Summary: We attempted to clarify functional interhemispheric connections of motor cortex (MC) by investigating cortico-cortical evoked potentials from human brains in vivo. Three patients with intractable epilepsy who underwent invasive EEG monitoring with subdural electrodes as presurgical evaluation were studied. Electric pulse stimuli were delivered in a bipolar fashion to two adjacent electrodes on and around MC. Cortico-cortical evoked potentials were recorded by averaging electrocorticograms from the contralateral hemisphere. An initial positive triphasic or an initial negative biphasic wave was recorded when the contralateral MCs were stimulated. When the non-MC electrodes were stimulated, no response was recorded. The latencies ranged from 9.2 to 23.8 ms for the initial positive peak, and 25.4 to 39.4 ms for the initial or the second negative peak. The cortico-cortical evoked potentials responses were maximal around the homonymous electrodes with the stimulated electrodes. Our results directly demonstrate the presence of the functional interhemispheric connections originating in MC. The interhemispheric transit time is indicated. The homotopic distribution of the responses indicates that motor coordination of the bilateral bodies is, at least partially, controlled within MC.
The aim of this study was to investigate the usefulness of a short train of high-frequency (500 Hz) cortical stimulation to delineate the primary motor cortex (MI), supplementary motor area (SMA), primary somatosensory cortex (SI), supplementary sensory area (SSA), negative motor area (NMA), and supplementary negative motor area (SNMA) in patients with epilepsy who were undergoing functional mapping.Seventeen patients were studied, all of whom underwent functional mapping using 50-Hz electrical stimulation. After these clinical evaluations, cortical stimulations with a short train of electrical pulses at 500 Hz were performed through subdural electrodes placed at the MI, SMA, SI, SSA, NMA, and SNMA, which had been identified by 50-Hz stimulation, and surrounding cortical areas, while surface electromyography readings were recorded.Stimulation of the MI elicited motor evoked potentials (MEPs) in contralateral muscles. Stimulation of the SMA also induced MEPs in contralateral muscles but with longer latencies compared with the MI stimulation. Stimulation of the SMA did not elicit MEPs in ipsilateral muscles. Stimulation of the SI, SSA, NMA, and SNMA did not induce MEPs in any muscle. In one patient, MEPs were elicited without seizure induction by 500-Hz stimulation of the electrodes, whereas a 50-Hz stimulation of the same electrodes induced his habitual seizures.Extraoperative high-frequency stimulation with MEP monitoring is a useful complementary method for cortical mapping without inducing seizure. Stimulation of SMA induces MEPs in contralateral muscles, with longer latencies compared with the stimulation of MI. This finding may be useful for the differentiation between MI and SMA, especially in the foot motor areas.
Purpose : Patients with epilepsy often have headaches. It has been reported that some of these headaches have the same characteristics as migraine headaches and that a common etiology for migraine and epilepsy may exist. However, this supposition is still controversial, partly because there have been few studies on the relation between epilepsy and headaches. To address this issue, we investigated the frequency and characteristics of headaches independent of seizures (interictal headaches, 1Hs) and after seizures (postictal headaches, PHs) among a large number of patients. We also evaluated the associations between these headaches and other clinical features of the epilepsy. Methods : Two‐hundred and fifty‐six (1I1 male and 145 female; aged 13–82 years; mean, 41 years) patients with epilepsy who attended Hokkaido University Hospital were questioned by epileptologists using a questionnaire. The questionnaire addressed frequency, characteristics, duration, severity, and accompanying symptoms of IHs and PHs. Medical charts were reviewed for each patient, and we analyzed the sex, age, age at onset of epilepsy, duration and classification of epilepsy, type and frequency of seizures, and family history of headaches. Results : One‐hundred and twenty‐four (48%) patients had IHs. Among those patients, 80 (65%) were female patients. In contrast, among those with no IHs, 65 (49%) were female patients (p < 0.05). The mean age of those with IHs was 38 years and that of the patients with no IHs wab 45 years (p < 0.05). No significant difference was found for age at onset of epilepsy, duration and classification of epilepsy, or type and fequency of seizure between those patients with or without IHs. Thirty‐six (29%) patients with IHs had a family history of headaches as compared with only 21 (16%) patients in the group with no IHs (p < 0.05).Among the patients with IHs, 53 (43%) patients had pounding characteristics for their headaches; the frequency was daily in seven (6%) patients, weekly in 25 (20%), monthly