Enhanced theta-gamma coupling associated with hippocampal volume increase following high-frequency left prefrontal repetitive transcranial magnetic stimulation in patients with major depression

doi:10.1016/j.ijpsycho.2018.07.004

International Journal of Psychophysiology

Volume 133, November 2018, Pages 169-174

https://doi.org/10.1016/j.ijpsycho.2018.07.004 Get rights and content

Highlights

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Significant relationship exists between changes of the HIPP volume and TGC locally induced by rTMS.
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The finding showed the hippocampal structure-function linkage of the rTMS-induced neuroplasticity.
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Prefrontal rTMS may exert its cognitive effect via plasticity of prefrontal-hippocampus circuit.

Abstract

The underlying mechanism of repetitive transcranial magnetic stimulation (rTMS) effects on cognition has not been fully examined. Previously, we have reported the left hippocampal volume increase and theta-gamma coupling (TGC) enhancement associated with working memory improvement following rTMS in depression. This study was aimed to examine whether there is a structure-function relationship in hippocampal neuroplasticity induced by prefrontal rTMS. Thirty-one patients with major depression underwent longitudinal MRI scans and resting-state EEG recordings with the 10–20 system using averaged ear-lobes reference, following 10 sessions of high-frequency rTMS over the left dorsolateral prefrontal cortex. Pearson's correlation analyses were applied for the longitudinal changes among the left and right hippocampal volumes as measured by manual volumetry, theta and gamma spectral powers, and TGC as measured by resting-state EEG. The analyses demonstrated that the left hippocampus volume increases correlated with TGC increases at the left central area (r = 0.576, p = 0.001, N = 31), whereas no significant correlations were observed among changes of right hippocampal volume, right central TGC, bilateral gamma or theta powers. These finding suggests structure-function relationship in rTMS-induced neuroplastic changes mediated through the hippocampus and prefrontal network at the stimulated side. Therefore, high-frequency prefrontal rTMS may exert its cognitive effect through the hippocampal structural-functional neuroplasticity.

Introduction

Major depression is one of the debilitating forms of mental illnesses and the second largest global burden of disease as indexed by the DALYs (Ferrari et al., 2013; Whiteford et al., 2013), especially in the context of treatment resistance. Recently, repetitive transcranial magnetic stimulation (rTMS) has emerged as a promising treatment option for treatment-resistant depression and its therapeutic effect has been demonstrated in well over 100 clinical trials (McClintock et al., 2017; Milev et al., 2016). However, the underlying biological mechanisms of action of rTMS, especially in terms of its cognitive effects, have not been fully elucidated (Martin et al., 2017).

Specifically, it is known that hippocampal and prefrontal cortex interactions play an important role in cognitive functioning and disruptions in these interactions may contribute to the pathophysiology in various psychiatric diseases including depression (Godsil et al., 2013; Uhlhaas and Singer, 2012). Moreover, electrophysiological studies in rats have shown that neural activities between the hippocampus and the prefrontal cortex are often synchronized in time and the interaction of both neuroanatomical structures are required to coordinate the appropriate cognitive functions (Gruart et al., 2015; Jones and Wilson, 2005). In addition, a functional MRI study in humans has demonstrated that hippocampus and DLPFC coupling may represent a systematic mechanism that implements working memory (Bahner et al., 2015).

The hippocampus has distinct electrophysiological characteristics of the theta-phase and gamma-amplitude coupling (TGC), which means the gamma oscillations (30-100 Hz) onto the theta rhythms (5–10 Hz: typically a 4–8 Hz band) (Marmpena et al., 2016; Scheffer-Teixeira and Tort, 2016). Furthermore, the TGC is thought to play an important role in learning and memory associated with neuroplasticity in the hippocampal-cortical network, facilitating cognitive functioning (Colgin, 2015; Tamura et al., 2017). For example, a rat study using a chronic stress model demonstrated that the TGC between hippocampus and prefrontal cortex was disrupted, which resulted in the impairment of synaptic plasticity in this pathway (Zheng and Zhang, 2015). Further, in the same rat model of chronic stress, between hippocampus and prefrontal cortex, the theta phase coupling was decreased with the injection of dopamine D1 receptor antagonist while the gamma oscillations increased with the 5-HT1A receptor agonist (Xu et al., 2016). Thus, monoaminergic antidepressants may exert its pro-cognitive effect through the potentiation of synaptic plasticity mediated by dopaminergic and serotonergic modulations in the hippocampal and prefrontal network.

Our group has previously reported that high-frequency left dorsolateral prefrontal cortex (DLPFC) rTMS induced a significant increase of TGC on resting-state EEG at the C3 electrode site over the left central area in patients with major depression, and further this increased TGC was significantly associated with cognitive improvement as assessed by the Wisconsin Cord Sorting Test (WCST) following rTMS treatment (Noda et al., 2017). Furthermore, rTMS treatment using the same protocol induced a lateralized hippocampal volume increase as measured by MRI on the left side that was the stimulated site of rTMS (Hayasaka et al., 2017). In our previous study, there was no significant relationship between MRI hippocampal volume changes and cognitive outcomes following rTMS in this population, however, the relationship between hippocampal volumetric changes and TGC has not been previously evaluated.

