An interesting review paper:

Is docosahexaenoic acid, an n-3 long-chain polyunsaturated fatty acid, required
for development of normal brain function? An overview of evidence from
cognitive and behavioral tests in humans and animals
Joyce C McCann and Bruce N Ames

American Journal of Clinical Nutrition, Vol. 82, No. 2, 281-295, August 2005
http://www.ajcn.org/cgi/content/abstract/82/2/281

This review is part of a series intended for nonspecialists that will summarize
evidence relevant to the question of whether causal relations exist between
micronutrient deficiencies and brain function. Here, we focus on experiments
that used cognitive or behavioral tests as outcome measures in experimental
designs that were known to or were likely to result in altered brain
concentrations of the n-3 fatty acid docosahexaenoic acid (DHA) during the
perinatal period of "brain growth spurt." Experimental designs reviewed include
observational breastfeeding studies and randomized controlled trials in humans
and studies in rodents and nonhuman primates. This review is based on a large
number of expert reviews and commentaries and on some 50 recent studies in
humans and animals that have not yet been included in published reviews. Expert
opinion regarding the strengths and weaknesses of the major experimental
systems and uncertainties associated with interpreting results is summarized.
On the basis of our reading of this literature, we conclude that evidence from
several types of studies, particularly studies in animals, suggests that,
within the context of specific experimental designs, changes in brain
concentrations of DHA are positively associated with changes in cognitive or
behavioral performance. Additional experimental information required to
conclude that a causal association exists is discussed, as are uncertainties
associated with applying results from specific experimental designs to the
question of whether infant formula should be supplemented with DHA.

Tom Billings