Diffusion MRI-guided theta burst stimulation enhances memory and functional connectivity along the inferior longitudinal fasciculus in mild cognitive impairment

Repetitive transcranial magnetic stimulation may promote the reversion of mild cognitive impairment to normal cognition

Purpose

This study aimed to investigate the potential effects of repetitive transcranial magnetic stimulation (rTMS) on the reversion of mild cognitive impairment (MCI) to normal cognitive function and to elucidate the underlying mechanisms.

Methods

The study enrolled 25 MCI participants, who underwent a 10-day of rTMS treatment and an 18-month follow-up, along with 15 healthy subjects. Participants with MCI were categorized into MCI reverters (MCI-R) and MCI maintainers (MCI-M). We assessed differences in baseline cognitive performance, functional connectivity, and changes of cognitive functions after rTMS between MCI-R and MCI-M to identify possible predictors of reversion of MCI and explore the neural modulation mechanisms.

Results

MCI-M exhibited more severe cognitive impairments across more domains, particularly in language function (p < 0.05). Functional connectivity was more severely damaged in MCI-M participants, notably within the default mode network (DMN), executive control network (ECN), and frontoparietal network (FPN). After rTMS therapy, MCI-R participants demonstrated more significantly improved immediate and delayed recall memory scores (p < 0.05). These memory function changes and baseline functional connectivity of DMN, ECN, and FPN were predictive of the reversion of MCI.

Conclusions

The efficacy of rTMS in memory function may promote the reversion of MCI to normal cognition, with the functional connectivity of DMN, ECN, and FPN playing a crucial important role. The severity of cognitive impairment and functional connectivity damage correlated with the likelihood of the reversion of MCI to normal cognition, underscoring the importance of early rTMS intervention for dementia prevention.

Quantifying and reporting the precision of transcranial magnetic stimulation targeting

The precise positioning of the transcranial magnetic stimulation (TMS) coil on a person's head is crucial for the efficacy and reliability of the delivered stimulation protocol. Sophisticated techniques have been developed to define subject-specific stimulation targets, and advancements in the use of MRI-guided neuronavigation allows for real-time monitoring of the coil location during the TMS session. However, there is a need for TMS users to objectively quantify and report the accuracy of their targeting. Here, we share our technique (open-source scripts) that extracts the location of each TMS pulse delivered in a session from an MRI-guided neuronavigation system and outputs measures of targeting precision. Such measures include the variance in coil location over the duration of a session, detection of 'off-target' pulses, and the distance error relative to the intended cortical target. Reporting these metrics in publications may aid in the replicability of methodology and reproducibility of results of TMS research and clinical treatments. Furthermore, these measures can be used in training TMS operators. We encourage others to adapt our technique to their system(s) and specific needs and to report their targeting precision.

Reproducible routes: reliably navigating the connectome to enrich personalized brain stimulation strategies

Non-invasive brain stimulation (NIBS) technologies, such as repetitive transcranial magnetic stimulation (rTMS), offer significant therapeutic potential for a growing number of neuropsychiatric conditions. Concurrent with the expansion of this field is the swift evolution of rTMS methodologies, including approaches to optimize stimulation site planning. Traditional targeting methods, foundational to early successes in the field and still widely employed today, include using scalp-based heuristics or integrating structural MRI co-registration to align the transcranial magnetic stimulation (TMS) coil with anatomical landmarks. Recent evidence, however, supports refining and personalizing stimulation sites based on the target's structural and/or functional connectivity profile. These connectomic approaches harness the network-wide neuromodulatory effects of rTMS to reach deeper brain structures while also enabling a greater degree of personalization by accounting for heterogenous network topology. In this study, we acquired baseline multimodal magnetic resonance (MRI) at two time points to evaluate the reliability and reproducibility of distinct connectome-based strategies for stimulation site planning. Specifically, we compared the intra-individual difference between the optimal stimulation sites generated at each time point for (1) functional connectivity (FC) guided targets derived from resting-state functional MRI and (2) structural connectivity (SC) guided targets derived from diffusion tensor imaging. Our findings suggest superior reproducibility of SC-guided targets. We emphasize the necessity for further research to validate these findings across diverse patient populations, thereby advancing the personalization of rTMS treatments.

