Electroencephalography and Clinical Neurophysiology, Jul 1, 1996
Ten patients with complex partial epileptic seizures undergoing invasive video/EEG-monitoring wer... more Ten patients with complex partial epileptic seizures undergoing invasive video/EEG-monitoring were recorded with a combination of 10 subdural strip electrode contacts (subtemporal + lateral temporal), and 22 extracranial recording sites. In each patient several spikes with different intracranial distributions were identified, and spikes with similar distributions were averaged together with their extracranial activity. Dipole analysis of the extracranial activity was performed with the BESA program (Scherg, Garching Instrumente, München). In the horizontal plane subtemporal spikes gave oblique posterior, and lateral temporal spikes straight lateral or oblique anterior dipole orientations. In the coronal plane all spikes had an elevated orientation, most pronounced for medial subtemporal spikes. Dipole locations did not separate as well as dipole orientations. In our opinion our results would be difficult to explain without postulating a substantial degree of volume conduction from deep temporal areas to the surface. We conclude that dipole analysis of the interictal epileptiform activity does provide substantial information about which parts of the temporal lobe are involved in the epileptogenic process, making the method a useful tool in the preoperative investigation of patients with drug resistant partial epilepsy.
... of equation I, can be written for the linear case as (Grave and Gonzalez, 1998),: ... to inco... more ... of equation I, can be written for the linear case as (Grave and Gonzalez, 1998),: ... to incorporate the functional image f into the solution j is the use of space ... during self-paced finger movement performance, tactile somatosensory stimulation and binaural auditory stimulation using ...
Over the past few decades, diverse brain imaging techniques have been applied in different areas ... more Over the past few decades, diverse brain imaging techniques have been applied in different areas of experimental psychology and neuroscience, and have begun to provide unprecedented windows on the functional and the structural anatomy of the human brain. Recent technological innovations have achieved to convert conventional electrophysiological methods (e.g. electroencephalogram or EEG) into modern functional brain imaging procedures (i.e. electric source imaging or ESI); allowing neuroscientists to measure the spatial and temporal dynamics of the brain. In patients with drug-resistant epilepsy who are candidates for surgery, non-invasive functional imaging methods are helpful in guiding placement of surgical resections or invasive EEG recordings. ESI consists in a non-invasive recording of the electrical potential field on the scalp while using dense array EEG (up to 256 channels), which allows estimating intra-cerebral electric sources. Nowadays, ESI became an accessible technique mainly due to the increase in computational power and the appearance of user-friendly sophisticated analysis software. Despite the large amount of literature supporting the validity of ESI in terms of localization, the introduction of this technique into clinical routine has been rather slow. In this review we intend to tackle the theoretical aspects, practical procedures and ESI clinical studies; in addition, we will compare with other well established imaging tools used in presurgical evaluation of epilepsy workup.
Question: Non-invasively recorded high-frequency (>400 Hz) components of somatosensory evoked pot... more Question: Non-invasively recorded high-frequency (>400 Hz) components of somatosensory evoked potentials (hf-SEP) are generated by cortical population spikes, as revealed by microelectrode recordings in primates. Until now it was a critical drawback that this approach required averaging hundreds of responses for reliable hf-SEP detection. Here, we establish how to detect human hf-SEP non-invasively in single trials. Methods: Inside a shielded room median nerve hf-SEP were recorded in four subjects spanning the hf-SEP signal-to-noise ratio characteristic for a larger population, utilizing a custom-built 29-channel low-noise EEG amplifier. Features were extracted from band-pass filtered (400-900 Hz) trials by bilinear Common Spatial Patterns (bCSP) to construct both, optimized spatial and temporal filters, and then classified by a weighted Extreme Learning Machine (w-ELM). Results: Human hf-SEP were detected in single trials with a sensitivity of up to 98% and a specificity up to 97% in two subjects, even without any recourse to stimulus timing. Since for the two subjects with lower signal-to-noise ratio these rates dropped to 62-79% sensitivity and 18-28% specificity, optimal recording quality is a critical prerequisite for efficient single-trial detection. Conclusions: Non-invasive low-noise recordings can extract high-frequency EEG components otherwise buried in background noise. Specifically, a refined supervised filter optimization and classification can enable reliable single-trial hf-SEP detection, representing a non-invasive correlate of cortical population spikes. Thus, while low-frequency EEG reflects summed postsynaptic potentials and thereby neuronal input, we suggest that hf-SEP provides non-invasive access to the output of neuronal computation: spiking activity in the responsive neuronal ensemble.
