Abnormal brain wave activity identified through electroencephalographic (EEG) monitoring and is known to occur in up to 40 percent of depressed patients. Abnormal findings called 'small sharp spikes' are often present in severely depressed suicidal patients. QEEG analysis of unipolar depressed patients typically reveals increased alpha or theta power and decreased interhemispheric coherence. In contrast, bipolar depressed patients often have reduced alpha activity and increased beta power.
Reduced alpha brain wave activity and increased beta power are more likely in bipolar disorder. EEG changes frequently associated with anxiety include decreased alpha activity in generalized anxiety, increased theta activity in obsessive-compulsive disorder (OCD), and paroxysmal activity in patients who experience panic attacks. QEEG findings may predict differential response rates of patients with OCD to conventional medications. In one series, approximately 80 percent of OCD patients who exhibited increased alpha power responded to SSRIs, compared to 80 percent of OCD patients with increased theta activity who failed to respond to SSRIs. Abnormal QEEG findings associated with other anxiety disorders are highly inconsistent.
Neurometric brain mapping is a specialized QEEG approach that compares EEG characteristics of the individual being evaluated with normative databases for the same age. Neurometric mapping helps clarify functional brain correlates of cognitive impairment and yields information that is useful for planning EEG biofeedback protocols addressing specific kinds of dysfunction (see later discussion of EEG biofeedback). Neurometric brain mapping is increasingly being used to differentiate cognitive impairments due to head injuries, medical disorders, progressive dementia, alcohol or substance abuse, depressed mood, and learning disorders.