Different techniques used to measure the electrical activity of the brain include, electroencephalograph (EEG), ERP (evoked response potential), MEG (magnetoencephalography) and single cell recording.
Single cell recording measures the action potentials occurring in a single neuron by inserting the fine electrodes into the brain. The electrodes can be placed either into the cells (for intracellular recording) or next to cells (for extracellular recording).
Thus, the blank can be filled with action potential.