Non-invasive induction of plasticity in the human cortex: uses and limitations

The last couple of decades have seen the development of a number of non-invasive brain stimulation (NIBS) techniques that are capable of inducing short-lasting plasticity in the human cortex. Importantly, the induction of lasting plastic changes can, under some conditions, reversibly modify behaviour and interact with learning. These techniques have provided novel opportunities to study human cortical plasticity and examine the role of cortical regions in behaviour. In this review we briefly summarise current NIBS techniques, outline approaches to characterise and quantify cortical plastic change, and describe mechanisms that are implicated in the induced plastic changes. We then outline the areas in which these techniques might be useful, namely, investigating the mechanisms of human cortical plasticity, the characterisation of influences on plasticity, and the investigation of the role of cortical regions in behaviour. Finally, we conclude by highlighting some current limitations of the techniques and suggest that further development of the current NIBS paradigms and more focussed targeting should further enhance the utility of these powerful non-invasive techniques for the investigation of the cortical plasticity and pathophysiology

Non-invasive induction of plasticity in the human cortex: uses and limitations

The last couple of decades have seen the development of a number of non-invasive brain stimulation (NIBS) techniques that are capable of inducing short-lasting plasticity in the human cortex. Importantly, the induction of lasting plastic changes can, under some conditions, reversibly modify behaviour and interact with learning. These techniques have provided novel opportunities to study human cortical plasticity and examine the role of cortical regions in behaviour. In this review we briefly summarise current NIBS techniques, outline approaches to characterise and quantify cortical plastic change, and describe mechanisms that are implicated in the induced plastic changes. We then outline the areas in which these techniques might be useful, namely, investigating the mechanisms of human cortical plasticity, the characterisation of influences on plasticity, and the investigation of the role of cortical regions in behaviour. Finally, we conclude by highlighting some current limitations of the techniques and suggest that further development of the current NIBS paradigms and more focussed targeting should further enhance the utility of these powerful non-invasive techniques for the investigation of the cortical plasticity and pathophysiology

Asymmetrical facilitation of motor-evoked potentials following motor practice

Use-dependent facilitation of motor-evoked potentials evoked by transcranial magnetic stimulation with repetition of simple movements has been well established. Motor-evoked potentials were recorded from two intrinsic hand muscles before and after blocks of motor practice in which study participants made repeated ballistic pinch responses with either their left or their right hand. Despite similar increases in behavioral performance by each hand (measured by the peak acceleration of the force generated by the index finger), practice-related increases in the amplitude of the motor-evoked potentials were greater in the left than in the right motor cortex of right-handed participants. This finding supports the hypothesis that the dominant motor cortex has a greater ability to reorganize with experience than the non-dominant motor cortex

A comparison of neuroplastic responses to non-invasive brain stimulation protocols and motor learning in healthy adults

Non-invasive brain stimulation (NBS) techniques can induce neuroplastic changes similar to those associated with motor learning and there is evidence for the involvement of common mechanisms. Whether there are correlations between the changes induced by NBS and those associated with motor learning remains unclear. We investigated whether there was any relationship between an individual's neuroplastic responses to several different NBS protocols (continuous theta-burst stimulation (cTBS); intermittent theta-burst stimulation (iTBS); facilitatory paired associative stimulation (PAS: inter-stimulus interval 25ms)) and whether these responses correlated with the neuroplastic response associated with a motor training (MT) task involving repeated fast-as-possible thumb abductions. Changes in motor evoked potential (MEP) amplitude were used to assess the neuroplastic response to each protocol. MEP amplitude decreased significantly following cTBS, however there was no significant change in MEP amplitude following iTBS, PAS or MT. There were no significant correlations between individuals' neuroplastic responses to any of the NBS protocols tested or between individuals' neuroplastic responses to the NBS protocols and motor learning. These results provide no support for an association between individuals' neuroplastic responses to several plasticity-inducing protocols. Although there is evidence for involvement of common mechanisms in the neuroplastic changes induced by NBS and motor learning, the results of this study suggest (1) the mechanisms mediating TBS-, PAS-, and MT-induced plasticity may only partially overlap, and (2) additional factors, including large intra and inter-subject response variability, may make the demonstration of associations between neuroplastic responses to the various protocols difficult

Increase in flexor but not extensor corticospinal motor outputs following ischemic nerve block

Human motor cortex is capable of rapid and long-lasting reorganization, evident globally, as shifts in body part representations, and at the level of individual muscles as changes in corticospinal excitability. Representational shifts provide an overview of how various body parts reorganize relative to each other but do not tell us whether all muscles in a given body part reorganize in the same manner and to the same extent. Transcranial magnetic stimulation (TMS) provides information about individual muscles and can therefore inform us about the uniformity of plastic changes within a body part. We used TMS to investigate changes in corticospinal excitability of forearm flexors and extensors after inflation of a tourniquet around the wrist. Motor evoked potential (MEP) amplitudes and input/output (I/O) curves were obtained from wrist flexors and extensors simultaneously before and during block. TMS was delivered to the optimal site for eliciting MEPs in flexors in experiment 1, extensors in experiment 2, and both flexors and extensors in experiment 3. In all experiments flexor MEP amplitude increased during block while extensor MEP amplitude showed no systematic change, and the slope of flexor but not extensor I/O curves increased. Flexor H-reflex amplitude normalized to maximal M wave showed negligible changes during block, suggesting that the increase in corticospinal excitability in the flexors cannot be completely explained by increased excitability at the spinal cord level. These findings show that forearm flexors and extensors differ in their potential for plastic changes, highlight the importance of investigating how experimentally induced plasticity affects anatomically close, but functionally distinct, muscle groups, and suggest that rehabilitation interventions aiming to alter cortical organization should consider the differential sensitivity of various muscle groups to plasticity processes

