Induction of plasticity in the human motor system by motor imagery and transcranial magnetic stimulation

Abstract

Key points 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. Abstract 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.

Imagined paralysis reduces motor cortex excitability

“…A limitation of this study is the number of participants, which was relatively small (n = 12), although not unusual in this field of research (Fadiga et al, 1998;Foysal & Baker, 2020;Pitcher et al, 2005;Yahagi & Kasai, 1998). Nevertheless, given the high consistency in the individual patterns (note that 11 of 12 participants followed the pattern of the main result that imagined paralysis of the arm reduced MEP amplitudes compared to baseline), together with the reliability of our measurement and the Bayesian hierarchical regression analysis approach, we think that our results are robust and make a valid contribution to the field.…”

Towards a mechanistic approach for the development of non‐invasive brain‐computer interfaces for motor rehabilitation

“…Future studies of this type of BCI therefore should also aim to quantify the possible changes of cortical networks involved (Ibáñez et al 2020). Since the first proof of concept of plastic changes induced by pairing the SCP peak with stimulation, a number of different BCI modalities based on the idea of tightly linking brain states with different forms of brain stimulation have been proposed (Gharabaghi et al 2014;Kraus et al 2016Kraus et al , 2018Foysal & Baker, 2020). However, it is unlikely that these fulfil the tight coupling in time (within milliseconds) between the two inputs as was the original idea of the PAS protocol for inducing LTP-like plasticity (Stefan et al 2000).…”

“…2014; Kraus et al . 2016, 2018; Foysal & Baker, 2020). However, it is unlikely that these fulfil the tight coupling in time (within milliseconds) between the two inputs as was the original idea of the PAS protocol for inducing LTP‐like plasticity (Stefan et al .…”

Motor Point Stimulation in Spinal Paired Associative Stimulation can Facilitate Spinal Cord Excitability

“…Given changes to MEP size are related to both stimulation intensity and duration (Maeda et al, 2000;Modugno et al, 2001;Fitzgerald et al, 2002) it is possible lower intensity, but longer durations produce similar effects to high intensity repetitive TMS at 0.1 Hz. Alternatively, a study by Foysal and Baker (2020) found that repetitive low frequency TMS at an intensity of 110%RMT coupled with motor imagery for 90 stimuli was sufficient to increase MEP sizes. This may suggest that while our subjects were instructed to relax throughout the intervention, there may have been some underlying activity in the motor cortex during the PAS intervention.…”