The localizing value of ictal consciousness and its constituent functions - A video-EEG study in patients with focal epilepsy

Using ictal neuropsychological testing in pre-surgical patients with focal epilepsies, we examined the localizing value of the constituent functions of consciousness as opposed to 'conscious behaviour' as a unitary variable. 'Conscious behaviour' was defined in terms of awareness and responsiveness. The constituent functions of consciousness examined included the orientation to the examiner, intentional behaviour demonstrated by expressive or receptive speech, and postictal memory. Frequency and patterns of impairment of constituent functions and 'conscious behaviour' were assessed. To achieve this, pre-surgical video-EEG (n = 40) or video-electrocorticography recordings (n = 76) of ictal neuropsychological assessments were reviewed retrospectively. Patients were divided into groups with frontal (n = 29), right temporal (n = 21), left temporal (n = 38) and bitemporal (n = 28) seizure activity. Consciousness was most commonly impaired in patients with bitemporal and left temporal seizure activity. There were different patterns of impairment of the assessed constituent functions in the four groups: patients with frontal seizure activity showed loss of orientation behaviour and expressive speech whereas patients with left temporal seizure activity had impairments of memory, expressive and receptive speech. Patients with seizure activity limited to the right temporal lobe rarely exhibited ictal impairment of any of the assessed functions. In contrast, patients with bitemporal seizure activity showed impairment of all examined functions. Hence, normal functioning of the left temporal lobe or both temporal lobes is necessary for the preservation of all constituent aspects of consciousness. The localizing value of patterns of impairment of constituent functions is superior to that of 'consciousness' as a whole.