Interhemispheric propagation time of human hippocampal seizures. I. Relationship to surgical outcome

Involvement of the posterior cingulate gyrus in temporal lobe epilepsy: A study using stereo-EEG

OBJECTIVE

To analyze the involvement of the posterior cingulate gyrus (PCG) during mesial temporal lobe seizures (MTLS).

METHODS

We retrospectively reviewed the stereo-EEG (SEEG) recordings of patients with MTLS performed in our institution from February 2013 to December 2020. Only patients who had electrode implantation in the PCG were included. Patients with lesions that could potentially alter the seizure spread pathways were excluded. We assessed the propagation patterns of MTLS with respect to the different structures sampled.

RESULTS

Nine of 97 patients who had at least one seizure originating in the mesial temporal region met the inclusion criteria. A total of 174 seizures were analyzed. The PCG was the first site of propagation in most of the cases (8/9 patients and 77.5% of seizures, and 7/8 patients and 65.6% of seizures after excluding an outlier patient). The fastest propagation times were towards the contralateral mesial temporal region and ipsilateral PCG. Seven patients underwent standard anterior temporal lobectomy and, of these, all but one were Engel 1 at last follow up.

CONCLUSION

We found the PCG to be the first propagation site of MTLS in this group of patients. These results outline the relevance of the PCG in SEEG planning strategies. Further investigations are needed to corroborate whether fast propagation to the PCG predicts a good surgical outcome.

Ipsilateral preictal alpha rhythm attenuation (IPARA): An EEG sign of side of seizure onset in temporal lobe epilepsy

PURPOSE

Identification of the seizure onset zone is critically important for outlining the surgical plan in the treatment of pharmacoresistant focal epilepsy. In patients with temporal lobe epilepsy (TLE), bilateral ictal scalp EEG changes frequently occur and can make lateralization of the seizure onset zone difficult. We investigated the incidence and clinical utility of unilateral preictal alpha rhythm attenuation as a lateralizing sign of seizure onset in TLE.

METHODS

Scalp EEG recordings of the seizures acquired during presurgical video-EEG monitoring of 57 consecutive patients with TLE were reviewed retrospectively. Included patients had interictal baseline recordings demonstrating symmetrical posterior alpha rhythm and seizures occurring during wakefulness.

RESULTS

We identified a total of 649 seizures in the 57 patients, of which 448 seizures in 53 patients fulfilled the inclusion criteria. Among the 53 included patients, 7 patients (13.2%) exhibited a distinct attenuation of the posterior alpha rhythm prior to the first ictal EEG changes, in 26 of 112 (23.2%) included seizures. Preictal alpha rhythm attenuation in these seizures was ipsilateral to the ultimately determined side of seizure onset (based on video-EEG or intracranial EEG findings) in 22 (84.6%) of these seizures and bilateral in 4 (15.4%), and occurred on average 5.9 ± 2.6 s prior to ictal EEG onsets.

CONCLUSION

Our findings suggest that in some patients with TLE lateralized preictal attenuation of the posterior alpha rhythm may be a useful indicator of side of seizure onset, presumably due to early disruption of thalamo-temporo-occipital network function, likely mediated through the thalamus.

Stereo-Encephalographic Presurgical Evaluation of Temporal Lobe Epilepsy: An Evolving Science

Drug-resistant epilepsy is present in nearly 30% of patients. Resection of the epileptogenic zone has been found to be the most effective in achieving seizure freedom. The study of temporal lobe epilepsy for surgical treatment is extensive and complex. It involves a multidisciplinary team in decision-making with initial non-invasive studies (Phase I), providing 70% of the required information to elaborate a hypothesis and treatment plans. Select cases present more complexity involving bilateral clinical or electrographic manifestations, have contradicting information, or may involve deeper structures as a part of the epileptogenic zone. These cases are discussed by a multidisciplinary team of experts with a hypothesis for invasive methods of study. Subdural electrodes were once the mainstay of invasive presurgical evaluation and in later years most Comprehensive Epilepsy Centers have shifted to intracranial recordings. The intracranial recording follows original concepts since its development by Bancaud and Talairach, but great advances have been made in the field. Stereo-electroencephalography is a growing field of study, treatment, and establishment of seizure pattern complexities. In this comprehensive review, we explore the indications, usefulness, discoveries in interictal and ictal findings, pitfalls, and advances in the science of presurgical stereo-encephalography for temporal lobe epilepsy.

Localizing and Lateralizing Value of Seizure Onset Pattern on Surface EEG in FCD Type II

BACKGROUND

Surface ictal electroencephalographic (EEG) monitoring has an important role in the presurgical evaluation of patients with focal cortical dysplasia (FCD). This study aimed to examine the characteristics of seizure onset pattern (SOP) on surface ictal EEG. This information will be useful for invasive monitoring planning.

METHODS

We reviewed 290 seizures from 31 patients with intractable seizures related to FCD type II (6 patients with FCD IIa and 25 patients with FCD IIb). We categorized the SOPs into five patterns and evaluated the relationships between the SOPs and the location and pathology of the FCD II subtype.

RESULTS

The most common SOP was no apparent change (39.0%), followed by rhythmic slow wave and repetitive spikes/sharp waves. The SOP of rhythmic slow wave was associated with FCD II in the temporal lobe (P < 0.001), and the SOP of no apparent change was associated with FCD II in the occipital lobe (P = 0.012). The SOPs of rhythmic slow waves and fast activity were most common in FCD IIa, P < 0.001 and 0.031, respectively. The repetitive spikes/sharp waves SOP was the most common pattern in FCD IIb (P < 0.001). The surface SOPs provided correct localization and lateralization of epileptic foci in FCD in 62.1% and 62.7%, respectively. In 61.3% of the patients, over 50% of the SOPs in each patient indicated accurate localization.

CONCLUSIONS

SOPs in surface EEG monitoring are beneficial for presurgical evaluation and lead to localization of epileptic foci and pathologic subtypes of FCD.

