Figure 4.

Mapping of systematic review outcomes by mean age of participant sample (x-axis, numbers in brackets refers to the age range) and intervention duration (y-axis) for each included study in which outcomes were categorized as effects in the desired direction (e.g., decreased anxiety, stress, or improved cognition vs. placebo), effects in the undesirable direction (e.g., increased anxiety, stress, or diminished cognitive effects vs. placebo), or no effects for pre- (A) and probiotic (B) interventions separately. Numbers in each panel refer to each specific study (indexed below), and letter subscripts refer to the categorical outcome (specified below). The key for each panel is as follows. (A). Studies using prebiotic interventions: ¹ [74],² [70], ³ [76],⁴ [58], ⁵ [77], ⁶ [78], ⁷ [64], ⁸ [62], ⁹ [79], ¹⁰ [80], ¹¹ [81], ¹² [82], ¹³ [83], ¹⁴ [68], ¹⁵ [85], ¹⁶ [86], ¹⁷ [66]. a = anxiety outcome, s = stress outcome, c = cognition outcome. (B). Studies using probiotic interventions: ¹ [55], ² [56], ³ [57], ⁴ [59], ⁵ [60], ⁶ [61], ⁷ [63], ⁸ [65], ⁹ [71], ¹⁰ [67], ¹¹ [84], ¹² [69]. a = anxiety outcome, s = stress outcome, c = cognition outcome.