Abstract *Hiroyuki Shimizu, *Kensuke Kawai, and *Shigeki Sunaga *Department of Neurosurgery, Tokyo Metropolitan Neurological Hospital, Fuchu, Tokyo, Japan . Background: Despite good surgical outcomes after temporal lobectomy, postoperative impairment of verbal memory remains a serious problem to be solved, especially when surgery is performed on the left (dominant) side in patients without hippocampal atrophy on preoperative magnetic resonance imaging (MRI). To solve this long-standing problem, we developed a new surgical technique for the treatment of left temporal lobe epilepsy that preserves verbal memory. Surgical Technique: An ∼2-cm corticotomy is placed on the anterior superior temporal gyrus along the sylvian veins. After aspiration of the gray matter along the sylvian fissure, the inferior horn is accessed through the temporal stem. Intraoperative electrocorticogram (ECoG) is recorded over the surface of the hippocampus and amygdala, and the extent of epileptic areas is determined. After cutting the alveus, the pyramidal layer is transected with a 2-mm ring transector. The transection lines are ∼5 mm apart and parallel to the alveus fibers to preserve neuronal connections. A 4-mm ring transector is used at both ends to transect the CA4 and the transitional zone from the CA1 to the subiculum. Subjects and Methods: For the past 40 months, a total of 19 patients underwent hippocampal transaction; right side in six, left side in seven, and bilateral in six. For all patients, complex partial seizures were the most disabling habitual seizures. Preoperative MRI demonstrated no hippocampal atrophy and no structural lesions. In most of the patients, intracranial electrodes were placed, and prolonged ECoG and video monitoring were carried out to confirm the exact distribution of epileptic areas. Neuropsychometry was performed preoperatively and postoperatively. For evaluation of verbal memory, an auditory verbal learning test (AVLT) was performed. In the AVLT test, a patient tried to memorize 15 different words, and the ability to recall these words immediately was assessed. This test was repeated 5 times. After that, a different list of 15 words was presented, and immediate recall was again tested. Twenty minutes after this interference test, the patient was asked to recall the first list of 15 words. The score of this delayed recall was used to examine verbal memory function of the hippocampus. Results: The seizure outcome after hippocampal transection was excellent in cases with unilateral focus. All 13 patients with unilateral transection achieved a seizure-free outcome for >6 months after surgery. On the contrary, various outcomes were obtained in patients with bilateral foci; two cases became seizure free, another two cases showed >90% and 50–90% reduction of seizures, and the remaining two developed new types of seizures after surgery. The WAIS-R and Benton visual retention tests showed no remarkable changes in any of the cases. Verbal memory function evaluation by the AVLT showed no significant changes in the right-sided cases. Of the left-sided cases, four cases with only hippocampal transection showed preservation of the AVLT scores immediately after surgery; the remaining three cases with additional excision of the temporal tip showed transient decreases of the AVLT scores after surgery and recovered to the preoperative level within 6 months. In cases with bilateral transections, all cases recovered to a level near the preoperative score within 5–9 months after the last surgery. Conclusions: These results show that our new method of hippocampal transection is very effective for controlling seizures in temporal lobe epilepsy. Verbal memory can be preserved even in left (dominant) temporal lobe cases. This technique also opens a possibility for surgical treatment of bilateral temporal lobe epilepsy.