Neural connection between bilateral basal temporal regions: cortico-cortical evoked potential analysis in patients with temporal lobe epilepsy.

OBJECTIVE: In patients with temporal lobe epilepsy, invasive electroencephalographic study has shown that epileptic activities arising from the unilateral temporal lobe often propagate to the contralateral temporal lobe. Which commissural pathways are responsible for this spreading remains controversial. Some previous studies, however, have suggested that interhemispheric connections between bilateral basal temporal regions (BTR) might have a significant role in propagation of epileptic activities.

METHODS: We attempted to elucidate the neural connections between bilateral BTRs using the cortico-cortical evoked potential (CCEP) method. Five consecutive patients with temporal lobe epilepsy who underwent intracranial electroencephalographic monitoring were studied.

RESULTS: CCEP responses were recorded from a total of 24 electrodes after stimulation of the contralateral BTRs (24 CCEPs/720 recordings; 3.33%). There were 3 types of CCEP waveform: type N-P (16 of 24; 66.7%) consisting of an initial negative peak followed by a positive peak; type N (4 of 24; 16.7%) showing a negative peak only, and type P (4 of 24; 16.7%) showing a positive peak only. The latencies ranged from 48.2 to 102.3 ms (mean, 65.5 ms) for negative peaks and 70.2 to 122.0 ms (mean, 95.2 ms) for positive peaks. In all patients, the basal temporal language area was associated with at least 1 CCEP, either as a stimulated region or a recorded region (11 of 24; 45.8%).

CONCLUSION: These data indicate that there is a neural connection between bilateral BTRs. In consideration of the involvement of the basal temporal language area, we speculate that these responses may reflect some physiological connections between bilateral BTRs.