Forgetting is the apparent loss of previously learned information from long-term memory over time. There are several theories for why forgetting occurs, including trace decay theory which states that memory traces fade without use over long periods, and interference theory which suggests that new learning can inhibit recall of older memories. Causes of forgetting include faulty memory processes, lack of motivation, physical damage, and genetic factors. Techniques to improve memorization include repeated recitation, overlearning, spaced practice, the use of mnemonics, organization, selection, review and sleep.