PubMed Health⌕ Search

Biomedical subjects

Richard A Wennberg

Publications and source records attributed to Richard A Wennberg.

18 recordsLinked to original sources
PubMed2006

Propagation of interictal discharges in temporal lobe epilepsy: correlation of spatiotemporal mapping with intracranial foramen ovale electrode recordings.

OBJECTIVE: We have investigated intracerebral propagation of interictal epileptiform discharges (IED) in patients with mesial temporal lobe epilepsy (MTLE) by using spatiotemporal source maps based on statistical nonparametric mapping (SNPM) of low resolution electromagnetic tomography (LORETA) values. METHODS: We analyzed 30 patterns of IED recorded simultaneously with scalp and intracranial foramen ovale (FO) electrodes in 15 consecutive patients with intractable MTLE. The scalp EEG signals were averaged time-locked to the peak activity in bilateral 10-contact FO electrode recordings. SNPM was applied to LORETA values and spatiotemporal source maps were created by allocating the t-values over time to their corresponding Brodmann areas. Propagation was defined as secondary statistically significant involvement of distinct cortical areas separated by >15 ms. The results were correlated with intracranial data obtained from FO electrode recordings and with scalp EEG recordings. All patients underwent subsequent amygdalo-hippocampectomy and outcome was assessed one year after surgery. RESULTS: We found mesial to lateral propagation in 6/30 IED patterns (20%, four patients), lateral to mesial propagation in 4/30 IED patterns (13.3%, four patients) and simultaneous (within 15 ms) activation of mesial and lateral temporal areas in 6/30 IED patterns (20%, five patients). Propagation generally occurred within 30 ms and was always limited to ipsilateral cortical regions. Nine/30 IED patterns (30%) showed restricted activation of mesial temporal structures and no significant solutions were found in 5/30 IED patterns (16.7%). There was no clear association between the number or characteristics of IED patterns and the postsurgical outcome. CONCLUSIONS: Spatiotemporal mapping of SNPM LORETA accurately describes mesial to lateral temporal propagation of IED, and vice versa, which commonly occur in patients with MTLE. SIGNIFICANCE: Intracerebral propagation must be considered when using non-invasive source algorithms in patients with MTLE. Spatiotemporal mapping might be useful for visualizing this propagation.

Adult↗
PubMed2006

Rhythmic cortical EEG synchronization with low frequency stimulation of the anterior and medial thalamus for epilepsy.

OBJECTIVE: To investigate the neurophysiological characteristics and prognostic impact of EEG synchronization with low frequency thalamic stimulation in patients with intractable epilepsy. METHODS: Electrical stimuli were delivered through deep brain stimulating (DBS) electrodes at 2, 5 or 10Hz to the anterior nucleus (AN) and the dorsomedial nucleus (DM) of six patients using the implanted programmable stimulation device. EEGs were recorded from 27 scalp electrodes. "Modeled" responses for 5 and 10Hz stimulation were computed based on the cerebral responses (CRs) evoked by "single pulse" (2Hz) stimulation and compared with the recorded EEG results. RESULTS: Rhythmic cortical 5Hz EEG synchronization occurred in 4/6 patients, with stimulation at 6/11 AN and 5/11 DM sites. Three of four patients with synchronization, but neither of the two patients without, had a significant reduction in seizure frequency. The magnitude of 5 and 10Hz EEG synchronization was positively related to the amplitudes of "single pulse" CRs. Simple temporal superposition of "single pulse" CRs resulted in "modeled" responses with strikingly similar morphology and scalp voltage distribution. CONCLUSIONS: Rhythmic EEG synchronization with low frequency stimulation primarily reflects spatiotemporal summation (interference) of "single pulse" CRs. SIGNIFICANCE: Rhythmic EEG synchronization might not serve as a physiologic verification of optimal localization of DBS electrodes. Its usefulness for the prediction of clinical efficacy is questionable.

Adult↗
PubMed2006

Depth electrode recorded cerebral responses with deep brain stimulation of the anterior thalamus for epilepsy.