Ictal wavefront propagation in slices and simulations with conductance-based refractory density model

The mechanisms determining ictal discharge (ID) propagation are still not clear. In the present study, we aimed to examine these mechanisms in animal and mathematical models of epileptiform activity. Using double-patch and extracellular potassium ion concentration recordings in rat hippocampal-cortical slices, we observed that IDs moved at a speed of about 1 mm/s or less. The mechanisms of such slow propagation have been studied with a mathematical, conductance-based refractory density (CBRD) model that describes the GABA- and glutamatergic neuronal populations’ interactions and ion dynamics in brain tissue. The modeling study reveals two main factors triggerring IDs: (i) increased interneuronal activity leading to chloride ion accumulation and a consequent depolarizing GABAergic effect and (ii) the elevation of extracellular potassium ion concentration. The local synaptic transmission followed by local potassium ion extrusion and GABA receptor-mediated chloride ion accumulation underlies the ID wavefront’s propagation. In contrast, potassium ion diffusion in the extracellular space is slower and does not affect ID’s speed. The short discharges, constituting the ID, propagate much faster than the ID front. The accumulation of sodium ions inside neurons due to their hyperactivity and glutamatergic currents boosts the Na⁺/K⁺ pump, which terminates the ID. Knowledge of the mechanism of ID generation and propagation contributes to the development of new treatments against epilepsy.

During an epileptic seizure, neuronal excitation spreads across the brain tissue and is accompanied by significant changes in ionic concentrations. Ictal discharge front spreads at low speeds, less than 1 mm/s. Mechanisms underlying this phenomenon are not yet well understood. We study these mechanisms using electrophysiological recordings in brain slices and computer simulations. Our detailed biophysical model describing neuronal populations’ interaction, spatial propagation, and ionic dynamics reproduces the generation and propagation of spontaneously repeating ictal discharges. The simulations are consistent with our recordings of the electrical activity and the extracellular potassium ion concentration. We distinguished between the two alternative mechanisms of the ictal wavefront propagation: (i) the diffusion of potassium ions released from excited neurons, which depolarizes distant neurons and thus supports excitation, and (ii) the axonal spread of excitation followed by the local extracellular potassium ion accumulation that supports the excitation. Our simulations provide evidence in favor of the latter mechanism. Our experiment-based modeling contributes to a mathematical description of brain tissue functioning and potentially contributes to developing new treatments against epilepsy.

Simultaneous scalp EEG improves seizure lateralization during unilateral intracranial EEG evaluation in temporal lobe epilepsy

PURPOSE

To determine if simultaneous bilateral scalp EEG (scEEG) can accurately detect a contralateral seizure onset in patients with unilateral intracranial EEG (IEEG) implantation.

METHODS

We evaluated 39 seizures from 9 patients with bitemporal epilepsy who underwent simultaneous scEEG and IEEG (SSIEEG). To simulate conditions of unilateral IEEG implantation with a missed contralateral seizure onset, we analyzed the IEEG recording contralateral to the seizure onset (CL- IEEG), in conjunction with simultaneous scEEG. The following criteria were evaluated between scEEG and CL- IEEG (1) latency: the time to onset of EEG seizure (2) location: concordance of ictal onset zones and (3) pattern: congruence of EEG morphology and frequency.

RESULTS

SSIEEG correctly lateralized 36/39 (92.3%) seizures compared to 13/39 (33.3%) seizures using CL- IEEG alone (OR = 24.0, p < 0.01), 33 (84.6%) seizures using scEEG alone (OR = 2.2, p = 0.29) and 26 (66.9%) seizures using time of clinical onset alone (OR = 6.0, p = 0.01). For the three criteria evaluated, (1) 22/39 (56.4%) seizures had an earlier onset on the scEEG, compared to CL- IEEG; (2) lack of congruence of location of seizure onset was noted in 33/39 (84.6%) of the seizures; and (3) 22/39 (56.4%) seizures did not have a congruent ictal pattern.

CONCLUSIONS

The chronological, topographic and morphologic features of SSIEEG can accurately detect the hemisphere of seizure onset in most cases with unilateral IEEG implantation. SSIEEG is significantly better than, IEEG, scEEG or clinical onset alone in this scenario. We propose that SSIEEG should be considered in all cases of intractable focal epilepsy undergoing unilateral IEEG evaluation.

The Value of Diagnostic Bilateral Intracranial Electroencephalography in Treatment-Resistant Focal Epilepsy

OBJECTIVES

We assessed the efficacy and risks of diagnostic bilateral intracranial electroencephalography (bICEEG) in patients with treatment-resistant epilepsy (TRE) with poorly lateralized epileptogenic zone on noninvasive studies as reflected by progress to resection, Engel outcome, and complication rate.

METHODS

This is a retrospective chart review of 199 patients with TRE who had diagnostic bICEEG at New York University Medical Center between 1994 and 2013. Study end points were progress to resection, surgical outcome, and perioperative complications. Univariate analysis was performed with analysis of variance, t test, or Fisher exact test; multivariable analysis was performed using discriminant function analysis.

RESULTS

bICEEG lateralized the epileptogenic zone and the patient had resection in 60.3% of cases. The number of depth electrodes used was positively correlated with resection, and surgical complications during bICEEG negatively correlated. Vagal nerve stimulators were implanted in 58.2% of patients who did not undergo resection and 20.7% of those who did. Among the 87 patients who progressed to resection and had more than 1-year follow-up, 47.1% were seizure free compared with 12.7% of the 55 who did not. Male sex correlated with good postoperative seizure control. The most common complication was infection requiring debridement, occurring in 3.1% of admissions (9 of 290).

CONCLUSIONS

At our center, 60% of patients undergoing bICEEG progress to resection and 57% of these had more than 90% reduction in seizures. We conclude that bICEEG allows the benefits of epilepsy surgery to be extended to patients with poorly lateralized and localized TRE.

