Related Experiment Video
Updated: Aug 8, 2026
09:52
Measuring and Manipulating Functionally Specific Neural Pathways in the Human Motor System with Transcranial Magnetic Stimulation
Published on: February 23, 2020
Associative plasticity in human motor cortex during voluntary muscle contraction
Kayoko Kujirai1, Takashi Kujirai, Thomas Sinkjaer
1Center for Sensory-Motor Interaction, Department of Health Science and Technology, Aalborg University, Aalborg, Denmark.
Journal of Neurophysiology
|May 26, 2006
Summary
Anterior-posterior (AP) transcranial magnetic stimulation (TMS) paired associative stimulation (PAS) facilitates motor cortex plasticity during muscle contraction. This AP-PAS method enhances motor-evoked potentials and reduces motor threshold, unlike posterior-anterior (PA) stimulation.
Area of Science:
- Neuroscience
- Motor Control
- Brain Stimulation
Background:
- Transcranial magnetic stimulation (TMS) current direction influences motor cortex synaptic activation.
- Paired associative stimulation (PAS) combines peripheral nerve stimulation with TMS to induce neuroplasticity.
Purpose of the Study:
- To investigate the effect of TMS current direction (posterior-anterior vs. anterior-posterior) on PAS-induced neuroplasticity.
- To determine if AP-PAS is more effective than PA-PAS in modulating motor cortex excitability.
Main Methods:
- Paired associative stimulation (PAS) was applied using either AP or PA TMS pulses.
- Stimulation was tested in resting and voluntarily contracting muscles.
- Motor-evoked potentials (MEPs) and resting motor threshold were measured.
Main Results:
- AP-PAS, but not PA-PAS, facilitated MEPs and reduced motor threshold during voluntary contraction.
- Subthreshold AP-PAS (AP-Sub-PAS) induced significant MEP facilitation and threshold reduction.
- PA-Sub-PAS showed no excitatory effect, and digital nerve stimulation yielded no facilitation.
Conclusions:
- AP-PAS is more effective than PA-PAS in inducing associative plasticity in the human motor cortex.
- AP TMS likely activates specific corticospinal neuron inputs (I3) crucial for associative plasticity.
- The findings highlight the importance of TMS current direction in optimizing PAS protocols.
Related Concept Videos
01:15Muscle Contraction
01:10Muscle Contraction
In skeletal muscles, acetylcholine is released by nerve terminals at the motor endplate—the point of synaptic communication between motor neurons and muscle fibers. The binding of acetylcholine to its receptors on the sarcolemma allows entry of sodium ions into the cell and triggers an action potential in the muscle cell. Thus, electrical signals from the brain are transmitted to the muscle. Subsequently, the enzyme acetylcholinesterase breaks down acetylcholine to prevent excessive muscle...
01:20Motor Unit Stimulation
When the neuron of a motor unit fires an action potential, it triggers a series of events, leading to a twitch contraction in the muscle fibers. The process of excitation-contraction coupling is crucial in relaying the action potential to the muscle fibers.
The latent period of contraction marks the onset of excitation-contraction coupling, when the action potential propagates across the sarcolemma, preparing the muscle fibers for contraction. As the fibers enter the contraction phase, the...
The latent period of contraction marks the onset of excitation-contraction coupling, when the action potential propagates across the sarcolemma, preparing the muscle fibers for contraction. As the fibers enter the contraction phase, the...
01:14Motor and Sensory Areas of the Cortex
The cerebral cortex, the brain's outermost layer, is pivotal in processing complex cognitive tasks, emotions, and various sensory inputs and executing voluntary motor activities. This intricate structure is divided into three primary functional areas: the motor areas, sensory areas, and association areas.
Motor Areas
The motor areas located in the frontal lobe are central to controlling voluntary movements. This region is further subdivided into the primary motor cortex and the premotor cortex.
Motor Areas
The motor areas located in the frontal lobe are central to controlling voluntary movements. This region is further subdivided into the primary motor cortex and the premotor cortex.
01:23Somatosensory, Motor, and Association Cortex
The somatosensory cortex in the parietal lobes is crucial for interpreting sensory data such as touch, temperature, and proprioception. The somatosensory cortex, situated in the parietal lobes, plays a vital role in interpreting sensory information like touch, temperature, and proprioception—awareness of body position. This specialized brain region features an organized structure wherein neurons at the top primarily process sensations originating from the lower body. In contrast, those at the...
01:11Direct Motor Pathways
The direct motor pathways, also known as the pyramidal tracts, are a group of neural pathways that originate in the brain and descend through the spinal cord. They control the voluntary movement of the body. There are two major direct motor pathways: the corticospinal and the corticobulbar tracts.
The corticospinal tract is responsible for the voluntary movement of the limbs and trunk. It originates in the cerebral cortex of the brain and descends through the cerebrum's internal capsule and the...
The corticospinal tract is responsible for the voluntary movement of the limbs and trunk. It originates in the cerebral cortex of the brain and descends through the cerebrum's internal capsule and the...