In addition to its immediate consequences, hypoxia generates delayed functional and metabolic abnormalities, which can lead to cell death. Parts of the hippocampus, the dorsolateral caudate nucleus, and the reticular nucleus of the thalamus are the brain areas most vulnerable to this sort of lesion. Over time, these changes could contribute to the development of dementia or other neurological disorders. Hypoxia occurs when the body is unable to supply enough oxygen to meet the demands of the tissues. This can happen during acute events such as heart attacks or strokes, but it can also occur gradually over time without any apparent cause. Exposure to low levels of oxygen over a long period of time can damage many parts of the brain, causing memory problems, learning difficulties, depression, and anxiety. This is because certain cells in these regions need a fairly constant level of oxygen to function properly. If these cells are deprived of oxygen for an extended period of time, they will die. The brain is very sensitive to fluctuations in oxygen levels. Even when exposed to chronic hypoxia, some people develop severe symptoms while others do not. One factor that may explain why some individuals are more susceptible to oxygen deprivation than others is genetics. Some studies have shown that families with several members who suffer from Alzheimer's disease or another type of cognitive impairment have a higher rate of blood circulation problems in those family members who already have brain lesions.