Showing papers by "François Mauguière published in 2000"

The role of the insular cortex in temporal lobe epilepsy.

Abstract: The role of the insular cortex in the genesis of temporal lobe epileptic (TLE) seizures has been investigated in 21 patients with drug-refractory TLE using chronic depth stereotactic recordings of the insular cortex activity and video recordings of ictal symptoms during 81 spontaneous electroclinical seizures. All of the recorded seizures were found to invade the insula, most often after a relay in the ipsilateral hippocampus (19/21 patients). However, 2 patients had seizures that originated in the insular cortex itself. Ictal symptoms associated with the insular discharges were similar to those usually attributed to mesial temporal lobe seizures, so that scalp video-electroencephalographic monitoring does not permit making any difference between ictal symptoms of temporo-mesial and insular discharges. A favorable outcome was obtained after a temporal cortectomy sparing the insular cortex in 15 of 17 operated patients. Seizures propagating to the insular cortex were found to be fully controlled by surgery, whereas those originating in the insular cortex persisted after temporal cortectomy. The fact that seizures originating in the insular cortex are not influenced by temporal lobectomy is likely to explain some of the failures of this surgical procedure in TLE.

Functional Mapping of the Insular Cortex: Clinical Implication in Temporal Lobe Epilepsy

Abstract: Summary: Purpose: We report the results of 75 intracortical electrical stimulations of the insular cortex performed in 14 patients during stereo-electroencephalography (SEEG) investigation of drug-resistant partial epilepsy. The insular cortex was investigated on electroclinical arguments suggesting the possibility of a perisylvian spread or a rapid multilobar diffusion of the discharges during video EEG. Methods: In these 14 patients, 27 stereotactically implanted transopercular electrodes reached the insular cortex (11 the right insula, 16 the left insula). Square pulses of current were applied between the two deepest adjacent contacts of each transopercular electrode using low (1 Hz) or high-frequency (50 Hz) stimulation. Only symptoms evoked in the absence of afterdischarges were analyzed. Results: Clinical responses were evoked in 10 of the 14 patients (in 20 of the 27 insular sites) and showed a clear topographic specificity inside the insular cortex. Viscerosensitive and visceromotor responses, similar to those evoked by temporomesial stimulation, were evoked by anterior insular stimulation and somesthetic sensation, similar to those evoked by opercular cortex stimulation, by posterior insular stimulation. Conclusions: The topographic organization of the induced responses within the insular cortex suggest that two different cortical networks, a visceral network extending to the temporomesial structures and a somesthetic network reaching the opercular cortex, are disturbed with stimulation of the anterior or the posterior insula, respectively. Thus ictal symptoms associated with the spread of the epileptic discharges to the insular cortex might be difficult to distinguish from those usually reported during temporomesial or opercular discharges.

Abnormal central integration of a dual somatosensory input in dystonia. Evidence for sensory overflow.

Abstract: Several observations suggest impaired central sensory integration in dystonia. We studied median and ulnar nerve somatosensory evoked potentials (SEPs) in 10 patients who had dystonia involving at least one upper limb (six had generalized, two had segmental and two had focal dystonia) and in 10 normal subjects. We compared the amplitude of spinal N13, brainstem P14, parietal N20 and P27 and frontal N30 SEPs obtained by stimulating the median and ulnar nerves simultaneously (MU), the amplitude value being obtained from the arithmetic sum of the SEPs elicited by stimulating the same nerves separately (M + U). Throughout the somatosensory system, the MU : (M + U) ratio indicates the interaction between afferent inputs from the two peripheral nerves. No significant difference was found between SEP amplitudes and latencies for individually stimulated median and ulnar nerves in dystonic patients and normal subjects, but recordings in patients yielded a significantly higher percentage ratio [MU : (M + U)x100] for spinal N13 brainstem P14 and cortical N20, P27 and N30 components. The SEP ratio of central components obtained in response to stimulation of the digital nerves of the third and fifth fingers was also higher in patients than in controls but the difference did not reach a significant level. The possible contribution of subliminal activation was ruled out by recording the ratio of SEPs in six normal subjects during voluntary contraction. This voluntary contraction did not change the ratio of SEP suppression. These findings suggest that the inhibitory integration of afferent inputs, mainly proprioceptive inputs, coming from adjacent body parts is abnormal in dystonia. This inefficient integration, which is probably due to altered surrounding inhibition, could give rise to an abnormal motor output and might therefore contribute to the motor impairment present in dystonia.

Parietal and cingulate processes in central pain. A combined positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) study of an unusual case.

Abstract: Parietal, insular and anterior cingulate cortices are involved in the processing of noxious inputs and genesis of pain sensation. Parietal lesions may generate central pain by mechanisms generally assumed to involve the 'medial' pain system (i.e. medial thalamic nuclei and anterior cingulate cortex (ACC)). We report here PET and fMRI data in a patient who developed central pain and allodynia in her left side after a bifocal infarct involving both the right parietal cortex (SI and SII) and the right ACC (Brodmann areas 24 and 32), thus questioning the schematic representation of cortical pain processing. No rCBF increase was found in any part of the residual cingulate cortices, neither in the basal state (which included spontaneous pain and extended hypoperfusion around the infarct), nor during left allodynic pain. Thus, as previously observed in patients with lateral medullary infarct, neither spontaneous pain nor allodynia reproduce the cingulate activation observed after noxious pain in normal subjects. Conversely, both PET and fMRI data argue in favour of plastic changes in the 'lateral discriminative' pain system. Particularly, allodynia was associated with increased activity anteriorly to the infarct in the right insula/SII cortex. This response is likely to be responsible for the strange and very unpleasant allodynic sensation elicited on the left side by a non-noxious stimulation.