Excitability of intracortical inhibitory and facilitatory circuits during ischemic nerve block

Purpose: The primary motor cortex is capable of rapid, reversible plastic changes and longer-term, more permanent reorganization. Ischemic nerve block (INB) is a model of deafferentation-induced short-term plasticity. We used transcranial magnetic stimulation to examine whether changes in the excitability of short- and/or long-interval intracortical inhibitory (SICI, LICI) or short-interval intracortical facilitatory (SICF) circuits underlie the corticospinal excitability increases observed during INB. Methods: SICI and LICI recruitment curves, obtained by varying conditioning stimulus intensity, and SICF were measured at multiple inter-stimulus intervals (ISIs). Results: Forearm flexor MEP amplitude increased during INB at the wrist; this was not accompanied by changes in SICI at ISIs of 1 or 2 ms, in SICF at ISIs of 1.2, 2.7, or 4.4 ms, or in LICI at an ISI of 80 ms, but was accompanied by an increase in LICI at an ISI of 150 ms. Conclusions: The results suggest that (1) the increased excitability of forearm flexors is not due to reduced SICI or LICI or increased SICF, and (2) LICI measured at ISIs of 80 and 150 ms are distinct processes. We discuss the importance of identifying distinct processes of LICI and speculate regarding other mechanisms that could potentially underlie INB-induced plasticity

Student learning: "the heart of quality" in education and training

This paper surveys the development of various approaches to quality that are essentially learning-centred: &bull;In the Schools sector: a brief overview of the Victorian Quality in Schools project; &bull;In Higher Education: work in progress at two Australian universities (Victoria University of Technology and Swinburne Universities of Technology in Melbourne); and &bull;In Vocational Education and Training: work in progress in re-orienting the policy approach to Quality towards a more flexible and learning-centred model.This paper will argue that when looked at from the perspective of the individual learner, there is a strong case for student learning to be placed at the very heart of Quality Systems in all sectors of education, and also therefore in related sectoral Quality Assurance programs and processes. <br /

The influence of cortical alpha oscillatory activity on motor cortical excitability and plasticity induction

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Transcranial direct current stimulation to optimise participation in stroke rehabilitation – A sham-controlled cross-over feasibility study

Background: Fatigue and attentional decline limit the duration of many therapy sessions in older adults poststroke. Transcranial direct current stimulation (tDCS) may facilitate participation in rehabilitation, potentially via reduced fatigue and improved sustained attention poststroke. Objective: To evaluate whether tDCS results in an increase in the number of completed rehabilitation therapy sessions in stroke survivors. Methods: Nineteen participants were randomly allocated to receive 10 sessions of 2-mA anodal (excitatory) tDCS, or sham tDCS, applied to the left dorsolateral prefrontal cortex (DLPFC) for 20 minutes within 1 hour prior to the first rehabilitation therapy session of the day. After a 2-day washout period, participants then crossed-over. Researchers applying the tDCS, and those recording measures were blinded to group allocation. The number of first rehabilitation therapy sessions completed as planned, as well as the total duration of rehabilitation therapy, were used to determine the influence of tDCS on participation in stroke rehabilitation. Results: The total number of first therapy sessions completed as planned did not vary according to group allocation (111 of 139 sessions for tDCS, 110 of 147 sessions for sham treatment; chi-square 1.0; P =.31). Conclusions: Our results suggest that, while tDCS to the DLPFC was well tolerated, it did not significantly influence the number of completed rehabilitation therapy sessions in stroke survivors. © The Author(s) 2020

Transcranial direct current stimulation to optimise participation in stroke rehabilitation – A Sham-Controlled Cross-Over feasibility study

Background: Fatigue and attentional decline limit the duration of many therapy sessions in older adults poststroke. Transcranial direct current stimulation (tDCS) may facilitate participation in rehabilitation, potentially via reduced fatigue and improved sustained attention poststroke. Objective: To evaluate whether tDCS results in an increase in the number of completed rehabilitation therapy sessions in stroke survivors. Methods: Nineteen participants were randomly allocated to receive 10 sessions of 2-mA anodal (excitatory) tDCS, or sham tDCS, applied to the left dorsolateral prefrontal cortex (DLPFC) for 20 minutes within 1 hour prior to the first rehabilitation therapy session of the day. After a 2-day washout period, participants then crossed-over. Researchers applying the tDCS, and those recording measures were blinded to group allocation. The number of first rehabilitation therapy sessions completed as planned, as well as the total duration of rehabilitation therapy, were used to determine the influence of tDCS on participation in stroke rehabilitation. Results: The total number of first therapy sessions completed as planned did not vary according to group allocation (111 of 139 sessions for tDCS, 110 of 147 sessions for sham treatment; chi-square 1.0; P = .31). Conclusions: Our results suggest that, while tDCS to the DLPFC was well tolerated, it did not significantly influence the number of completed rehabilitation therapy sessions in stroke survivors