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Updated: Jun 26, 2026

Measuring and Manipulating Functionally Specific Neural Pathways in the Human Motor System with Transcranial Magnetic Stimulation
Published on: February 23, 2020
Associative motor cortex plasticity: direct evidence in humans
V Di Lazzaro1, M Dileone, F Pilato
1Institute of Neurology, Università Cattolica, Rome, Italy. vdilazzaro@rm.unicatt.it
Paired associative stimulation (PAS) enhances motor evoked potentials by affecting later descending waves in the corticospinal tract. This suggests PAS acts at the cortical level, potentially through long-term potentiation-like synaptic changes.
Area of Science:
- Neuroscience
- Motor control research
- Cortical plasticity studies
Background:
- Paired associative stimulation (PAS) enhances motor evoked potentials (MEPs) amplitude.
- Evidence suggests PAS involves long-term potentiation (LTP)-like synaptic changes.
- The precise central nervous system level of PAS effects remains under investigation.
Purpose of the Study:
- To determine the central nervous system level at which PAS exerts its effects.
- To investigate the impact of PAS on corticospinal excitability.
- To differentiate between spinal and cortical contributions to PAS-induced MEP enhancement.
Main Methods:
- Recording of corticospinal descending volleys evoked by single-pulse transcranial magnetic stimulation (TMS) in 4 subjects.
- Utilizing epidural electrodes in the cervical space for precise measurement of descending activity.
- Administering PAS protocol involving peripheral nerve stimuli followed by motor cortex TMS.
Main Results:
- PAS significantly enhanced the amplitude of later descending waves in corticospinal volleys.
- The earliest descending wave, potentially reflecting direct spinal cord activity, showed no significant modification.
- These findings indicate a modulation of postsynaptic activity within the corticospinal neurons.
Conclusions:
- The results support a cortical origin for the effects of PAS.
- PAS appears to modulate synaptic efficacy at the cortical level.
- This study provides evidence for PAS-induced plasticity within the motor cortex.
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