Secondary generalization of focal-onset seizures: examining the relationship between seizure propagation and epilepsy surgery outcome

Surgical intervention often fails to achieve seizure-free results in patients with intractable epilepsy. Identifying features of the epileptic brain that dispose certain patients to unfavorable outcomes is critical for improving surgical candidacy assessments. Recent research by Martinet, Ahmad, Lepage, Cash, and Kramer (J Neurosci 35: 9477-9490, 2015) suggests that pathways of secondary seizure generalization distinguish patients with favorable (i.e., seizure free) vs. unfavorable (i.e., seizure persistent) surgical outcomes, lending insights into the network mechanisms of epilepsy surgery failure.

Evolution of Network Synchronization during Early Epileptogenesis Parallels Synaptic Circuit Alterations

In secondary epilepsy, a seizure-prone neural network evolves during the latent period between brain injury and the onset of spontaneous seizures. The nature of the evolution is largely unknown, and even its completeness at the onset of seizures has recently been challenged by measures of gradually decreasing intervals between subsequent seizures. Sequential calcium imaging of neuronal activity, in the pyramidal cell layer of mouse hippocampal in vitro preparations, during early post-traumatic epileptogenesis demonstrated rapid increases in the fraction of neurons that participate in interictal activity. This was followed by more gradual increases in the rate at which individual neurons join each developing seizure, the pairwise correlation of neuronal activities as a function of the distance separating the pair, and network-wide measures of functional connectivity. These data support the continued evolution of synaptic connectivity in epileptic networks beyond the latent period: early seizures occur when recurrent excitatory pathways are largely polysynaptic, while ongoing synaptic remodeling after the onset of epilepsy enhances intranetwork connectivity as well as the onset and spread of seizure activity.

Slow Spatial Recruitment of Neocortex during Secondarily Generalized Seizures and Its Relation to Surgical Outcome

Understanding the spatiotemporal dynamics of brain activity is crucial for inferring the underlying synaptic and nonsynaptic mechanisms of brain dysfunction. Focal seizures with secondary generalization are traditionally considered to begin in a limited spatial region and spread to connected areas, which can include both pathological and normal brain tissue. The mechanisms underlying this spread are important to our understanding of seizures and to improve therapies for surgical intervention. Here we study the properties of seizure recruitment-how electrical brain activity transitions to large voltage fluctuations characteristic of spike-and-wave seizures. We do so using invasive subdural electrode arrays from a population of 16 patients with pharmacoresistant epilepsy. We find an average delay of ∼30 s for a broad area of cortex (8 × 8 cm) to be recruited into the seizure, at an estimated speed of ∼4 mm/s. The spatiotemporal characteristics of recruitment reveal two categories of patients: one in which seizure recruitment of neighboring cortical regions follows a spatially organized pattern consistent from seizure to seizure, and a second group without consistent spatial organization of activity during recruitment. The consistent, organized recruitment correlates with a more regular, compared with small-world, connectivity pattern in simulation and successful surgical treatment of epilepsy. We propose that an improved understanding of how the seizure recruits brain regions into large amplitude voltage fluctuations provides novel information to improve surgical treatment of epilepsy and highlights the slow spread of massive local activity across a vast extent of cortex during seizure.

Features of scalp EEG in unilateral mesial temporal lobe epilepsy due to hippocampal sclerosis: Determining factors and predictive value for epilepsy surgery

OBJECTIVE

To investigate determining factors of the ictal scalp EEG pattern at seizure onset and its predictive value for postsurgical outcome in people with unilateral MTLE due to hippocampal sclerosis (MTLE-HS).

METHODS

Review of consecutive people with chronic MTLE-HS undergoing presurgical video-EEG telemetry. Exclusion criteria were additional epileptogenic lesions or seizure generators or compromised EEG traces at seizure-onset. Mixed linear or logistic regression models were used.

RESULTS

Inclusion of 63 patients with 219 seizures with a favorable outcome (no seizures or auras only) in 43 patients at last follow-up. Rhythmic activity at seizure-onset (RA) had a frequency of 4.7±1.5/s (range 1-8/s), mostly localized in the anterior temporal region. Postsurgical seizure outcome was not associated with any clinical or electrophysiological feature. RA in the delta-band was more often observed with shorter epilepsy duration (p=0.002).

CONCLUSIONS

RA on scalp EEG gets faster with increasing epilepsy duration, possibly via time-dependent alterations of epileptogenic networks. Neither the frequency of RA nor other EEG-features appeared to predict postsurgical seizure outcome.

SIGNIFICANCE

The results challenge the view that if patients with apparent MTLE display RA in the delta-band, seizure-onset in neocortical structures rather than in temporo-mesial tissue should be considered and further investigations should be prompted.

Prognostic value of the second ictal intracranial pattern for the outcome of epilepsy surgery

OBJECTIVE

To investigate the prognostic value of the second ictal pattern (SIP) that follows the first ictal pattern (FIP) seen at seizure onset in order to predict seizure control after epilepsy surgery.

METHODS

SIPs were analysed in 344 electro-clinical and subclinical seizures recorded with intracranial electrodes in 63 patients. SIPs were classified as (a) electrodecremental event (EDE); (b) fast activity (FA); (c) runs of spikes; (d) spike-wave activity; (e) sharp waves; (f) alpha activity; (g) delta activity and (h) theta activity. Engel surgical outcome scale was used.

RESULTS

The mean follow-up period was 42.1 months (SD=30.1). EDE was the most common SIP seen (41%), followed by FA (19%), spike-wave activity (18%), alpha activity (8%), sharp-wave activity (8%), delta activity (3%), runs of spikes (2%) and theta activity (2%). EDE as SIP was associated with favourable outcome when compared with FA (p=0.0044) whereas FA was associated with poor outcome when compared with any other pattern (p=0.0389). FA as SIP tends to occur after EDE (75%) whereas EDE tends to evolve from a FIP containing FA (77%). SIP extent was focal in 46% of patients, lobar in 24%, multilobar in 14% and bilateral in 16%. There is a gradual decrease in the proportion of Engel grade I with the extent of SIP. Focal and delayed (in temporal lobe epilepsy) SIPs appear to be associated with better outcome.