Comparative efficacy of intermittent theta burst stimulation and high-frequency repetitive transcranial magnetic stimulation in amnestic mild cognitive impairment patients

Intermittent theta burst stimulation, a derivative of repetitive transcranial magnetic stimulation, has been applied to improve cognitive deficits. However, its efficacy and mechanisms in enhancing cognitive function in patients with amnestic mild cognitive impairment compared with traditional repetitive transcranial magnetic stimulation paradigms remain unclear. This study recruited 48 amnestic mild cognitive impairment patients, assigning them to intermittent theta burst stimulation, repetitive transcranial magnetic stimulation, and sham groups (5 times/wk for 4 wk). Neuropsychological assessments and functional magnetic resonance imaging data were collected pre- and post-treatment. Regarding efficacy, both angular gyrus intermittent theta burst stimulation and repetitive transcranial magnetic stimulation significantly improved general cognitive function and memory compared to the sham group, with no significant difference between the 2 treatment groups. Mechanistically, significant changes in brain activity within the temporoparietal network were observed in both the intermittent theta burst stimulation and repetitive transcranial magnetic stimulation groups, and these changes correlated with improvements in general cognitive and memory functions. Additionally, intermittent theta burst stimulation showed stronger modulation of functional connectivity between the hippocampus, parahippocampal gyrus, and temporal regions compared to repetitive transcranial magnetic stimulation. The intermittent theta burst stimulation and repetitive transcranial magnetic stimulation can improve cognitive function in amnestic mild cognitive impairment patients, but intermittent theta burst stimulation may offer higher efficiency. Intermittent theta burst stimulation and repetitive transcranial magnetic stimulation likely enhance cognitive function, especially memory function, by modulating the temporoparietal network.

Efficacy and safety of transcranial magnetic stimulation on cognition in mild cognitive impairment, Alzheimer's disease, Alzheimer's disease-related dementias, and other cognitive disorders: a systematic review and meta-analysis

OBJECTIVE

We aim to analyze the efficacy and safety of TMS on cognition in mild cognitive impairment (MCI), Alzheimer's disease (AD), AD-related dementias, and nondementia conditions with comorbid cognitive impairment.

DESIGN

Systematic review, Meta-Analysis.

SETTING

We searched MEDLINE, Embase, Cochrane database, APA PsycINFO, Web of Science, and Scopus from January 1, 2000, to February 9, 2023.

PARTICIPANTS AND INTERVENTIONS

RCTs, open-label, and case series studies reporting cognitive outcomes following TMS intervention were included.

MEASUREMENT

Cognitive and safety outcomes were measured. Cochrane Risk of Bias for RCTs and MINORS (Methodological Index for Non-Randomized Studies) criteria were used to evaluate study quality. This study was registered with PROSPERO (CRD42022326423).

RESULTS

The systematic review included 143 studies (n = 5,800 participants) worldwide, encompassing 94 RCTs, 43 open-label prospective, 3 open-label retrospective, and 3 case series. The meta-analysis included 25 RCTs in MCI and AD. Collectively, these studies provide evidence of improved global and specific cognitive measures with TMS across diagnostic groups. Only 2 studies (among 143) reported 4 adverse events of seizures: 3 were deemed TMS unrelated and another resolved with coil repositioning. Meta-analysis showed large effect sizes on global cognition (Mini-Mental State Examination (SMD = 0.80 [0.26, 1.33], p = 0.003), Montreal Cognitive Assessment (SMD = 0.85 [0.26, 1.44], p = 0.005), Alzheimer's Disease Assessment Scale-Cognitive Subscale (SMD = -0.96 [-1.32, -0.60], p < 0.001)) in MCI and AD, although with significant heterogeneity.

