Identifying transcranial magnetic stimulation induced EEG signatures of different neuronal elements in primary motor cortex

Highlights

• Corticospinal neurons were tested with transcranial magnetic stimulation with posteriorly and anteriorly directed currents.

• Topographic distribution of cortical potentials recorded by electroencephalography changed with different current directions.

• Activation of corticospinal neurons is affected by various neuronal elements with inputs from different cortical areas.

Abstract

Objective

To investigate the neuronal elements involved in the activation of corticospinal neurons in the primary motor cortex (M1).

Methods

We studied 10 healthy subjects. Cortical evoked potentials with different components induced by monophasic transcranial magnetic stimulation (TMS) in anterior-posterior and posterior-anterior currents recorded with electroencephalography (EEG) were analyzed.

Results

EEG signatures with P25 and N45 components recorded at the C3 electrode with posterior-anterior current were larger than those with anterior-posterior current, while the signatures with P180 and N280 components recorded at the FC1 electrode with anterior-posterior current were larger than those with posterior-anterior current. The source localization analysis revealed that the cortical evoked potential with anterior-posterior current distributed both in the M1 and premotor cortex while that with posterior-anterior current only located in the M1.

Conclusions

We conclude that the activation of corticospinal pyramidal neurons in the M1 is affected by various neuronal elements including the local intracortical circuits in the M1 and inputs from premotor cortex with different sensitivities to TMS in opposite current directions.

Significance

Our finding helped answer a longstanding question about how the corticospinal pathway from the M1 is functionally organized and activated.