Assessment of neuroplasticity in late-life depression with transcranial magnetic stimulation

Age-related changes in responsiveness to non-invasive brain stimulation neuroplasticity paradigms: A systematic review with meta-analysis

OBJECTIVES

We aimed to summarise and critically appraise the available evidence for the effect of age on responsiveness to non-invasive brain stimulation (NBS) paradigms delivered to the primary motor cortex.

METHODS

Four databases (Medline, Embase, PsycINFO and Scopus) were searched from inception to February 7, 2023. Studies investigating age group comparisons and associations between age and neuroplasticity induction from NBS paradigms were included. Only studies delivering neuroplasticity paradigms to the primary motor cortex and responses measured via motor-evoked potentials (MEPs) in healthy adults were considered.

RESULTS

39 studies, encompassing 40 experiments and eight NBS paradigms were included: paired associative stimulation (PAS; n = 12), repetitive transcranial magnetic stimulation (rTMS; n = 2), intermittent theta burst stimulation (iTBS; n = 8), continuous theta burst stimulation (cTBS; n = 7), transcranial direct and alternating current stimulation ((tDCS; n = 7; tACS; n = 2)), quadripulse stimulation (QPS; n = 1) and i-wave periodic transcranial magnetic stimulation (iTMS; n = 1). Pooled findings from PAS paradigms suggested older adults have reduced post-paradigm responses, although there was considerable heterogeneity. Mixed results were observed across all other NBS paradigms and post-paradigm timepoints.

CONCLUSIONS/SIGNIFICANCE

Whilst age-dependent reduction in corticospinal excitability is possible, there is extensive inter- and intra-individual variability both within and between studies, making it difficult to draw meaningful conclusions from pooled analyses.

A new era of current and future treatment applications of transcranial magnetic stimulation

Background

Transcranial magnetic stimulation (TMS) equipment has advanced dramatically over the years thanks to considerable advancements in signal motors, coils, placement devices, and modeling, optimization, and treatment scheduling programs. In this review, a primary assessment of the impact of transcranial magnetic stimulation (TMS) on seizure course in people with and without epilepsy has been done through search in the Embase, PubMed, Scopus, and Web of Science databases. Other proposed roles of TMS in various studies has been reported. The features of TMS protocols for several potential disorders was assessed and the key TMS findings has been documented starting from 1985 until 2023.

Results

More than 500 papers were found that describe various research populations, TMS techniques, and TMS functions in 16 various medical conditions.

Conclusion

After reviewing recent updates in TMS, further researches are needed to improve the technical part of the used TMS protocols and to have definitive results not experimental one with regard to TMS usage in various psychiatric and neurological disorders.

Efficacy and tolerability of repetitive transcranial magnetic stimulation for late-life depression: A systematic review and meta-analysis

BACKGROUND

Repetitive transcranial magnetic stimulation (rTMS) is a widely available treatment for major depression, but its efficacy and tolerability are uncertain for patients with late-life depression (LLD). To assess the existing evidence of rTMS for LLD treatment, we conducted a systematic review and meta-analysis of randomized controlled trials (RCTs) according to PRISMA guidelines.

METHODS

We retrieved RCTs from four databases published between 1 January 2000 and 10 September 2021 comparing the effects of active and sham stimulation in LLD patients. We performed subgroup analyses to examine the impact of different parameters. The primary outcomes were the response and discontinuation rates of rTMS for LLD patients, representing for efficacy and tolerability, respectively. Secondary outcomes were remission and dropout rates. Discontinuation referred to patients who withdrew for any reason, while dropout referred to participants who withdrew early because of adverse events.

RESULTS

Nine articles describing 11 studies (two articles each contained two studies) met the eligibility criteria. All outcomes were analyzed using a random-effects model. The summary analysis of nine suitable RCTs revealed a cumulative response rate of 2.86 (95 % confidence interval (95 % CI), 1.87-4.37) and a remission rate of 4.02 (95 % CI, 1.83-8.81) in the active group compared to the sham group. The pooled odds ratios (ORs) for discontinuation and dropout rates were not significantly different between the two groups. In addition, some rTMS parameters were associated with better efficacy.

CONCLUSIONS

The meta-analysis suggested that rTMS is an effective, well-tolerated treatment for patients with LLD. Future efforts should enhance study methodologies to improve their efficacy and increase the homogeneity of rTMS parameters to promote comparability between studies.

