Biomedical subjects

Akio Ikeda

Publications and source records attributed to Akio Ikeda.

51 records · Page 3Linked to original sources

PubMed2004

Electric stimulation on human cortex suppresses fast cortical activity and epileptic spikes.

PURPOSE: To investigate underlying mechanisms and adequate parameters for electric cortical stimulation to inhibit epileptic focus in humans. METHODS: A patient with intractable partial epilepsy had subdural electrodes implanted for preoperative evaluation. Cortical functional mapping was performed by using 50-Hz alternating square pulse of 0.3-ms duration, 1 to 7 mA, within 5 s. Spike frequency and electrocorticogram (ECoG) power spectra were compared before and after the stimulation when epileptic focus and distant area were stimulated. A similar comparison also was performed in low-frequency stimulation of 0.9 Hz applied for 15 min. RESULTS: Interictal spikes were reduced after electric cortical stimulation of the epileptic area at a frequency of 50 Hz as well as 0.9 Hz, with concomitant decrease in the electrographic fast activities at 50-Hz stimulation. CONCLUSIONS: These data suggest that electric cortical stimulation at both high and low frequency has a suppressive effect on epileptic activities in human cortex, possibly through distinct mechanisms.

Adult↗

PubMed2004

Preoperative mapping for patients with supplementary motor area epilepsy: multimodality brain mapping.

Surgical management and strategies for the supplementary motor area (SMA) epilepsy are described. The following is our preoperative evaluations. The steps include functional magnetic resonance imaging (fMRI), interictal dipole tracing (DT), subdural electrodes mapping, measurements of movement-related cortical potential (MRCP), and the use of the intraoperative open MRI under conscious craniotomy. Six patients with SMA epilepsy underwent surgery after the mapping procedures and are now seizure-free. Combinations of preoperative (fMRI, subdural electrodes mapping) and intraoperative mapping allow exact localization and identification of the critical functional areas. Early postoperative deficits in motor and speech function were profound but patients recovered rapidly. It is concluded that the step of mapping procedures plays an important role in the management of SMA epilepsy surgery.

Adolescent↗

PubMed2004

A combined subtemporal and transventricular/transchoroidal fissure approach to medial temporal lesions.

OBJECTIVE: To minimize therapeutic morbidity such as cognitive function disturbance and vascular injury to perforating arteries, preoperative functional mapping of the basal temporal lobe functions was performed and the medial temporal lesions were resected via a combined subtemporal and transventricular/transchoroidal fissure approach. METHODS: Twenty-one patients with medial temporal lesions including tumors, arteriovenous malformations, and medial temporal lobe epilepsy underwent operation. The neurovascular structures in the ambient cistern were first dissected free from the medial temporal lobe with a conventional subtemporal approach. Then, the temporal horn was opened through the basal surface of the temporal lobe. Finally, the ambient cistern was accessed from the temporal horn through the choroidal fissure. In five patients whose lesions were revealed to be located on the dominant side by preoperative intracarotid amytal administration test (Wada test), functional mapping of the basal temporal lobe language cortex was monitored for 1 week by use of a subdural electrocorticogram grid before the extirpation surgery. The entrance point from the temporal base to the temporal horn was determined by the result of the functional mapping. RESULTS: The lesions were resected safely and completely in all cases. Language and cognitive functions were preserved even in patients with the basal language area on the dominant side. CONCLUSION: Surgeons can confirm the important neurovascular structures from the subtemporal route and from the transtemporal horn route by a combined subtemporal and transventricular/transchoroidal fissure approach. This approach is especially effective for avoiding ischemic complications by allowing direct confirmation of the anterior choroidal and thalamoperforating arteries.

Adult↗

PubMed2003

Role of primary sensorimotor cortex and supplementary motor area in volitional swallowing: a movement-related cortical potential study.

