Effects of intermittent theta burst stimulation on cerebral blood flow and cerebral vasomotor reactivity

The effect of intermittent theta burst stimulation for cognitive dysfunction: a meta-analysis

BACKGROUND

Growing evidence suggests that cognitive dysfunction significantly impacts patients' quality of life. Intermittent theta burst stimulation (iTBS) has emerged as a potential intervention for cognitive dysfunction. However, consensus on the iTBS protocol for cognitive impairment is lacking.

METHODS

We conducted searches in the Cochrane Central Register of Controlled Trials, EMBASE, PubMed, Chinese National Knowledge Infrastructure, Wanfang Database and the Chongqing VIP Chinese Science and Technology Periodical Database from their inception to January 2024. Random-effects meta-analyzes were used to calculate standardized mean differences and 95% confidence intervals. The quality of evidence was assessed using the Grading of Recommendations Assessment, Development, and Evaluation approach.

RESULTS

Twelve studies involving 506 participants were included in the meta-analysis. The analysis showed a trend toward improvement of total cognitive function, activities of daily living and P300 latency compared to sham stimulation in patients with cognitive dysfunction. Subgroup analysis demonstrated that these effects were restricted to patients with post-stroke cognitive impairment but not Alzheimer's disease or Parkinson's disease. Furthermore, subthreshold stimulation also exhibited a significant improvement.

CONCLUSIONS

The results suggest that iTBS may improve cognitive function in patients with cognitive dysfunction, although the quality of evidence remains low. Further studies with better methodological quality should explore the effects of iTBS on cognitive function.

Modulation of the prefrontal blood oxygenation response to intermittent theta-burst stimulation in depression: A sham-controlled study with functional near-infrared spectroscopy

OBJECTIVE

To better understand the neural mechanisms behind the effect of intermittent theta-burst stimulation (iTBS), we investigated how the prefrontal blood oxygenation response measured by changes in oxygenated haemoglobin (oxy-Hb) was modulated during a sham-controlled iTBS treatment course, and whether this was related to depressive symptom change.

METHODS

In this randomised, double-blind study, patients with ongoing treatment-resistant depression received either active (n = 18) or sham (n = 21) iTBS over the dorsomedial prefrontal cortex for ten to fifteen days with two sessions daily. Event-related functional near-infrared spectroscopy (fNIRS) was measured during each iTBS train, and resting-state oxy-Hb was compared before and after each iTBS session at the first, fifth, and last treatment day.

RESULTS

Patients receiving active iTBS had an increase of the event-related oxy-Hb response compared to the sham group on the fifth (bilateral prefrontal cortices p < .001) and last (left prefrontal p = .007, right prefrontal p = .025) treatment day. Resting-state analysis showed suppressed oxy-Hb change in active iTBS compared to sham iTBS on the last treatment day (p = .024). Oxy-Hb change was unrelated to depressive symptom change (p = .474).

CONCLUSIONS

This study describes a modulation of the blood oxygenation response over the prefrontal cortex that was built up during the course of active iTBS treatment in depression.

Non-invasive brain stimulation in the modulation of cerebral blood flow after stroke: A systematic review of Transcranial Doppler studies

OBJECTIVE

Non-invasive brain stimulation (NIBS), such as repetitive TMS (rTMS) and transcranial direct current stimulation (tDCS), are promising neuromodulatory priming techniques to promote task-specific functional recovery after stroke. Despite promising results, clinical application of NIBS has been limited by high inter-individual variability. We propose that there is a possible influence of neuromodulation on cerebral blood flow (CBF), as neurons are spatially and temporally related to blood vessels. Transcranial Doppler (TCD), a clinically available non-invasive diagnostic tool, allows for evaluation of CBF velocity (CBFv). However, little is known about the role of neuromodulation on CBFv.

METHODS

A systematic review of literature to understand the effects of NIBS on CBFv using TCD in stroke was conducted.

RESULTS

Twelve studies fit our inclusion criteria and are included in this review. Our review suggested that CBFv and/or vasomotor reactivity maybe influenced by rTMS dosage (intensity and frequency) and the type of tDCS electrode montage.

CONCLUSION

There is limited evidence regarding the effects of NIBS on cerebral hemodynamics using TCD and the usefulness of TCD to capture changes in CBFv after NIBS is not evident from this review. We highlight the variability in the experimental protocols, differences in the applied neurostimulation protocols and discuss open questions that remain regarding CBF and neuromodulation.

SIGNIFICANCE

TCD, a clinically accessible tool, may potentially be useful to understand the interaction between cortical neuromodulation and CBFv.

Use of theta-burst stimulation in changing excitability of motor cortex: A systematic review and meta-analysis

Noninvasive brain stimulation has been demonstrated to modulate cortical activity in humans. In particular, theta burst stimulation (TBS) has gained notable attention due to its ability to induce lasting physiological changes after short stimulation durations. The present study aimed to provide a comprehensive meta-analytic review of the efficacy of two TBS paradigms; intermittent (iTBS) and continuous (cTBS), on corticospinal excitability in healthy individuals. Literature searches yielded a total of 87 studies adhering to the inclusion criteria. iTBS yielded moderately large MEP increases lasting up to 30 min with a pooled SMD of 0.71 (p<0.00001). cTBS produced a reduction in MEP amplitudes lasting up to 60 min, with the largest effect size seen at 5 min post stimulation (SMD=-0.9, P<0.00001). The collected studies were of heterogeneous nature, and a series of tests conducted indicated a degree of publication bias. No significant change in SICI and ICF was observed, with exception to decrease in SICI with cTBS at the early time point (SMD=0.42, P=0.00036). The results also highlight several factors contributing to TBS efficacy, including the number of pulses, frequency of stimulation and BDNF polymorphisms. Further research investigating optimal TBS stimulation parameters, particularly for iTBS, is needed in order for these paradigms to be successfully translated into clinical settings.