Over the past few decades, diverse brain imaging techniques have been applied in different areas ... more Over the past few decades, diverse brain imaging techniques have been applied in different areas of experimental psychology and neuroscience, and have begun to provide unprecedented windows on the functional and the structural anatomy of the human brain. Recent technological innovations have achieved to convert conventional electrophysiological methods (e.g. electroencephalogram or EEG) into modern functional brain imaging procedures (i.e. electric source imaging or ESI); allowing neuroscientists to measure the spatial and temporal dynamics of the brain. In patients with drug-resistant epilepsy who are candidates for surgery, non-invasive functional imaging methods are helpful in guiding placement of surgical resections or invasive EEG recordings. ESI consists in a non-invasive recording of the electrical potential field on the scalp while using dense array EEG (up to 256 channels), which allows estimating intra-cerebral electric sources. Nowadays, ESI became an accessible technique mainly due to the increase in computational power and the appearance of user-friendly sophisticated analysis software. Despite the large amount of literature supporting the validity of ESI in terms of localization, the introduction of this technique into clinical routine has been rather slow. In this review we intend to tackle the theoretical aspects, practical procedures and ESI clinical studies; in addition, we will compare with other well established imaging tools used in presurgical evaluation of epilepsy workup.
Electroencephalography and Clinical Neurophysiology, 1996
Ten patients with complex partial epileptic seizures undergoing invasive video/EEG-monitoring wer... more Ten patients with complex partial epileptic seizures undergoing invasive video/EEG-monitoring were recorded with a combination of 10 subdural strip electrode contacts (subtemporal + lateral temporal), and 22 extracranial recording sites. In each patient several spikes with different intracranial distributions were identified, and spikes with similar distributions were averaged together with their extracranial activity. Dipole analysis of the extracranial activity was performed with the BESA program (Scherg, Garching Instrumente, München). In the horizontal plane subtemporal spikes gave oblique posterior, and lateral temporal spikes straight lateral or oblique anterior dipole orientations. In the coronal plane all spikes had an elevated orientation, most pronounced for medial subtemporal spikes. Dipole locations did not separate as well as dipole orientations. In our opinion our results would be difficult to explain without postulating a substantial degree of volume conduction from deep temporal areas to the surface. We conclude that dipole analysis of the interictal epileptiform activity does provide substantial information about which parts of the temporal lobe are involved in the epileptogenic process, making the method a useful tool in the preoperative investigation of patients with drug resistant partial epilepsy.
In terms MMN are at Fz À3.9 uV (±1.8), at Cz À5.0 uV (±3.8), and at Pz À3.3 (±3.2). These differe... more In terms MMN are at Fz À3.9 uV (±1.8), at Cz À5.0 uV (±3.8), and at Pz À3.3 (±3.2). These differences are not significant. The maximal peak was measured in the preterm group at Fz after 233.7 ms (±39.5), at Cz after 222 ms (±19.9), and at Pz after 212.3 ms (±30.1), in the term group at Fz after 231 ms (±26), at Cz after 215.6 ms (±21.3), and at Pz after 207.7 ms (±25.4). These differences are not statistically significant. In both groups. From the first to the third stimulus block a decrease of the MMN amplitude is observed. Conclusion: In the gestational age of 40 weeks preterms and terms did not differ in their capability to discriminate tones with a different frequency.
