Patients with Alzheimer's disease experience more sleep disruption than the healthy elderly. Studies have shown that in patients with Alzheimer's disease, there is a decrease in fast spindles. It has also been reported that spindle density the night before a memory test correlate positively with accuracy on an immediate recall task.[44] A positive correlation between time spent in SWS and next day autobiographical memory recall has also been reported in Alzheimer's patients.[49]