Devices and Technology in Transcranial Magnetic Stimulation: A Systematic Review

The technology for transcranial magnetic stimulation (TMS) has significantly changed over the years, with important improvements in the signal generators, the coils, the positioning systems, and the software for modeling, optimization, and therapy planning. In this systematic literature review (SLR), the evolution of each component of TMS technology is presented and analyzed to assess the limitations to overcome. This SLR was carried out following the PRISMA 2020 statement. Published articles of TMS were searched for in four databases (Web of Science, PubMed, Scopus, IEEE). Conference papers and other reviews were excluded. Records were filtered using terms about TMS technology with a semi-automatic software; articles that did not present new technology developments were excluded manually. After this screening, 101 records were included, with 19 articles proposing new stimulator designs (18.8%), 46 presenting or adapting coils (45.5%), 18 proposing systems for coil placement (17.8%), and 43 implementing algorithms for coil optimization (42.6%). The articles were blindly classified by the authors to reduce the risk of bias. However, our results could have been influenced by our research interests, which would affect conclusions for applications in psychiatric and neurological diseases. Our analysis indicates that more emphasis should be placed on optimizing the current technology with a special focus on the experimental validation of models. With this review, we expect to establish the base for future TMS technological developments.

Transcranial magnetic stimulation neurophysiology of patients with major depressive disorder: a systematic review and meta-analysis

Major depressive disorder (MDD) is a mental illness with high socio-economic burden, but its pathophysiology has not been fully elucidated. Recently, the cortical excitatory and inhibitory imbalance hypothesis and neuroplasticity hypothesis have been proposed for MDD. Although several studies have examined the neurophysiological profiles in MDD using transcranial magnetic stimulation (TMS), a meta-analysis of TMS neurophysiology has not been performed. The objective of this study was to compare TMS-electromyogram (TMS-EMG) findings between patients with MDD and healthy controls (HCs). To this end, we examined whether patients with MDD have lower short-interval cortical inhibition (SICI) which reflects gamma-aminobutyric acid (GABA)A receptor-mediated activity, lower cortical silent period (CSP) which represents GABAB receptor-mediated activity, higher intracortical facilitation (ICF) which reflects glutamate N-methyl-D-aspartate receptor-mediated activity, and the lower result of paired associative stimulation (PAS) paradigm which shows the level of neuroplasticity in comparison with HC. Further, we explored the effect of clinical and demographic factors that may influence TMS neurophysiological indices. We first searched and identified research articles that conducted single- or paired-pulse TMS-EMG on patients with MDD and HC. Subsequently, we extracted the data from the included studies and meta-analyzed the data with the comprehensive meta-analysis software. Patients with MDD were associated with lower SICI, lower CSP, potentially higher ICF, and lower PAS compared with HC. Our results confirmed the proposed hypotheses, suggesting the usefulness of TMS neurophysiology as potential diagnostic markers of MDD.

An inverse relationship between cortical plasticity and cognitive inhibition in late-life depression

Executive dysfunction is a common and disabling component of late-life depression (LLD), yet its neural mechanisms remain unclear. In particular, it is not yet known how executive functioning in LLD relates to measures of cortical physiology that may change with age and illness, namely cortical inhibition/excitation and plasticity. Here, we used transcranial magnetic stimulation (TMS) to measure cortical inhibition/excitation (n = 51), and the potentiation of cortical activity following paired associative stimulation, which is thought to reflect long-term potentiation (LTP)-like cortical plasticity (n = 32). We assessed the correlation between these measures of cortical physiology and two measures of executive functioning: cognitive inhibition, assessed using the Delis-Kaplan Executive Function System Color-Word Interference ["Stroop"] Test, and cognitive flexibility, assessed using the Trail Making Test. Correlations with recall memory and processing speed were also performed to assess the specificity of any associations to executive functioning. A significant correlation was found between greater LTP-like cortical plasticity and poorer cognitive inhibition, a core executive function (rp = -0.56, p < 0.001). We did not observe significant associations between cortical inhibition/excitation and executive functioning, or between any neurophysiological measure and cognitive flexibility, memory, or processing speed. Our finding that elevated cortical plasticity is associated with diminished cognitive inhibition emphasizes the importance of balanced synaptic strengthening to healthy cognition. More specifically, our findings suggest that hyper-excitability of cortical circuits following repeated cortical activation may promote inappropriate prepotent responses in LLD. LTP-like cortical plasticity might therefore represent a neural mechanism underlying an inhibitory control cognitive endophenotype of LLD.