Simulation of transcranial magnetic stimulation in head model with morphologically-realistic cortical neuronsTranscranial magnetic stimulation (TMS) enables non-invasive modulation of brain activity with both clinical and research applications, but fundamental questions remain about the neural types and elements TMS activates and how stimulation parameters affect the neural response.
Direction of TDCS current flow in human sensorimotor cortex influences behavioural learningRecent studies have shown that neurophysiological outcomes of transcranial direct current stimulation (TDCS) are influenced by current flow in brain regions between the electrodes, and in particular the orientation of current flow relative to the cortical surface.
Dual-site high-density 4Hz transcranial alternating current stimulation applied over auditory and motor cortical speech areas does not influence auditory-motor mappingLearning to speak and speaking require the continuous mapping of speech sounds onto articulatory motor plans (auditory-motor mapping). Previous studies using various techniques (histology, lesion mapping, diffusion tensor-imaging, and transcranial magnetic stimulation) have provided converging evidence for the relevance of a dorsal cortical processing stream, including auditory and motor areas, for auditory-motor mapping [1–4].
Motor training modulates intracortical inhibitory dynamics in motor cortex during movement preparationThe primary motor cortex (M1) has a vital role to play in the learning of novel motor skills. However, the physiological changes underpinning this learning, particularly in terms of dynamic changes during movement preparation, are incompletely understood. In particular, a substantial decrease in resting gamma-amino butyric acid (GABA) activity, i.e. a release of resting inhibition, is seen within M1 as a subject prepares to move. Although there is evidence that a decrease in resting inhibition occurs within M1 during motor learning it is not known whether the pre-movement “release” of GABAergic inhibition is modulated during skill acquisition.
Vagus nerve stimulation intensity influences motor cortex plasticityVagus nerve stimulation (VNS) paired with forelimb motor training enhances reorganization of movement representations in the motor cortex. Previous studies have shown an inverted-U relationship between VNS intensity and plasticity in other brain areas, such that moderate intensity VNS yields greater cortical plasticity than low or high intensity VNS. However, the relationship between VNS intensity and plasticity in the motor cortex is unknown.
Multi-session anodal tDCS enhances the effects of postural training on balance and postural stability in older adults with high fall risk: Primary motor cortex versus cerebellar stimulationPostural control impairment is a key target for rehabilitation of older adults with high fall risk.
Transcranial magnetic stimulation modulation of corticospinal excitability by targeting cortical I-waves with biphasic paired-pulsesTranscranial magnetic stimulation (TMS) induced I-wave behavior can be demonstrated at neuronal population level using paired-pulses and by observing short-interval cortical facilitation (SICF). Advancements in stimulator technology have made it possible to apply biphasic paired-pulses to induce SICF.
Where and what TMS activates: Experiments and modelingDespite recent developments in navigation and modeling techniques, the type and location of the structures that are activated by transcranial magnetic stimulation (TMS) remain unknown.
Modulation of motor cortex excitability predicts antidepressant response to prefrontal cortex repetitive transcranial magnetic stimulationRepetitive transcranial magnetic stimulation (rTMS) targeting the left dorsolateral prefrontal cortex (DLPFC) is a treatment option for patients with medication-resistant major depressive disorder (MDD). However, antidepressant response is variable and there are currently no response predictors with sufficient accuracy for clinical use.
Cortical inhibitory and excitatory function in drug-naive generalized anxiety disorderA growing body of evidence suggests that deficits in GABAergic inhibitory and glutamatergic excitatory neurotransmission may be involved in the core pathophysiology of generalized anxiety disorder (GAD), a disease characterized by pathological anxious worrying. The aim of the present study was to measure motor cortical excitability by paired-pulse transcranial magnetic stimulation (ppTMS) in patients with GAD.