Objective: Nocturnal frontal lobe epilepsy (NFLE) seizures occur primarily during non-rapid eye m... more Objective: Nocturnal frontal lobe epilepsy (NFLE) seizures occur primarily during non-rapid eye movement sleep stage 2. We observed in several patients rhythms of same localization and frequency as sleep spindles, immediately preceding and sometimes continuing at seizure onsets. We aimed to study the link between sleep spindles and seizure onsets. Methods: We used intracerebral stereo-EEG ictal recordings of two MRI-negative patients with clinically defined NFLE. For each of the six studied seizures, sustained activity in the frontal sleep spindle frequency (12 Hz) was observed around seizure onset. The duration of this pre-seizure sleep spindle was compared to that of the 10 preceding sleep spindles. Results: The pre-seizure sleep spindles were clearly of longer duration than the ''interictal'' sleep spindles for all seizures. This sustained pre-seizure 12 Hz activity could be differentiated from normal awakenings, and showed no spatial relation to the ictal onset. Conclusions: We demonstrated a functional alteration of the sleep spindle-generating thalamocortical loop concomitant with the seizure onsets. This defect may also be involved in seizure generation. Significance: A thalamic participation in NFLE pathogenesis is likely in our two patients. The study of additional patients will allow to evaluate the role of the thalamocortical circuits in NFLE.
Hemispheric specialization is reliably demonstrated in patients with unilateral lesions or discon... more Hemispheric specialization is reliably demonstrated in patients with unilateral lesions or disconnected hemispheres, but is inconsistent in healthy populations. The reason for this paradox is unclear. We propose that functional hemispheric specialization in healthy participants depends upon functional brain states at stimulus arrival (FBS). Brain activity was recorded from 123 surface electrodes while 22 participants (11 women) performed lateralized lexical decisions (left hemisphere processing) on neutral and emotional (right hemisphere processing) words. We determined two classes of stable FBS, one with right anterior-left posterior orientations (RA-LP maps) and one with left anterior-right posterior orientations (LA-RP maps). Results show that functional hemispheric specialization is dependent upon the class of FBS and gender. Of those with LA-RP maps, only men showed a strong emotional word advantage (EWA) after left visual field (right hemisphere) presentation, but no EWA after right visual field (left hemisphere) presentation. Subsequent to all other brain states, there was an almost equal EWA after presentation to either visual field. Only about half of the FBS in men led to the pattern of functional hemispheric specialization. We suggest that 'split-brain' research may be marginally describable by a model, but only in exceptional situations, while in connected brains this functional hemispheric specialization is only one of many dynamic states.
Objectives: Characterization of the EEG pattern during the early phase of a seizure is crucial fo... more Objectives: Characterization of the EEG pattern during the early phase of a seizure is crucial for identifying the epileptic focus. The purpose of the present investigation was to evaluate a method that divides ictal EEG activity into segments of relatively constant surface voltage distribution, and to provide a 3-dimensional localization of the activity during the different segments. Methods: For each timepoint the electrical voltage distribution on the scalp (the voltage map) was determined from the digitized EEG recording. Through a spatial cluster analysis time sequences where the maps did not change much (segments) were identi®ed, and a 3dimensional source reconstruction of the activity corresponding to the different mean maps was performed using a distributed linear inverse solution algorithm. Results: Segments dominating early in seizure development were identi®ed, and source reconstruction of the EEG activity corresponding to the maps of these segments yielded results which were consistent with the results from invasive recordings. In some cases a sequence of consecutive segments was obtained, which might re¯ect ictal propagation. Conclusions: Segmentation of ictal EEG with subsequent 3-dimensional source reconstruction is a useful method to non-invasively determine the initiation and perhaps also the spread of epileptiform activity in patients with epileptic seizures.
