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?
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
TREATMENT
Masking
TRIPLE
Enrollment
76
Ecologic® Barrier (1x1010 CFU/day).
Matched placebo
School of Psychology and Clinical Languages
London, United Kingdom
Leiden Index of Depression Sensitivity - Revised (LEIDS-R) vulnerability/sensitivity for depression.
A standardised measure of cognitive reactivity. This questionnaire consists of 34 items, in which participants rate on a scale from 0 to 4, how strongly they feel each statement relates to them when they feel somewhat sad.
Time frame: Baseline and 16 weeks
Leiden Index of Depression Sensitivity - Revised (LEIDS-R). The following subscales are of interest: rumination, hopelessness/suicidality, acceptance/coping, aggression, control, and risk aversion.
A standardised measure of cognitive reactivity. This questionnaire consists of 34 items, in which participants rate on a scale from 0 to 4, how strongly they feel each statement relates to them when they feel somewhat sad.
Time frame: Baseline, 24 hours, and 16 weeks
Beck Depression Inventory (BDI-II)
A robust tool consisting of 21 items used to measure the severity of depression. It focuses on symptoms experienced in the last 2 weeks, such as cognitive and affective symptoms.
Time frame: Screening, baseline, 24 hours, and 16 weeks
Mini-International Neuropsychiatric Interview (MINI)
A short diagnostic interview designed to screen for 17 psychiatric disorders and the risk of suicide.
Time frame: Baseline, 24 hours, and 16 weeks
Rumination Response Scale (RRS)
A self-report questionnaire measuring the tendency to focus on negative thinking, distressing symptoms, and their causes when people feel down, sad, or depressed.
Time frame: Baseline, 24 hours, and 16 weeks
Neural Activity
P300 event-related potential (ERP) amplitude and latency during the n-back task. Resting-state and active-state alpha and theta power oscillations. An exploratory measure of the N2 ERP may be analysed alongside the P300.
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Time frame: baseline, 24 hours, and 16 weeks
Task-switching Task
This is a measure of executive function and sustained attention. Participants will be shown a circle with 8 equally spaced radii, 2 of which form a bold bisecting line. Numbers are chosen randomly from a set of 1-4 \& 6-9 and displayed sequentially in a clockwise direction. A response of higher or lower than 5 is made for trials below the line, and a response of even or odd for numbers above the line. Accuracy and reaction time (RT) on correct trials, as well as accuracy and RT on trials where there is a 'switch cost' from stimuli moving from below to above the bold line and vice versa, are the main outcome measures.
Time frame: Baseline, 24 hours, and 16 weeks
N-back task
This is an executive function and working memory task. There are varying difficulties of this task, but this trial will use the 0-back and 2-back versions. The 0-back task involves participants being shown a sequence of letters and having to respond when the current letter matches that of the previous letter. In the 2-back task, participants will have to respond when the current letter matches the letter from two trials ago.
Time frame: baseline, 24 hours, and 16 weeks
Profile of Mood States short form (POMS-SF)
This is a condensed self-report questionnaire used to measure changes in mood, assessed across 6 sub-scales (tension-anxiety, depression-dejection, anger-hostility, vigour-activity, fatigue-inertia, and confusion-bewilderment) with 40 total items. A total mood disturbance score is provided.
Time frame: Baseline, 24 hours, and 16 weeks
Visual Analogue Scale (VAS) of Positive and Negative feelings
Visual Analogue Scale of positive/negative feelings via a daily assessment. This includes two questions asking participants to rate on a scale from 0 to 100 the extent to which they felt positive or negative feelings.
Time frame: Every day from baseline to the final 16-week time point.
Quality of Life (SF12)
The Quality of Life (SF12) is a questionnaire which asks for participants' views about their health. This information keeps track of how they feel and how well they can do their usual activities.
Time frame: Baseline, 24 hours, and 16 weeks
Gastrointestinal Symptom Rating Scale (GSRS)
This is a 15-item self-reported questionnaire assessing the severity of gastrointestinal symptoms. It uses a 7-point Likert scale, covering five symptom domains: reflux, abdominal pain, indigestion, diarrhoea, and constipation symptoms.
Time frame: Baseline, 24 hours, and 16 weeks