An electrode system comprises a flexible circuit substrate and a plurality of electrode modules. The flexible circuit substrate comprises a flexible material and traces supported by the flexible material. The flexible circuit substrate extends through at least two of the electrode modules such that the electrode modules encompass portions of the flexible circuit substrate. Each electrode module comprises at least one rigid circuit member configured to process ERPs of a test subject. The rigid circuit members are layered against the flexible circuit substrate such that the rigid circuit members and the flexible circuit substrate together form a rigid-flex circuit. A sensor may be removably disposed through a substantially central opening defined by each electrode module.
