But Dr Seeley thinks an important part of the answer has now been found, for in Alzheimer's and four similar but rarer dementias the pattern of spread seems to match the networks of co-ordinated metabolism described by Dr Raichle.
Previously, Alzheimer's could be distinguished with certainty from other dementias only by post-mortem examination.
He argues that "benign senescent forgetfulness"—as opposed to severe dementias such as Alzheimer's is in part a result of deterioration in the production of activator CREB.
And they might come to understand dementias, such as Alzheimer's disease, that threaten to cripple both many elderly people and the budgets of rich countries, whose populations are ageing rapidly.
If asked why, the shamans reply that they are looking for drugs to treat the effects of Alzheimer's disease, attention-deficit disorder, strokes, and the dementias associated with Parkinson's disease and schizophrenia and that is the truth.
Conversely, it is not clear how Alzheimer's and other dementias whose physical traces can easily be seen with existing techniques actually spread through the brain.
And they might come to understand dementias, such as Alzheimer's disease, that threaten to cripple both many elderly people and the national budgets of the world's currently rich countries, whose populations are ageing rapidly.
This figure included the cost of medical care, residential care, social services, and even unpaid care from family and friends for patients with Alzheimer disease and related dementias.
Involutional melancholia and presenile dementias typically occur in late middle age, while senile and arteriosclerotic dementias are characteristic of the elderly.
Despite these problems, progress has been made in unraveling the biochemistry of mood disorders, schizophrenia, and some of the dementias.
In these dementias there is a progressive intellectual impairment that proceeds to lethargy, inactivity, and gross physical deterioration and eventually to death within a few years.
