Electroencephalography (EEG) records the brain's electrical activity through electrodes placed on the scalp. Because neural electrical signals propagate at near-instantaneous speed, EEG provides millisecond temporal resolution — far superior to fMRI — enabling researchers to track the time course of cognitive processes in real time. The trade-off is poorer spatial resolution (centimeters) due to the smearing of electrical signals through the skull and scalp.
Key Structures
- Whole brain cortical surface (measures summed postsynaptic potentials from cortical pyramidal neurons)
- Working Memory — A limited-capacity system for temporarily holding and manipulating information during complex cognitive tasks such as reasoning, comprehension, and learning.
- Event-Related Potentials — Voltage changes in the EEG time-locked to specific events, providing precise temporal markers of cognitive processes including attention, perception, language, and memory.
- fMRI — Functional magnetic resonance imaging, a neuroimaging technique that measures brain activity by detecting changes in blood oxygenation, providing detailed spatial maps of which brain regions are engag.
Key Functions
A non-invasive neuroimaging technique that records electrical activity from the scalp using electrodes, providing millisecond temporal resolution of brain oscillations, event-related potentials, and neural dynamics.
Oscillations and Frequency Bands
EEG signals contain oscillations at characteristic frequency bands: delta (0.5-4 Hz, deep sleep), theta (4-8 Hz, memory, navigation), alpha (8-13 Hz, idle visual cortex, attention), beta (13-30 Hz, motor planning, active thinking), and gamma (30-100 Hz, binding, consciousness). These oscillations are thought to coordinate neural activity across brain regions, and changes in their power and coherence index different cognitive states.
By averaging EEG signals time-locked to repeated events (stimuli, responses), researchers extract event-related potentials (ERPs) — voltage changes reflecting specific stages of cognitive processing. The N400 indexes semantic processing, the P300 indexes attention and working memory updating, the N170 indexes face processing, and the error-related negativity (ERN) indexes error detection. ERPs provide precise temporal information about when different cognitive operations occur.
Disorders
- Epilepsy (seizure detection/localization) — A neurological condition characterized by recurrent unprovoked seizures due to abnormal excessive neural synchronization, particularly in relation to seizure detection/localization.
- Sleep disorders — Conditions disrupting normal sleep patterns, impairing cognitive function, memory consolidation, and emotional regulation.
- ADHD — Attention-Deficit/Hyperactivity Disorder — a neurodevelopmental condition characterized by persistent patterns of inattention, hyperactivity, and impulsivity affecting cognitive functioning.
- Traumatic brain injury — Brain damage caused by external mechanical force — from concussions to severe injuries — producing cognitive, emotional, and behavioral consequences that illuminate brain-cognition relationships.
- Brain death assessment