Two classes of functional neuroimaging methods exist: hemodynamic techniques such as PET and fMRI... more Two classes of functional neuroimaging methods exist: hemodynamic techniques such as PET and fMRI, and electromagnetic techniques such as EEG/ERP and MEG. In order to fusion these images with anatomical information, co-registration with volumetric MRI is needed. While such co-registration techniques are well established for hemodynamic images, additional steps are needed for electromagnetic recordings, because the activity is only recorded
Multidimensional Systems and Signal Processing, 2002
We present a new method for signal extraction from noisy multichannel epileptic seizure onset EEG... more We present a new method for signal extraction from noisy multichannel epileptic seizure onset EEG signals. These signals are non-stationary which makes time-invariant filtering unsuitable. The new method assumes a signal model and performs denoising by filtering the signal of each channel using a time-variable filter which is an estimate of the Wiener filter. The approximate Wiener filters are obtained
By means of a longitudinal case study, we demonstrated the course of cerebral reorganization of l... more By means of a longitudinal case study, we demonstrated the course of cerebral reorganization of language representation due to epilepsy in a child with benign epilepsy with centro-temporal spikes (BECTS) evolving to Landau-Kleffner Syndrome (LKS) and returning to BECTS. The child underwent the following procedures at the ages of 8.2, 8.6, and 9.3 years: 3D source EEG imaging, language fMRI (sentence generation and reading), and neuropsychological testing. He had a follow-up testing at the age of 10.8 years. Further, 24-h EEGs were regularly performed. At the age of around 8 years, the child was diagnosed initially with left-hemispheric BECTS, which evolved to LKS with continuous bilateral discharges. In addition, 3D source imaging data revealed a left anterior temporal focus with a spreading to the right parietal and left centro-parietal areas. The patient had verbal agnosia with poor verbal yet good performance indices. Functional magnetic resonance imaging (fMRI) showed a left-hemispheric reading network but sentence generation was impossible to perform. After initiation of adequate treatment, continuous discharges disappeared, and only very rare left-hemispheric centro-temporal spikes remained. Verbal IQ and performance IQ increased at the age of 8.6 years. Functional magnetic resonance imaging showed, at this time, a right-hemispheric language activation pattern for sentence generation and reading. At the ages of 9.3 and 10.8 years, language tasks remained right-hemispheric and verbal IQ remained stable, but right-hemispheric non-verbal functions decreased due to possible crowding-out mechanisms.
Electroencephalography and Clinical Neurophysiology, Jul 1, 1996
Ten patients with complex partial epileptic seizures undergoing invasive video/EEG-monitoring wer... more Ten patients with complex partial epileptic seizures undergoing invasive video/EEG-monitoring were recorded with a combination of 10 subdural strip electrode contacts (subtemporal + lateral temporal), and 22 extracranial recording sites. In each patient several spikes with different intracranial distributions were identified, and spikes with similar distributions were averaged together with their extracranial activity. Dipole analysis of the extracranial activity was performed with the BESA program (Scherg, Garching Instrumente, München). In the horizontal plane subtemporal spikes gave oblique posterior, and lateral temporal spikes straight lateral or oblique anterior dipole orientations. In the coronal plane all spikes had an elevated orientation, most pronounced for medial subtemporal spikes. Dipole locations did not separate as well as dipole orientations. In our opinion our results would be difficult to explain without postulating a substantial degree of volume conduction from deep temporal areas to the surface. We conclude that dipole analysis of the interictal epileptiform activity does provide substantial information about which parts of the temporal lobe are involved in the epileptogenic process, making the method a useful tool in the preoperative investigation of patients with drug resistant partial epilepsy.
... of equation I, can be written for the linear case as (Grave and Gonzalez, 1998),: ... to inco... more ... of equation I, can be written for the linear case as (Grave and Gonzalez, 1998),: ... to incorporate the functional image f into the solution j is the use of space ... during self-paced finger movement performance, tactile somatosensory stimulation and binaural auditory stimulation using ...
