The authors regret the inclusion of an error in their article ‘Effects of a multi-strain probiotic on hippocampal structure and function, cognition, and emotional well-being in healthy individuals: a double-blind randomized-controlled trial’.

While the scientific rationale for the choice of Vivomixx® in our study remains unchanged, we acknowledge that the sentence “Albeit, to our knowledge, the European market equivalent to VSL#3 (Vivomixx®) has never been formally tested in healthy human subjects concerning effects on hippocampal structure, and (relatedly) cognitive performance and mental health, and the (antibiotically treated/ ageing) mouse/ rat models are certainly not directly transferrable to humans, there are additional arguments why testing this product in healthy human volunteers is relevant’ (p. 5) is not accurate. The studies cited in this paper using VSL#3® (Distrutti et al. 2014; Möhle et al. 2016) did contain the original De Simone formulation, which is now contained in the Vivomixx® product used in our study. However, the product presently sold as VSL#3, does not contain the original De Simone formulation anymore, which is why the assertion that ‘Vivomixx® is the European market equivalent of VSL#3®’ is incorrect. Currently, Visbiome® (USA) and Vivomixx® (Europe) contain the original de Simone formulation.