OBJECTIVE: We investigated the relation between anterior thalamic stimulation and the morphology of the evoked cerebral responses (CRs) using intracerebral depth electrodes in patients with intractable epilepsy undergoing deep brain stimulation (DBS) of the thalamus. METHODS: Monopolar cathodic and bipolar stimuli were delivered at a rate of 2 or 1 Hz to the anterior nucleus (AN) and the dorsomedian nucleus (DM) of two patients using the programmable stimulation device (Medtronic ITREL II) or a GRASS stimulation device (S12). CRs were recorded from depth or DBS electrodes, situated bilaterally in mesial temporal (hippocampus, both patients), lateral temporal (one patient), orbitofrontal (Brodmann area 11, one patient) and anterior thalamic sites (one patient). RESULTS: The distribution and morphology of the CRs depended primarily on the site of stimulation within the anterior thalamic region. Overall, monopolar cathodic and bipolar stimulation of the AN elicited CRs mainly in ipsilateral mesial temporal cortical areas, whereas stimulation of the DM evoked high-amplitude CRs predominantly in ipsilateral orbitofrontal areas. The amplitude of the CR was positively related to the strength of the stimulus and generally higher with monopolar than with bipolar stimulation. The differences between CRs elicited during wakefulness or slow wave sleep were minimal. CONCLUSIONS: The distribution of the CRs corresponded with the intracerebral pathways of the involved structures and the findings are in good accordance with those of our previous study investigating the sources of CRs using statistical non-parametric mapping of low resolution electromagnetic tomography (LORETA) values. SIGNIFICANCE: Our findings indicate a certain degree of point-to-point specificity within the thalamocortical circuitry, which may make optimal localization of DBS electrodes important in patients with epilepsy.

Adult↗
PubMed2006

Source localization of small sharp spikes: low resolution electromagnetic tomography (LORETA) reveals two distinct cortical sources.

OBJECTIVE: We have investigated the cortical sources and electroencephalographic (EEG) characteristics of small sharp spikes (SSS) by using statistical non-parametric mapping (SNPM) of low resolution electromagnetic tomography (LORETA). METHODS: We analyzed 7 SSS patterns (501 individual SSS) in 6 patients who underwent sleep EEG studies with 29 or 23 scalp electrodes. The scalp signals were averaged time-locked to the SSS peak activity and subjected to SNPM of LORETA values. RESULTS: All 7 SSS patterns (mean 72 individual SSS, range 11-200) revealed a very similar and highly characteristic transhemispheric oblique scalp voltage distribution comprising a first negative field maximum over ipsilateral lateral temporal areas, followed by a second negative field maximum over the contralateral subtemporal region approximately 30 ms later. SNPM-LORETA consistently localized the first component into the ipsilateral posterior insular region, and the second component into ipsilateral posterior mesial temporo-occipital structures. CONCLUSIONS: SSS comprise an amalgam of two sequential, distinct cortical components, showing a very uniform and peculiar EEG pattern and cortical source solutions. As such, they must be clearly distinguished from interictal epileptiform discharges in patients with epilepsy. SIGNIFICANCE: The awareness of these peculiar EEG characteristics may increase our ability to differentiate SSS from interictal epileptiform activity. The finding of a posterior insular source might serve as an inspiration for new physiological considerations regarding these enigmatic waveforms.

Adult↗
PubMed2006

Source localization of interictal epileptiform discharges: comparison of three different techniques to improve signal to noise ratio.

OBJECTIVE: To investigate the localization accuracy of low-resolution electromagnetic tomography (LORETA) for mesial temporal interictal epileptiform discharges (IED) using a new relative averaging (RELAVG) technique for noise reduction. METHODS: We analyzed 19 patterns of mesial temporal IED recorded simultaneously with scalp and foramen ovale (FO) electrodes in 15 consecutive patients who underwent presurgical assessment for intractable temporal lobe epilepsy. The scalp signals were time-locked to the peak activity in the FO electrode recordings and source modeling was performed using the RELAVG technique. Random noise of various amounts was then applied. The results were compared to intracranial data obtained from the FO electrode recordings and to LORETA source solutions obtained using two other approaches to improve signal to noise ratio (SNR): statistical non-parametric mapping (SNPM) and the commonly applied averaging (AVG) technique. RESULTS: The RELAVG technique allowed for reasonable mesial temporal localization in 52.6% (10/19) of IED patterns, compared with 73.7% (14/19) using SNPM. The AVG technique provided no strictly mesial temporal solutions. Nine of the IED patterns revealed relative current density quotient changes >10; all of these were accurately localized by RELAVG into mesial temporal structures. Increasing amounts of white and physiological noise had no influence on the accuracy of RELAVG and SNPM solutions, whereas AVG source reconstructions became progressively spurious. CONCLUSION: The RELAVG technique and SNPM, but not the commonly used AVG technique, allow for reasonable source localization of mesial temporal IED. SNPM is the most accurate but also the most time-consuming noise reduction technique. SIGNIFICANCE: The RELAVG LORETA technique might provide a simple and fast semi-quantitative alternative for localizing IED with low single to noise ratio.