CONCLUSION

The reviewed studies provide favorable evidence of improved cognition with TMS across all groups with cognitive impairment. TMS was safe and well tolerated with infrequent serious adverse events.

Brain structural changes in diabetic retinopathy patients: a combined voxel-based morphometry and surface-based morphometry study

The aim of this study was to investigate alterations in gray matter structure among individuals diagnosed with diabetic retinopathy (DR). This study included a cohort of 32 diabetic patients with retinopathy (DR group, n = 32) and 38 healthy adults (HC group, n = 38). Both cohorts underwent comprehensive psychological and cognitive assessments alongside structural magnetic resonance imaging. The brain's gray matter volume and morphology were analyzed using voxel-based morphometry (VBM) and surface-based morphometry (SBM). Partial correlation analysis was employed to investigate the associations between differences in gray matter volume (GMV) across diverse brain regions and the outcomes of cognitive psychological tests as well as clinical indicators. The VBM results revealed that, in comparison to the healthy control (HC) group, patients with diabetic retinopathy (DR) exhibited reduced gray matter volume (GMV) in the right fusiform gyrus, inferior frontal gyrus, opercular part, and left hippocampus; conversely, an increase in GMV was observed in the right thalamus. The SBM results indicated cortical thinning in the left caudal anterior cingulate cortex, left superior frontal gyrus, left parahippocampal gyrus, and bilateral lingual gyrus in the DR group. Sulcal depth (SD) exhibited increased values in the bilateral rostral middle frontal gyrus, superior frontal gyrus, frontal pole, left precentral gyrus, postcentral gyrus, lateral orbitofrontal gyrus, and right paracentral gyrus. Local gyrification indices (LGIs) decreased in the left caudal middle frontal gyrus and superior frontal gyrus. The fractal dimension (FD) decreased in the posterior cingulate gyrus and isthmus of the cingulate gyrus. The left hippocampal gray matter volume (GMV) in patients with diabetic retinopathy was negatively correlated with disease duration (r = -0.478, p = 0.008) and self-rating depression scale (SAS) score (r = -0.381, p = 0.038). The structural alterations in specific brain regions of individuals with DR, which may contribute to impairments in cognition, emotion, and behavior, provide valuable insights into the neurobiological basis underlying these dysfunctions.

Effects of Priming Intermittent Theta Burst Stimulation With High-Definition tDCS on Upper Limb Function in Hemiparetic Patients With Stroke: A Randomized Controlled Study

BACKGROUND

Preconditioning with cathodal high-definition transcranial direct current stimulation (HD-tDCS) can potentiate cortical plasticity induced by intermittent theta burst stimulation (iTBS) and enhance the after-effects of iTBS in healthy people. However, it is unclear whether this multi-modal protocol can enhance upper limb function in patients with stroke.

OBJECTIVE

The aim of this study was to investigate whether priming iTBS with cathodal HD-tDCS over the ipsilesional M1 can augment upper limb motor recovery in poststroke patients.

METHODS

A total of 66 patients with subacute stroke were randomly allocated into 3 groups. Group 1 received priming iTBS with HD-tDCS (referred to as the tDCS + iTBS group), Group 2 received non-priming iTBS (the iTBS group), and Group 3 received sham stimulation applied to the ipsilesional M1. One session was performed per day, 5 days per week, for 3 consecutive weeks. In Group 1, iTBS was preceded by a 20-minute session of cathodal HD-tDCS at a 10-minute interval. The primary outcome measure was the Fugl-Meyer Assessment-Upper Extremity (FMA-UE) score. Moreover, the secondary outcome measures for muscle strength and spasticity were the Motricity Index-Upper Extremity (MI-UE) and the Modified Ashworth Scale Upper-Extremity (MAS-UE), respectively, and the Hong Kong Version of the Functional Test for the Hemiplegic Upper Extremity (FTHUE-HK) and the Modified Barthel Index (MBI) for activity and participation.

