There is a great deal of overlap between neural plasticity and development; both areas are concerned with the mechanisms by which the nervous system changes. In neural plasticity, researchers examine responses to internal and external factors such as transgenic genes, hormones, learning and memory, sensory deprivation, circadian cues, trauma, stroke, and degenerative diseases such as Alzheimer's disease and Parkinson's disease. In neural development, researchers examine the mechanisms by which the nervous system develops, and the relationship between genes and environmental cues in shaping the nervous system.