Distinct behavioral and EEG topographic correlates of loss of consciousness in absences

Purpose: To describe the behavioral and EEG topographic correlates of absen ces with 3-Hz generalized spike-waves and partitioned impairment of conscio usness. Methods: Two adult women had so-called "phantom" absences, characterized by brief and mild impairments of consciousness that were previously inconspic uous to both patient and physician. Neuropsychological examination was perf ormed under video-EEG monitoring during absence status. EEG topographic map ping of spike-wave discharges was obtained in the two cases. Results: Only mild attentional and executive disturbances were observed Jur ing absence status despite prolonged discharges. Spike-wave bursts were ass ociated with selective impairment in the initiation of response and self-ge nerated action, whereas short-term storage of external information during d ischarges was fully preserved. This is consistent with a predominant involv ement of frontomesial cortex demonstrated by topographic mapping of spike-w ave discharges in the two cases. By contrast, in two other patients with ty pical absences and a complete lack of retention for information given durin g the discharges, topographic mapping found a more lateral frontal involvem ent by spike-wave activity. Conclusions: Different types of absence seizures may impair distinct compon ents of conscious behavior. A predominant involvement of frontomesial thala mocortical circuitry may underlie an "inconspicuous" disorder of consciousn ess as seen in phantom absences with selective loss of initiation and goal- oriented behavior, whereas involvement of more lateral frontal areas in typ ical absences may additionally disrupt working memory processes.