Do probiotics improve cognition? Here's what research reveals
Key Takeaways
Cognitive dysfunction, including difficulty with memory, is a common symptom associated with major depressive disorder (MDD).
New research shows that a probiotic supplement may improve immediate recall in patients with MDD.
This research sheds light on how the gut microbiome may affect the hippocampus, which in turn governs the brain’s ability to switch from the default mode network to tasks.
For decades, the armamentarium for treating major depressive disorder (MDD) has largely consisted of two options: antidepressants and psychotherapy. Now, research indicates that a new option may be on the horizon.
Publishing in the Journal of Psychiatry and Neuroscience, an international team of researchers has shed light on the biological underpinnings of the brain-gut axis.[] Their work may have future implications for symptom management in MDD.
Cognition and MDD
MDD’s effects on cognition—specifically in the realms of concentration, decisiveness, long-term memory, and episodic memory—are sometimes overlooked. But these symptoms can be debilitating for patients.
A 2020 study published in Comprehensive Psychiatry screened 387 people, 124 of which were in a healthy control group, for quality of life stemming from cognitive dysfunction. The researchers concluded that immediate and delayed memory deficits may diminish quality of life in patients with acute MDD.[]
“Memory should be considered important cognitive treatment targets for MDD patients suffering specifically from reduced mental QOL,” researchers wrote.
Inside the study
The research team behind the Journal of Psychiatry and Neuroscience study may just help the MDD disease burden.
The study group of 43 participants is admittedly small, but the results further elucidate the complex connection between the human gut microbiome and how its composition affects cognition.
Over the course of 31 days, patients received either a probiotic supplement or a placebo in addition to their prescribed depression treatments. Researchers administered the Verbal Learning Memory Test (VLMT), Corsi Block Tapping Test, and both versions of the Trail Making Test before, after, and 4 weeks following supplementation. They also measured brain-derived neurotrophic factor levels at the same intervals and tested brain activation changes in the hippocampus during working memory before and immediately after intervention.
When comparing baseline VLMT results with results obtained after the intervention, immediate recall scores significantly improved for patients who received probiotics. Moreover, participants who received probiotics continued to show immediate-recall improvement 4 weeks after the intervention.
Furthermore, an FMRI investigation of participants while performing the 2-back task found improved hippocampal function in the probiotic group. Researchers documented an activation decrease in the group that received probiotics and an activation increase in the placebo group.
The other assessments didn’t reveal significant changes in cognition.
Hippocampal changes
According to lead researcher Else Schneider, PhD, the hippocampal involvement is especially interesting. In an interview with MDLinx, Dr. Schneider said that it’s assumed that the hippocampus plays a major role in MDD and cognition because it orchestrates activity in the prefrontal cortex.
“We found changes in the left hippocampus,” Dr. Schneider said.
"The patients who got the probiotics showed decreased attention, which would be good because usually there’s some hyper-activation of the hippocampus."
— Else Schneider, PhD
Dr. Schneider explained that this is a positive development—one that could benefit cognition—stemming from how the brain handles tasks.
“If you have to do a task, then you have to switch from doing nothing to doing the task. Then, in the brain, you have to switch from the default mode network to the task-specific network. And switching between these two networks is incredibly hard for depressed patients,” she said.
Dr. Schneider added that the structure responsible for this mode-switching is the hippocampus. “Our idea was that the reduced activation of the hippocampus might be a sign of more rebalanced switching activity between these two networks,” she said.
Behavioral changes
Dr. Schneider said that the behavioral changes highlighted in the study—chiefly the improvement in verbal episodic memory—are absolutely tied to the hippocampus.
“Maybe that’s the reason why we only found it in this cognitive domain,” Dr. Schneider speculated. “It supports our hypothesis that the hippocampus is the main structure that benefits from probiotics, and that’s why we only see improvement in the episodic memory and not in other cognitive domains, which are less hippocampus dependent.”
Due to the heterogeneity of results on studies evaluating microbiota and cognition, Dr. Schneider hypothesized that there may very well be a link between microbiota, cognition, and diseases such as Alzheimer's, as well.
Future research
Dr. Schneider’s research raises additional questions. How might the microbiome affect other diseases and disorders that hinge on hippocampal involvement?
The future, Dr. Schneider said, may be in transdiagnostic studies that compare the microbiome of patients with depression and Alzheimer's, for example.
This type of research could identify whether the diseases have a common bacterial origin, since we now know that the microbiome is responsible for cognitive as well as affective symptoms in memory and depression.
There’s also the question of which specific strains in the probiotic supplement were responsible for the improvements in cognition. In the study, patients consumed an 8-strain, over-the-counter probiotic supplement called Vivomixx in Europe and Visbiome in the US.
This was intentional, Dr. Schneider said, and her explanation may please mental health professionals:
“It’s easily accessible and you can buy it in drug stores, so it’s easy to implement in a clinical routine or in your daily routine.”
But, in this case, convenience comes at the expense of certainty. Which of the 8 strains (or what combination) was responsible for the cognitive improvements? And what are the possible synergies between the patients’ conventional therapies?
Hopefully time, and future research, will tell.
What this means for you
This small study suggests that patients with MDD who are experiencing difficulties with cognition may benefit from Visbiome, an over-the-counter probiotic supplement. Specifically, the supplement may improve patients’ immediate recall ability, and this improvement may be linked to improvements to the hippocampus’ ability to switch from the default mode network to task-oriented operations.