EEG artifact handling strategies

Best efforts should always be made to prevent artifacts from entering EEG recordings. Nonetheless a certain level of artifact intrusion remains unavoidable, especially in the increasing field of mobile EEG and out-of-lab settings. But don’t worry, despite the unavoidability of artifacts, it is possible to obtain good quality signals with the right tools and artifact handling strategies.

EEG Physiological artifacts Eye blink ICA regression-based subtraction

The blink artifact is generated by the eye’s potential difference between the positively charged cornea and the negative retina: as the eyelid slides and the eyeball rotates during blinking the polarity is inverted and a positive current towards the scalp is created. The artifact is most prominent at frontal channels close to the eyes, reaching over a hundred microvolts in amplitude. In the frequency domain, it contains frequencies mostly in the EEG delta and theta bands.

EEG Physiological artifacts Eye movements artifact rejection ICA regression-based subtraction

Similar to blinks, lateral eye movements such as saccades generate a current away from the eyeballs, but this time towards the sides of the head, producing a box-shaped deflection with opposite polarity on each side. They are most prominent over channels close to the temples, but also affect channels outside these regions. In the frequency spectrum, the box shape created by eye movements peaks in the delta and theta bands, but has effects up to 20 Hz.

EEG Physiological artifacts Muscular artifacts

Most notably, activation during teeth clenching generates large noise that extends to the whole scalp. However, slighter artifacts are produced by other muscle groups of the head such as jaw or forehead.
Shoulder and neck tension lead to a persistent artifact that reaches lower electrodes including the mastoid region. In this case, if mastoid channels are used for re-referencing, the muscular artifact is introduced into all other channels. In frequency space, muscular artifacts are most prominent above 20 Hz, and up to 300 Hz.

EEG Physiological artifacts Pulse artifact

Pulsation of the head arteries generated by the heartbeat can lead to a slight rhythmical movement of the electrodes. In simultaneous EEG-fMRI recordings, the participant’s supine position and scanner environment magnify the artifact. However, pulse artifacts also occur sporadically under normal laboratory conditions, in participants with hypertension, or related to physical activity.

EEG Physiological artifacts Sweating - skin potentials

Even mild sweating leads to changes in the conductivity of the skin. This produces a drifting voltage on the scalp that shows as slow drifts in the recording. The drifts can vary widely in frequency and magnitude. This artifact is caused by warm environments, during physical activity, or during stress. The fluctuation induced by these drifts affects the timing and amplitude of signals in the time domain such as ERPs. In frequency space, this artifact contains power mostly in slow frequencies.

EEG Physiological artifacts Body movement

Movement of the body leads to slight displacement of the EEG cap over the scalp, especially when the cap is loose. This alters electrode impedance levels in the process, leading to artifacts. Gross movements produce large shifting voltages that can even saturate amplifiers momentarily. Slight body sway leads to gradual drift in the channels. Complex movements in certain tasks produce equally complex movements of the cap involving pulling, sliding and shaking, which affect all channels.

EEG Technical artifacts - Notch filters of 50 or 60 Hz

BrainSupport Solution for Neuroscience Researchers - EEG NIRS 

Neuroscience to Improve Latin American Identity

BrainSupport Solution for Neuroscience Researchers - Neuroscience to improve Latin American Identity. Scientific questions and experimental designs for the development of culture, behavior, perception and Latin American consciousness. 

Line noise / Electromagnetic interference