Issues in brain mapping...Polymorphic delta activity and its brainmap counterpart

This document discusses various brain mapping terminologies used in EEGs including absolute power, relative power, coherence, symmetry, and polymorphic delta activity (PDA). PDA consists of arrhythmic slow waves that vary in frequency, amplitude, and morphology. It is commonly seen with subcortical white matter lesions and indicates deafferentation of cortical neurons from a subcortical pacemaker due to a destructive focal lesion interrupting thalamocortical pathways. PDA is nonspecific but suggests an underlying structural abnormality.