We investigated the role of the cerebral cortex, particularly the face/tongue area of the primary sensorimotor (SMI) cortex (face/tongue) and supplementary motor area (SMA), in volitional swallowing by recording movement-related cortical potentials (MRCPs). MRCPs with swallowing and tongue protrusion were recorded from scalp electrodes in eight normal right-handed subjects and from implanted subdural electrodes in six epilepsy patients. The experiment by scalp EEG in normal subjects revealed that premovement Bereitschaftspotentials (BP) activity for swallowing was largest at the vertex and lateralized to either hemisphere in the central area. The experiment by epicortical EEG in patients confirmed that face/tongue SMI and SMA were commonly involved in swallowing and tongue protrusion with overlapping distribution and interindividual variability. BP amplitude showed no difference between swallowing and tongue movements, either at face/tongue SMI or at SMA, whereas postmovement potential (PMP) was significantly larger in tongue protrusion than in swallowing only at face/tongue SMI. BP occurred earlier in swallowing than in tongue protrusion. Comparison between face/tongue SMI and SMA did not show any difference with regard to BP and PMP amplitude or BP onset time in either task. The preparatory role of the cerebral cortex in swallowing was similar to that in tongue movement, except for earlier activation in swallowing. Postmovement processing of swallowing was lesser than that of tongue movement in face/tongue SMI; probably suggesting that the cerebral cortex does not play a significant role in postmovement processing of swallowing. SMA plays a supplementary role to face/tongue SMI both in swallowing and tongue movements.

Adult↗

PubMed2003

Movement-related cortical potentials before jaw excursions in oromandibular dystonia.

Oromandibular dystonia is a neurological disorder characterized by involuntary contraction of masticatory and/or tongue muscles. Cortical negative shifts preceding voluntary movements called "movement-related cortical potentials" (MRCPs) reflect a central motor control process. Reduced amplitude of MRCPs has been reported in other types of dystonia. To elucidate whether the abnormality is observed also in oromandibular dystonia, we compared MRCPs associated with mandibular movements in 6 patients with this condition and in 8 normal subjects. Electroencephalograms (EEGs) were recorded from 11 electrodes, and electromyograms (EMGs) were recorded from the masseter muscle and the suprahyoid muscles. The subjects were asked to repeat mouth opening, closing, and left and right lateral mandibular excursions. MRCPs were obtained by averaging the EEG using the EMG onset as the trigger signal. In the patient group, MRCP amplitudes over central and parietal areas for mouth opening and lateral movements were significantly reduced compared to normal subjects. In normal controls, the MRCPs at mouth opening and closing were symmetrically distributed, whereas those at lateral movements showed predominance over the hemisphere ipsilateral to the direction of the movement. This laterality was lost in the patient group. These results suggest impaired cortical preparatory process for jaw movements in oromandibular dystonia.

Adult↗

PubMed2003

Motor-related functional subdivisions of human lateral premotor cortex: epicortical recording in conditional visuomotor task.

OBJECTIVE: To clarify the functional subdivisions of the human lateral premotor cortex (PM) in the visuomotor control. METHODS: Event-related potentials (ERPs) were epicortically recorded from PM in 5 epilepsy patients. S1-Go/NoGo choice delayed reaction time (RT), S1-warned S2-Go simple RT and control fixation paradigms were compared using paired visual stimuli (S1, S2). RESULTS: Signal-related activity peaked at 176-194 ms after S1 in the ventrorostral PM (PMvr) in all 3 paradigms, indicating its role in signal perception. Early set-related activity was recorded with its peak <810 ms after S1 in the dorsorostral PM (PMdr) and was larger in the choice than in the simple RT paradigm, suggesting its role in signal selection. Its cognitive component was recorded as surface-positive transients at PMdr, while its motoric aspect, seen as negative transients, extended to the caudal PM. Late sustained set-related activity was observed in preparation for hand movement in the caudal PM at the hand and face positive motor areas. After presentation of S2, movement-related activity was observed at the hand sensorimotor area for motor execution, following the signal-related activity at PMvr. CONCLUSIONS: The present ERP study suggests the temporally sequential representation of predominantly 'cognitive' function in the rostral PM and 'motor' function in the caudal PM. SIGNIFICANCE: The rostrocaudal cognitive-motor gradient was demonstrated in the lateral premotor cortex in humans by means of an epicortical ERP approach.

