Linoleic and a-linolenic acid are essential for normal cellular function, a
nd act as precursors for the synthesis of longer chained polyunsaturated fa
tty acids (PUFAs) such as arachidonic (AA), eicosapentaenoic (EPA) and doco
sahexaenoic acids (DHA), which have been shown to partake in numerous cellu
lar functions affecting membrane fluidity, membrane enzyme activities and e
icosanoid synthesis. The brain is particularly rich in PUFAs such as DHA, a
nd changes in tissue membrane composition of these PUFAs reflect that of th
e dietary source. The decline in structural and functional integrity of thi
s tissue appears to correlate with loss in membrane DHA concentrations. Ara
chidonic acid, also predominant in this tissue, is a major precursor for th
e synthesis of eicosanoids, that serve as intracellular or extracellular si
gnals. With aging comes a likely increase in reactive oxygen species and he
nce a concomitant decline in membrane PUFA concentrations, and with it, cog
nitive impairment. Neurodegenerative disorders such as Parkinson's and Alzh
eimer's disease also appear to exhibit membrane loss of PUFAs. Thus it may
be that an optimal diet with a balance of n-6 and n-3 fatty acids may help
to delay their onset or reduce the insult to brain Functions which these di
seases elicit. Published by Elsevier Science Ltd.