Motor cortex compensates for lack of sensory and motor experience during auditory speech perception

Four electric field modeling methods of Dosing Prefrontal Transcranial Magnetic Stimulation (TMS): Introducing APEX MT dosimetry

Cortical inhibition (CI) is measured by transcranial magnetic stimulation (TMS) combined with electromyography (EMG) through long-interval CI (LICI) and cortical silent period (CSP) paradigms. Recently, we illustrated that LICI can be measured from the dorsolateral prefrontal cortex (DLPFC) through combined TMS with electroencephalography (EEG). We further demonstrated that LICI had different effects on cortical oscillations in the DLPFC compared with motor cortex. The purpose of this study was to establish the validity and reliability of TMS-EEG indices of CI and to replicate our previous findings in an extended sample. The validity of TMS-EEG was examined by evaluating its relationship to standard EMG measures of LICI and the CSP in the left motor cortex in 36 and 16 subjects, respectively. Test-retest reliability was examined in 14 subjects who returned for a repeat session within 7 days of the first session. LICI was applied to the left DLPFC in 30 subjects to compare LICI in the DLPFC with that in the motor cortex. In the motor cortex, EEG measures of LICI correlated with EMG measures of LICI and CSP. All indices of LICI showed high test-retest reliability in motor cortex and DLPFC. Gamma and beta oscillations were significantly inhibited in the DLPFC but not in the motor cortex, confirming previous findings in an extended sample. These findings demonstrate that indexing LICI through TMS combined with EEG is a valid and reliable method to evaluate inhibition from motor and prefrontal regions.

1. Suppression of voluntary muscle activity of hand and arm muscles in response to transcranial magnetic stimulation (TMS) of the motor cortex has been investigated in man. 2. Suppression could be elicited by low levels of TMS without any prior excitatory response. The latency of the suppression was 3-8 ms longer than the excitation observed at a higher stimulus intensity. The duration of the suppression ranged from 8 to 26 ms. 3. A circular stimulating coil was used to determine threshold intensity for excitation and suppression of contraction of thenar muscles in response to TMS at different locations over the motor cortex. The locations for lowest threshold excitation coincided with those for lowest threshold suppression. Suppression was elicited at a lower threshold than excitation at all locations. 4. A figure-of-eight stimulating coil was positioned over the left motor cortex at the lowest threshold point for excitation of the right thenar muscles. The orientation for the lowest threshold excitatory and inhibitory responses was the same for all subjects. That orientation induced a stimulating current travelling in an antero-medial direction. Suppression was invariably elicited at lower thresholds than excitation. 5. When antagonistic muscles (second and third dorsal interosseus) were co-contracted, TMS evoked coincident suppression of voluntary EMG in the two muscles without prior excitation of either muscle. This suggests that the suppression is not mediated via corticospinal activation of spinal interneurones. 6. Test responses to electrical stimulation of the cervical spinal cord were evoked in both relaxed and activated thenar muscles. In the relaxed muscle, prior TMS at an intensity that would suppress voluntary activity failed to influence the test responses, suggesting absence of inhibition at a spinal level. However, in the activated muscle, prior TMS could reduce the test response. This may be explained by disfacilitation of motoneurones due to inhibition of corticospinal output. 7. We propose that suppression of voluntary muscle activity by TMS is due in large part to activation of a mechanism within the motor cortex that reduces the corticospinal output to the muscle. It is concluded that TMS evokes excitation and inhibition via neuronal structures lying close to one another and having similar orientations.

Non-invasive brain stimulation as a tool to decrease chronic pain in current opiate users: A parametric evaluation of two promising cortical targets

