Definition and Overview
Quantitative electroencephalography (QEEG) is a brain function evaluation method that digitally processes electroencephalographic (EEG) signals recorded from multiple electrodes on the scalp to quantitatively analyze frequency components, power spectrum, phase relationships (coherence) between electrodes, and asymmetry.
Electrical signals are measured simultaneously from multiple areas of the brain with 19 to 256 channels of electrodes according to the standard international 10-20 electrode placement system. The analysis results are visualized in the form of a brain map, allowing you to understand the functional status of each brain region at a glance.
While regular EEG mainly qualitatively evaluates epileptic seizure waveforms and local abnormalities, QEEG objectifies functional problems by quantitatively comparing the brain's functional connectivity, activation patterns, and deviations from a normal reference database.
Frequency Bands and Clinical Implications
Brain waves are classified according to vibration frequency as follows.
Delta wave (1~4Hz)
It mainly occurs during normal deep sleep (slow wave sleep). Increased delta waves during wakefulness may indicate brain damage, stroke, or severe metabolic abnormalities. Local delta wave increases reflect the area of a stroke or tumor.
Theta waves (4~8Hz)
Theta waves in the frontal lobe are related to attention and working memory. Excessive frontal theta waves are linked to ADHD, depression, and cognitive decline. The alpha-theta transition state is a period of relaxation and creative insight.
Alpha waves (Alpha, 8~13Hz)
This is a representative brain wave in a relaxed state of wakefulness. It increases in the occipital lobe when the eyes are closed (alpha synchronization) and decreases when the eyes are opened or a cognitive task is initiated (alpha desynchronization). Prefrontal alpha asymmetry is associated with emotional processing, and a pattern of increased left frontal alpha is observed in depression.
Beta waves (Beta, 13~30Hz)
It increases with active thinking, concentration, and problem solving. Excessive beta waves (especially high-frequency beta) are associated with anxiety, hyperarousal, and increased muscle tension. Low beta waves may reflect poor concentration and decreased cognitive function.
Gamma waves (30~100Hz)
Involved in higher-order cognitive processes, perceptual binding, and attention focus. Decreased gamma waves are reported in Alzheimer's disease.
clinical application
ADHD
Increased theta waves and decreased beta waves (increased theta/beta ratio) in the fronto-central region are characteristically observed in ADHD. QEEG is used to distinguish ADHD subtypes and monitor the effects of neurofeedback treatment. According to a meta-analysis, attention and hyperactivity were significantly improved in children with ADHD through neurofeedback treatment.
depression
Left frontal alpha excess (frontal alpha asymmetry) and increased frontal theta waves are associated with depression. Research is underway to use QEEG patterns to predict response to antidepressant treatment. In QEEG-guided TMS treatment, protocols targeting asymmetric areas are used.
Anxiety Disorders and Post-Traumatic Stress Disorder (PTSD)
Excessive frontal beta waves and decreased frontal alpha reflect states of anxiety and hyperarousal. Neurofeedback training aimed at alpha enhancement is used to reduce anxiety.
Autonomic function evaluation
The insula and anterior cingulate cortex are key cortical structures in autonomic regulation. Assessing the functional activity and connectivity of this region with QEEG can help understand the central mechanisms of autonomic dysfunction. By combining HRV analysis and QEEG, peripheral autonomic nerve status and central regulatory function can be evaluated simultaneously.
rehabilitation after stroke
The distribution of delta-theta waves around the stroke lesion is correlated with the area of nerve function damage, and brain wave changes can be tracked during recovery. Neuroplasticity responses are monitored through QEEG changes before and after TMS treatment.
Traumatic Brain Injury (TBI)
Asymmetrical increase in delta-theta waves and decrease in alpha waves can be observed in diffuse axonal damage after head trauma. QEEG is a complementary means of assessing functional impairment not visible on MRI.
QEEG test process
Preparing for inspection
- On the day of the test, wash your hair and do not use hair products (gel, spray).
- Avoid caffeine intake 12 hours before the test.
- Take the test after getting enough sleep (lack of sleep affects brain wave patterns).
inspection process
1. Wear an EEG electrode cap with conductive gel applied to the scalp according to the international 10-20 system. 2. Maintain the impedance (resistance) of each electrode below 5kΩ. 3. Brain waves are recorded for 3 to 5 minutes with open eyes and 3 to 5 minutes with closed eyes. 4. Brain waves are additionally recorded while performing cognitive tasks (reading, calculations, etc.). 5. After removing artifacts (eye movements, muscle noise), frequency analysis is performed.
Interpretation of results
Compare with a normative database and calculate the deviation as z-score. A color-coded brain map visualizes the excess (red) or deficiency (blue) state of each region in each frequency band.
QEEG-based neurofeedback
Design a personalized neurofeedback protocol based on QEEG results. Patients receive real-time brainwave feedback (visual and auditory signals) and train their brainwave patterns in the desired direction. For example, protocols aimed at reducing frontal theta waves and increasing beta waves are used to improve concentration.