Magazine article Psychology Today

A Bug in the System

Magazine article Psychology Today

A Bug in the System

Article excerpt

IT'S BECOMING an axiom of medicine: "You can't have a healthy mind without a healthy gut," as Timothy G. Dinan, one of the world's foremost researchers on the microbiome puts it. Actually, you can't have a healthy anything without a healthy gut. In many ways still not fully understood, the gut influences the integrity of the immune system, metabolism, cardiovascular function, to name just a few systems.

As for the mind, maintain the best troops among the vast army of bacteria in the gut and you can resist stress and related disorders such as depression and anxiety, says Dinan, of Ireland's University College Cork. The body's response to stress intrinsically involves the gut microbiome. Hormones released by the brain's hypothalmicpituitary-adrenal axis in response to the perception of threat prepare the body to meet a challenge or flee from it. An array of changes occurs quickly, including the way the gut functions. One result, Dinan finds, is an alteration in the diversity of the gut bacteria.

In addition to influencing daily functioning, there is also growing evidence that there are particular "windows" during development of the nervous system when its very threshold of responsiveness is set by the diversity ofbacteria that make up the microbiome. Those periods-pre- and perinatal development and again at adolescence-may be especially critical in creating susceptibility to or resilience to stress throughout the lifetime.

The microbiome not only seems to set the level of stress susceptibility, it also plays a role in learning, researchers find. Specific strains of gut bacteria influence fear learning and extinction, processes dependent on the amygdala and central to anxiety conditions such as PTSD. The research raises the possibility of engineering stress resistance, especially in soldiers, through a probiotic-rich diet.

When Dinan and colleagues supplied the probiotic Bifidobacterium longum 1714 to 22 healthy male volunteers for a month and subjected them to a specific challenge, they found reduced levels of stress measured psy- chologically and physiologically. The researchers recorded improvements in visuospatial memory as well as a blunted hormonal response to stress.

The bacterial composition of the microbiome may also be responsible for much of the ebb and flow of symptoms in such psychiatric conditions as bipolar disorder and schizophrenia. Researchers at Johns Hopkins, for example, have found a more than fivefold increase in manic episodes among psychiatric patients taking antibiotics.

There is a direct channel of communication between the gut and the brain via the vagus nerve, and gut bacteria produce specific neural signaling molecules by which messages are transmitted to the brain, influencing mood and cognition. …

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