page_title: Sleep and memory
section_title: Increases in sleep spindles
hierarchical_section_title: Sleep and memory / Declarative memory / Slow wave sleep (SWS) / Increases in sleep spindles
context_page_description: The relationship between sleep and memory has been studied since at least the early 19th century. Memory, the cognitive process of storing and retrieving past experiences, learning and recognition, is a product of brain plasticity, the structural changes within synapses that create associations between stimuli. Stimuli are encoded within milliseconds; however, the long-term maintenance of memories can take additional minutes, days, or even years to fully consolidate and become a stable memory that is accessible. Therefore, the formation of a specific memory occurs rapidly, but the evolution of a memory is often an ongoing process.
  Memory processes have been shown to be stabilized and enhanced and memories better consolidated by nocturnal sleep and daytime naps. Certain sleep stages have been demonstrated as improving an individual's memory, though this is task-specific. Generally, declarative memories are believed to be enhanced by slow-wave sleep, while non-declarative memories are enhanced by rapid eye movement sleep, although there are some inconsistencies among experimental results.
context_section_description: Sleep spindles are short and intense bursts of neurons firing in sync, occurring in the thalamo-cortical networks. These peak late in the night and are defining characteristics of stage two sleep. Sleep spindles are thought to aid in information consolidation during sleep and have been shown to increase after training on a motor task.
  A study using 49 rats indicated the increase of sleep spindles during slow-wave sleep following learning. It gave evidence to the increase of spindle frequency during non-REM sleep following paired associate of motor-skill learning tasks. Using an EEG, sleep spindles were detected and shown to be present only during slow-wave sleep. Beginning with a preliminary study, rats underwent six hours of monitored sleep, after a period of learning. Results showed that during the first hour following learning, there was the most evident effect on learning-modulated sleep spindle density. However, this increase in spindle density was not dependent on the training condition. In other words, there was an increase in spindles regardless of how the rats were trained. EEG patterns showed a significant difference in the density of sleep spindles compared to the density of a control group of rats, who did not undergo any training before their sleep spindles were measured. This effect of increased spindle density only lasted for the first hour into sleep following training, and then disappeared within the second hour into sleep.
caption: A typical EEG during stage 2 sleep