CONCLUSIONS

As SIP, EDE was associated with favourable surgical outcome whereas FA was associated with poor outcome, probably because outcome is dominated by FIP.

SIGNIFICANCE

EDE as SIP should not discourage surgery. However, FA as SIP should be contemplated with caution. SIP focality and latency can have prognostic value in epilepsy surgery.

Rapid brief feedback intracerebral stimulation based on real-time desynchronization detection preceding seizures stops the generation of convulsive paroxysms

OBJECTIVE

To investigate the abortion of seizure generation using "minimal" intervention in hippocampi using two rat models of human temporal lobe epilepsy.

METHODS

The recording or stimulation electrodes were implanted into both hippocampi (CA1 area). Using the kainic acid (chronic: experiment duration 24 days) and the 4-aminopyridine (acute: experiment duration 2 h) models of paroxysms in rats, a real-time feedback stimulation paradigm was implemented, which triggered a short periodic electrical stimulus (5 Hz for 5 s) upon detecting a seizure precursor. Our seizure precursor detection algorithm relied on the monitoring of the real-time phase synchronization analysis, and detected/anticipated electrographic seizures as early as a few seconds to a few minutes before the behavioral and electrographic seizure onset, with a very low false-positive rate of the detection.

RESULTS

The baseline mean seizure frequencies were 5.39 seizures per day (chronic) and 13.2 seizures per hour (acute). The phase synchrony analysis detected 88% (434 of 494) of seizures with a mean false alarm of 0.67 per day (chronic) and 83% (86 of 104) of seizures with a mean false alarm of 0.47 per hour (acute). The feedback stimulation reduced the seizure frequencies to 0.41 seizures per day (chronic) and 2.4 seizures per hour (acute). Overall, the feedback stimulation paradigm reduced seizure frequency by a minimum of 80% to a maximum of 100% in 10 rats, with 83% of the animals rendered seizure-free.

SIGNIFICANCE

This approach represents a simple and efficient manner for stopping seizure development. Because of the short on-demand stimuli, few or no associated side effects are expected in clinical application in patients with epilepsy. Abnormal synchrony patterns are common features in epilepsy and other neurologic and psychiatric syndromes; therefore, this type of feedback stimulation paradigm could be a novel therapeutic modality for use in various neurologic and psychiatric disorders.

Incidence of functional bi-temporal connections in the human brain in vivo and their relevance to epilepsy surgery

The incidence of functional connections between human temporal lobes and their latencies were investigated using intracranial EEG responses to electrical stimulation with 1 msec single pulses in 91 patients assessed for surgery for treatment of epilepsy. The areas studied were amygdala, hippocampus, parahippocampal gyrus, fusiform gyrus, inferior and mid temporal gyrus. Furthermore, we assessed whether the presence of such connections are related to seizure onset extent and postsurgical seizure control. Responses were seen in any region of the contralateral temporal lobe when stimulating temporal regions in 30 patients out of the 91 (32.96%). Bi-hippocampal or bi-amygdalar projections were seen in only 5% of temporal lobes (N = 60) and between both fusiform gyri in 7.1% (N = 126). All other bilateral connections occurred in less than 5% of hemispheres. Depending on the structures, latencies ranged between 20 and 90 msec, with an average value of 60.2 msec. There were no statistical difference in the proportion of patients showing Engel Class I between patients with and without contralateral temporal connections. No difference was found in the proportion of patients showing bilateral or unilateral seizure onset among patients with and without contralateral temporal projections. The present findings corroborate that the functionality of bilateral temporal connections in humans is limited and does not affect the surgical outcome.

Ictal and postictal semiology in patients with bilateral temporal lobe epilepsy

Bilateral temporal lobe epilepsy is characterized by evidence of seizure onset independently in both temporal lobes. The main aim of the present study was to determine whether patients with evidence of independent bilateral temporal lobe epilepsy (biTLE) can be identified noninvasively on the basis of seizure semiology analysis. Thirteen patients with biTLE, as defined by invasive EEG, were matched with 13 patients with unilateral temporal lobe epilepsy (uniTLE). In all 26 patients, the frequency of predefined clusters of ictal and periictal signs were evaluated: ictal motor signs (IMSs), periictal motor signs (PIMSs), periictal vegetative signs (PIVSs), the frequency of early oroalimentary automatisms (EOAs), and the duration of postictal unresponsiveness (PU). Some other noninvasive and clinical data were also evaluated. A lower frequency of IMSs was noted in the group with biTLE (patients = 46.2%, seizures = 20.7%) than in the group with uniTLE (patients = 92.3%, seizures = 61.0%) (p = 0.030; p < 0.001, respectively). The individual IMS average per seizure was significantly lower in the group with biTLE (0.14; range = 0-1.0) than in the group with uniTLE (0.80; range = 0-2.6) (p = 0.003). Postictal unresponsiveness was longer than 5 min in more patients (75.0%) and seizures (42.9%) in the group with biTLE than in the group with uniTLE (patients = 30.8%, seizures = 18.6%) (p = 0.047; p = 0.002). The frequency of EOAs, PIMSs, PIVSs, and other clinical data did not differ significantly. There is a lower frequency of ictal motor signs and longer duration of postictal unresponsiveness in patients with biTLE.

Prognostic value of intracranial seizure onset patterns for surgical outcome of the treatment of epilepsy

OBJECTIVE

To investigate if intracranial EEG patterns at seizure onset can predict surgical outcome.

METHODS

Ictal onset patterns from intracranial EEG were analysed in 373 electro-clinical seizures and subclinical seizures from 69 patients. Seizure onset patterns were classified as: (a) Diffuse electrodecremental (DEE); (b) Focal fast activity (FA); (c) Simultaneous onset of fast activity and diffuse electrodecremental event (FA-DEE); (d) Spikes; (e) Spike-wave activity; (f) Sharp waves; (g) Alpha activity; (h) Delta activity. Presence of preceding epileptiform discharge (PED) was also studied. Engel and ILAE surgical outcome scales were used.

