Real-time measurement of cerebral blood flow during and after repetitive transcranial magnetic stimulation: A near-infrared spectroscopy study

Impact of repetitive transcranial magnetic stimulation on cortical activity: a systematic review and meta-analysis utilizing functional near-infrared spectroscopy evaluation

BACKGROUND

Repeated transcranial magnetic stimulation (rTMS) could induce alterations in cortical excitability and promote neuroplasticity. To precisely quantify these effects, functional near-infrared spectroscopy (fNIRS), an optical neuroimaging modality adept at detecting changes in cortical hemodynamic responses, has been employed concurrently alongside rTMS to measure and tailor the impact of diverse rTMS protocols on the brain cortex.

OBJECTIVE

This systematic review and meta-analysis aimed to elucidate the effects of rTMS on cortical hemodynamic responses over the primary motor cortex (M1) as detected by fNIRS.

METHODS

Original articles that utilized rTMS to stimulate the M1 cortex in combination with fNIRS for the assessment of cortical activity were systematically searched across the PubMed, Embase, and Scopus databases. The search encompassed records from the inception of these databases up until April, 2024. The assessment for risk of bias was also conducted. A meta-analysis was also conducted in studies with extractable raw data.

RESULTS

Among 312 studies, 14 articles were eligible for qualitative review. 7 studies were eligible for meta-analysis. A variety of rTMS protocols was employed on M1 cortex. In inhibitory rTMS, multiple studies observed a reduction in the concentration of oxygenated hemoglobin [HbO] at the ipsilateral M1, contrasted by an elevation at the contralateral M1. Meta-analysis also corroborated this consistent trend. Nevertheless, certain investigations unveiled diminished [HbO] in bilateral M1. Several studies also depicted intricate inhibitory or excitatory interplay among distinct cortical regions.

CONCLUSION

Diverse rTMS protocols led to varied patterns of cortical activity detected by fNIRS. Meta-analysis revealed a trend of increasing [HbO] in the contralateral cortices and decreasing [HbO] in the ipsilateral cortices following low frequency inhibitory rTMS. However, due to the heterogeneity between studies, further research is necessary to comprehensively understand rTMS-induced alterations in brain activity.

Effects of rTMS combined with rPMS on stroke patients with arm paralysis after contralateral seventh cervical nerve transfer: a case-series

OBJECTIVE

We conducted this study to evaluate the effect of rTMS combined with rPMS on stroke patients with arm paralysis after CSCNTS.

METHODS

A case-series of four stroke patients with arm paralysis, ages ranging from 39 to 51 years, that underwent CSCNTS was conducted. Patients were treated with 10 HZ rTMS on the contralesional primary motor cortex combined with 20 HZ rPMS on groups of elbow and wrist muscles for 15 days.

RESULTS

The muscle tone of elbow flexor muscle (EFM), elbow extensor muscle (EEM), wrist flexor muscle (WFM) and flexor digitorum (FD) reduced immediately after operation followed by increasing gradually. After rehabilitation, the muscle tone of EEM and EFM reduced by 14% and 11%, respectively. There was a 13% and 45% change ratio in WFM and FD. The numeric rating scale (mean = 5.75 ± 1.71) was significantly lower (mean = 3.25 ± 1.90, t = 8.66, p = .00). Grip and pinch strength (mean = 23.65 ± 4.91; mean = 4.9 ± 0.59) were significantly higher (mean = 34.63 ± 5.23, t = -61.07, p = .00; mean = 7.1 ± 0.73, t = -13.91, p = .00).

CONCLUSIONS

The rehabilitation of stroke patients with arm paralysis after CSCNTS is a long, complicated process which includes great change of neuropathic pain, muscle tone, and muscle strength. In order to enhance the neural connection between the contralesional hemisphere and the hemiplegic limb, alleviate postoperative complications, as well as accelerate the rehabilitation process, we can consider to use rTMS combined with rPMS.

