Amygdala-hippocampus relationships in temporal lobe seizures: a phase-coherence study

We analyzed temporal lobe seizures in patients with intracerebral electrodes to assess which of hippocampus and amygdala have a predominant role at seizure onset. Seizures were divided into those of mesial temporal onset, in which amygdala and hippocampus were involved but the neocortex was not (77 seizures from 17 patients), and those of regional onset in which mesial structures and neocortex were involved (89 seizures from 16 patients). We measured coherence and phase between one amygdala channel and one or two hippocampal channels during the first 10 s to determine which structure was leading the discharge. The following results are from 33 focal-mesial seizures and 30 regional seizures in which amygdala-hippocampus coherence was sufficiently high to measure time delays: the amygdala was leading in 21.2% of focal-mesial and 53.3% of regional seizures, and the hippocampus was leading in 48.5% of focal-mesial and 26.7% of regional seizures (chi-square, P < 0.02); in the remaining seizures, discharges were synchronous in the two structures. We conclude that the amygdala is more likely to lead when seizures are of regional onset, whereas the hippocampus is more likely to lead in focal-mesial seizures. This is probably due to the many connections of the amygdala with surrounding temporal neocortex.