Role of probiotics as memory enhancer

Sir,

The health benefits gained from the ingestion of probiotics have been widely reported in the scientific literature. However, definitive mechanism(s) have yet to be identified for the ability of orally administered bacteria to modulate a number of biological processes ranging from the production of inflammatory cytokines by immune cells within the gastrointestinal tract to the adhesion of pathogenic bacteria to the mucosal gut wall. Whereas multiple mechanisms may be operative in these situations, an alternative hypothesis described is that there may be a shared mechanism that essentially links the neural and immune responses to probiotic administration that leads to the claimed prophylactic effects.[1]

The idea that probiotic bacteria administered to the intestine could influence the brain seemed almost unbelievable.[2] One of the researches demonstrated the ability of probiotics to influence psychological states imply that the mechanism(s) by which probiotics influence the host may extend beyond those, which address their well-recognized ability to influence immune-related pathways. For example, administration of the probiotic Bifidobacterium infantis to rats subjected to a forced swim test resulted in neurochemical alterations in addition to attenuation of pro-inflammatory responses that suggested a potential antidepressant capability for the administered probiotic. In human volunteers, as well as in a rat model, administration of a probiotic formulation consisting of Lactobacillus helveticus R0052 and Bifidobacterium longum R0175A significantly attenuated psychological distress and reduced anxiety-like behavior, respectively.[3] This ability of a probiotic to function as an anxiolytic may have profound clinical applications given the well-documented occurrence of psychosocial abnormalities that accompany a number of gastrointestinal disorders such as those associated with chronic intestinal inflammation.

In Mark Lyte's hypothesis paper, such a concept is supported by studies showing that microbes can produce, and respond to, neurochemicals. These compounds can induce neurological and immunological effects in the host. The immunomodulatory effects of probiotics have been well-documented, but so far not linked specifically with neurological outcomes.[1]

The researchers, from the University of Toronto, Massachusetts Institute of Technology, and University of Calgary, found that the mice did not display behavioral abnormalities while infected or even after the infection cleared. However, when exposed to stress, they displayed memory dysfunction. When the infected mice were given daily probiotics prior to, and during, infection, memory was not impaired.[4] They concluded that “probiotics could provide benefit in relation to behavioral abnormalities in patients with irritable bowel syndrome.”[4]

Many Irritable Bowel Syndrome (IBS) patients report difficulty with memory, often attributing it to the pain they suffer during flare-ups. This study suggests that probiotics are not only helpful in preserving memory during bouts with intestinal infection, but necessary, proven by the deficits exhibited by the mice with completely sterile systems. It also suggests that rather than remedies for memory problems, such as Omega 3, which addresses brain health, a regular diet that includes probiotics may prove to be more effective.[4]

To date, there is evidence showing anti-inflammatory effects of lactobacilli in the gut, but less strong evidence that they or bifido bacteria confer immunomodulatory effects in inflammatory bowel disease patients that induce clinically significant amelioration of the disease. This does not rule out strains being identified with this benefit in the future, or being used to induce neurological effects (against pain, depression) in conjunction with immunomodulatory drugs that target the site of inflammation.

Studies on clinical populations, such as the chronic fatigue syndrome, and fibromyalgia, where lower levels of bifidobacterium and higher levels of lactic acid bacteria have been reported, have found evidence to suggest that poorer gut health is correlated with more severe neurological and cognitive deficits such as nervousness, memory loss, forgetfulness, and confusion. There have been few studies to directly assess the effects of probiotics on cognition. A study by Benton et al.,[5] has been one of the few chronic intervention studies to directly investigate the effects of probiotics on cognition. However, the effects on cognition were not in the direction that might have been expected. At day 20 of the intervention, individuals in the probiotic group were found to perform significantly worse on a test of semantic memory in comparison with placebo.[5] However, considering the scarcity of other studies to investigate the cognitive effects associated with probiotics, further research is required to corroborate these findings.

Microbial endocrinology-based hypothesis thus can guide the selection of probiotics based on a matching of the specific probiotic organism's capacity to produce a particular neurochemical and the physiological or behavioral condition that is responsive to that neurochemical. Thus probiotic treatment could be tailored to treat the pathology and/or symptomology associated with specific disease or psychological states.