The Comparison of Early Hemodynamic Response to Single-Pulse Transcranial Magnetic Stimulation following Inhibitory or Excitatory Theta Burst Stimulation on Motor Cortex

We present a new study design aiming to enhance the understanding of the mechanism by which continuous theta burst stimulation (cTBS) or intermittent theta burst stimulation (iTBS) paradigms elicit cortical modulation. Using near-infrared spectroscopy (NIRS), we compared the cortical hemodynamics of the previously inhibited (after cTBS) or excited (after iTBS) left primary motor cortex (M1) as elicited by single-pulse TMS (spTMS) in a cross-over design. Mean relative changes in hemodynamics within 6 s of the stimulus were compared using a two-sample t-test (p < 0.05) and linear mixed model between real and sham stimuli and between stimuli after cTBS and iTBS. Only spTMS after cTBS resulted in a significant increase (p = 0.04) in blood volume (BV) compared to baseline. There were no significant changes in other hemodynamic parameters (oxygenated/deoxygenated hemoglobin). spTMS after cTBS induced a larger increase in BV than spTMS after iTBS (p = 0.021) and sham stimulus after cTBS (p = 0.009). BV showed no significant difference between real and sham stimuli after iTBS (p = 0.37). The greater hemodynamic changes suggest increased vasomotor reactivity after cTBS compared to iTBS. In addition, cTBS could decrease lateral inhibition, allowing activation of surrounding areas after cTBS.

Efficacy of repetitive transcranial magnetic stimulation and agomelatine on sleep quality and biomarkers of adult patients with mild to moderate depressive disorder

BACKGROUND

Mild to moderate depressive disorder (DD), which accounts for much larger patient population, has been largely neglected in previous studies exploring the sleep quality of DD patients; in addition, most of these patients had comorbid insomnia. Thus, this study aimed to explore the effect of repetitive transcranial magnetic stimulation (rTMS) and agomelatine on sleep quality of adult patients with mild to moderate DD.

METHODS

100 participants were randomly divided into high-frequency rTMS group and sham rTMS group (n = 50 each). All patients were administered agomelatine simultaneously. Hamilton Depression Scale-17 Items (HAMD-17), Pittsburgh Sleep Index (PSQI), and polysomnography were used to evaluate the efficacy. Serum norepinephrine (NE), 5-hydroxytryptamine, brain-derived neurotrophic factor (BDNF), and melatonin were also determined.

RESULTS

The HAMD-17 and PSQI scores in high-frequency rTMS group were lower than those in sham rTMS group at the 4th and 8th weekend after treatment (P < 0.05). Post-treatment total sleep time, sleep efficiency, and N3 percentage in high-frequency rTMS group were better than those in sham rTMS group (P < 0.05); while post-treatment sleep latency, awakening time, micro-awakening times, and N1 percentage were significantly less than those in sham rTMS group (P < 0.01). Post-treatment serum levels of NE and BDNF in high-frequency rTMS group were higher than those in sham rTMS group (P < 0.05).

LIMITATIONS

Small sample size and short follow-up duration.

CONCLUSION

The combination of high-frequency rTMS and agomelatine is effective in the treatment of mild to moderate DD, which can improve the sleep quality and increase the levels of some neurotransmitters and neurotrophic factors.

Prolonged Continuous Theta Burst Stimulation Can Regulate Sensitivity on Aβ Fibers: An Functional Near-Infrared Spectroscopy Study

Objective

High-frequency repetitive transcranial magnetic stimulation (rTMS) induces analgesic effects in both experimental pain and clinical pain conditions. However, whether rTMS can modulate sensory and pain thresholds on sensory fibers is still unclear. Here, we compared the effects of three rTMS paradigms on sensory and pain thresholds conducted by different sensory fibers (Aβ, Aδ, and C fibers) with sham stimulation and investigate the potential brain activation using functional near-infrared spectroscopy (fNIRS).

Methods

Forty right-handed healthy subjects were randomly allocated into one of four groups. Each subject received one session rTMS [prolonged continuous theta-burst stimulation (pcTBS), intermittent theta-burst stimulation (iTBS), 10 Hz rTMS or sham]. Current perception threshold (CPT), pain tolerance threshold (PTT), and fNIRS were measured at baseline, immediately after stimulation, and 1 h after stimulation, respectively.