Attention-deficit/hyperactivity disorder (ADHD) is a childhood-onset behavioral diagnosis in which children often fail to meet age norms in development of motor control, particularly timed repetitive and sequential movements, motor overflow, and balance. The neural substrate of this motor delay may include mechanisms of synaptic inhibition in or adjacent to the motor cortex. The primary objective of this study was to determine whether transcranial magnetic stimulation (TMS)-evoked measures, particularly short interval cortical inhibition (SICI), in motor cortex correlate with the presence and severity of ADHD in childhood as well as with commonly observed delays in motor control. In this case-control study, behavioral ratings, motor skills, and motor cortex physiology were evaluated in 49 children with ADHD (mean age 10.6 years, 30 boys) and 49 typically developing children (mean age 10.5 years, 30 boys), all right-handed, aged 8-12 years. Motor skills were evaluated with the Physical and Neurological Examination for Subtle Signs (PANESS) and the Motor Assessment Battery for Children version 2. SICI and other physiologic measures were obtained using TMS in the left motor cortex. In children with ADHD, mean SICI was reduced by 40% (p < 0.0001) and less SICI correlated with higher ADHD severity (r = -0.52; p = 0.002). Mean PANESS motor development scores were 59% worse in children with ADHD (p < 0.0001). Worse PANESS scores correlated modestly with less SICI (r = -.30; p = 0.01). Reduced TMS-evoked SICI correlates with ADHD diagnosis and symptom severity and also reflects motor skill development in children.

Cumulative effects of single TMS pulses during beta-tACS are stimulation intensity-dependent

Delivering transcranial magnetic brain stimulation over the motor cortex during motor imagination leads to enhanced motor output, which is selective for the muscles primarily involved in the imagined movement. This novel protocol may be useful to enhance function after damage to the motor system, such as after stroke. Several paired stimulation paradigms are known to induce plasticity in the motor cortex, reflected by changes in the motor evoked potential (MEP) following the paired stimulation. Motor imagery (MI) is capable of activating the motor system and affecting cortical excitability. We hypothesized that it might be possible to use MI in conjunction with transcranial magnetic stimulation (TMS) to induce plasticity in the human motor system. TMS was delivered to the motor cortex of healthy human subjects, and baseline MEPs recorded from forearm flexor, forearm extensor and intrinsic hand muscles. Subjects were then asked to imagine either wrist flexion or extension movements during TMS delivery (n=90 trials). Immediately after this intervention, MEP measurement was repeated. Control protocols tested the impact of imagination or TMS alone. Flexion imagination with TMS increased MEPs in flexors and an intrinsic hand muscle. Extensor imagination with TMS increased MEPs in extensor muscles only. The control paradigms did not produce significant changes. We conclude that delivering TMS during MI is capable of inducing plastic changes in the motor system. This new protocol may find utility to enhance functional rehabilitation after brain injury.

Studies on the influence of motor imagery (MI) on brain structure and function are limited to traditional imaging techniques and the mechanism for MI therapy is not clear. By observing the brain activation mode during MI and motor execution (ME) in healthy adults, this study aims to use near-infrared brain imaging technology to provide theoretical basis for the treatment of MI. A total of 30 healthy adults recruited to the public from June 2021 to August 2021. The MI and ME of the right knee movement served as the task mode. Block design was repeated 5 times alternately in a 20 s task period and a 30 s resting period. The activation patterns of brain regions were compared between the 2 tasks, and the regression coefficient was calculated to reflect the activation intensity of each brain region by Nirspark and SPSS 23.0 softwares. Lane 2, 3, 4, 5, 7, 9, 19, 20, 21, 24, 25, 26, 27, 32, 33, and 34 were significantly activated during the ME task (P<0.05, corrected by FDR) and lane 2, 5, 9, 16, 27, 29, 33, 34, and 35 were significantly activated during the MI task (P<0.05, corrected by FDR). According to the channel brain region registration information, the brain region activation pattern was similar during both MI and ME tasks in healthy adults, including left primary motor cortex (LM1), left primary sensory cortex (LS1), prefrontal pole, Broca area, and right supramarginal gyrus. Both LM1 and left pre-motor cortex (LPMC) were activated during MI in healthy adults, whereas dorsolateral prefrontal cortex (DLPFC) and only LM1 of the motor region were activated during ME. Compared to MI, the activation intensity of left sensory and left motor cortex was significantly enhanced in ME, and that of left and right prefrontal cortex especially left and right pars triangularis Broca's area (P<0.001, corrected by FDR) were significantly enhanced. The rationality of MI therapy is proved by functional near-infrared spectroscopy. The involvement of DLPFC in motor decision-making may regulate the two-way feedback of premoter cortex-M1 during ME; and Broca area, closely related to the motor program understanding, participates in MI and ME.

