Background: There is renewed interest in the use of ancient herbal remedies for their potential health benefits, particularly in the psychological domain. One herb that is receiving growing attention is lemon balm (Melissa officinalis L.) which has received considerable interest for its influence on the brain. Lemon balm boasts an array of phytochemicals, including rosmarinic acid, citral, oleanolic acid, and ursolic acid, which are believed to underpin these effects on psychological well-being. Pharmacological evidence from animal and cellular work reveals that lemon balm and its components may modulate several brain signalling pathways, including GABAergic, cholinergic, and serotonergic systems. Results/Conclusions: Although further robust randomised controlled trials using lemon balm are required, existing research indicates that lemon balm holds promise as a calming agent exhibiting both anxiolytic and anti-depressant properties and can elicit cognitive and sleep-quality enhancement.

Probiotic supplements are increasingly being used to target the gut microbiome with a view to improving cognitive and psychological function via the gut-brain axis. One possible mechanism behind the effect of probiotics is through alterations to microbially-derived metabolites including short-chain fatty acids (SCFA) and neurotransmitters. However, research to date has largely been conducted in animal models or under conditions irrelevant to the human gastrointestinal tract (GIT). The aim of the current work was therefore to use anaerobic, pH controlled in vitro batch cultures to (a) assess the production of neuroactive metabolites in human faecal microbiota under conditions relevant to the human GIT, and (b) to explore how several pre-selected probiotic strains may affect bacterial composition and metabolite production. Enumeration of bacteria was assessed using fluorescence in situ hybridisation with flow cytometry, and concentrations of SCFAs and neurotransmitters were measured using gas chromatography and liquid chromatography mass spectroscopy, respectively. GABA, serotonin, tryptophan, and dopamine were successfully detected, suggesting some level of microbial derivation. The addition of Lactococcus lactis W58 and Lactobacillus rhamnosus W198 resulted in a significant increase in lactate after 8 h of fermentation, while no significant effect of probiotics on bacterial composition or neurotransmitter production was found.

Ageing, is associated with a decline in cognitive function and vulnerability to depression. Probiotic supplements have shown beneficial effects on cognition and mood in clinical populations, but the potential benefit for healthy older adults experiencing age-related decline in cognition remains unclear. The primary aim of the present work was to explore the effect of a chronic (long-term) multi-species probiotic intervention on cognition in healthy ageing adults. Secondary aims included exploring the chronic effect on mood outcomes and gut microbiota community, as well as a novel investigation into the acute effect of supplementation on cognition and mood. The study employed a randomised, placebo-controlled, cross-over trial in 30 healthy older adults to explore the acute (1 day) and chronic (8 weeks) effects of a probiotic supplement on cognitive domains of memory and executive function, alongside mood measures of stress, anxiety, depression, and cognitive reactivity to sad mood. 16s rRNA sequencing of stool samples was also performed pre- and post- chronic intervention to assess potential effects on the gut microbiota. Acute probiotic supplementation was associated with faster reaction times on cognitively demanding trials during a task of executive function [-64.91ms, CI -115.70, -14.15]. Chronic supplementation was associated with improvement in cognitive biases such as hopelessness [-0.97, CI -1.72, -0.23], rumination [-1.58, CI -2.86, -0.29] and aggression [-1.57, CI -2.63, -0.51] that contribute to reactivity to sad mood and therefore vulnerability to depression, and may improve executive function under higher cognitive demand [0.43%, CI -0.53%, 1.38%]. The current work provides novel evidence for an acute effect of probiotics on reaction times during executive function, which should be replicated in future work. Additionally, this work replicates previous findings of improved cognitive reactivity to sad mood following chronic probiotic supplementation, indicating probiotics may reduce the risk of developing depression in a healthy ageing population. This trial was registered at https://clinicaltrials.gov/study/NCT04951687.