This chapter considers the basic principles behind the electrophysiological methods of single-cell recordings and electroencephalography (EEG). Single-cell recording is an invasive method in which the number of action potentials generated by a neuron is recorded. The rate and timing of this measure can be used to infer the functional properties of a neuron (e.g., what it is specialized for). By contrast, EEG measures the summed electrical activity of many (millions of) neurons detected at the scalp. The most common use of EEG in cognitive neuroscience is the method known as ERP, event-related potentials. The EEG waveform reflects neural activity from all parts of the brain. Changes in the timing or amplitude of this waveform can be linked to differences in cognitive function. Magnetoencephalography can be regarded as a parallel method to EEG, based on measuring magnetic fields generated by neural activity, that is similar in many regards. <\/p>\n\n\n\n