Brain lesions that produce delta waves in the EEG.

Localized delta activity appears in cortex overlying a circumscribed white matter lesion. Less commonly, localized delta activity may result from a localized thalamic lesion. Unilateral diffuse delta activity appears on the side of thalamic or hypothalamic lesions. Bilateral delta activity results from bilateral lesions of the midbrain tegmentum. Localized lesions of the cerebral cortex, unilateral mesencephalic tegmental lesions, and vasogenic edema of the cerebral white matter do not produce delta activity. Marked edema of a cerebral hemisphere when no surgical decompression is provided may produce unilateral delta activity by pressure on or displacement of the brain stem or diencephalon.