Clinical and electroencephalographic correlates of breach activity

In order to define the EEG spectrum and the prevalence of breach activity, as well as the factors contributing to its genesis, we studied 50 patients with surgically induced skull defects. We observed breach activity in 32 (64%) patients. Focally enhanced alpha, beta, and mu rhythms with or without decreased amplitude of eye movement artifacts were the EEG findings encountered in our patients. The amplitude asymmetry never exceeded a factor of 3 or more. Of the variables compared between patients with and without breach activity, only the time between surgery and the EEG recording correlated positively with the development of breach activity. The delay in the development of breach activity may indicate that breach activity is not due solely to the discontinuity of bone. The development of meningocortical adhesions and gliosis could contribute to the pathogenesis of breach activity.