measure the amount of muscle activity. Half the rats experienced a six-hour REM sleep deprivation period, while the other half experienced a six-hour sleep period, containing all sleep cycles.