Adult↗
PubMed2006

Mesial temporal inhibition in a patient with deep brain stimulation of the anterior thalamus for epilepsy.

We investigated the electrophysiological effects of high-frequency anterior thalamic deep brain stimulation using intracerebral mesial and lateral temporal depth electrodes in a patient with intractable focal epilepsy. Monopolar and bipolar stimulation delivered to the thalamic anterior nucleus using the programmable ITREL II stimulation device led to a significant decrease of cross power spectral density and a nonsignificant decrease of coherence in ipsilateral hippocampal structures. No such effect was found in lateral temporal or contralateral sites. The hippocampal inhibition was clearly related to the voltage (> or =7 V) and frequency (> or =70 Hz) of the thalamic stimulus and occurred with a delay of approximately 60 s after stimulus onset.

Adult↗
PubMed2005

Cortical activation with deep brain stimulation of the anterior thalamus for epilepsy.

OBJECTIVE: We studied the relation between thalamic stimulation parameters and the morphology, topographic distribution and cortical sources of the cerebral responses in patients with intractable epilepsy undergoing deep brain stimulation (DBS) of the thalamus. METHODS: Bipolar and monopolar stimuli were delivered at a rate of 2 Hz to the anterior (AN, four patients), the dorsomedian (DM, four patients), and the centromedian nucleus (CM, one patient) using the programmable stimulation device (Medtronic ITREL II). Source modeling was carried out by using statistical non-parametric mapping of low-resolution electromagnetic tomography (LORETA) values. RESULTS: All patients demonstrated reproducible time-locked cortical responses (CRs) consisting of a sequence of components with latencies between 20 and 320 ms. The morphology of these CRs, however, was very heterogeneous, depending primarily on the site of stimulation. Following AN stimulation, cortical activation was most prominent in ipsilateral cingulate gyrus, insular cortex and lateral neocortical temporal structures. Stimulation of the DM mainly showed activation of the ipsilateral orbitofrontal and mesial and lateral frontal areas, but also involvement of mesial temporal structures. Stimulation of the CM showed a rather diffuse (though still mainly ipsilateral) increase of cortical activity. The magnitude of cortical activation was positively related to the strength of the stimulus and inversely related to the impedance of the electrode. CONCLUSIONS: The pattern of cortical activation corresponded with the hodology of the involved structures and may underscore the importance of optimal localization of DBS electrodes in patients with epilepsy. SIGNIFICANCE: The method of analyzing sources of CRs could potentially be a useful tool for titration of DBS parameters in patients with electrode contacts in clinically silent areas. Furthermore, the inverse relation of the cortical activation and the impedance of the electrode contacts might suggest that these impedance measurements should be taken into consideration when adjusting DBS parameters in patients with epilepsy.

Adult↗
PubMed2005

Source localization of mesial temporal interictal epileptiform discharges: correlation with intracranial foramen ovale electrode recordings.

OBJECTIVE: We have investigated the localization accuracy of low-resolution electromagnetic tomography (LORETA) for mesial temporal interictal epileptiform discharges (IED) on a statistical basis by using clinical electroencephalographic (EEG) data of simultaneous scalp and intracranial foramen ovale (FO) electrode recordings. METHODS: We retrospectively analyzed the IED of 15 patients who underwent presurgical assessment for intractable temporal lobe epilepsy. All patients have subsequently undergone amygdalohippocampectomy. The scalp signals were averaged time-locked to the peak activity in bilateral 10-contact FO electrode recordings. Source modeling was carried out by using statistical non-parametric mapping (SNPM) of LORETA values and by calculating raw LORETA values of averaged IED. The results were compared to intracranial data obtained from FO electrode recordings. RESULTS: Two thousand six hundred and fifteen discharges could be attributed to 19 different patterns of intracranial mesial temporal IED. SNPM of LORETA revealed confined ipsilateral mesial temporal solutions for 14 (73.7%) and no significant solutions for five (26.3%) of these patterns. Raw LORETA current density distributions of the 19 averaged IED patterns revealed ipsilateral basal to lateral temporal solutions for the 14 IED patterns with a sufficient signal to noise ratio (SNR), but spurious results for those five IED with a low SNR. CONCLUSIONS: SNPM of LORETA but not LORETA analysis of averaged IED patterns accurately localizes the source generators of mesial temporal IEDs. SIGNIFICANCE: SNPM of raw LORETA values might be appropriate for localizing restricted mesial temporal lobe sources.