RESULTS

Significant differences were detected in the changes in FMA-UE, MI-UE, and MBI scores between the 3 groups from baseline to post-intervention (χ2FMA-UE = 10.856, P = .004; χ2MI-UE = 6.783, P = .034; χ2MBI = 9.608, P = .008). Post hoc comparisons revealed that the priming iTBS group demonstrated substantial improvements in FMA-UE (P = .004), MI-UE (P = .028), and MBI (P = 0.006) compared with those in the sham group. However, no significant difference was observed between the iTBS group and the sham group. Moreover, no significant differences were found in the changes in MAS-UE or FTHUE-HK between the groups.

CONCLUSIONS

Priming iTBS with HD-tDCS over the ipsilesional M1 cortex had beneficial effects on augmenting upper limb motor recovery and enhancing daily participation among subacute stroke patients.

EEG microstates analysis after TMS in patients with subacute stroke during the resting state

To investigate whether intermittent theta burst stimulation over the cerebellum induces changes in resting-state electroencephalography microstates in patients with subacute stroke and its correlation with cognitive and emotional function. Twenty-four stroke patients and 17 healthy controls were included in this study. Patients and healthy controls were assessed at baseline, including resting-state electroencephalography and neuropsychological scales. Fifteen patients received lateral cerebellar intermittent theta burst stimulation as well as routine rehabilitation training (intermittent theta burst stimulation-RRT group), whereas 9 patients received only conventional rehabilitation training (routine rehabilitation training group). After 2 wk, baseline data were recorded again in both groups. Stroke patients exhibited reduced parameters in microstate D and increased parameters in microstate C compared with healthy controls. However, after the administration of intermittent theta burst stimulation over the lateral cerebellum, significant alterations were observed in the majority of metrics for both microstates D and C. Lateral cerebellar intermittent theta burst stimulation combined with conventional rehabilitation has a stronger tendency to improve emotional and cognitive function in patients with subacute stroke than conventional rehabilitation. The improvement of mood and cognitive function was significantly associated with microstates C and D. We identified electroencephalography microstate spatiotemporal dynamics associated with clinical improvement following a course of intermittent theta burst stimulation therapy.

Effects of a periodic intermittent theta burst stimulation in Alzheimer's disease

BACKGROUND

Previous studies have demonstrated that excitatory repetitive transcranial magnetic stimulation (rTMS) can improve the cognitive function of patients with Alzheimer's disease (AD). Intermittent theta burst stimulation (iTBS) is a novel excitatory rTMS protocol for brain activity stimulation with the ability to induce long-term potentiation-like plasticity and represents a promising treatment for AD. However, the long-term effects of iTBS on cognitive decline and brain structure in patients with AD are unknown.

AIMS

We aimed to explore whether repeating accelerated iTBS every three months could slow down the cognitive decline in patients with AD.

METHODS

In this randomised, assessor-blinded, controlled trial, iTBS was administered to the left dorsolateral prefrontal cortex (DLPFC) of 42 patients with AD for 14 days every 13 weeks. Measurements included the Montreal Cognitive Assessment (MoCA), a comprehensive neuropsychological battery, and the grey matter volume (GMV) of the hippocampus. Patients were evaluated at baseline and after follow-up. The longitudinal pipeline of the Computational Anatomy Toolbox for SPM was used to detect significant treatment-related changes over time.

