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Unlabelled: Our knowledge about the influence of nutritional supplements on human cognition, especially in the elderly, rests largely on animal behavioural research and neurochemical experiments in vitro, while only a few epidemiological studies and even fewer controlled experiments in humans are reported. This is an inherent problem, due partly to the difficulty of conducting controlled nutritional experiments in humans, but may also partly be due to the gap between the research disciplines of nutritional and neurobehavioral experimental science., Learning Objectives: The aim of this paper is to discuss some new findings in this line of research, and to stress the importance of the need to start bridging the gap between disciplines by identifying possible human experimental models of altered cognitive function, which can elucidate the specific mechanisms of action through which nutritional supplements may enhance cognitive performance in humans in vivo. These experimental models are important because the research in this field is mostly based on epidemiological studies, which describe associations between nutrients and cognitive functions. Contrary to epidemiological studies, experimental models mimic associations between nutrients and cognition by manipulating their presumed mechanisms of action and can eventually explain the causal nature of found associations., (Copyright 2002 Elsevier Science Ltd. All rights reserved.)

Many nutrients or indices of nutritional status are associated with cognitive functioning, although the size of the effects on cognitive performance may be small. Results from recent studies, however, seem consistently to indicate that supplementation with beta-carotene and alpha-tocopherol, substances that promote antioxidant vitamins A and E, respectively, can be beneficial to cognitive function in elderly people. Folate rather than vitamin B12 appears to be associated with cognitive functioning. Furthermore the daily intake of ginkgo biloba extract can enhance cognitive performance and has been proved to delay cognitive decline in dementia. A proper dietary composition with regard to the ratio of carbohydrates to proteins, as well as the inclusion of sufficient micronutrients, seems to be favourable in the maintenance of cognitive function in the elderly. Glucose can enhance cognitive function, but a rapid decline of glucose levels may impair cognitive function or may induce feelings of lack of energy. Low doses of caffeine may also enhance cognitive function, although most studies on caffeine and cognition, as with studies on glucose and cognition, have not been carried out in elderly individuals. The effects of nutritional supplements are modest but do not seem to be very different from those of medicinal or investigational cognition-enhancing or anti-dementia drugs.

WJ Riedel, BL Jorissen, E Hogervorst. Nutritional manipulation and psychiatric conditions: focus on mood and cognition. In this paper, several experimental models of human depression and cognitive dysfunction, which are designed specifically to mimic the proposed mechanisms of action of many nutritional supplements, are illustrated. These mechanisms of interest are antioxidant effects, glucose utilization, neuronal membrane function and neurotransmitter effects, with particular reference to nutrient-based amino acid manipulations of neurotransmission, such as tryptophan depletion. It is concluded that the application of experimental human models of altered mood and cognitive function may illuminate substantially the quest for nutritional enhancement of human mood and cognitive function. [ABSTRACT FROM AUTHOR]

Animal and human studies have provided evidence for serotonergic modulation of cognitive processes. However, the exact nature of this relationship is not clear. We used the acute tryptophan depletion (ATD) method to investigate the effects of lowered serotonin synthesis on cognitive functions in 17 healthy young volunteers. The study was conducted according to a placebo-controlled, double-blind, crossover design. Cognitive performance and mood were assessed at baseline and 5 and 9 h after administration of ATD. A specific impairment of word recognition, without effects on short-term memory, occurred during ATD. No memory deficits were seen if ATD was induced after acquisition of new words. The Stroop Test and dichotic listening task demonstrated a modality independent improvement of focussed attention after ATD. Fluency was also improved after ATD. ATD did not alter speed of information processing, divided attention or planning functions. These results indicate that serotonin is essential in the process of long-term memory consolidation, primarily in the first 30 min after acquisition. Improvement of specific cognitive processes by lowered 5-HT function may be linked to the removal of inhibitory actions of 5-HT in the cortex. [ABSTRACT FROM AUTHOR]