RESULTS

The mean follow-up period was 42.1 months (SD=30.1). Fast activity was the most common seizure onset pattern seen (33%), followed by (FA-DEE) (20%), DEE (19%), spike-wave activity (12%), sharp-waves (6%), alpha activity (6%), delta activity (3%) and spikes (1%). Preceding epileptiform discharges were present in 75% of patients. FA was associated with favourable outcome (p=0.0083) whereas DEE was associated with poor outcome (p=0.0025). A widespread PED was not associated with poor outcome (p=0.9559). There was no clear association between seizure onset pattern and specific pathology, except possibly between sharp/spike waves and mesial temporal sclerosis.

CONCLUSIONS

FA activity is associated with favourable outcome. DEE at onset was associated with poor surgical outcome. Widespread/bilateral PEDs were not associated with poor or good outcome.

SIGNIFICANCE

FA appears to be the best marker for the epileptogenic zone. Surgery should be contemplated with caution if DEE is the first ictal change. However, a widespread/bilateral PED at onset is common and should not discourage surgery.

Ictal spread of medial temporal lobe seizures with and without secondary generalization: an intracranial electroencephalography analysis

OBJECTIVE

Secondary generalization of seizures has devastating consequences for patient safety and quality of life. The aim of this intracranial electroencephalography (icEEG) study was to investigate the differences in onset and propagation patterns of temporal lobe seizures that remained focal versus those with secondary generalization, in order to better understand the mechanism of secondary generalization.

METHODS

A total of 39 seizures were analyzed in nine patients who met the following criteria: (1) icEEG-video monitoring with at least one secondarily generalized tonic-clonic seizure (GTCS), (2) pathologically proven hippocampal sclerosis, and (3) no seizures for at least 1 year after anteromedial temporal lobe resection. Seizures were classified as focal or secondary generalized by behavioral analysis of video. Onset and propagation patterns were compared by analysis of icEEG.

RESULTS

We obtained data from 22 focal seizures without generalization (FS), and 17 GTCS. Seizure-onset patterns did not differ between FS and GTCS, but there were differences in later propagation. All seizures started with low voltage fast activity, except for seven seizures in one patient (six FS, one GTCS), which started with sharply contoured theta activity. Fifteen of 39 seizures started from the hippocampus, and 24 seizures (including six seizures in a patient without hippocampal contacts) started from other medial temporal lobe areas. We observed involvement or more prominent activation of the posterior-lateral temporal regions in GTCS prior to propagation to the other cortical regions, versus FS, which had no involvement or less prominent activation of the posterior lateral temporal cortex. Occipital contacts were not involved at the time of clinical secondary generalization.

SIGNIFICANCE

The posterior-lateral temporal cortex may serve as an important "gateway" controlling propagation of medial temporal lobe seizures to other cortical regions. Identifying the mechanisms of secondary generalization of focal seizures could lead to improved treatments to confine seizure spread.

Changing patterns of propagation in a super-refractory status of the temporal lobe. Over 900 seizures recorded over nearly one year

Objective

Our goals were to study the propagation models in a situation of persistent temporal epileptic seizures with varying degrees of bitemporal excitability and to analyze which propagation models were found at times of high temporal excitability and which occurred with lower levels of excitability.

Methods

A patient with super-refractory status arising from the temporal lobes was studied daily using video-electroencephalography (VEEG), with a large number of electroclinical seizures recorded. The analysis focused on the method and type of seizure propagation and classified them either according to the propagation models described in the literature or as undetermined.

Results

Video-EEG monitoring was carried out daily for 310 days. A total of 990 electroclinical seizures were recorded; 135 seizures were recorded during the first week, and 523 were recorded in the first month. From the beginning, the interictal recording showed independent discharges over both temporal lobes. The seizures showed independent onset in both temporal lobes. During periods of the highest number of seizures, certain models of propagation begin to predominate through switch of lateralization, temporal asynchrony, early remote propagation, total contralateral propagation, seizures with nonlocalized onset, or models that are difficult to classify. Conversely, when the condition was brought relatively under control, we observed fewer propagation models with predominantly simple patterns: only hemispheric propagation or graduated sequential propagation with a few nonlateralized onset seizures.

Conclusions

Upon analyzing the seizures, we found that the propagation models vary as the status evolved, with the change reflecting the degree of excitability in the mesial temporal–limbic network at a given time. In clinical practice, these changes in propagation models are more likely to be observed in temporal status that extends over time and with an onset of the seizures in both temporal lobes.

Significance

The analysis of the propagation models may provide information about the excitability of the mesial temporal–limbic network.

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Studies with ictal scalp electroencephalography (ISE) have identified different propagation models.

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Propagation models change, probably related to the excitability at different times of the mesial temporal–limbic network.

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During periods of poor seizure control, complex propagation models predominate.

Simulating memory outcome before right selective amygdalohippocampectomy

In this paper we present the case of a left-sided speech dominant patient with right medial temporal sclerosis (RMTS) and pharmacoresistant epilepsy who showed improved verbal memory during intracarotid amobarbital test (IAT) at his right hemisphere as compared with his own performance before the drug injection (baseline), as well as after right selective amygdalohippocampectomy. We suggest that the defective verbal memory shown by this patient is due to abnormal activity of his right hippocampus that interfered with the function of his left hippocampus. This hypothesis was demonstrated by the fact that disconnection of the two hippocampi, either by anesthetisation or by resection of the right hippocampus, disengaged the left hippocampus and, consequently improved its function. This paper main objective is twofold: first to contribute to the field of neuropsychology of epilepsy surgery by emphasising on postoperative memory outcomes in right medial temporal lobe epilepsy (RMTLE) patients, particularly those undergoing amygdalohippocampectomy, as the pattern of memory changes after resection of the right temporal lobe is less clear; second, by focusing on memory performance asymmetries during IAT, and comparatively considering them with neuropsychological memory performance, because of their possible prognostic-simulating value.