Therefore, in the present study, we hypothesized that the left hippocampal volume increases in depression induced by high-frequency left DLPFC rTMS would be associated with functional neuroplasticity, which is relevant to the cognitive executive functioning, as indexed by TGC on resting-state EEG. We examined the relationship between changes of hippocampal structural changes and TGC, gamma and theta powers by rTMS treatment in patients with depression using our previous datasets to elucidate the underlying therapeutic mechanism of cognitive improvement associated with rTMS treatment in major depression.

Section snippets

Participants

Thirty-one medicated patients with major depression diagnosed with the ICD-10 (43 ± 11 (mean ± S.D.) years; 21 males) were included in the present study (Noda et al., 2017). There was no special reason for the untypical ratio of male to female patients with depression who participated in this study. All participants were screened with the Structured Clinical Interview for DSM-IV Axis I Disorders (First et al., 1996) prior to study participation and they had no neuropsychiatric comorbidities and

Results

Following an acute course of rTMS, clinical symptoms as measured by the score on the HAM-D17 were improved by 43.3 ± 30.0% (mean ± S.D.) (t₃₀ = 8.088, p < 0.0001; Grass' Δ = −1.83: large effect size) and percentage responders was 51.6%. Furthermore, the left hippocampal volume was increased by 4.4 ± 5.8% (t₃₀ = −4.106, p < 0.001; Grass' Δ = 0.44: small effect size) and TGC at C3 electrode site was enhanced by 52.7 ± 60.1% (t₃₀ = −4.491, p = 0.0001; Grass' Δ = 1.57: large effect size) in this

Discussion

The present study suggests that there may be a structure-function relationship in the rTMS-induced neuroplasticity via the hippocampus and prefrontal network (Godsil et al., 2013). Further, the structural and functional neuroplastic changes in the hippocampus may represent a potential underlying therapeutic mechanism of the left prefrontal rTMS in patients with depression. Previously, we have demonstrated the significant left hippocampal volume increases following rTMS in patients with

Funding source

None.

Conflicts of interest statement

YN receives research support from Otsuka Pharmaceutical Co., Ltd., Shionogi & Co., Ltd., and Meiji Seika Pharma Co., Ltd. YN also receives research grants from Japan Health Foundation, Meiji Yasuda Mental Health Foundation, Mitsui Life Social Welfare Foundation, Takeda Science Foundation, SENSHIN Medical Research Foundation, Health Science Center Foundation, and Daiichi Sankyo Scholarship Donation Program. He receives equipment-in-kind support for an investigator-initiated study from Magventure

Acknowledgments

None.

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In MDD, left fronto-central TGC decreased during stimulation, while right fronto-central TGC increased during baseline. The area under ROC curve for altered TGC was 0.863. Furthermore, during stimulation, moderate and major MDD groups exhibited significantly lower TGC than mild group, and fronto-central TGC was negatively correlated with depression scale scores.
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Citation Excerpt :
The 2017 study by Noda et al. (2017) assessed whether a course of repetitive TMS (rTMS) would increase the resting state gamma power and the modulation index (MI) of theta-gamma coupling. The 2018 study by Noda et al. (2018) investigated whether left hippocampal volume increase induced by rTMS at the left DLPFC would correlate with resting state theta-gamma PAC. The study by Chattun et al. (2020) examined whether participants with depression and suicidality had an abnormality in the cortico-striato-thalamo-cortical loop, which is involved in executive function and working memory (among various other motor and cognitive functions) (Poppelaars et al., 2018).
Cross-frequency coupling (CFC), an electrophysiologically derived measure of oscillatory coupling in the brain, is believed to play a critical role in neuronal computation, learning and communication. It has received much recent attention in the study of both health and disease. We searched for literature that studied CFC during resting state and task-related activities during electroencephalography and magnetoencephalography in psychiatric disorders. Thirty-eight studies were identified, which included attention-deficit hyperactivity disorder, Alzheimer’s dementia, autism spectrum disorder, bipolar disorder, depression, obsessive compulsive disorder, social anxiety disorder and schizophrenia. The systematic review was registered with PROSPERO (ID#CRD42021224188). The current review indicates measurable differences exist between CFC in disease states vs. healthy controls. There was variance in CFC at different regions of the brain within the same psychiatric disorders, perhaps this could be explained by the mechanisms and functionality of CFC. There was heterogeneity in methodologies used, which may lead to spurious CFC analyses. Going forward, standardized methodologies need to be established and utilized in further research to understand the neuropathophysiology associated with psychiatric disorders.

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Enhanced theta-gamma coupling associated with hippocampal volume increase following high-frequency left prefrontal repetitive transcranial magnetic stimulation in patients with major depression

Highlights

Abstract

Introduction

Section snippets

Participants

Results

Discussion

Funding source

Conflicts of interest statement

Acknowledgments

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