RESULTS

The iTBS group maintained MoCA scores relative to the control group (t=3.26, p=0.013) and reduced hippocampal atrophy, which was significantly correlated with global degeneration scale changes. The baseline Mini-Mental State Examination (MMSE) score, apolipoprotein E genotype and Clinical Dementia Rating were indicative of MoCA scores at follow-up. Moreover, the GMV of the left (t=0.08, p=0.996) and right (t=0.19, p=0.977) hippocampus were maintained in the active group but significantly declined in the control group (left: t=4.13, p<0.001; right: t=5.31, p<0.001). GMV change in the left (r=0.35, p=0.023) and right (r=0.36, p=0.021) hippocampus across the intervention positively correlated with MoCA changes; left hippocampal GMV change was negatively correlated with global degeneration scale (r=-0.32, p=0.041) changes.

CONCLUSIONS

DLPFC-iTBS may be a feasible and easy-to-implement non-pharmacological intervention to slow down the progressive decline of overall cognition and quality of life in patients with AD, providing a new AD treatment option.

TRIAL REGISTRATION NUMBER

NCT04754152.

In-vivoverified anatomically aware deep learning for real-time electric field simulation

Objective.Transcranial magnetic stimulation (TMS) has emerged as a prominent non-invasive technique for modulating brain function and treating mental disorders. By generating a high-precision magnetically evoked electric field (E-field) using a TMS coil, it enables targeted stimulation of specific brain regions. However, current computational methods employed for E-field simulations necessitate extensive preprocessing and simulation time, limiting their fast applications in the determining the optimal coil placement.Approach.We present an attentional deep learning network to simulate E-fields. This network takes individual magnetic resonance images and coil configurations as inputs, firstly transforming the images into explicit brain tissues and subsequently generating the local E-field distribution near the target brain region. Main results. Relative to the previous deep-learning simulation method, the presented method reduced the mean relative error in simulated E-field strength of gray matter by 21.1%, and increased the correlation between regional E-field strengths and corresponding electrophysiological responses by 35.0% when applied into another dataset.In-vivoTMS experiments further revealed that the optimal coil placements derived from presented method exhibit comparable stimulation performance on motor evoked potentials to those obtained using computational methods. The simplified preprocessing and increased simulation efficiency result in a significant reduction in the overall time cost of traditional TMS coil placement optimization, from several hours to mere minutes.Significance.The precision and efficiency of presented simulation method hold promise for its application in determining individualized coil placements in clinical practice, paving the way for personalized TMS treatments.

Optogenetic Stimulation of CA1 Pyramidal Neurons at Theta Enhances Recognition Memory in Brain Injured Animals

Abstract The hippocampus plays a prominent role in learning and memory formation. The functional integrity of this structure is often compromised after traumatic brain injury (TBI), resulting in lasting cognitive dysfunction. The activity of hippocampal neurons, particularly place cells, is coordinated by local theta oscillations. Previous studies aimed at examining hippocampal theta oscillations after experimental TBI have reported disparate findings. Using a diffuse brain injury model, the lateral fluid percussion injury (FPI; 2.0 atm), we report a significant reduction in hippocampal theta power that persists for at least three weeks after injury. We questioned whether the behavioral deficit associated with this reduction of theta power can be overcome by optogenetically stimulating CA1 neurons at theta in brain injured rats. Our results show that memory impairments in brain injured animals could be reversed by optogenetically stimulating CA1 pyramidal neurons expressing channelrhodopsin (ChR2) during learning. In contrast, injured animals receiving a control virus (lacking ChR2) did not benefit from optostimulation. These results suggest that direct stimulation of CA1 pyramidal neurons at theta may be a viable option for enhancing memory after TBI.

Brain Structural Correlates of Obstacle Negotiation in Mild Cognitive Impairment: Results from the Gait and Brain Study

INTRODUCTION

Mild cognitive impairment (MCI) affects obstacle negotiation capabilities, potentially increasing the risk of falls in older adults. However, it is unclear whether smaller brain volumes typically observed in older individuals with MCI are related to the observed hazardous obstacle negotiation in this population.