Neocortical temporal lobe epilepsy

Complex partial seizures (CPSs) can present with various semiologies, while mesial temporal lobe epilepsy (mTLE) is a well-recognized cause of CPS, neocortical temporal lobe epilepsy (nTLE) albeit being less common is increasingly recognized as separate disease entity. Differentiating the two remains a challenge for epileptologists as many symptoms overlap due to reciprocal connections between the neocortical and the mesial temporal regions. Various studies have attempted to correctly localize the seizure focus in nTLE as patients with this disorder may benefit from surgery. While earlier work predicted poor outcomes in this population, recent work challenges those ideas yielding good outcomes in part due to better localization using improved anatomical and functional techniques. This paper provides a comprehensive review of the diagnostic workup, particularly the application of recent advances in electroencephalography and functional brain imaging, in neocortical temporal lobe epilepsy.

Gray matter loss correlates with mesial temporal lobe neuronal hyperexcitability inside the human seizure-onset zone

PURPOSE

Patient studies have not provided consistent evidence for interictal neuronal hyperexcitability inside the seizure-onset zone (SOZ). We hypothesized that gray matter (GM) loss could have important effects on neuronal firing, and quantifying these effects would reveal significant differences in neuronal firing inside versus outside the SOZ.

METHODS

Magnetic resonance imaging (MRI) and computational unfolding of mesial temporal lobe (MTL) subregions was used to construct anatomic maps to compute GM loss in presurgical patients with medically intractable focal seizures in relation to controls. In patients, these same maps were used to locate the position of microelectrodes that recorded interictal neuronal activity. Single neuron firing and burst rates were evaluated in relation to GM loss and MTL subregions inside and outside the SOZ.

KEY FINDINGS

MTL GM thickness was reduced inside and outside the SOZ in patients with respect to controls, yet GM loss was associated more strongly with firing and burst rates in several MTL subregions inside the SOZ. Adjusting single neuron firing and burst rates for the effects of GM loss revealed significantly higher firing rates in the subregion consisting of dentate gyrus and CA2 and CA3 (CA23DG), as well as CA1 and entorhinal cortex (EC) inside versus outside the SOZ where normalized MRI GM loss was ≥1.40 mm. Firing rates were higher in subicular cortex inside the SOZ at GM loss ≥1.97 mm, whereas burst rates were higher in CA23DG, CA1, and EC inside than outside the SOZ at similar levels of GM loss.

SIGNIFICANCE

The correlation between GM loss and increased firing and burst rates suggests GM structural alterations in MTL subregions are associated with interictal neuronal hyperexcitability inside the SOZ. Significant differences in firing rates and bursting in areas with GM loss inside compared to outside the SOZ indicate that synaptic reorganization following cell loss could be associated with varying degrees of epileptogenicity in patients with intractable focal seizures.

Differences in corpus callosum volume and diffusivity between temporal and frontal lobe epilepsy

We analyzed volume and diffusivity measures of the corpus callosum (CC) in patients with temporal (TLE) and frontal (FLE) lobe epilepsy in comparison with healthy subjects. On high-resolution T1-weighted scans of 18 controls and 44 patients the volumes (cm(3)) of Witelson regions (WRs) and the entire CC were measured. The apparent diffusion coefficients (ADCs, 10(-5)mm(2)s(-1)) for the entire CC and three areas of interest were measured from co-registered ADC maps. The CC of patients with TLE and FLE, corrected for total brain volume, was smaller than that of controls. Patients' ADC values were higher than those of controls. Findings were significant for WR1, WR2, and WR6, the CC regions connecting the frontal and temporal lobes. Patients with FLE had smaller WR1 and higher ADC values; in patients with TLE, the findings were similar for WR6. Atrophy and increased diffusivity in subregions of the CC connecting homotopic contralateral cortical regions indicate anatomical abnormalities extending beyond the epileptogenic zone in FLE and TLE.

Two types of remote propagation in mesial temporal epilepsy: analysis with scalp ictal EEG

The purpose of this study was to describe the propagation pattern of ictal discharges, particularly remote patterns from a localized onset in patients with mesial temporal epilepsy, and to determine whether this provides additional information to that obtained from prolonged presurgery scalp EEG monitoring. This is a retrospective and analytical study that included a historical open cohort of 18 patients with mesial temporal epilepsy, among whom 56 regionalized-lateralized onset seizures were recorded. These seizures were analyzed as to whether remote propagation occurred and as to their temporal characteristics. Thirty-eight regionalized-lateralized onset seizures did not show remote propagation, whereas 18 did. Two types of remote propagation were identified, one early and one late, depending on whether the remote propagation occurred before or after 10 seconds had elapsed from the onset of the electroencephalographic seizure. When the seizures were compared according to the type of propagation, those with early remote propagation showed a correlation, not statistically significant, with the intractability of the epilepsy (P = 0.0754), toward independent bitemporal interictal discharges (P = 0.1667), and from the MRI perspective, to occur with temporal lesions other than pure mesial sclerosis (P = 0.6329). Early remote propagation seizures were not associated with nonlateralized onset (P = 0.2682). The only patient in our study with switch of lateralization seizures experienced early remote propagation seizures. Patients with late remote propagation seizures and those without remote propagation showed no statistically significant differences with respect to these variables. Ictal recording with scalp EEG allows for differentiating between early and late remote propagation in patients with mesial temporal epilepsy and regionalized-lateralized onset seizures. Early remote propagation probably identifies a subgroup of these patients with greater uni- or bitemporal hyperexcitability.

Long-term outcome of extratemporal epilepsy surgery among 154 adult patients

Object

The goal of this study was to evaluate the long-term outcome of patients who underwent extratemporal epilepsy surgery and to assess preoperative prognostic factors associated with seizure outcome.