Results

Significant differences between treatments were observed for changes for CPT 2,000 Hz between baseline and 1 h after rTMS (F = 6.551, P < 0.001): pcTBS versus sham (P = 0.004) and pcTBS versus 10 Hz rTMS (P = 0.007). There were significant difference in average HbO μm in the right frontopolar cortex (FPC) [channel 23: P = 0.030 (pcTBS versus sham: P = 0.036)], left dorsolateral prefrontal cortex (DLPFC) [channel 7: P = 0.006 (pcTBS versus sham: P = 0.004)], left FPC [channel 17: P = 0.014 (pcTBS versus sham: P = 0.046), channel 22: P = 0.004 (pcTBS versus sham: P = 0.004)] comparing four group in 1 h after stimulation in PTT 2000 Hz (Aβ-fiber).

Conclusion

Prolonged continuous theta-burst stimulation can regulate sensitivity on Aβ fibers. In addition, single-session pcTBS placed on left M1 can increase the excitability of DLPFC and FPC, indicating the interaction between M1 and prefrontal cortex may be a potential mechanism of analgesic effect of rTMS. Studies in patients with central post-stroke pain are required to confirm the potential clinical applications of pcTBS.

Acupuncture With deqi Modulates the Hemodynamic Response and Functional Connectivity of the Prefrontal-Motor Cortical Network

As a world intangible cultural heritage, acupuncture is considered an essential modality of complementary and alternative therapy to Western medicine. Despite acupuncture’s long history and public acceptance, how the cortical network is modulated by acupuncture remains largely unclear. Moreover, as the basic acupuncture unit for regulating the central nervous system, how the cortical network is modulated during acupuncture at the Hegu acupoint is mostly unclear. Here, multi-channel functional near-infrared spectroscopy (fNIRS) data were recorded from twenty healthy subjects for acupuncture manipulation, pre- and post-manipulation tactile controls, and pre- and post-acupuncture rest controls. Results showed that: (1) acupuncture manipulation caused significantly increased acupuncture behavioral deqi performance compared with tactile controls. (2) The bilateral prefrontal cortex (PFC) and motor cortex were significantly inhibited during acupuncture manipulation than controls, which was evidenced by the decreased power of oxygenated hemoglobin (HbO) concentration. (3) The bilateral PFC’s hemodynamic responses showed a positive correlation trend with acupuncture behavioral performance. (4) The network connections with bilateral PFC as nodes showed significantly increased functional connectivity during acupuncture manipulation compared with controls. (5) Meanwhile, the network’s efficiency was improved by acupuncture manipulation, evidenced by the increased global efficiency and decreased shortest path length. Taken together, these results reveal that a cooperative PFC-Motor functional network could be modulated by acupuncture manipulation at the Hegu acupoint. This study provides neuroimaging evidence that explains acupuncture’s neuromodulation effects on the cortical network.

A pilot study exploring the effect of repetitive transcranial magnetic stimulation (rTMS) treatment on cerebral blood flow and its relation to clinical outcomes in severe enduring anorexia nervosa

BACKGROUND

Repetitive transcranial magnetic stimulation (rTMS) is a novel treatment option for people with severe enduring anorexia nervosa (SE-AN), but associated neurobiological changes are poorly understood. This study investigated the effect of rTMS treatment on regional cerebral blood flow (CBF) and whether any observed changes in CBF are associated with changes in clinical outcomes in people with SE-AN.

METHODS

As part of a randomised sham-controlled feasibility trial of 20 sessions of high-frequency rTMS to the left dorsolateral prefrontal cortex, 26 of 34 trial participants completed arterial spin labelling (ASL) functional magnetic resonance imaging (fMRI) to quantify regional and global resting state CBF before (pre-randomisation baseline) and after real or sham treatment (1-month post-randomisation). A group of healthy females (n = 30) were recruited for baseline comparison. Clinical outcomes, including BMI, and depression and anxiety symptoms, were assessed at baseline, 1-, 4-, and 18-months post-randomisation.

