Abstracts

Rationale: Peri-ictal alternation of cortical excitability in focal cortical dysplasia (FCD) has not been well elucidated in vivo in humans. We studied this matter at and around the focus in two FCD patients by taking an incidental opportunity of seizure occurrence during single-pulse stimulation research protocol. Methods: Subjects are two intractable partial epilepsy patients who underwent invasive presurgical evaluations and had a pathological diagnosis of FCD. Patient 1 with the right basal temporal focus showed frequent interictal spikes in the right basal and lateral temporal region. Peri-ictally, spikes changed into repetitive polyspikes in the right basal temporal region, and then evolved into low voltage fast activities in the right basal and posterior lateral temporal region. During low frequency single-pulse stimulation of the focus (IRB #235 for suppression of epileptic activity), the patient developed a conventional seizure pattern 8 minutes after start of stimulation. The polyspike pattern changed into low voltage fast activities in 40 seconds, and a brief clinical seizure occurred. Patient 2 underwent single- and paired-pulse electrical stimulation of the epileptic focus at the left leg somatosensory area (IRB #443 for investigation of intracortical inhibition at the focus). Paraesthesia of the left foot occurred very frequently throughout the day without electrocorticographic change. The same somatosensory aura occurred during stimulation of the research protocol. The sensory aura evolved into a left leg clonic seizure in 8 minutes. Single-pulse stimulation was immediately stopped upon clinical seizure in both patients. By averaging electrocorticogram time-locked to repetitive single-pulse stimuli at the focus, cortico-cortical evoked potentials (CCEPs) were recorded from the adjacent and remote cortices via neuronal projections (Matsumoto et al., Brain 2004). Alternation of cortico-cortical excitability at and around the focus was evaluated by the CCEP amplitude and morphology associated with seizure generation. Results: Interictally, stimulation of the focus elicited CCEPs in the adjacent and remote areas. The distribution generally corresponded to that of interictal spikes. Peri-ictal CCEPs showed enlarged amplitude (both patients) and polyphasic morphology (patient 1) as compared with interictal CCEPs. In patient 1, the amplitude of CCEP became markedly decreased during the ictal phase of low voltage fast activity. Conclusions: In the two FCD patients investigated, cortico-cortical excitability at and around the focus became increased during transition from the interictal to ictal state, judging from increased CCEP amplitude. The increased cortico-cortical excitability then became diminished as initial ictal phase progressed into the state of EEG desynchronization. The study is supported by KAKENHI C20591022 from MEXT, Japan.