A systematic review of the effects of low-frequency repetitive transcranial magnetic stimulation on cognition.

Claudia Lage,Derek K Tracy,Katherine Wiles,Sukhwinder S Shergill

doi:10.1007/s00702-016-1592-8

Abstract

rTMS is increasingly used for a variety of neuropsychiatric conditions. There are data to support ‘fast’ rTMS (≥10 Hz) having some positive effects on cognitive functioning, but a dearth of research looking at any such effects of ‘slow’ rTMS. This question is important as cognitive dysfunction accompanies many neuropsychiatric conditions and neuromodulation that potentially enhances or hinders such functioning has important clinical consequences. To determine cognitive effects of slow (≤1 Hz) rTMS, a systematic review of randomized control trials assayed cognition in neurological, psychiatric, and healthy volunteer ≤1 Hz rTMS paradigms. Both active (fast rTMS) and placebo comparators were included. 497 Records were initially obtained; 20 met inclusion criteria for evaluation. Four major categories emerged: mood disorders; psychotic disorders; cerebrovascular accidents; and ‘other’ (PTSD, OCD, epilepsy, anxiety, and tinnitus). Cognitive effects were measured across several domains: attention, executive functioning, learning, and psychomotor speed. Variability of study paradigms and reporting precluded meta-analytical analysis. No statistically significant improvement or deterioration was consistently found in any cognitive domain or illness category. These data support the overall safety of rTMS in not adversely affecting cognitive functioning. There are some data indicating that rTMS might have cognitive enhancing potential, but these are too limited at this time to make any firm conclusions, and the literature is marked by considerable heterogeneity in study parameters that hinder interpretation. Greater consensus is required in future studies in cognitive markers, and particularly in reporting of protocols. Future work should evaluate the effects of rTMS on cognitive training.

Highlights

Transcranial magnetic stimulation (TMS) is a non-invasive cortical modulating tool, where a fluctuating magnetic field induces an electrical current that depolarises underlying neurons (Wassermann et al 2008)
There are data to support ‘fast’ Repetitive TMS (rTMS) (C10 Hz) having some positive effects on cognitive functioning, but a dearth of research looking at any such effects of ‘slow’ rTMS
Repetitive TMS can be applied as either low (B1 Hz) or high (C5 Hz) frequency; the former considered typically inhibitory to underlying neurons, the latter excitatory (Pell et al 2011)

Summary

Introduction

Transcranial magnetic stimulation (TMS) is a non-invasive cortical modulating tool, where a fluctuating magnetic field induces an electrical current that depolarises underlying neurons (Wassermann et al 2008). RTMS alters synaptic plasticity through long-term potentiation (LTP) and long-term depression (LTD) changes (Hoogendam et al 2010); the underlying mechanisms of these effects are not fully understood (Pell et al 2011; Ridding and Rothwell 2007). Rodent studies demonstrate that rTMS increases the expression of genes important for synaptic plasticity, such as c-Fos (Aydin-Abidin et al 2008; Doi et al 2001), but at present, data on rTMS-induced intracellular changes in gene expression, protein synthesis, or other alterations to secondary messenger signalling are largely understudied (Hulme et al 2013). The literature is overall marked by often conflicting results between trials and considerable methodological concerns about study size and the lack of consensus on optimal rTMS technique parameters (Tracy and David 2015)

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