Contribution of TMS and TMS-EEG to the Understanding of Mechanisms Underlying Physiological Brain Aging

In the human brain, aging is characterized by progressive neuronal loss, leading to disruption of synapses and to a degree of failure in neurotransmission. However, there is increasing evidence to support the notion that the aged brain has a remarkable ability to reorganize itself, with the aim of preserving its physiological activity. It is important to develop objective markers able to characterize the biological processes underlying brain aging in the intact human, and to distinguish them from brain degeneration associated with many neurological diseases. Transcranial magnetic stimulation (TMS), coupled with electromyography or electroencephalography (EEG), is particularly suited to this aim, due to the functional nature of the information provided, and thanks to the ease with which it can be integrated with behavioral manipulation. In this review, we aimed to provide up to date information about the role of TMS and TMS-EEG in the investigation of brain aging. In particular, we focused on data about cortical excitability, connectivity and plasticity, obtained by using readouts such as motor evoked potentials and transcranial evoked potentials. Overall, findings in the literature support an important potential contribution of TMS to the understanding of the mechanisms underlying normal brain aging. Further studies are needed to expand the current body of information and to assess the applicability of TMS findings in the clinical setting.

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Somatosensory cortical excitability changes precede those in motor cortex during human motor learning

Journal of Neurophysiology ◽

10.1152/jn.00383.2019 ◽

2019 ◽

Vol 122 (4) ◽

pp. 1397-1405 ◽

Cited By ~ 6

Author(s):

Hiroki Ohashi ◽

Paul L. Gribble ◽

David J. Ostry

Keyword(s):

Motor Cortex ◽

Motor Learning ◽

Evoked Potentials ◽

Somatosensory Cortex ◽

Somatosensory Evoked Potentials ◽

Motor Skill ◽

Cortical Excitability ◽

Motor Evoked Potentials ◽

Human Motor ◽

Motor Cortical

Motor learning is associated with plasticity in both motor and somatosensory cortex. It is known from animal studies that tetanic stimulation to each of these areas individually induces long-term potentiation in its counterpart. In this context it is possible that changes in motor cortex contribute to somatosensory change and that changes in somatosensory cortex are involved in changes in motor areas of the brain. It is also possible that learning-related plasticity occurs in these areas independently. To better understand the relative contribution to human motor learning of motor cortical and somatosensory plasticity, we assessed the time course of changes in primary somatosensory and motor cortex excitability during motor skill learning. Learning was assessed using a force production task in which a target force profile varied from one trial to the next. The excitability of primary somatosensory cortex was measured using somatosensory evoked potentials in response to median nerve stimulation. The excitability of primary motor cortex was measured using motor evoked potentials elicited by single-pulse transcranial magnetic stimulation. These two measures were interleaved with blocks of motor learning trials. We found that the earliest changes in cortical excitability during learning occurred in somatosensory cortical responses, and these changes preceded changes in motor cortical excitability. Changes in somatosensory evoked potentials were correlated with behavioral measures of learning. Changes in motor evoked potentials were not. These findings indicate that plasticity in somatosensory cortex occurs as a part of the earliest stages of motor learning, before changes in motor cortex are observed. NEW & NOTEWORTHY We tracked somatosensory and motor cortical excitability during motor skill acquisition. Changes in both motor cortical and somatosensory excitability were observed during learning; however, the earliest changes were in somatosensory cortex, not motor cortex. Moreover, the earliest changes in somatosensory cortical excitability predict the extent of subsequent learning; those in motor cortex do not. This is consistent with the idea that plasticity in somatosensory cortex coincides with the earliest stages of human motor learning.

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An Increase in Cortical Excitability with No Change in Spinal Excitability during Motor Imagery

Perceptual and Motor Skills ◽

10.2466/pms.1996.83.1.288 ◽

1996 ◽

Vol 83 (1) ◽

pp. 288-290 ◽

Cited By ~ 56

Author(s):

Susumu Yahagi ◽

Kuniyoshi Shimura ◽

Tatsuya Kasai

Keyword(s):

Transcranial Magnetic Stimulation ◽

Evoked Potentials ◽

Motor Imagery ◽

Magnetic Stimulation ◽

Cortical Excitability ◽

Motor Evoked Potentials ◽

Emg Activity ◽

Electrical Stimuli ◽

Spinal Excitability ◽

Flexor Carpi Radialis Muscle

During motor imagery, to estimate changes in excitability of flexor carpi radialis muscle motoneurons of the spinal and cortical levels, electrical stimuli for recording H-reflex and transcranial magnetic stimulation (TMS) for recording motor evoked potentials (MEPs) were used. In the absence of movement or detectable EMG activity during motor magery, there was an increase in cortical excitability with no change in spinal excitability