RESULTS

No group differences in regional CBF were identified between the SE-AN and healthy comparison participants. A significant treatment-by-time interaction in a medial temporal lobe cluster with the maximal peak in the right amygdala was identified, reflecting a greater reduction in amygdala CBF following real rTMS compared to sham. Participants with the greatest rTMS-related reduction in amygdala CBF (i.e., between baseline and 1-month post-randomisation) showed the greatest sustained weight gain at 18-months post-randomisation. Higher baseline CBF in the insula predicted greater weight gain between baseline and 1-month post-randomisation and between baseline and 4-months post-randomisation.

CONCLUSIONS

This exploratory pilot study identified rTMS treatment related changes in CBF in adults with SE-AN and these were associated with changes in weight. Our preliminary findings also suggest that CBF (as measured by ASL fMRI) may be a marker of rTMS treatment response in this patient group. Future rTMS studies in AN should employ longitudinal neuroimaging to further explore the neurobiological changes related to rTMS treatment.

TRIAL REGISTRATION

ISRCTN14329415 , registered 23rd July 2015.

Non-invasive brain stimulation for speech in Parkinson's disease: A randomized controlled trial

BACKGROUND

Hypokinetic dysarthria is a common but difficult-to-treat symptom of Parkinson's disease (PD).

OBJECTIVES

We evaluated the long-term effects of multiple-session repetitive transcranial magnetic stimulation on hypokinetic dysarthria in PD. Neural mechanisms of stimulation were assessed by functional MRI.

METHODS

A randomized parallel-group sham stimulation-controlled design was used. Patients were randomly assigned to ten sessions (2 weeks) of real (1 Hz) or sham stimulation over the right superior temporal gyrus. Stimulation effects were evaluated at weeks 2, 6, and 10 after the baseline assessment. Articulation, prosody, and speech intelligibility were quantified by speech therapist using a validated tool (Phonetics score of the Dysarthric Profile). Activations of the speech network regions and intrinsic connectivity were assessed using 3T MRI. Linear mixed models and post-hoc tests were utilized for data analyses.

RESULTS

Altogether 33 PD patients completed the study (20 in the real stimulation group and 13 in the sham stimulation group). Linear mixed models revealed significant effects of time (F(3, 88.1) = 22.7, p < 0.001) and time-by-group interactions: F(3, 88.0) = 2.8, p = 0.040) for the Phonetics score. Real as compared to sham stimulation led to activation increases in the orofacial sensorimotor cortex and caudate nucleus and to increased intrinsic connectivity of these regions with the stimulated area.

CONCLUSIONS

This is the first study to show the long-term treatment effects of non-invasive brain stimulation for hypokinetic dysarthria in PD. Neural mechanisms of the changes are discussed.

Theta burst stimulation over the prefrontal cortex: Effects on cerebral oximetry and cardiovascular measures in healthy humans

Theta Burst Stimulation (TBS) is a non-invasive neurophysiological technique, able to induce changes in synaptic activity. Research suggests that TBS may induce changes in cerebral oxygenation, cerebral blood flow, blood pressure and heart rate but there are conflicting results across studies. Thus, the objective of our sham-controlled study is to evaluate if TBS applied to the dorsolateral prefrontal cortex (DLPFC) of healthy volunteers produces changes in cerebral oximetry, heart rate and blood pressure. Forty-nine volunteers of both sexes were randomly allocated to one of five stimulation groups. Before and after real TBS or sham stimulation, blood pressure, heart rate, and cerebral oxygenation of the volunteers were measured. Cerebral oxygenation values were obtained with a near infra-red spectroscopy system. We found a significant reduction in left cortex oximetry after continuous TBS (cTBS) over the left DLPFC (p = 0.039) and a non-significant reduction in right cortex oximetry (p = 0.052). Right hemisphere inhibition (using cTBS) seemed to originate a significant reduction of 8 mmHg in systolic arterial pressure. No other changes were seen in oximetry, cardiac frequency and diastolic arterial pressure. In our group of normal subjects, cTBS applied to the left DLPFC was able to reduce oxygenation in the left cortex. Right hemisphere inhibition was associated with a significant reduction in systolic pressure.

