Probiotics for Depressive Symptomatology and Neural Activity.

The Acute and Chronic Effects of Ecologic® Barrier on Depressive Symptoms and Neural Activation.

This study aims to investigate the acute and chronic effects of 16-week probiotic supplementation (Ecologic® Barrier) on depressive symptoms and neural activity in those with mild-to-moderate depression.

This study will use a randomised, double-blind, placebo-controlled design. A total of 76 participants will be recruited and will receive either one sachet of the probiotic (Ecologic® Barrier) or one sachet of a placebo, matched in taste, smell, appearance, and packaging. Outcomes will be measured at baseline, 24 hours, and at 16 weeks for all participants. These include measures of general mood, depressive symptoms, executive function, and neural activity. Neural activation will be measured using electroencephalography (EEG), specifically measuring the P300 event-related potential (ERP) during an n-back task. In addition to the n-back task, executive function, specifically working memory and cognitive flexibility will be tested using the task-switching task.

The main question this study aims to answer is:

• Does probiotic supplementation result in improvements in the primary outcome measure of vulnerability and sensitivity to depression, as well as secondary measures of rumination, hopelessness/suicidality, acceptance/coping, aggression, control, and risk aversion?
• Does probiotic supplementation improve accuracy and response times in executive function and working memory, measured by the Task Switching Task (TST) and n-back task?
• Is probiotic supplementation associated with an increased P300 amplitude and shorter P300 latency compared to baseline measures during the n-back task, in parietal and frontal lobe regions, with more pronounced effects in the 2-back task?
• Is probiotic supplementation associated with changes in alpha and theta band activity and symmetry, particularly after completing a demanding working-memory task?

Inclusion Criteria:

• Mild to moderate depression symptoms (BDI-II 12-28)
• Males and females
• Age range will be 25-40 years
• Right-handed participants only (required for EEG)

Exclusion Criteria:

• Taking antidepressants (up to 2 months prior to inclusion)
• Undergoing psychological treatment in the form of counselling, therapy or similar (up to 1 month prior to inclusion)
• Any diagnosed chronic medical condition (e.g. diabetes) or psychiatric illness.
• Use of antibiotics or laxatives (up to 3 months prior to inclusion)
• Use of probiotics and/or prebiotics (up to 1 month prior to inclusion)
• Enrolled in any other clinical trial (up to 1 month prior to inclusion)
• Following restrictive and/or unbalanced diets
• Smoking
• Continuous use of a weight-loss medication for more than one month prior to screening
• Significant gastrointestinal conditions affecting absorption, including but not limited to: inflammatory bowel disease; total colectomy or bariatric surgery; irritable bowel disease; end-stage renal disease; active cancer or cancer treatment within the past three years