Bipolarly

It is usually recorded from electrodes on the scalp. It can be recorded bipolarly from two electrodes placed over the same part of the cortex, or monopolarly with one “active” electrode over the cortex and a second “reference” electrode on some other part of the head.

Source: wiktionary

A ground electrode located between Fpz and Fz. The electro-oculogram (EOG) was recorded bipolarly from two electrodes placed at the outer canthi of the right eye and below the left eye.

Source: wiktionary