Variability in neural excitability and plasticity induction in the human cortex: A brain stimulation studyThe potential of non-invasive brain stimulation (NIBS) for both probing human neuroplasticity and the induction of functionally relevant neuroplastic change has received significant interest. However, at present the utility of NIBS is limited due to high response variability. One reason for this response variability is that NIBS targets a diffuse cortical population and the net outcome to stimulation depends on the relative levels of excitability in each population. There is evidence that the relative excitability of complex oligosynaptic circuits (late I-wave circuits) as assessed by transcranial magnetic stimulation (TMS) is useful in predicting NIBS response.
Modulation of the Direction and Magnitude of Hebbian Plasticity in Human Motor Cortex by Stimulus Intensity and Concurrent InhibitionOne of the most fascinating and important properties of the mammalian brain is its remarkable capacity for plasticity. Synaptic plasticity is considered to be the primary neuronal substrate for learning and memory . As predicted in Hebb's postulate of associative plasticity in 1949 , synapses are strengthened if presynaptic activity precedes and contributes to postsynaptic firing, referred to as long term potentiation (LTP) , and weakened if the order is reversed, termed long term depression (LTD) .
Repetitive Transcranial Magnetic Stimulation Educes Frequency-Specific Causal Relationships in the Motor NetworkRepetitive transcranial magnetic stimulation (rTMS) has the potential to treat brain disorders by modulating the activity of disease-specific brain networks. A prime example of this approach may be seen in the rTMS treatments of the fronto-limbic network of major depressive disorder [1–3], in which rTMS is delivered to the dorsolateral prefrontal cortex to indirectly modulate the activity levels of the subgenual cingulate, which is too deep for standard rTMS coils to reach. Traditionally, rTMS rate has been applied in rTMS treatment protocols in either an inhibitory (≤1 Hz) or excitatory (>1 Hz) fashion [4,5], where it is assumed that these inhibitory or excitatory rTMS treatments affect the targeted brain networks in the same linear way – i.e.
Reorganization of Motor Cortex by Vagus Nerve Stimulation Requires Cholinergic InnervationNeuromodulatory interventions have been extensively investigated as potential therapies to reverse maladaptive plasticity or boost limited plasticity to treat neurological disease. Recently, vagus nerve stimulation (VNS) has emerged as one such potential adjunctive intervention to enhance neuroplasticity . Repeated presentation of auditory stimuli paired with short bursts of VNS drives long-lasting plasticity in auditory cortex [2–4]. Moreover, VNS paired with forelimb training drives robust, specific reorganization in motor cortex .
Inter-subject Variability in Electric Fields of Motor Cortical tDCSThe sources of inter-subject variability in the efficacy of transcranial direct current stimulation (tDCS) remain unknown. One potential source of variations is the brain's electric field, which varies according to each individual's anatomical features.
Intracortical Microstimulation (ICMS) Activates Motor Cortex Layer 5 Pyramidal Neurons Mainly TranssynapticallyIntracortical microstimulation (ICMS) is a technique used for a number of purposes including the derivation of cortical movement representations (motor maps). Its application can activate the output layer 5 of motor cortex and can result in the elicitation of body movements depending upon the stimulus parameters used.
Variability in Response to Transcranial Direct Current Stimulation of the Motor CortexResponses to a number of different plasticity-inducing brain stimulation protocols are highly variable. However there is little data available on the variability of response to transcranial direct current stimulation (TDCS).
Influence of Waveform and Current Direction on Short-Interval Intracortical Facilitation: A Paired-Pulse TMS StudyTranscranial magnetic stimulation (TMS) of the human primary motor hand area (M1-HAND) can produce multiple descending volleys in fast-conducting corticospinal neurons, especially so-called indirect waves (I-waves) resulting from trans-synaptic excitation. Facilitatory interaction between these I-waves can be studied non-invasively using a paired-pulse paradigm referred to as short-interval intracortical facilitation (SICF).
Induction of Late LTP-Like Plasticity in the Human Motor Cortex by Repeated Non-Invasive Brain StimulationNon-invasive brain stimulation enables the induction of neuroplasticity in humans, however, with so far restricted duration of the respective cortical excitability modifications. Conventional anodal transcranial direct current stimulation (tDCS) protocols including one stimulation session induce NMDA receptor-dependent excitability enhancements lasting for about 1 h.