Prestimulus cortical EEG oscillations can predict the excitability of the primary motor cortex

In 1 split-brain patient and 13 patients with circumscript surgical lesions within different parts of the corpus callosum (CC), the topography of fibers within the CC mediating an interhemispheric inhibition between the motor cortices was investigated in the phase of a stable disconnection syndrome. The aim of the study was to characterize the system of callosal fibers activated by transcranial magnetic brain stimulation in more detail as a basis for a diagnostic application of this technique. The locations and areas of the lesions were measured on sagittal magnetic resonance (MR) slices and attributed to five segments of the CC, because the borders of the anatomic subdivisions of the CC are not clearly defined. Transcallosal inhibition (TI) of tonic electromyographical hand muscle activity was elicited by focal transcranial magnetic stimulation over the primary motor cortex. In a reference group of normal subjects, TI started after 35.8+/-3.6 msec had a duration of 24.8+/-2.7 msec and an estimated transcallosal conduction time of 15.5+/-3.0 msec (range, 10.2-20.0 msec, n = 24 hands). No significant differences were found for the TI originating from the right and left motor cortices. From the absence and presence of TI in patients with lesions in different parts of the CC it can be concluded that most of the fibers mediating TI pass through the posterior third and anterior fourth segment of the CC, that is, through the posterior half of the trunk of the CC. The clinical findings suggest a role for TI in the performance of fast and complex hand motor tasks.

GABA and cortical inhibition in motor and non-motor regions using combined TMS–EEG: A time analysis

Background: The results of high-frequency repetitive transcranial magnetic stimulation (rTMS) over the dorsolateral prefrontal cortex for migraine have been inconsistent. However, high-frequency rTMS over the motor cortex is a treatment that may be effective in relieving symptoms of migraine with a low risk of side effects. Methods: A systematic review of high-frequency rTMS over the brain motor cortex areas in human participants was conducted to assess efficacy in treating migraine. Articles that were not looking at migraine patients, stimulation over the left motor cortex, or were not in English were excluded. Nine articles representing eight experiments using high-frequency rTMS over the motor cortex areas for migraine in human participants were extracted from the databases of PubMed, PsycINFO, MedLine, CINAHL, and BioMed Central. Results: Two-hundred and seven of 213 patients completed treatment throughout all the studies examined. High-frequency rTMS over the motor cortex areas for migraine improved migraine frequency in seven of eight studies. Two of the eight studies were randomized controlled trials at low risk for biases and found high-frequency rTMS over the motor cortex areas effective in improving migraine frequency and severity. Other details of treatment prescription and symptoms were also examined. Conclusion: High-frequency rTMS over the motor cortex areas for migraine demonstrated efficacy as a migraine treatment, had minimal side effects, and should be further investigated.

Contact forces evoked by transcranial magnetic stimulation of the motor cortex in a multi-finger grasp

Transcranial magnetic stimulation (TMS) is known to elicit a conditioning effect on cortical excitability. The purpose of this study was to investigate changes in cortical excitability induced by peripheral stimulation with differing frequency and stimulation site. A magnetic stimulator with a flat figure-eight coil was used for TMS and was performed on the left primary motor cortex. The electrical stimulation and magnetic stimulation were used in peripheral stimulation and the stimulus sites were the right and left supination of the forearm. Peripheral stimulation was performed at a stimulus frequency of 1 Hz or 10 Hz. Alterations of cortical excitability induced by peripheral stimulation were evaluated by comparing the mean of the motor evoked potential amplitude elicited by TMS each before and after peripheral stimulation. We found that cortical excitability varied according to the stimulation site and frequency in both the electrical and magnetic stimulation over the forearm. The inhibition of cortical excitability was observed in both 1 Hz electrical and magnetic stimulation over the right forearm. In contrast, the facilitation of cortical excitability was observed at 1 Hz electrical and magnetic stimulation over the left forearm, and it was confirmed for both the right and left forearms at 10 Hz electrical and magnetic stimulation. Moreover, regarding the alteration of cortical excitability induced by peripheral stimulation, it was confirmed that magnetic stimulation has more the significant difference than electrical stimulation. We suggest that peripheral stimulation by electrical and magnetic stimulation have a similar effect to TMS, and can induce both facilitation and inhibition of cortical excitability. Moreover, in the case of peripheral stimulation of the same stimulus frequency, we expect that the magnetic stimulation has more the significant effect than electrical stimulation to cortical excitability.

P279 Short-latency afferent inhibition from the dorsolateral prefrontal cortex in patients with schizophrenia: A TMS-EEG study