Adult↗
PubMed2005

Enhanced synchrony in epileptiform activity? Local versus distant phase synchronization in generalized seizures.

Synchronization is a fundamental characteristic of complex systems and a basic mechanism of self-organization. A traditional, accepted perspective on epileptiform activity holds that hypersynchrony covering large brain regions is a hallmark of generalized seizures. However, a few recent reports have described substantial fluctuations in synchrony before and during ictal events, thus raising questions as to the widespread synchronization notion. In this study, we used magnetoencephalographic recordings from epileptic patients with generalized seizures and normal control subjects to address the extent of the phase synchronization (phase locking) in local (neighboring) and distant cortical areas and to explore the ongoing temporal dynamics for particular ranges of frequencies at which synchrony occurs, during interictal and ictal activity. Synchronization patterns were found to differ somewhat depending on the epileptic syndrome, with primary generalized absence seizures displaying more long-range synchrony in all frequency bands studied (3-55 Hz) than generalized tonic motor seizures of secondary (symptomatic) generalized epilepsy or frontal lobe epilepsy. However, all seizures were characterized by enhanced local synchrony compared with distant synchrony. There were fluctuations in the synchrony between specific cortical areas that varied from seizure to seizure in the same patient, but in most of the seizures studied, regardless of semiology, there was a constant pattern in the dynamics of synchronization, indicating that seizures proceed by a recruitment of neighboring neuronal networks. Together, these data indicate that the concept of widespread "hypersynchronous" activity during generalized seizures may be misleading and valid only for very specific neuronal ensembles and circumstances.

Adolescent↗
PubMed2005

Atypical absences and recurrent absence status in an adult with Angelman syndrome due to the UBE3A mutation.

Angelman syndrome is a neurogenetic disorder resulting in refractory epilepsy and profound psychomotor retardation in its most prevalent form, caused by deletion of maternal chromosome 15q11-13. We report the case of a 29-year-old, mentally retarded man with unusual electroencephalographic changes during periods of atypical absence status epilepticus, a previously unreported manifestation of the usually milder, drug-responsive epilepsy associated with Angelman syndrome due to the UBE3A mutation.[Published with video sequences].

Adult↗
PubMed2003

Intracranial volume conduction of cortical spikes and sleep potentials recorded with deep brain stimulating electrodes.