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Evaluation of tDCS-induced Cortical Excitability Changes by Motor Evoked Potentials Amplitude

Brain Stimulation ◽

10.1016/j.brs.2015.01.207 ◽

2015 ◽

Vol 8 (2) ◽

pp. 377

Author(s):

A.V. Masliukova ◽

N.A. Smirnov

Keyword(s):

Evoked Potentials ◽

Cortical Excitability ◽

Motor Evoked Potentials

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A single bout of aerobic exercise promotes motor cortical neuroplasticity

Journal of Applied Physiology ◽

10.1152/japplphysiol.01378.2012 ◽

2013 ◽

Vol 114 (9) ◽

pp. 1174-1182 ◽

Cited By ~ 94

Author(s):

Michelle N. McDonnell ◽

Jonathan D. Buckley ◽

George M. Opie ◽

Michael C. Ridding ◽

John G. Semmler

Keyword(s):

Motor Cortex ◽

Evoked Potentials ◽

Aerobic Exercise ◽

Neurotrophic Factor ◽

Cortical Excitability ◽

Motor Evoked Potentials ◽

Moderate Intensity ◽

Single Session ◽

Low Intensity ◽

First Dorsal Interosseus

Regular physical activity is associated with enhanced plasticity in the motor cortex, but the effect of a single session of aerobic exercise on neuroplasticity is unknown. The aim of this study was to compare corticospinal excitability and plasticity in the upper limb cortical representation following a single session of lower limb cycling at either low or moderate intensity, or a control condition. We recruited 25 healthy adults to take part in three experimental sessions. Cortical excitability was examined using transcranial magnetic stimulation to elicit motor-evoked potentials in the right first dorsal interosseus muscle. Levels of serum brain-derived neurotrophic factor and cortisol were assessed throughout the experiments. Following baseline testing, participants cycled on a stationary bike at a workload equivalent to 57% (low intensity, 30 min) or 77% age-predicted maximal heart rate (moderate intensity, 15 min), or a seated control condition. Neuroplasticity within the primary motor cortex was then examined using a continuous theta burst stimulation (cTBS) paradigm. We found that exercise did not alter cortical excitability. Following cTBS, there was a transient inhibition of first dorsal interosseus motor-evoked potentials during control and low-intensity conditions, but this was only significantly different following the low-intensity state. Moderate-intensity exercise alone increased serum cortisol levels, but brain-derived neurotrophic factor levels did not increase across any condition. In summary, low-intensity cycling promoted the neuroplastic response to cTBS within the motor cortex of healthy adults. These findings suggest that light exercise has the potential to enhance the effectiveness of motor learning or recovery following brain damage.

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Motor cortex excitability does not increase during sustained cycling exercise to volitional exhaustion

Journal of Applied Physiology ◽

10.1152/japplphysiol.00486.2012 ◽

2012 ◽

Vol 113 (3) ◽

pp. 401-409 ◽

Cited By ~ 45

Author(s):

Simranjit K. Sidhu ◽

Andrew G. Cresswell ◽

Timothy J. Carroll

Keyword(s):

Motor Cortex ◽

Evoked Potentials ◽

Cortical Neurons ◽

Cortical Excitability ◽

Motor Evoked Potentials ◽

Vastus Lateralis ◽

Rectus Femoris ◽

Cycling Exercise ◽

Motor Cortex Excitability ◽

Stimulation Of

The excitability of the motor cortex increases as fatigue develops during sustained single-joint contractions, but there are no previous reports on how corticospinal excitability is affected by sustained locomotor exercise. Here we addressed this issue by measuring spinal and cortical excitability changes during sustained cycling exercise. Vastus lateralis (VL) and rectus femoris (RF) muscle responses to transcranial magnetic stimulation of the motor cortex (motor evoked potentials, MEPs) and electrical stimulation of the descending tracts (cervicomedullary evoked potentials, CMEPs) were recorded every 3 min from nine subjects during 30 min of cycling at 75% of maximum workload (Wmax), and every minute during subsequent exercise at 105% of Wmax until subjective task failure. Responses were also measured during nonfatiguing control bouts at 80% and 110% of Wmax prior to sustained exercise. There were no significant changes in MEPs or CMEPs ( P > 0.05) during the sustained cycling exercise. These results suggest that, in contrast to sustained single-joint contractions, sustained cycling exercise does not increase the excitability of motor cortical neurons. The contrasting corticospinal responses to the two modes of exercise may be due to differences in their associated systemic physiological consequences.

