Summary:Purpose: To investigate the clinical, electroencephalographic (EEG), and histopathologic effects of subacute electrical stimulation of the hippocampal formation or gyrus (SAHCS) on 10 patients with intractable temporal lobe seizures.Methods: Bilateral, depth, hippocampal or unilateral, subdural, basotemporal electrodes were implanted in all 10 patients for a topographic diagnosis of the site and extent of the epileptic focus before a temporal lobectomy. In all patients, antiepileptic drugs (AEDs) were discontinued from 48 to 72 h before a program of continuous SAHCS, which was performed for 2-3 weeks. Stimulation parameters were biphasic Lilly wave pulses, 1301s in frequency, 450 p. s in duration, and 200-400 p,A in amplitude. The stimuli were delivered 23 of every 24 h for the 2-3-week SAHCS period. The effects of SAHCS on the number of clinical seizures per day and the percentage of interictal EEG spikes per 10-second samples of maximal paroxysmal activity at the epileptic focus were determined daily during the 16 days of SAHCS. At the completion of this program, patients underwent an en bloc temporal lobectomy, and the histopathologic effects of SAHCS on the stimulated tissue were analyzed by means of light-microscopy studies.Results: In seven patients whose stimulation electrode contacts were placed within the hippocampal formation or gyrus and who experienced no interruption in the stimulation pro- creased the number of interictal EEG spikes at the focus after 5-6 days. The most evident and fast responses were found by stimulating either the anterior pes hippocampus close to the amygdala or the anterior parahippocampal gyrus close to the entorhinal cortex. Other surface, hippocampal, and basotemporal EEG signs predicted and accompanied this antiepileptic response. These included an electropositive DC shift and monomorphic delta activity at the medial hippocampal and parahippocampal regions, and a normalization of the background EEG activity and signs of slow-wave sleep in surface, depth, and subdural regions. In contrast, no evident antiepileptic responses or no responses at all were found in three patients when stimulation was either interrupted or when it was adniinistered outside the hippocampus.Light microscopy analysis of the stimulated hippocampal tissue showed histopathological abnormalities attributable to the depth-electrode penetration damage or to the pial surface reaction to the subdural, Silastic electrode plate. However, no evident histopathological differences were found between the stimulated and nonstimulated hippocampal tissue.Conclusions: SAHCS appears to be a safe procedure that can suppress temporal lobe epileptogenesis with no additional damage to the stimulated tissue.

Summary: Purpose:The efficacy and safety of cerebellar stimulation (CS) was reevaluated in a double-blind, randomized controlled pilot study on five patients with medically refractory motor seizures, and especially generalized tonic-clonic seizures.Methods: Bilateral modified four-contact plate electrodes were placed on the cerebellar superomedial surface through two suboccipital burr holes. The implanted programmable, batteryoperated stimulator was adjusted to 2.0 µC/cm 2 /phase with the stimulator case as the anode; at this level, no patient experienced the stimulation. Patients served as their own controls, comparing their seizure frequency in preimplant basal phase (BL) of 3 months with the postimplant phases from 10 months to 4 years (average, eight epochs of 3 months each). During the month after implantation, the stimulators were not activated. The patient and the evaluator were blinded as to the next 3-month epoch, as to whether stimulation was used. The patients were randomized into two groups: three with the stimulator ON and two with the stimulator OFF. After a 4-month postimplantation period, all patients had their stimulator ON until the end of the study and beyond. Medication was maintained unchanged throughout the study. EEG paroxysmal discharges also were measured.Results: Generalized tonic-clonic seizures: in the initial 3-month double-blind phase, two patients were monitored with the stimulation OFF; no change was found in the mean seizure rate (patient 1, 100%, and patient 5, 85%; mean, 93%), whereas the three patients with the stimulation initially ON had a reduction of seizures to 33% (patient 2, 21%; patient 3, 46%; patient 4, 32%) with a statistically significant difference between OFF and ON phase of p = 0.023. All five patients then were stimulated and monitored. At the end of the next 6 months of stimulation, the five patients had a mean seizure rate of 41% (14-75%) of the BL. The second patient developed an infection in the implanted system, which had to be removed after 11 months of stimulation; the seizures were being reduced with stimulation to a mean of one per month from a mean of 4.7 per month (BL level) before stimulation. At the end of 24 months, three patients were monitored with stimulation, resulting in a further reduction of seizures to 24% (11-38%). Tonic seizures: four patients had these seizures, which at 24 months were reduced to 43% (10-76%). Follow-up surgery was necessary in four patients because of infection in one patient and lead/electrode displacement needing repositioning in three patients. The statistical analysis showed a significant reduction in tonic-clonic seizures (p < 0.001) and tonic seizures (p < 0.05).Conclusions: The superomedial cerebellar cortex appears to be a significantly effective and safe target for electrical stimulation for decreasing motor seizures over the long term. The effect shows generalized tonic-clonic seizure reduction after 1-2 months and continues to decrease over the first 6 months and then maintains this effectiveness over the st...

ESCM is an efficient and safe procedure for controlling certain seizure types, if patient selection and stereotactic placement are satisfactory.

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MRI and electrophysiological techniques to localize the primary motor cortex (MC) were performed on patients considered for MC stimulation for the treatment of deafferentation pain. The representation and trajectory of the rolandic fissure (RF) were accurately localized by external cranial landmarks and radiopaque fiducials superimposed on oblique MRI sections. In addition, the scalp distribution of the corticocortical responses elicited by acute epidural stimulation [motor cortex (MC) in frontal and sensory cortex (SC) in parietal scalp regions], and analgesic responses at the topographical representation of the painful periphery elicited by subacute epidural stimulation were found to be simple and reliable procedures to localize MC, SC and RF.

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