For human health, dietary fat is frequently considered an enemy. But current research is beginning to focus on the positive effects of dietary fats. Two specific dietary fats, docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), belonging to the group of omega-3 fatty acids, have been associated with prevention of cancer and cardiovascular disease and with enhancement of brain function, though research results have been inconsistent.

DHA and EPA cannot be manufactured by the human body but must be supplied through the diet, either as themselves or as α-linolenic acid (LNA), a precursor that can be converted into DHA and EPA. The conversion of LNA into DHA and EPA is a competitive process, and so substantial accumulation of DHA and EPA in body tissues is improved when DHA and EPA are obtained directly from food rather than converted from LNA.

A new study led by Norman Salem Jr. and Irina Fedorova at the National Institutes of Health (Bethesda, MD) examines more closely the effects of different formulations of dietary omega-3 fatty acids on nervous system function in mice. In the study, pregnant mice were fed one of four diets with different amounts and types of omega-3 fatty acids: omega-3-deficient, low LNA, high LNA, or DHA plus EPA. The offspring were fed the same diet as the mother mice after weaning. Researchers then evaluated the prepulse inhibition (PPI) of the acoustic startle response as a test of nervous system function in the offspring. In this test, mice are exposed to a sudden loud noise; normally, they react by flinching. If they are exposed to a softer noise first, however, normal mice flinch less. The softer noise seems to warn mice that some other stimulus may be coming next. This response is termed PPI and is part of an adaptive process called sensorimotor gating that acts to filter out distracting stimuli to prevent sensory overload and to allow selective processing of relevant information. Deficits in sensorimotor gating are characteristic of many nervous system disorders in humans, including bipolar, obsessive-compulsive and attention-deficit hyperactivity disorders.

In Salem and Fedorova's study, only mice that were raised on a diet containing DHA plus EPA had normal sensorimotor gating (Behav. Neurosci. 123, 1218–1225; 2009). Mice in the other groups, even those that were fed a relatively large amount of LNA, had deficits in sensorimotor gating. The results suggest that lack of DHA in the diet may decrease the brain's ability to manage sensory input, further raising interest in the therapeutic potential of DHA for human nervous system disorders.