Over the past few decades, diverse brain imaging techniques have been applied in different areas ... more Over the past few decades, diverse brain imaging techniques have been applied in different areas of experimental psychology and neuroscience, and have begun to provide unprecedented windows on the functional and the structural anatomy of the human brain. Recent technological innovations have achieved to convert conventional electrophysiological methods (e.g. electroencephalogram or EEG) into modern functional brain imaging procedures (i.e. electric source imaging or ESI); allowing neuroscientists to measure the spatial and temporal dynamics of the brain. In patients with drug-resistant epilepsy who are candidates for surgery, non-invasive functional imaging methods are helpful in guiding placement of surgical resections or invasive EEG recordings. ESI consists in a non-invasive recording of the electrical potential field on the scalp while using dense array EEG (up to 256 channels), which allows estimating intra-cerebral electric sources. Nowadays, ESI became an accessible technique mainly due to the increase in computational power and the appearance of user-friendly sophisticated analysis software. Despite the large amount of literature supporting the validity of ESI in terms of localization, the introduction of this technique into clinical routine has been rather slow. In this review we intend to tackle the theoretical aspects, practical procedures and ESI clinical studies; in addition, we will compare with other well established imaging tools used in presurgical evaluation of epilepsy workup.
Question: Non-invasively recorded high-frequency (>400 Hz) components of somatosensory evoked pot... more Question: Non-invasively recorded high-frequency (>400 Hz) components of somatosensory evoked potentials (hf-SEP) are generated by cortical population spikes, as revealed by microelectrode recordings in primates. Until now it was a critical drawback that this approach required averaging hundreds of responses for reliable hf-SEP detection. Here, we establish how to detect human hf-SEP non-invasively in single trials. Methods: Inside a shielded room median nerve hf-SEP were recorded in four subjects spanning the hf-SEP signal-to-noise ratio characteristic for a larger population, utilizing a custom-built 29-channel low-noise EEG amplifier. Features were extracted from band-pass filtered (400-900 Hz) trials by bilinear Common Spatial Patterns (bCSP) to construct both, optimized spatial and temporal filters, and then classified by a weighted Extreme Learning Machine (w-ELM). Results: Human hf-SEP were detected in single trials with a sensitivity of up to 98% and a specificity up to 97% in two subjects, even without any recourse to stimulus timing. Since for the two subjects with lower signal-to-noise ratio these rates dropped to 62-79% sensitivity and 18-28% specificity, optimal recording quality is a critical prerequisite for efficient single-trial detection. Conclusions: Non-invasive low-noise recordings can extract high-frequency EEG components otherwise buried in background noise. Specifically, a refined supervised filter optimization and classification can enable reliable single-trial hf-SEP detection, representing a non-invasive correlate of cortical population spikes. Thus, while low-frequency EEG reflects summed postsynaptic potentials and thereby neuronal input, we suggest that hf-SEP provides non-invasive access to the output of neuronal computation: spiking activity in the responsive neuronal ensemble.
Over the past few decades, diverse brain imaging techniques have been applied in different areas ... more Over the past few decades, diverse brain imaging techniques have been applied in different areas of experimental psychology and neuroscience, and have begun to provide unprecedented windows on the functional and the structural anatomy of the human brain. Recent technological innovations have achieved to convert conventional electrophysiological methods (e.g. electroencephalogram or EEG) into modern functional brain imaging procedures (i.e. electric source imaging or ESI); allowing neuroscientists to measure the spatial and temporal dynamics of the brain. In patients with drug-resistant epilepsy who are candidates for surgery, non-invasive functional imaging methods are helpful in guiding placement of surgical resections or invasive EEG recordings. ESI consists in a non-invasive recording of the electrical potential field on the scalp while using dense array EEG (up to 256 channels), which allows estimating intra-cerebral electric sources. Nowadays, ESI became an accessible technique mainly due to the increase in computational power and the appearance of user-friendly sophisticated analysis software. Despite the large amount of literature supporting the validity of ESI in terms of localization, the introduction of this technique into clinical routine has been rather slow. In this review we intend to tackle the theoretical aspects, practical procedures and ESI clinical studies; in addition, we will compare with other well established imaging tools used in presurgical evaluation of epilepsy workup.