Adolescent↗

PubMed2003

Distinct cortical areas for motor preparation and execution in human identified by Bereitschaftspotential recording and ECoG-EMG coherence analysis.

OBJECTIVE: To clarify the cortical areas involved in motor preparation and execution by investigating Bereitschaftspotentials (BPs) and electrocorticogram-electromyogram (ECoG-EMG) coherence from subdural electrodes placed around the rolandic area. METHODS: BPs and ECoG-EMG coherence were investigated for presurgical evaluation in a patient with cavernoma in the left frontal lobe. BPs were recorded in association with the tongue, right hand and right foot movements. ECoG-EMG coherence was calculated in association with weak muscle contraction of the right hand. RESULTS: Two cortical areas related to voluntary motor control were identified; one in the primary hand motor area, which generated surface-negative BPs with hand movements and showed significant coherence of ECoG with EMG of the contralateral hand muscle, and the other in the ventral rolandic area posterior to the central sulcus, which generated surface-positive BPs with voluntary movements of multiple sites (hand, tongue and foot) but did not show any ECoG-EMG coherence. CONCLUSIONS: It is postulated that the former area represents the primary motor area involved in both motor preparation and execution, and the latter area represents the non-primary motor area involved in motor preparation. SIGNIFICANCE: BP recording combined with ECoG-EMG coherence analysis could reveal the functional roles of motor cortices and the reorganization induced by structural brain lesion.

Brain Mapping↗

PubMed2003

Conversion of semantic information into phonological representation: a function in left posterior basal temporal area.

A unique feature of Japanese language is that its written sentences consist of both morphograms (kanji) and syllabograms (kana). Despite extensive research by PET, functional MRI and magnetoencephalography, the issues of the difference (or the similarities) between the processing of kanji and kana, and between word reading and object/picture naming have not been resolved as yet. This study investigated the function of the posterior basal temporal area in the language dominant hemisphere in auditory and visual language processing, with special emphasis on semantic and phonological recognition. Subdural electrode grids were placed on the left temporal area of a right-handed woman with intractable temporal lobe epilepsy as part of a pre-surgical evaluation. Her dominant hemisphere for language was shown to be the left on the Wada test. Electric stimulation of 50 Hz was applied to the electrodes during the tasks related to language. Our results showed a clear distinction in the responses and/or performance of the subject depending on the type of characters presented and the tasks employed. Electric stimulation of a localized area in the posterior basal temporal lobe caused neither comprehensive nor productive deficit in the tasks using auditory stimuli. In the tasks using visual stimuli, in contrast, impairments were observed in (i) reading of kanji words and (ii) naming of objects/pictures and geometric designs, but not in (iii) reading of kana, (iv) copying of kanji, kana and geometric designs, and (v) using tools. The subject maintained full comprehension of spoken language, suggesting that the auditory tasks are not processed in the posterior basal temporal area. The fact that the impairment of kanji reading and disturbance of object/picture naming were elicited by electric stimulation of the same area indicates that there is at least one anatomical area that is used commonly for kanji (but not kana) and object processing. The conceptual entity of the test items supposedly was recognized correctly, but the concept failed to be matched to correct phonological representation. The left posterior basal temporal area, therefore, has an important function of connecting visual semantic information into phonological representation.

Adult↗

PubMed2003

Painful focal sensory seizure arising from the primary somatosensory cortex.

