ABSTRACT
Transcranial magnetic stimulation (TMS) is a non-invasive, non-pharmacological technique that is able to modulate cortical activity beyond the stimulation period. The residual aftereffects are akin to the plasticity mechanism of the brain and suggest the potential use of TMS for therapy. For years, TMS has been shown to transiently improve symptoms of neuropsychiatric disorders, but the underlying neural correlates remain elusive. Recently, there is evidence that altered connectivity of brain network dynamics is the mechanism underlying symptoms of various neuropsychiatric illnesses. By combining TMS and electroencephalography (EEG), the functional connectivity patterns among brain regions, and the causal link between function or behaviour and a specific brain region can be determined. Nonetheless, the brain network connectivity are highly complex and involve the dynamics interplay among multitude of brain regions. In this review article, we present previous TMS-EEG co-registration studies, which explore the functional connectivity patterns of human cerebral cortex. We argue the possibilities of neural correlates of long-term potentiation/ depression (LTP-/LTD)-like mechanisms of synaptic plasticity that drive the TMS aftereffects as shown by the dissociation between EEG and motor evoked potentials (MEP) cortical output. Here, we also explore alternative explanations that drive the EEG oscillatory modulations post TMS. The precise knowledge of the neurophysiological mechanisms underlying TMS will help characterise disturbances in oscillatory patterns, and the altered functional connectivity in neuropsychiatric illnesses.
ABSTRACT
Background: Transcranial magnetic stimulation (TMS) is a non-invasive tool that is able to modulate the electrical activity of the brain depending upon its protocol of stimulation. Theta burst stimulation (TBS) is a high-frequency TMS protocol that is able to induce prolonged plasticity changes in the brain. The induction of plasticity-like effects by TBS is useful in both experimental and therapeutic settings; however, the underlying neural mechanisms of this modulation remain unclear. The aim of this study was to investigate the effects of continuous TBS (cTBS) on the intrahemispheric and interhemispheric functional connectivity of the resting and active brain. Methods: A total of 26 healthy humans were randomly divided into two groups that received either real cTBS or sham (control) over the left primary motor cortex. Surface electroencephalogram (EEG) was used to quantify the changes of neural oscillations after cTBS at rest and after a choice reaction time test. The cTBS-induced EEG oscillations were computed using spectral analysis of event-related coherence (ERCoh) of theta (4–7.5 Hz), low alpha (8–9.5 Hz), high alpha (10–12.5 Hz), low beta (13–19.5 Hz), and high beta (20–30 Hz) brain rhythms. Results: We observed a global decrease in functional connectivity of the brain in the cTBS group when compared to sham in the low beta brain rhythm at rest and high beta brain rhythm during the active state. In particular, EEG spectral analysis revealed that high-frequency beta, a cortically generated brain rhythm, was the most sensitive band that was modulated by cTBS. Conclusion: Overall, our findings suggest that cTBS, a TMS protocol that mimics the mechanism of long-term depression of synaptic plasticity, modulates motor network oscillations primarily at the cortical level and might interfere with cortical information coding.
ABSTRACT
The study evaluated the function of median sensory nerve fibers, as well as determining the relationship between its function with the duration of Carpal Tunnel Syndrome (CTS) and body mass index (BMI) among CTS patients in Physiotherapy Unit, Universiti Kebangsaan Malaysia Hospital (HUKM). Thirty subjects (6 males and 24 females) with mean age 53.30 ± 9.20 years and duration of the CTS 51.17 ± 50.22 months participated in this study. The sensitivity of median sensory nerve was evaluated using Current Perception Threshold (CPT) Test with stimulation frequencies of 5 Hz, 250 Hz and 2000 Hz; which demonstrated the function of C, Aδ and Aβ nerve fiber respectively. Majority of the CTS patients had normal function in the 3 types of median sensory nerve fiber. Forty percents of the subjects had abnormality in the Aâ function, 7% had abnormality of the Aβ function and 27% demonstrated abnormality in the C fiber function. Spearman Correlation Test showed no significant relationship between the function of median sensory nerve and the duration of CTS and body mass index (BMI) (p > 0.05). In conclusion, although majority of the patients demonstrated normal median sensory nerve function, abnormality of the Aβ, Aδ and C fibers sensitivity in some patients requires attention to prevent worsening of the nerve function thus avoiding related complications. Physiotherapists in HUKM may intensify the use of nervestimulating modalities such as Transcutaneous Electrical Nerve Stimulation (TENS) to normalize the nerve functions of these patients.