How was the patient diagonsed with brain death?
What movement do you see to call it a seizure?
A true brain death is ceased all eletrical activity---ie. not compatible with seizure.
A clinical diagnosis of brain death includes cease all brainstem function examed 6 hours apart, and also failed apnea test. There might be residual cortical activity with neurons dying with transient electrical activity, but the movement is not c/w seizure. may be random, non-purposeful, non-stereotypical myoclonic like jerks.
If patient truely has seizure, by definition, patient is not brain dead.