Differential effects of continuous theta burst stimulation over left premotor cortex and right prefrontal cortex on modulating upper limb somatosensory input

The Neurophysiological Effects of Theta Burst Stimulation as Measured by Electroencephalography: A Systematic Review

Theta burst stimulation (TBS) is a non-invasive brain stimulation technique that can modulate neural activity. The effect of TBS on regions beyond the motor cortex remains unclear. With increased interest in applying TBS to non-motor regions for research and clinical purposes, these effects must be understood and characterised. We synthesised the electrophysiological effects of a single session of TBS, as indexed by electroencephalography (EEG) and concurrent transcranial magnetic stimulation and EEG (TMS-EEG), in non-clinical participants. We reviewed 79 studies that administered either continuous TBS (cTBS) or intermittent TBS (iTBS) protocols. Broadly, cTBS suppressed and iTBS facilitated evoked response component amplitudes. Response to TBS as measured by spectral power and connectivity was much more variable. Variability increased in the presence of task stimuli. There was a large degree of heterogeneity in the research methodology across studies. Additionally, the effect of individual differences on TBS response is insufficiently investigated. Future research investigating the effects of TBS as measured by EEG must consider methodological and individual factors that may affect TBS outcomes.

Long-term effects of concussion on relevancy-based modulation of somatosensory-evoked potentials

OBJECTIVE

The purpose of this investigation was to better understand the effects of concussions on the ability to selectively up or down-regulate incoming somatosensory information based on relevance.

METHODS

Median nerve somatosensory-evoked potentials (SEPs) were elicited from electrical stimulation and recorded from scalp electrodes while participants completed tasks that altered the relevance of specific somatosensory information being conveyed along the stimulated nerve.

RESULTS

Within the control group, SEP amplitudes for task-relevant somatosensory information were significantly greater than for non-relevant somatosensory information at the earliest cortical processing potentials (N20-P27). Alternatively, the concussion history group showed similar SEP amplitudes for all conditions at early processing potentials, however a pattern similar to controls emerged later in the processing stream (P100) where both movement-related gating and facilitation of task-relevant information were present.

CONCLUSIONS

Previously concussed participants demonstrated impairments in the ability to up-regulate relevant somatosensory information at early processing stages. These effects appear to be chronic, as this pattern was observed on average several years after participants' most recent concussion.

SIGNIFICANCE

Given the role of the prefrontal cortex in relevancy-based facilitation during movement-related gating, these findings lend support to the notion that this brain area may be particularly vulnerable to concussive forces.

EEG μ-rhythm reactivity in children during imitation of biological and non-biological motion

The development of brain-computer interfaces based on the use of EEG sensorimotor rhythms reactivity parameters and designed for the rehabilitation of people (including children) with impaired motor functions is currently relevant. The study was aimed to analyse the EEG μ-rhythm in the individual frequency range in children during imitation of biological and non-biological motion. EEG was recorded at frontal, central and parietal cortical regions in 136 normally developing right-handed children aged 4–15, at rest and during the execution and imitation of movements using the computer mouse. When the children moved the computer mouse on their own (F1, 132 = 31.17; p < 0.001) and executed the concentric moving of the coloured circle (F1, 132 = 90.34; p < 0.001), the μ-rhythm desynchronization developed in the frontal, central and parietal neocortical regions. The μ-rhythm synchronization was detected during the non-biologocal motion imitation (F1, 132 = 12.65; p < 0.001), compared to the task on the autonomous movement execution. The μ-rhythm desynchronization was observed during the biologocal motion imitation in relation to autonomous movement execution (F1, 132 = 9.58; p = 0.002). The described effects had their own features in the groups of children aged 4–6, 7–9, 10–12 and 13–15. The study results demonstrate the desirability of taking into account the μ-rhythm reactivity age-related features and the visual stimuli nature when developing software for the brain-computer interfaces.

Acquisition of chopstick-operation skills with the non-dominant hand and concomitant changes in brain activity

Despite their common use as eating utensils in East Asia, chopsticks require complex fine motor-skills for adequate operation and are thus most frequently used with the dominant hand; however, the effect of training time on the proficiency of using chopsticks with the non-dominant hand, as well as the brain activity underlying changes in skill, remain unclear. This study characterised the effect of time spent training in chopstick operation with the non-dominant hand on chopstick-use proficiency and the related brain activity to obtain data that may help individuals who are obliged to change handedness due to neurological disease to learn to use their non-dominant hand in performing daily activities. Thirty-two healthy right-handed students were randomly allocated to training (n = 16) or control (n = 16) groups; the former received 6 weeks of training in chopstick use with their non-dominant (left) hand, and the latter received none. After training, significant improvements in the execution speed and smoothness of upper extremity joints were observed in the training group. Moreover, left dorsolateral prefrontal cortex activity significantly decreased, and bilateral premotor cortex activity significantly increased across training. These results indicated that 6 weeks of chopstick training with the non-dominant hand effectively improved chopstick operation.