A 31-year-old, right-handed woman had frequent focal painful seizures involving the right hand without any movement. EEG demonstrated an ictal activity arising from the left centroparietal region. No cerebral structural abnormality was seen on MRI. Ictal single photon emission CT showed markedly increased activity in the left perirolandic cortex, which remained active following the ictal symptoms when the EEG seizure pattern had completely disappeared. It is concluded that the painful seizures in the present patient originated from the primary somatosensory cortex. The prolonged increase of regional blood flow in the perirolandic area may reflect the possibility of persistent subclinical epileptogenicity.

Adult↗

PubMed2002

"Supplementary motor area (SMA) seizure" rather than "SMA epilepsy" in optimal surgical candidates: a document of subdural mapping.

PURPOSE: To clarify the relationship between epileptogenic zone and supplementary motor area (SMA) in patients who were regarded as the optimal surgical candidates for their intractable SMA seizures. METHODS: We analyzed the epileptogenic zone at/or adjacent to the SMA in four patients with clinical SMA seizures. All four patients had noninvasive presurgical evaluations (long-term video/EEG monitoring, MRI, and neuroimaging with radioisotopes), which provided convergent results between ictal semiology and the epileptogenic area, and thus, they had chronically implanted subdural electrodes, and finally had focus resection with a follow-up period of more than 2 years. RESULTS: Three patients had lesions shown by MRI outside the SMA, and one patient had a lesion within the SMA. Interictal epileptiform discharges were seen at/or outside the SMA. Ictal EEG pattern originated from the SMA in one patient, from the high lateral frontal area in two patients, and from the precuneus in one patient. In the latter three patients, the ictal EEG pattern immediately spread to the SMA. Those ictal onset zones were consistently localized within/or just adjacent to the lesions revealed by MRI. Only one patient had SMA resection, and three had the resection of epileptogenic zone by preserving the SMA. No neurological deficits developed and good seizure control was achieved. CONCLUSION: Among surgical candidates for intractable SMA seizures, frontal cortex other than SMA or even parietal cortex can be epileptogenic, and thus, the SMA itself may not necessarily have to be resected. This notion is clinically important when selecting surgical candidates as well as when planning presurgical invasive evaluation in patients with intractable SMA seizures.

Adolescent↗

PubMed2002

Nausea as a complication of low-frequency repetitive transcranial magnetic stimulation of the posterior fossa.

BACKGROUND: Transcranial magnetic stimulation (TMS) can non-invasively investigate the function of human brain. However, it can induce a focal pain at the stimulated site on the scalp or seizures when applied with high frequency (>1 Hz). Here we report an induction of nausea as a complication of low-frequency repetitive TMS (rTMS) of the cerebellum. SUBJECTS AND METHODS: Eight right-handed normal volunteers underwent low-frequency (0.9 Hz) rTMS of the right cerebellum. The stimulus intensity was set at 90% of the resting motor threshold determined by TMS to motor cortex. RESULTS: Nausea lasted as long as 10 min after the end of rTMS without apparent neurological deficit in two subjects. This symptom was replicated when the same protocol was applied on a different day in the same subjects. CONCLUSIONS: Low-frequency rTMS of cerebellum is still a safe procedure, but the experimenters should keep in mind the possibility of inducing nausea.

Adult↗

PubMed2002

Low-frequency electric cortical stimulation has an inhibitory effect on epileptic focus in mesial temporal lobe epilepsy.

PURPOSE: This study was conducted to investigate the effect of low-frequency electric cortical stimulation on epileptic focus in humans. METHODS: We stimulated the epileptic focus in a patient with medically intractable mesial temporal lobe epilepsy (MTLE) by means of subdural electrodes and evaluated the change in the number of interictal epileptiform discharges. We used biphasic electric current of 0.3-ms duration presented at 0.9-Hz frequency for 250 s, comparing stimulus intensity of 7.5, 2, and 0.5 mA. RESULTS: Interictal epileptiform discharges at the ictal focus occurred less frequently after the stimulation with the intensity of 0.5 mA. With the intensity of 7.5 mA and 2.0 mA, however, habitual auras were elicited by the stimulation, and afterdischarges were seen on the cortical EEG. CONCLUSIONS: Low-frequency, low-intensity electric cortical stimulation could produce inhibitory effects on epileptic activity. At the same time, however, a caution for possible induction of EEG seizures is needed, even when applying low-frequency electric stimulation.