Electroencephalography and Clinical Neurophysiology, 1996
Ten patients with complex partial epileptic seizures undergoing invasive video/EEG-monitoring wer... more Ten patients with complex partial epileptic seizures undergoing invasive video/EEG-monitoring were recorded with a combination of 10 subdural strip electrode contacts (subtemporal + lateral temporal), and 22 extracranial recording sites. In each patient several spikes with different intracranial distributions were identified, and spikes with similar distributions were averaged together with their extracranial activity. Dipole analysis of the extracranial activity was performed with the BESA program (Scherg, Garching Instrumente, München). In the horizontal plane subtemporal spikes gave oblique posterior, and lateral temporal spikes straight lateral or oblique anterior dipole orientations. In the coronal plane all spikes had an elevated orientation, most pronounced for medial subtemporal spikes. Dipole locations did not separate as well as dipole orientations. In our opinion our results would be difficult to explain without postulating a substantial degree of volume conduction from deep temporal areas to the surface. We conclude that dipole analysis of the interictal epileptiform activity does provide substantial information about which parts of the temporal lobe are involved in the epileptogenic process, making the method a useful tool in the preoperative investigation of patients with drug resistant partial epilepsy.
In terms MMN are at Fz À3.9 uV (±1.8), at Cz À5.0 uV (±3.8), and at Pz À3.3 (±3.2). These differe... more In terms MMN are at Fz À3.9 uV (±1.8), at Cz À5.0 uV (±3.8), and at Pz À3.3 (±3.2). These differences are not significant. The maximal peak was measured in the preterm group at Fz after 233.7 ms (±39.5), at Cz after 222 ms (±19.9), and at Pz after 212.3 ms (±30.1), in the term group at Fz after 231 ms (±26), at Cz after 215.6 ms (±21.3), and at Pz after 207.7 ms (±25.4). These differences are not statistically significant. In both groups. From the first to the third stimulus block a decrease of the MMN amplitude is observed. Conclusion: In the gestational age of 40 weeks preterms and terms did not differ in their capability to discriminate tones with a different frequency.
Objective: Nocturnal frontal lobe epilepsy (NFLE) seizures occur primarily during non-rapid eye m... more Objective: Nocturnal frontal lobe epilepsy (NFLE) seizures occur primarily during non-rapid eye movement sleep stage 2. We observed in several patients rhythms of same localization and frequency as sleep spindles, immediately preceding and sometimes continuing at seizure onsets. We aimed to study the link between sleep spindles and seizure onsets. Methods: We used intracerebral stereo-EEG ictal recordings of two MRI-negative patients with clinically defined NFLE. For each of the six studied seizures, sustained activity in the frontal sleep spindle frequency (12 Hz) was observed around seizure onset. The duration of this pre-seizure sleep spindle was compared to that of the 10 preceding sleep spindles. Results: The pre-seizure sleep spindles were clearly of longer duration than the ''interictal'' sleep spindles for all seizures. This sustained pre-seizure 12 Hz activity could be differentiated from normal awakenings, and showed no spatial relation to the ictal onset. Conclusions: We demonstrated a functional alteration of the sleep spindle-generating thalamocortical loop concomitant with the seizure onsets. This defect may also be involved in seizure generation. Significance: A thalamic participation in NFLE pathogenesis is likely in our two patients. The study of additional patients will allow to evaluate the role of the thalamocortical circuits in NFLE.
Hemispheric specialization is reliably demonstrated in patients with unilateral lesions or discon... more Hemispheric specialization is reliably demonstrated in patients with unilateral lesions or disconnected hemispheres, but is inconsistent in healthy populations. The reason for this paradox is unclear. We propose that functional hemispheric specialization in healthy participants depends upon functional brain states at stimulus arrival (FBS). Brain activity was recorded from 123 surface electrodes while 22 participants (11 women) performed lateralized lexical decisions (left hemisphere processing) on neutral and emotional (right hemisphere processing) words. We determined two classes of stable FBS, one with right anterior-left posterior orientations (RA-LP maps) and one with left anterior-right posterior orientations (LA-RP maps). Results show that functional hemispheric specialization is dependent upon the class of FBS and gender. Of those with LA-RP maps, only men showed a strong emotional word advantage (EWA) after left visual field (right hemisphere) presentation, but no EWA after right visual field (left hemisphere) presentation. Subsequent to all other brain states, there was an almost equal EWA after presentation to either visual field. Only about half of the FBS in men led to the pattern of functional hemispheric specialization. We suggest that 'split-brain' research may be marginally describable by a model, but only in exceptional situations, while in connected brains this functional hemispheric specialization is only one of many dynamic states.