Methods

This retrospective study included 154 consecutive adult patients who underwent epilepsy surgery at Bethel Epilepsy Centre, Bielefeld, Germany between 1991 and 2001. Seizure outcome was categorized based on the modified Engel classification. Survival statistics were calculated using Kaplan–Meier curves, life tables, and Cox regression models to evaluate the risk factors associated with outcomes.

Results

Sixty-one patients (39.6%) underwent frontal resections, 68 (44.1%) had posterior cortex resections, 15 (9.7%) multilobar resections, 6 (3.9%) parietal resections, and 4 (2.6%) occipital resections. The probability of an Engel Class I outcome for the overall patient group was 55.8% (95% confidence interval [CI] 52–58% at 0.5 years), 54.5% (95% CI 50–58%) at 1 year, and 51.1% (95% CI 48–54%) at 14 years. If a patient was in Class I at 2 years postoperatively, the probability of remaining in Class I for 14 years postoperatively was 88% (95% CI 78–98%). Factors predictive of poor long-term outcome after surgery were previous surgery (p = 0.04), tonic–clonic seizures (p = 0.02), and the presence of an auditory aura (p = 0.03). Factors predictive of good long-term outcome were surgery within 5 years after onset (p = 0.015) and preoperative invasive monitoring (p = 0.002).

Conclusions

Extratemporal epilepsy surgery is effective according to findings on long-term follow-up. The outcome at the first 2-year follow-up visit is a reliable predictor of long-term Engel Class I postoperative outcome.

Frontal and temporal functional connections of the living human brain

Connections between human temporal and frontal cortices were investigated by intracranial electroencephalographic responses to electrical stimulation with 1-ms single pulses in 51 patients assessed for surgery for treatment of epilepsy. The areas studied were medial temporal, entorhinal, lateral temporal, medial frontal, lateral frontal and orbital frontal cortices. Findings were assumed to be representative of human brain as no differences were found between epileptogenic and non-epileptogenic hemispheres. Connections between intralobar temporal and frontal regions were common (43-95%). Connections from temporal to ipsilateral frontal regions were relatively uncommon (seen in 0-25% of hemispheres). Connections from frontal to ipsilateral temporal cortices were more common, particularly from orbital to ipsilateral medial temporal regions (40%). Contralateral temporal connections were rare (< 9%) whereas contralateral frontal connections were frequent and faster, particularly from medial frontal to contralateral medial frontal (61%) and orbital frontal cortices (57%), and between both orbital cortices (67%). Orbital cortex receives profuse connections from the ipsilateral medial (78%) and lateral (88%) frontal cortices, and from the contralateral medial (57%) and orbital (67%) frontal cortices. The high incidence of intralobar temporal connections supports the presence of temporal reverberating circuits. Frontal cortex projects within the lobe and beyond, to ipsilateral and contralateral structures.

Temporal lobe surgery in patients with normal MRI

PURPOSE OF REVIEW

The surgical approach to nonlesional temporal lobe epilepsy presents a significant challenge due to uncertainties regarding the extent of resection necessary to result in a seizure-free state. To outline an optimum surgical strategy, an understanding of the clinical and diagnostic presentation of mesial and lateral temporal epilepsy is required in order to properly characterize the location of the ictal onset zone. This review focuses on several methods used to identify this ictal onset zone, with emphasis on the impact each modality has on surgical outcome.

RECENT FINDINGS

Factors predicting an excellent surgical outcome include the presence of a discrete zone of low voltage fast activity and prolonged propagation time on the electroencephalogram, and the absence of metabolic dysfunction in the contralateral temporal lobe. Identifying epileptogenic regions in the temporal lobe using magnetic source imaging is a recent technique that has also yielded promising surgical outcomes. Recent prospective studies have shown that a temporal neocortical resection is very effective in providing a seizure free outcome given strict localization of the ictal onset zone to the lateral temporal region, highlighting the need for accurate characterization of mesial versus lateral nonlesional epilepsy.

SUMMARY

With accurate identification of the ictal onset zone with intracranial electroencephalography, a tailored temporal resection can yield excellent surgical results.

Persistent seizures following left temporal lobe surgery are associated with posterior and bilateral structural and functional brain abnormalities

PURPOSE

To perform a quantitative MRI and retrospective electrophysiological study to investigate whether persistent post-surgical seizures may be due to brain structural and functional abnormalities in temporal lobe cortex beyond the margins of resection and/or bilateral abnormalities in patients with temporal lobe epilepsy (TLE).

METHODS

In 22 patients with left TLE and histopathological evidence of hippocampal sclerosis, we compared pre-surgical brain morphology between patients surgically remedied (Engel's I) and patients with persistent post-surgical seizures (PPS, Engel's II-IV) using voxel-based morphometry (VBM). Routine pre-surgical EEG and invasive and non-invasive telemetry investigations were additionally compared between patient groups.

RESULTS

Results indicated widespread structural and functional abnormalities in patients with PPS relative to surgically remedied patients. In particular, patients with PPS had significantly reduced volume of the ipsilateral posterior medial temporal lobe and contralateral medial temporal lobe relative to surgically remedied patients. Furthermore, successful surgery was associated with clear anterior (89%) and unilateral (100%) temporal lobe EEG abnormalities, whilst PPS were associated with widespread ipsilateral (91%) and bilateral (82%) temporal lobe abnormalities.

DISCUSSION

We suggest that these preliminary data support the hypothesis that PPS after temporal lobe surgery are due to functionally connected epileptogenic cortex remaining in the ipsilateral posterior temporal lobe and/or in temporal lobe contralateral to resection.

Comment communiquent les lobes temporaux au cours des crises d’origine médio-temporale?

INTRODUCTION

Spatial and temporal patterns of the spread of partial epileptic seizures depend on the site from which they originate. Characterising seizure propagation patterns may help to better define the seizure focus. In medial temporal lobe epilepsies, seizure propagation to the contralateral temporal lobe is especially studied.