Adolescent↗

PubMed2002

Partial epilepsy manifesting atonic seizure: report of two cases.

PURPOSE: Atonic seizures are commonly seen in patients with generalized epilepsy but only infrequently in patients with partial epilepsy. Clinically generalized atonic seizures as a partial epilepsy have not been studied in detail with video/EEG monitoring. Here we describe the clinical and physiologic characteristics of atonic seizures due to partial epilepsy and discuss the underlying mechanism. METHODS: Two patients with partial epilepsy manifesting atonic seizures, one with frontal lobe epilepsy (FLE) and the other with parietal lobe epilepsy (PLE), were reported. The long-term video/EEG monitoring, magnetic resonance imaging (MRI), and interictal fluorodeoxyglucose-positron emission tomography (FDG-PET) were investigated in each patient. RESULTS: Paroxysmal diminution of muscle tone mainly involved the axial muscles in both patients. In contrast with the abrupt falls seen in patients with Lennox-Gastaut syndrome, the falls in these patients were slow, taking 2-5 s to fall down. Ictal EEG records showed low-voltage fast activity in the frontocentral area followed by repetitive spikes at the midline frontocentral area in the patient with FLE, and rhythmic spikes in the left central area in the patient with PLE. Interictal FDG-PET disclosed hypometabolic regions consistent with the clinical and EEG findings. CONCLUSIONS: Slow falls might be a feature of atonic seizures in partial epilepsy. Long-lasting atonia in partial epilepsy could be due to either one of the following two possible mechanisms: (a) epileptic activities arising from the negative motor area, of which 50-Hz electric stimulation causes motor inhibition, or (b) sustained atonia with successive electromyogram (EMG) silent periods caused by epileptic discharges arising from the inhibitory area of the primary sensorimotor area.

Adult↗

PubMed2002

Cortical motor mapping in epilepsy patients: information from subdural electrodes in presurgical evaluation.

It is essential to delineate an epileptogenic zone and to define the eloquent cortices at or close to the epileptogenic zone in patients with neocortical epilepsy for epilepsy surgery. Prolonged implantation of the subdural electrode in presurgical evaluation is currently one of the best clinical methods to provide the essential information before epilepsy surgery. Electric cortical stimulation and recording of sensory evoked potentials by means of subdural electrodes are widely used for functional cortical mapping. Bereitschaftspotential (BP) is clinically useful to delineate the primary and nonprimary motor cortices such as supplementary motor area proper (SMA proper) and pre-SMA, because BP occurs for any type of voluntary movements of the body, and because it is not associated with the risk of seizure induction in contrast with high-frequency cortical electric stimulation. Single-pulse electric cortical stimulation to record motor evoked potentials (MEPs) also could complement currently used high-frequency cortical electric stimulation, especially for mapping of the primary motor and premotor cortices with lower risk of seizure induction.

Brain Mapping↗

PubMed2002

Adaptive EEG spike detection: determination of threshold values based on conditional probability.

Determination of the threshold value for automatic EEG spike detection was investigated adopting conditional probability. An adaptive spike detection method was constructed and evaluated. A discriminant function for detecting spikes was obtained by conditional probability calculated from the EEG spike data. The relationship among false-negatives, false-positives and threshold values for the discriminant function was investigated. An adaptive detection algorithm was developed by combining different threshold values. False-negative and false-positive rates for spike detection depended on the threshold values. The adaptive spike detection algorithm achieved a high detection rate and accuracy. The advantage of the proposed method is to construct an adaptive detection algorithm by combining the threshold values according to the purpose of spike detection. Since the threshold can be easily changed in the proposed method, it is practically effective for clinical use.

Adult↗