Table 1.

Behavioral seizure classification grading scale

Seizure grade	Description of corresponding seizure behavior*
Grade 1	Loss of posture associated with facial clonus, including chewing, and clonus of forelimbs and/or hindlimbs
Grade 2	Grade 1 seizure followed by recovery of the righting reflex and low intensity bouncing
Grade 3	Grade 1 and/or 2 features with recovery of the righting reflex followed by wild running and popcorning
Grade 4	Grade 3 followed by forelimb and/or hindlimb treading
Grade 5	Grades 3 and/or 4 followed by bilateral tonic extension of the forelimbs
Grade 6	Grade 5 followed by bilateral tonic extension of the hindlimbs
Grade 7	Grade 6 followed by immediate death

^*In general, grades 1 and 2 are clonic-forebrain seizures comparable to a grade 5 seizure on the Racine scale for electrical kindling (Racine, 1972). Grades 3–7 are brainstem seizures. Importantly, mice recover their righting reflex before transitioning into grades 3–7 (Kreindler et al., 1958; Browning and Nelson, 1986). We categorize mice having seizure grades 3–7 as forebrain→brainstem seizures to denote the progression of this type of seizure.