In MEP studies, where should the anode be placed in relation to the cathode?

In motor evoked potential (MEP) studies, the placement of the anode in relation to the cathode is critically important for the proper stimulation of the motor pathways. The anode should be placed rostral (towards the head) to the cathode. This positioning is due to the way electrical stimulation influences the direction of current flow and the resulting activation of neurons.

When the anode is positioned rostral to the cathode, it helps to create an effective field that maximizes the depolarization of motor neurons. The flow of current from the anode to the cathode enhances the excitability of the targeted motor cortex and allows for more reliable and consistent evoked responses. Proper anode-cathode placement contributes significantly to the accuracy of MEP recordings, which are essential in intraoperative monitoring to ensure the integrity of motor pathways during surgical procedures.

Understanding this positioning is vital for practitioners in neurophysiologic intraoperative monitoring as it directly affects the quality and interpretability of the MEP data collected during surgery.