Theta burst stimulation ameliorates symptoms of experimental autoimmune encephalomyelitis and attenuates reactive gliosis

Multiple sclerosis (MS) is a chronic neurodegenerative disease caused by inflammatory processes in the central nervous system (CNS). Decades of research led to discovery of several disease-modifying therapeutics strategies with moderate success. Experimental autoimmune encephalomyelitis (EAE) is currently the most commonly used experimental model for MS and for studying various therapeutic approaches. Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive neurostimulation technique with multiple beneficial effects on healthy as well as CNS with pathology. However, the molecular and cellular mechanisms of rTMS on acute EAE are scarce. Our study demonstrated beneficial effects of theta-burst stimulation (TBS), an experimental paradigm of rTMS, on disease course of acute EAE. TBS treatment attenuated reactive gliosis, restored myelin sheet and down-regulated expression of vimentin in EAE rats. These effects were reflected through reduced clinical parameters, shorter duration of illness and days spent in paralysis. Based on our research, rTMS deserves further considerations for its neuroprotective effect on EAE, and is an excellent candidate for further research and points that it could be used for more than for simple symptomatic therapy.

High frequency repetitive transcranial magnetic stimulation improves neuronal activity without affecting astrocytes and microglia density

Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive neuromodulation technique capable of producing changes in the electrical potential of neurons. Currently, the application of rTMS in clinical practice and as a neurophysiological tool is increasing. However, the exact cellular mechanisms underlying rTMS-based therapies are not completely clear. Additionally, glial cells have been studied less. Our aim was to investigate the effect of three days of high-frequency rTMS on neuronal metabolism and neuronal activation, in addition to its effect on glial cells. For this purpose, we performed histochemistry and immunohistochemistry procedures: the histochemistry of cytochrome oxidase (COx) to assess neuronal metabolic activity, and the immunohistochemistry of c-Fos (marker of neuronal activity), GFAP (marker of astrocytic reactivity), and Iba1 (selective marker of reactive microglia). Our results showed enhanced metabolic activity after rTMS in the retrosplenial and parietal cortex and CA1 and CA3 subfields of the hippocampus. Moreover, higher c-Fos activity was found in the agranular retrosplenial cortex. Finally, we did not find changes between groups in the induction of astrocyte and microglia reactivity in any of the immunostained regions. In conclusion, we can assume that three days of high-frequency rTMS applied in healthy rats does not alter astroglia reactivity or inflammatory responses, such as microglia proliferation. Because we have shown an upregulation of neuronal metabolic activity in many limbic brain structures, in addition to higher c-Fos levels in the nearest cortical area to the rTMS, our work provides novel insight into the effectiveness and safety of rTMS as a brain modulation therapy.

Cortical Hemodynamic Response and Connectivity Modulated by Sub-threshold High-Frequency Repetitive Transcranial Magnetic Stimulation

Repetitive transcranial magnetic stimulation (rTMS) at sub-threshold intensity is a viable clinical strategy to enhance the sensory and motor functions of extremities by increasing or decreasing motor cortical excitability. Despite this, it remains unclear how sub-threshold rTMS modulates brain cortical excitability and connectivity. In this study, we applied functional near-infrared spectroscopy (fNIRS) to investigate the alterations in hemodynamic responses and cortical connectivity patterns that are induced by high-frequency rTMS at a sub-threshold intensity. Forty high-frequency (10 Hz) trains of rTMS at 90% resting motor threshold (RMT) were delivered through a TMS coil placed over 1–2 cm lateral from the vertex. fNIRS signals were acquired from the frontal and bilateral motor areas in healthy volunteers (n = 20) during rTMS administration and at rest. A significant reduction in oxygenated hemoglobin (HbO) concentration was observed in most defined regions of interest (ROIs) during the stimulation period (p < 0.05). Decreased functional connectivity within prefrontal areas as well as between symmetrical ROI-pairs was also observed in most participants during the stimulation (p < 0.05). Results suggest that fNIRS imaging is able to provide a reliable measure of regional cortical brain activation that advances our understanding of the manner in which sub-threshold rTMS affects cortical excitability and brain connectivity.

