A meta-analysis of NIBS studies on verbal fluency

Area of Science:

• Neuroscience
• Cognitive Science
• Neuromodulation

Background:

• Non-invasive brain stimulation (NIBS) shows potential for modulating language production circuits.
• Systematic evaluation of NIBS effects on verbal fluency (VF) magnitude and variability is needed.

Purpose of the Study:

• To quantify the effects of various NIBS techniques on VF performance.
• To examine moderators of NIBS effects, including stimulation parameters, target regions, task domains, population characteristics, and language.

Main Methods:

• Meta-analysis of 38 studies (91 comparisons) from 1,667 records.
• Extracted data on stimulation modality, target site, intensity, duration, task type, and participant demographics.
• Used Hedges' g for effect sizes and meta-regression/subgroup analyses for moderators.

Main Results:

• Overall small-to-moderate effect of NIBS on VF (g = 0.18) with significant heterogeneity.
• Greater improvements observed with stimulation over left M1, left DLPFC, and right IFG; iTBS and tACS showed strongest effects.
• Semantic VF and clinical groups showed greater responsiveness; stimulation intensity, duration, sessions, and participant age were significant moderators.

Conclusions:

• NIBS can enhance verbal fluency, particularly with optimized targeting, modality, dosage, and patient selection.
• Findings support tailored NIBS protocols for cognitive rehabilitation and highlight key variables for efficacy.
• Further longitudinal studies are required to assess the durability and functional relevance of NIBS effects.