in 51 (41%). and yearly in 35 (28%); the severity was mild in 70 (56%) patients, moderate in 39 (32%), and severe in 15 (12%); 33 (27%) of these patients had accompanying symptoms. PHs occurred in 89 (35%) patients. There was no difference in any clinical factors between the patients with or without PHs. Thirty‐five (35%) patients had pounding characteristics: the severity was mild in 34 (38%) patients, moderate in 29 (33%), and severe in 34 (38%); 56 (33%) of these patients had accompanying symptoms. Forty‐seven (38%) patients had both IHs and PHs. Of these, 22 patients had IHs and PHs with common characteristics. Conclusions : In this study, the frequency of both IHs (48%) and PHs (35%) was similar to that found in studies by other researchers (36 64% and 13–51%, respectively). However, migrainous features (pounding characteristics, moderate to severe pain, and accompanying symptoms such as nausea, photophobia and/or phonophobia) were fewer in this study than those found in other studies from the United States and Europe. This finding may be due to racial difference (is., the low prevalence of migraine among Asians). Considering the higher frequency of a family history of headaches among the patients with IHs and the absence of any difference in the clinical features of epilepsy between those patients with or without IHs, IHs may be related to a genetic susceptibility to headaches and migraines. We found few common characteristics between IHs and PHs. This finding suggests that mechanisms that trigger IHs and PHs are different.
The generators of the initial cortical component of somatosensory evoked potentials in response to tibial nerve stimulation (Tib-somatosensory evoked potentials) are still uncertain. The purpose of this study is to localize the generators of it. A 15-year-old boy with intractable parietal lobe epilepsy was studied. Subdural electrodes were chronically implanted for presurgical evaluation of epilepsy surgery, covering the primary motor, primary sensory, and supplementary sensorimotor areas of the right leg. Tib-somatosensory evoked potentials were recorded from these areas. Highly localized prominent positive activities were recorded from electrodes on the primary motor area of the leg at 32.4 to 34.0 milliseconds. No corresponding large negative peak was recorded in any other electrodes. Weak negative activities distributed widely around the postcentral area at 33.2 to 33.6 milliseconds, accompanied by similar but positive activities in the precentral area at 32.8 to 33.2 milliseconds. There was an independent positive field on supplementary sensorimotor areas at 34.0 to 34.8 milliseconds. A small negative peak was also recorded but only from a single electrode within supplementary sensorimotor areas at 34.0 milliseconds. Our data suggest that the initial response of Tib-somatosensory evoked potentials has at least three independent generators: a radial dipole on the primary motor, a tangential dipole on the primary sensory area, and a dipole on the supplementary sensorimotor areas oriented perpendicularly to the mesial hemispheric surface.
The aims of this study were to record high-frequency oscillations (HFOs) associated with somatosensory-evoked potentials from subdural electrodes and to investigate their generators and clinical significance. Six patients who underwent long-term subdural electrode monitoring were studied. Somatosensory-evoked potentials were recorded directly from the subdural electrode after stimulation of the median nerve. Bandpass filter was 10 to 10,000 Hz for conventional somatosensory-evoked potential and 500 to 10,000 Hz for HFO. Three types of HFO were recorded. The first component was early HFO (407-926 Hz), which occurred before N20 peak. The second component was late HFO (408-909 Hz), which occurred after N20 peak. In addition, a novel component was recorded with a range from 1,235 to 2,632 Hz, and this component was termed very HFO. Early and late HFOs were recorded from relatively wide areas centering around the primary motor and primary sensory areas, whereas very HFO was localized around the primary sensory areas. In this study, at least three components of HFO could be identified. Only very HFO was localized around primary sensory areas, suggesting a possibility that very HFO may provide an effective method of identifying the central sulcus.
Using intracranial electroencephalographic recordings, we identified a distinct brain activity in 3 patients with refractory epilepsy characterized by very early occurrence from 8 minutes 10 seconds to 22 minutes 40 seconds prior to clinical seizure onset, periodical appearance of slow negative baseline shift, long interpeak interval of 40 to 120 seconds, and disappearance after clinical seizure. We named this activity "very low frequency oscillation" (VLFO), which reflected a dynamic process during the preictal state. This observation may render new insight into epileptogenesis and provide additional information concerning the epileptogenic zone as well as prediction of epileptic seizures.
