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Measuring and Manipulating Functionally Specific Neural Pathways in the Human Motor System with Transcranial Magnetic Stimulation
Published on: February 23, 2020
Homeostatic modulation of stimulation-dependent plasticity in human motor cortex
N V Ilić1, S Milanović, J Krstić
1Clinic of Rehabilitation Medicine, Clinical Center of Serbia, Belgrade, Serbia. tihoilic@gmail.com
Physiological Research
|July 23, 2011
Summary
Paired associative stimulation (PAS) can induce motor cortex plasticity, mimicking Hebbian learning. This study investigated the paradoxical effects of PAS on motor evoked potential (MEP) amplitudes, revealing complex homeostatic modulation of plasticity.
Area of Science:
- Neuroscience
- Motor Cortex Plasticity
- Noninvasive Brain Stimulation
Background:
- Noninvasive cortical stimulation, like paired associative stimulation (PAS), can induce plastic changes in the human motor cortex, mirroring Hebb's learning model.
- Repetitive transcranial magnetic stimulation (TMS) paired with peripheral electrical stimulation can lead to synaptic potentiation or weakening in the sensory-motor cortex.
- A paradox exists where optimal intervals for LTP-like effects during single-pair stimulation cause Motor Evoked Potential (MEP) amplitude inhibition (short-latency afferent inhibition).
Purpose of the Study:
- To resolve the paradox of paired associative stimulation (PAS) effects on motor cortex excitability.
- To investigate the impact of specific PAS protocols (PAS(LTP) and PAS(LTD)) on motor evoked potential (MEP) amplitudes.
- To explore the underlying mechanisms of plasticity induction by PAS, considering homeostatic modulation.
Main Methods:
- Paired associative stimulation (PAS) protocols were applied with 200 repetitions of TMS pulses paired with median nerve electrical stimulation.
- Two intervals were used: PAS(LTP) at the somatosensory evoked response latency (N(20)) and PAS(LTD) at N(20) minus 5 msec.
- Motor evoked potential (MEP) amplitudes were measured before, during, and after the PAS interventions to assess changes in motor cortex excitability.
Main Results:
- Post-intervention, PAS(LTP) facilitated MEP amplitudes, while PAS(LTD) depressed them, contrasting with during-intervention effects.
- During PAS(LTP), MEP amplitudes significantly decreased, whereas PAS(LTD) showed an upward trend.
- These findings indicate complex, state-dependent relationships in PAS-induced plasticity.
Conclusions:
- The paradoxical effects of PAS can be explained by homeostatic modulation of plasticity.
- Motor cortex excitability levels influence the development of stimulation-induced plasticity.
- PAS protocols demonstrate complex interactions affecting motor cortex plasticity and excitability.