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Local Differences in Cortical Excitability – A Systematic Mapping Study of the TMS-Evoked N100 Component

Frontiers in Neuroscience ◽

10.3389/fnins.2021.623692 ◽

2021 ◽

Vol 15 ◽

Author(s):

Daniela Roos ◽

Lea Biermann ◽

Tomasz A. Jarczok ◽

Stephan Bender

Keyword(s):

Motor Cortex ◽

Evoked Potentials ◽

Primary Motor Cortex ◽

Cortical Excitability ◽

Motor Evoked Potentials ◽

Hot Spot ◽

Source Analysis ◽

Systematic Mapping Study ◽

Stimulation Site ◽

Two Parameters

Transcranial magnetic stimulation (TMS) with simultaneous electroencephalography applied to the primary motor cortex provides two parameters for cortical excitability: motor evoked potentials (MEPs) and TMS-evoked potentials (TEPs). This study aimed to evaluate the effects of systematic coil shifts on both the TEP N100 component and MEPs in addition to the relationship between both parameters. In 12 healthy adults, the center of a standardized grid was fixed above the hot spot of the target muscle of the left primary motor cortex. Twelve additional positions were arranged in a quadratic grid with positions between 5 and 10 mm from the hot spot. At each of the 13 positions, TMS single pulses were applied. The topographical maximum of the resulting N100 was located ipsilateral and slightly posterior to the stimulation site. A source analysis revealed an equivalent dipole localized more deeply than standard motor cortex coordinates that could not be explained by a single seeded primary motor cortex dipole. The N100 topography might not only reflect primary motor cortex activation, but also sum activation of the surrounding cortex. N100 amplitude and latency decreased significantly during stimulation anterior-medial to the hot spot although MEP amplitudes were smaller at all other stimulation sites. Therefore, N100 amplitudes might be suitable for detecting differences in local cortical excitability. The N100 topography, with its maximum located posterior to the stimulation site, possibly depends on both anatomical characteristics of the stimulated cortex and differences in local excitability of surrounding cortical areas. The less excitable anterior cortex might contribute to a more posterior maximum. There was no correlation between N100 and MEP amplitudes, but a single-trial analysis revealed a trend toward larger N100 amplitudes in trials with larger MEPs. Thus, functionally efficient cortical excitation might increase the probability of higher N100 amplitudes, but TEPs are also generated in the absence of MEPs.

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Contraction intensity-dependent variations in the responses to brain and corticospinal tract stimulation after a single session of resistance training in men

Journal of Applied Physiology ◽

10.1152/japplphysiol.01106.2018 ◽

2019 ◽

Vol 127 (4) ◽

pp. 1128-1139 ◽

Cited By ~ 6

Author(s):

David Colomer-Poveda ◽

Salvador Romero-Arenas ◽

Jesper Lundbye-Jensen ◽

Tibor Hortobágyi ◽

Gonzalo Márquez

Keyword(s):

Electrical Stimulation ◽

Resistance Training ◽

Evoked Potentials ◽

Muscle Contraction ◽

Corticospinal Tract ◽

Cortical Excitability ◽

Motor Evoked Potentials ◽

Motor Evoked Potential ◽

Single Session ◽

Compound Muscle Action Potentials

The aim of this study was to determine the effects of acute resistance training (RT) intensity on motor-evoked potentials (MEPs) generated by transcranial magnetic brain stimulation and on cervicomedullary motor-evoked potentials (CMEPs) produced by electrical stimulation of the corticospinal tract. In four experimental sessions, 14 healthy young men performed 12 sets of eight isometric contractions of the elbow flexors at 0 (Control session), 25, 50, and 75% of the maximal voluntary contraction (MVC). Before and after each session, MEPs, CMEPs, and the associated twitch forces were recorded at rest. MEPs increased by 39% ( P < 0.05 versus 25% in the control condition, Effect size (ES) = 1.04 and 1.76, respectively) after the 50% session and by 70% ( P < 0.05 vs. all other conditions, ES = 0.91–2.49) after the 75% session. In contrast, CMEPs increased similarly after the 25%, 50%, and 75% sessions with an overall increase of 27% ( P < 0.05 vs. control condition, ES = 1.34). The amplitude of maximal compound muscle action potentials (Mmax) was unchanged during the experiment. The MEP- and CMEP-associated twitch forces also increased after RT, but training intensity affected only the increases in MEP twitch forces. The data tentatively suggest that the intensity of muscle contraction used in acute bouts of RT affects cortical excitability. NEW & NOTEWORTHY Resistance training (RT) can acutely increase the efficacy of the corticospinal-motoneuronal synapse, motoneuron excitability and motor cortical excitability. We show that motor-evoked potential generated by transcranial magnetic stimulation but not cervicomedullary electrical stimulation increased in proportion to the intensity of training used during a single session of RT. The data suggest that the intensity of muscle contraction used in acute bouts of RT affects cortical excitability.

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