METHODS

A total of 93 participants (71.9 ± 5.36 years of age; MCI = 53/control = 40) from the Gait and Brain Study were analyzed. Gray matter (GM) volumes from the frontal, temporal, and parietal lobes were entered in the analysis. Gait performance was recorded using a 6-m electronic walkway during two cognitive load conditions while approaching and stepping over an obstacle: (1) single-task and (2) while counting backwards by 1s from 100 (dual-task). Anticipatory adjustments in gait performance to cross an "ad hoc" obstacle were electronically measured during pre-crossing phases: early (3 steps before the late phase) and late (3 steps before obstacle). Association between the percentage of change in average gait speed and step length from early to late (i.e., anticipatory adjustments) and GM volumes was investigated using multivariate models adjusted for potential confounders.

RESULTS

Anticipatory adjustments in gait speed (Wilks' lambda: 0.35; Eta2: 0.64; p = 0.01) and step length (Wilks' lambda: 0.33; Eta2: 0.66; p = 0.01) during dual-task conditions were globally associated with GM volumes in MCI. Individuals with MCI with smaller GM volumes in the left inferior frontal gyrus, left hippocampus, right hippocampus, and right entorhinal cortex made significantly fewer anticipatory gait adjustments prior to crossing the obstacle.

CONCLUSION

Frontotemporal atrophy may affect obstacle negotiation capabilities potentially increasing the risk of falls in MCI.

Intermittent theta burst transcranial magnetic stimulation induces hippocampal mossy fibre plasticity in male but not female mice

Transcranial magnetic stimulation (TMS) induces electric fields that depolarise or hyperpolarise neurons. Intermittent theta burst stimulation (iTBS), a patterned form of TMS that is delivered at the theta frequency (~5 Hz), induces neuroplasticity in the hippocampus, a brain region that is implicated in memory and learning. One form of plasticity that is unique to the hippocampus is adult neurogenesis; however, little is known about whether TMS or iTBS in particular affects newborn neurons. Here, we therefore applied repeated sessions of iTBS to male and female mice and measured the extent of adult neurogenesis and the morphological features of immature neurons. We found that repeated sessions of iTBS did not significantly increase the amount of neurogenesis or affect the gross dendritic morphology of new neurons, and there were no sex differences in neurogenesis rates or aspects of afferent morphology. In contrast, efferent properties of newborn neurons varied as a function of sex and stimulation. Chronic iTBS increased the size of mossy fibre terminals, which synapse onto Cornu Ammonis 3 (CA3) pyramidal neurons, but only in males. iTBS also increased the number of terminal-associated filopodia, putative synapses onto inhibitory interneurons but only in male mice. This efferent plasticity could result from a general trophic effect, or it could reflect accelerated maturation of immature neurons. Given the important role of mossy fibre synapses in hippocampal learning, our results identify a neurobiological effect of iTBS that might be associated with sex-specific changes in cognition.

Causally mapping human threat extinction relevant circuits with depolarizing brain stimulation methods

Laboratory threat extinction paradigms and exposure-based therapy both involve repeated, safe confrontation with stimuli previously experienced as threatening. This fundamental procedural overlap supports laboratory threat extinction as a compelling analogue of exposure-based therapy. Threat extinction impairments have been detected in clinical anxiety and may contribute to exposure-based therapy non-response and relapse. However, efforts to improve exposure outcomes using techniques that boost extinction - primarily rodent extinction - have largely failed to date, potentially due to fundamental differences between rodent and human neurobiology. In this review, we articulate a comprehensive pre-clinical human research agenda designed to overcome these failures. We describe how connectivity guided depolarizing brain stimulation methods (i.e., TMS and DBS) can be applied concurrently with threat extinction and dual threat reconsolidation-extinction paradigms to causally map human extinction relevant circuits and inform the optimal integration of these methods with exposure-based therapy. We highlight candidate targets including the amygdala, hippocampus, ventromedial prefrontal cortex, dorsal anterior cingulate cortex, and mesolimbic structures, and propose hypotheses about how stimulation delivered at specific learning phases could strengthen threat extinction.