Objectives: Characterization of the EEG pattern during the early phase of a seizure is crucial fo... more Objectives: Characterization of the EEG pattern during the early phase of a seizure is crucial for identifying the epileptic focus. The purpose of the present investigation was to evaluate a method that divides ictal EEG activity into segments of relatively constant surface voltage distribution, and to provide a 3-dimensional localization of the activity during the different segments. Methods: For each timepoint the electrical voltage distribution on the scalp (the voltage map) was determined from the digitized EEG recording. Through a spatial cluster analysis time sequences where the maps did not change much (segments) were identi®ed, and a 3dimensional source reconstruction of the activity corresponding to the different mean maps was performed using a distributed linear inverse solution algorithm. Results: Segments dominating early in seizure development were identi®ed, and source reconstruction of the EEG activity corresponding to the maps of these segments yielded results which were consistent with the results from invasive recordings. In some cases a sequence of consecutive segments was obtained, which might re¯ect ictal propagation. Conclusions: Segmentation of ictal EEG with subsequent 3-dimensional source reconstruction is a useful method to non-invasively determine the initiation and perhaps also the spread of epileptiform activity in patients with epileptic seizures.
Two classes of functional neuroimaging methods exist: hemodynamic techniques such as PET and fMRI... more Two classes of functional neuroimaging methods exist: hemodynamic techniques such as PET and fMRI, and electromagnetic techniques such as EEG/ERP and MEG. In order to fusion these images with anatomical information, co-registration with volumetric MRI is needed. While such co-registration techniques are well established for hemodynamic images, additional steps are needed for electromagnetic recordings, because the activity is only recorded
Multidimensional Systems and Signal Processing, 2002
We present a new method for signal extraction from noisy multichannel epileptic seizure onset EEG... more We present a new method for signal extraction from noisy multichannel epileptic seizure onset EEG signals. These signals are non-stationary which makes time-invariant filtering unsuitable. The new method assumes a signal model and performs denoising by filtering the signal of each channel using a time-variable filter which is an estimate of the Wiener filter. The approximate Wiener filters are obtained
By means of a longitudinal case study, we demonstrated the course of cerebral reorganization of l... more By means of a longitudinal case study, we demonstrated the course of cerebral reorganization of language representation due to epilepsy in a child with benign epilepsy with centro-temporal spikes (BECTS) evolving to Landau-Kleffner Syndrome (LKS) and returning to BECTS. The child underwent the following procedures at the ages of 8.2, 8.6, and 9.3 years: 3D source EEG imaging, language fMRI (sentence generation and reading), and neuropsychological testing. He had a follow-up testing at the age of 10.8 years. Further, 24-h EEGs were regularly performed. At the age of around 8 years, the child was diagnosed initially with left-hemispheric BECTS, which evolved to LKS with continuous bilateral discharges. In addition, 3D source imaging data revealed a left anterior temporal focus with a spreading to the right parietal and left centro-parietal areas. The patient had verbal agnosia with poor verbal yet good performance indices. Functional magnetic resonance imaging (fMRI) showed a left-hemispheric reading network but sentence generation was impossible to perform. After initiation of adequate treatment, continuous discharges disappeared, and only very rare left-hemispheric centro-temporal spikes remained. Verbal IQ and performance IQ increased at the age of 8.6 years. Functional magnetic resonance imaging showed, at this time, a right-hemispheric language activation pattern for sentence generation and reading. At the ages of 9.3 and 10.8 years, language tasks remained right-hemispheric and verbal IQ remained stable, but right-hemispheric non-verbal functions decreased due to possible crowding-out mechanisms.
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