Event related potentials (ERP) are very small voltages generated in brain on response to specific events and stimuli. They are EEG changes that are time locked to sensory, motor and cognitive events. They are safe and non-invasive approach to study physiological correlations. ERP can be elicited by variety of sensory, motor and cognitive events. They are thought to reflect summed activity of PSP of large number of cortical pyramidal neurons which are in synchrony.
ERP represents input to cortical pyramidal neurons rather than output to neurons. The positive and negative polarity of ERP component at a given electrode site is related to several factors including the orientation of equivalent current dipole with respect to electrode, and it is not a reflection of inhibition and excitation of neurons.
Fig1: ERP recording system
Fig2: Typical ERP waveform
ERP researchers had made differences between ERP peak and components.
ERP peak: Reliable local positive or negative maximum in observed ERP waveform.
ERP component: It is a scalp recorded voltage changes that reflect a specific neural or psychological process.
Although ERP has many advantages, it has limitations of its own. Limitations of ERP include
- Inability to relate ERP to neural tissue directly below electrode site.
- The conduction of skull is not vertical, but it lateral causing the signal to blur.
- Super positioning of multiple components and blurring of voltage across head makes it impossible to localize source exactly.