A Systematic Review of Integrated Functional Near-Infrared Spectroscopy (fNIRS) and Transcranial Magnetic Stimulation (TMS) Studies

Background: The capacity for TMS to elicit neural activity and manipulate cortical excitability has created significant expectation regarding its use in both cognitive and clinical neuroscience. However, the absence of an ability to quantify stimulation effects, particularly outside of the motor cortex, has led clinicians and researchers to pair noninvasive brain stimulation with noninvasive neuroimaging techniques. fNIRS, as an optical and wearable neuroimaging technique, is an ideal candidate for integrated use with TMS. Together, TMS+fNIRS may offer a hybrid alternative to "blind" stimulation to assess NIBS in therapy and research. Objective: In this systematic review, the current body of research into the transient and prolonged effects of TMS on fNIRS-based cortical hemodynamic measures while at rest and during tasks are discussed. Additionally, studies investigating the relation of fNIRS to measures of cortical excitability as produced by TMS-evoked Motor-Evoked-Potential (MEP) are evaluated. The aim of this review is to outline the integrated use of TMS+fNIRS and consolidate findings related to use of fNIRS to monitor changes attributed to TMS and the relationship of fNIRS to cortical excitability itself. Methods: Key terms were searched in PubMed and Web-of-Science to identify studies investigating the use of both fNIRS and TMS. Works from Google-Scholar and referenced works in identified papers were also assessed for relevance. All published experimental studies using both fNIRS and TMS techniques in the study methodology were included. Results: A combined literature search of neuroimaging and neurostimulation studies identified 53 papers detailing the joint use of fNIRS and TMS. 22/53 investigated the immediate effects of TMS at rest in the DLPFC and M1 as measured by fNIRS. 21/22 studies reported a significant effect in [HbO] for 40/54 stimulation conditions with 14 resulting an increase and 26 in a decrease. While 15/22 studies also reported [HbR], only 5/37 conditions were significant. Task effects of fNIRS+TMS were detailed in 16 studies, including 10 with clinical populations. Most studies only reported significant changes in [HbO] related measures. Studies comparing fNIRS to changes in MEP-measured cortical excitability suggest that fNIRS measures may be spatially more diffuse but share similar traits. Conclusion: This review summarizes the progress in the development of this emerging hybrid neuroimaging & neurostimulation methodology and its applications. Despite encouraging progress and novel applications, a lack of replicated works, along with highly disparate methodological approaches, highlight the need for further controlled studies. Interpretation of current research directions, technical challenges of TMS+fNIRS, and recommendations regarding future works are discussed.

Early Detection of Cerebral Infarction With Middle Cerebral Artery Occlusion With Functional Near-Infrared Spectroscopy: A Pilot Study

Background: NIRSIT, a functional near-infrared spectroscopy (fNIRS) device with 204 channels, can measure oxyhemoglobin (HbO2) and deoxyhemoglobin (HbR) in non-pulsatile blood flow non-invasively using the absorption difference between HbO2 and HbR at a wavelength of 700–1,000 nm and can display the perfusion status in real time.

Objective: We applied NIRSIT to patients with stroke to evaluate the usefulness of NIRSIT as an fNIRS device for the early detection of stroke.

Methods: We performed a prospective pilot study in an emergency department (ED). Adult patients who had suspected symptoms and signs of stroke within 12 h of the first abnormal time and who underwent intravenous thrombolysis (IVT) or intra-arterial thrombectomy with acute middle cerebral artery (MCA) or internal carotid artery (ICA) infarction were enrolled. NIRSIT was applied to the patients before the imaging study, and the perfusion status of the brain was displayed in real time at the bedside. We compared the NIRSIT results with the mean transit time (MTT) map from perfusion computed tomography (PCT) and the time-to-peak (TTP) map from perfusion-weighted magnetic resonance imaging (PWI).

Results: Six male and three female patients were enrolled, and the median age was 74 years. The most common symptom was unilateral extremity weakness (77.8%), followed by dysarthria (33.3%) and aphasia (11.1%). The median National Institutes of Health Stroke Scale (NIHSS) score was 17. All cases of MCA infarction showed different cerebral oxygen saturation values between bilateral lobes of the brain in fNIRS imaging, and these values matched the PCT and PWI results.

Conclusions: The brain hemisphere with low oxygen saturation on fNIRS showed hypoperfusion on PCT or PWI. The fNIRS device could be useful in assessing the perfusion status of the brain and detecting MCA or ICA infarction in real time at the bedside.