OBJECTIVE: To examine interictal epileptiform and sleep potentials recorded intracranially from deep brain stimulation (DBS) electrodes in patients treated with DBS for epilepsy. Specifically, this study sought to determine whether the DBS-recorded potentials represent: (a) volume conduction from surface neocortical discharges or (b) transsynaptic propagation along cortical-subcortical pathways with local generation of the subcortical potentials near the DBS targets. METHODS: Six patients with intractable epilepsy treated with thalamic DBS of the central median nucleus (CM; one patient) or anterior thalamus (5 patients) who had focal interictal spikes were studied. Sleep potentials were also studied in a 7th patient with Parkinson disease treated with DBS of the subthalamic nucleus (STN). RESULTS: Focal interictal cortical spikes recorded by scalp electroencephalography (EEG) were recorded synchronously, but with opposite polarity, from the DBS electrodes in CM as well as the more superficial anterior thalamic contacts situated in the anterior nucleus (AN) and dorsal medial nucleus (DM). In referential montages, the subcortical potentials were of highest amplitude ipsilateral to the focal cortical spikes, with a small but reproducible amplitude decrement present at each electrode contact more distant from the cortical source, irrespective of the specific DBS target. Subcortical sleep potentials (K-complexes and sleep spindles) were also recorded synchronously and with inverse polarity compared to the corresponding scalp potentials, and appeared in a similar fashion at all subcortical sites sampled by the DBS electrodes. Amplitude attenuation in the thalamus of intracranial volume conducted potentials with increasing distance from their cortical spike sources was measured at approximately 5-10 microV/mm. DISCUSSION: Recent reports on scalp-CM or scalp-STN EEG recordings in patients treated with DBS for epilepsy have interpreted the intracranial waveforms as evidence of transsynaptic cortical-subcortical transmission across neuroanatomical pathways presumed to be involved in the generation of sleep potentials (Clin. Neurophysiol. 113 (2002) 25) and epileptiform activity (Clin. Neurophysiol. 113 (2002) 1391). However, our results show that the intracranial spikes recorded from DBS electrodes in various regions of the thalamus (CM, AN and DM) represent subcortical volume conduction of the synchronous cortical spikes recorded with scalp EEG. The same is true for the intracranial reflections of scalp EEG sleep potentials recorded from DBS electrodes in CM, AN, DM and STN. These interictal DBS waveforms thus cannot be used to support hypotheses of specific cortical-subcortical pathways of neural propagation or subcortical generation of the DBS-recorded potentials associated with scalp EEG interictal spikes and sleep potentials. SIGNIFICANCE: Detailed analysis of the intracranial potentials recorded from DBS electrodes in association with scalp EEG spikes and sleep discharges shows that the intracranial waveforms represent volume conduction from discharges generated in the neocortex and not, as has been suggested, locally generated activity resulting from cortical-subcortical neural propagation.

Adult↗
PubMed2002

Performance reassessment of a real-time seizure-detection algorithm on long ECoG series.

PURPOSE: Automated seizure detection and blockage requires highly sensitive and specific algorithms. This study reassessed the performance of an algorithm by using a more extensive database than that of a previous study and its suitability for safety/efficacy closed-loop studies to block seizures in humans. METHODS: Up to eight electrocorticography (EcoG) channels from 15 subjects were analyzed off-line. Visual and computerized analyses of the data were performed by different (blinded) investigators. Independent visual analysis also was performed for clinical seizures and for detections identified only by the algorithm. The following were computed: FP rate, number of FNs, latency to automated detection, warning rate for clinical onset and warning times, seizure duration/intensity, and interrater agreement. Adaptations to improve performance were performed when indicated. RESULTS: Fourteen subjects met inclusion criteria. Generic algorithm "relative sensitivity" for clinical seizures was 100%; two undetected subclinical seizures and two unclassified seizures were captured after adaptation. FPs/day were zero in seven and fewer than one in an additional three subjects. Adaptations for four subjects with greater than 1 FP/day (7.7-66.6/day) reduced the rate to 0 in one subject and to fewer than five FP/day (1.7-4.2/day) in the remainder. Generic latency to automated detection was <5 s in eight of 13 subjects, and in 12 of 13 after adaptation. Detections provided warning of clinical onset in three of four subjects in whom it always followed electrographic onset, and in four of four after adaptation. Interrater agreement was low for FPs and EDs. CONCLUSIONS: The generic algorithm demonstrated high sensitivity, specificity, and speed, characteristics further enhanced by adaptation. This algorithm is well suited for seizure detection/warning and use in safety/efficacy closed-loop therapy studies.

Adolescent↗
PubMed2002

Chronic anterior thalamus stimulation for intractable epilepsy.

PURPOSE: A significant number of patients with epilepsy remain poorly controlled despite antiepileptic medication (AED) treatment and are not eligible for resective surgery. Novel therapeutic methods are required to decrease seizure burden in this population. Several observations have indicated that the anterior thalamic region plays an important role in the maintenance and propagation of seizures. We investigated neuromodulation of the anterior thalamus by using deep-brain stimulation (DBS) in patients with intractable seizures. METHODS: Five patients with medically refractory epilepsy underwent stereotactic placement of and received stimulation through bilateral DBS electrodes in the anterior thalamus. RESULTS: Treatment showed a statistically significant decrease in seizure frequency, with a mean reduction of 54% (mean follow-up, 15 months). Two of the patients had a seizure reduction of > or =75%. No adverse effects were observed after DBS electrode insertion or stimulation. Unexpectedly, the observed benefits did not differ between stimulation-on and stimulation-off periods. CONCLUSIONS: DBS of the anterior thalamus is a safe procedure and possibly effective in patients with medically resistant seizures.

Adult↗