Anatomy of optic nerve radiations as assessed by static perimetry and MRI after tailored temporal lobectomy

Abstract: Aims—To determine the course of optic nerve radiations in the temporal lobe, especially their retinotopic organisation and the anterior limit of the Meyer’s loop. Methods—18 adult patients who had undergone a tailored temporal lobectomy for epilepsy were included in this study between 1994 and 1998. The rostrocaudal extent of the lateral temporal lobe resection assessed intraoperatively by the surgeon and by postoperative MRI was compared with the postoperative visual fields determined by automated static perimetry (ASP). Results—15 patients (83%) presented a postoperative visual field deficit (VFD) confined to the superior homonymous field contralateral to the side of the resection. All degrees from a minimal upper field loss to a complete quadrantanopia were observed. The VFDs were somewhat stereotyped, predominating along the vertical meridian. The smallest anteroposterior resection resulting in a VFD was limited to 20 mm from the tip of the temporal lobe. A relation was observed between the extent of the lateral resection in front of the second and third convolutions and the occurrence and extent of postoperative VFDs. No patient reported persisting subjective visual impairment. Conclusion—The high frequency of postoperative VFDs appears to be due to the greater sensitivity of ASP. The characteristics of the stereotyped VFDs allow new conclusions about the course and retinotopy of optic nerve radiations. The anterior limit of Meyer’s loop is likely to be located more rostrally than previously believed. (Br J Ophthalmol 2000;84:884‐889)

Functional dissociation of the early and late portions of human K-complexes.

Abstract: We analyzed K-complexes (KCs) evoked during sleep stage II by the subject's own name and by other names. KCs were composed either of four consecutive waves (full KCs, N2-P3-N3-P4) or of the two first components only (N2-P3). The amplitude of the late phase of KCs (N3-P4) was identical to all stimuli; conversely, own names enhanced selectively the N2-P3 waves, whether they were or not part of a full KC. Two independent phenomena appear to coexist during a full KC, one being connected to the physical characteristics of the stimulus (N3-P4) and the other to its intrinsic significance. This latter may appear either within a full KC or in isolation, and in this case it is reminiscent of the N200-P300 complex observed in wakefulness.

Central scalp projection of the N30 SEP source activity after median nerve stimulation

Abstract: Conflicting results have been reported about abnormalities of the N30 somatosensory evoked potential (SEP) in movement disorders. In these studies, the N30 amplitude was measured in the frontal scalp region. Our aim was to identify the scalp electrodes recording the genuine activity of the N30 generator. In 18 subjects, we recorded the scalp SEPs from 19 electrodes and found a negative potential around 30 ms reaching its maximal amplitude in the frontal region. However, neither simple visual inspection of the frontal traces nor topographic analysis could distinguish the N24 from the N30 component of the frontal negativity. Brain electrical source analysis of SEPs showed that a four dipolar source model could well explain the scalp SEP distribution. We calculated the scalp field distributions of the source activities as modeled from the scalp recordings and observed that the maximal field distribution reflecting the activity of the N30 source was in the central region, whereas that reflecting the N24 source activity was frontal. We conclude that the negative response recorded around 30 ms in the central traces represents "genuine" N30 source activity, whereas the frontal negativity, which is higher in amplitude, is a mixture of the activities of both the N30 and N24 sources.

Anatomic origin of the cervical N13 potential evoked by upper extremity stimulation.

Abstract: There is a large consensus, based on converging evidence, that N13 recorded at lower cervical levels has a segmental postsynaptic origin in the gray matter of the cervical cord and that because of the orientation of its dipole field, the Cv6-anterior cervical derivation should be used whenever the diagnostic problem requires that this potential be assessed selectively in terms of latency and amplitude. The diagnostic utility of the lower cervical N13 recording in dorsal horn deafferentation and in lesions at the Cv6-Cv8 metameric levels has been validated in all types of cervical cord lesions. Unfortunately, such clear-cut conclusions do not apply to the N13 potential recorded at upper cervical levels. Currently, this component is not considered to provide enough reliable information, in addition to P13-P14 scalp recordings, to be used routinely in the diagnosis of cervicomedullary lesions.

Towards an optimal reference region in single-photon emission tomography difference images in epilepsy

Abstract: There is marked variability in the cerebral blood flow (CBF) between the ictal and interictal state in epilepsy, and it would therefore be desirable to increase the reliability of ictal/interictal single-photon emission tomography (SPET) difference images We aimed to improve the step of quantitative normalization of images by finding the best possible reference region In 16 patients (11 with lateralization of the epileptogenic focus, five with bilateral foci) both ictal and inter-ictal SPET scans were performed after injection of technetium-99m labelled tracer Then, each region among a selected set (brain+cerebellum, brain, cerebellum, hemispheres, and for patients with an expected lateralization, cortical lobe containing the focus and symmetrical contralateral lobe) was investigated by comparison of the regional ictal/inter-ictal variance in counts Among patients with a suspected lateralized focus, the distribution of CBF in the contralateral cortical lobe appeared to vary less between ictal and inter-ictal states than in other investigated areas As a consequence, this latter region constitutes the best choice as a reference region For patients with bilateral foci, the cerebellum appears to be a good compromise even though it presents with significant CBF changes