We've known for quite awhile that certain Omega-3 Fatty Acids are important for the development of a puppy's brain and nervous system, but now we see that they are also important in adults as well.
Here are some excerpts from an article that I just came across :



Omega-3 fatty acids upregulate adult neurogenesis
Neuroscience Letters
March 26, 2007; 415(2): 154–158
Barbara S. Beltz, Michael F. Tlusty, Jeannie L. Benton, and David C.
Sandeman

FROM ABSTRACT:
Omega-3 fatty acids play crucial roles in the development and function of the
central nervous system.
These components, which must be obtained from dietary sources, have been
implicated in a variety of neurodevelopmental and psychiatric disorders.
The presence of omega-6 fatty acids may interfere with omega-3 fatty acid
metabolism.
The present study investigated whether changes in dietary ratios of
omega-3 : omega-6 fatty acids influence neurogenesis.
A quantitative analysis in the brain shows that short-term augmentation of
dietary omega-3 relative to omega-6 fatty acids results in significant
increases in neurogenesis.
It is proposed that the ratio of omega-3 : omega-6 fatty acids may alter
neurogenesis via modulatory influences on membrane proteins, cytokines
and/or neurotrophins.
THESE AUTHORS ALSO NOTE:
“Long chain polyunsaturated fatty acids (LC-PUFAs), which make up
20% of the brain’s dry weight, are critical for healthy brain development and
function because of their roles in membrane structure and cytokine
regulation.”
“The omega-3 fatty acids EPA (eicosapentaenoic acid, 20:5n3) and DHA
(docosahexaenoic acid, 22:6n3) are of particular importance in the nervous
system.” [these are from fish oil]
2
“Some fish and crustacean species can convert ALA into DHA and EPA,
although this mechanism does not appear to contribute significantly to DHA
and EPA levels in mammals.

DISCUSSION
Our experiments indicate that even a few weeks of dietary increase of
long chain omega-3s can increase the numbers of new neurons.
The ratio of omega-3 : omega-6 fatty acids is important because
undesirable ratios can inhibit the conversion of ALA [found in flax oil] to EPA
and DHA.
These authors believe that the observed increased neurogenesis is a
result of a favorable omega-3 : omega-6 ratio as a consequence of dietary
supplementation with omega-3s.
The increases in neuronal proliferation seen with long chain omega-3
enrichment imply that the nervous system benefits from this nutritional
enhancement.

1) Omega-3 fatty acids are incorporated into neuronal membranes, where they influence the structure of membrane proteins. Some of these membrane proteins act as transporters and receptors.
3
2) Omega-3 fatty acids alter membrane fluidity, which is important for
neurotransmitter binding. For instance, as serotonin binds better to neuronal
membranes, it stimulates neurogenesis in both vertebrate and the levels of
neuronal proliferation.
“Omega-3 fatty acids alter the rate of neurogenesis via their
contributions to the dynamic structure and function of neuronal membranes.”

3) Omega-3 fatty acids modulate cytokine levels, “which in turn regulate immune function.”



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