STATE OF THE ART

Intracranial EEG records permit more precise definition of patterns of contralateral propagation in medial temporal lobe epilepsies. Several pathways have been implicated, sometimes differently in distinct studies, in propagation to the contralateral temporal lobe: the three commissures (the corpus callosum, the ventral hippocampal commissure and the anterior commissure, which link the temporal lobes) and an indirect circuit via the frontal lobes. Delays measured for contralateral propagation of a seizure of temporo-limbic origin vary significantly around a mean value of about 30 seconds. This slow spread may depend in part on the relatively small size of human commissural projections from the amygdalo-hippocampal formation, which largely originate in the presubiculum. However, a larger commissural projection pathway originates in the paralimbic medial temporal lobe and electrical stimulation of the anterior perirhinal cortex can induce contralateral epileptic discharges with delays as short as 100 ms (Adam et al., 2004). Thus, seizure activity emerging from anterior paralimbic regions can propagate rapidly to the contralateral medial temporal lobe via the anterior commissure.

PERSPECTIVES

While the propagation of medial temporal lobe seizures is still debated, further studies are merited since the extent and speed of spread governs the electro-clinical semiology of seizures and our ability to identify their initiation site.

CONCLUSIONS

We review anatomical (Demeter et al., 1990) and neurophysiological (Wilson et al., 1990) data for a dual inter-temporal propagation of medial temporal lobe seizures at different speeds and via different pathways.

Clinico-electrical Characteristics of Lateral Temporal Lobe Epilepsy; Anterior and Posterior Lateral Temporal Lobe Epilepsy

BACKGROUND AND PURPOSE

This study aimed to determine whether there are clinicoelectrical differences between anterior lateral temporal lobe epilepsy (ALTLE) and posterior lateral temporal lobe epilepsy (PLTLE), taking medial temporal lobe epilepsy (MTLE) as a reference.

METHODS

We analyzed the historical information, ictal semiologies, and ictal EEGs of temporal lobe epilepsy patients with a documented favorable surgical outcome (Engel class I or II) at follow-up after more than one year. LTLE was defined when a discrete lesion on MRI or an ictal onset zone in invasive study was located outside the collateral sulcus. LTLE was further divided into ALTLE and PLTLE by reference to the line across the cerebral peduncle. Total 107 seizures of 13 ALTLE, 8 PLTLE and 21 MTLE patients were reviewed.

RESULTS

Initial hypomotor symptom was frequently observed in PLTLE (P<0.001). Oroalimentary automatism (OAA) was not observed initially in PLTLE. Generalized tonic-clonic seizures occurred significantly earlier in PLTLE than in ALTLE or MTLE (P< 0.001). Ictal scalp EEG was not helpful in differentiating between ALTLE and PLTLE.

CONCLUSIONS

Frequent hypomotor onset, the absence of initial oroalimentary automatism, and early generalization are characteristic findings of PLTLE, although they are insufficient to differentiate it from ALTLE or MTLE.

Long-term outcome of epilepsy surgery among 399 patients with nonlesional seizure foci including mesial temporal lobe sclerosis

OBJECT

The authors reviewed the long-term outcome of focal resection in a large group of patients who had intractable partial nonlesional epilepsy, including mesial temporal lobe sclerosis (MTS), and who were treated consecutively at a single institution. The goal of this study was to evaluate the long-term efficacy of epilepsy surgery and the preoperative factors associated with seizure outcome.

METHODS

This retrospective analysis included 399 consecutive patients who underwent epilepsy surgery at Mayo Clinic in Rochester, Minnesota, between 1988 and 1996. The mean age of the patients at surgery was 32 +/- 12 years (range 3-69 years), and the mean age at seizure onset was 12 +/- 11 years (range 0-55 years). There were 214 female (54%) and 185 male (46%) patients. The mean duration of epilepsy was 20 +/- 12 years (range 1-56 years). The preceding values are given as the mean +/- standard deviation. Of the 399 patients, 237 (59%) had a history of complex partial seizures, 119 (30%) had generalized seizures, 26 (6%) had simple partial seizures, and 17 (4%) had experienced a combination of these. Preoperative evaluation included a routine and video-electroencephalography recordings, magnetic resonance imaging of the head according to the seizure protocol, neuropsychological testing, and a sodium amobarbital study. Patients with an undefined epileptogenic focus and discordant preoperative studies underwent an intracranial study. The mean duration of follow up was 6.2 +/- 4.5 years (range 0.6-15.7 years). Seizure outcome was categorized based on the modified Engel classification. Time-to-event analysis was performed using Kaplan-Meier curves and Cox regression models to evaluate the risk factors associated with outcomes. Among these patients, 372 (93%) underwent temporal and 27 (7%) had extratemporal resection of their epileptogenic focus. Histopathological examination of the resected specimens revealed MTS in 113 patients (28%), gliosis in 237 (59%), and normal findings in 49 (12%). Based on the Kaplan-Meier analysis, the probability of an Engel Class I outcome (seizure free, auras, or seizures related only to medication withdrawal) for the overall patient group was 81% (95% confidence interval [CI] 77-85%) at 6 months, 78% (CI 74-82%) at 1 year, 76% (CI 72-80%) at 2 years, 74% (CI 69-78%) at 5 years, and 72% (CI 67-77%) at 10 years postoperatively. The rate of Class I outcomes remained 72% for 73 patients with more than 10 years of follow up. If a patient was in Class I at 1 year postoperatively, the probability of seizure remission at 10 years postoperatively was 92% (95% CI 89-96%); almost all seizures occurred during the 1st year after surgery. Factors predictive of poor outcome from surgery were normal pathological findings in resected tissue (p = 0.038), male sex (p = 0.035), previous surgery (p < 0.001), and an extratemporal origin of seizures (p < 0.001).

CONCLUSIONS

The response to epilepsy surgery during the 1st follow-up year is a reliable indicator of the long-term Engel Class I postoperative outcome. This finding may have important implications for patient counseling and postoperative discontinuation of anticonvulsant medications.

The role of synaptic reorganization in mesial temporal lobe epilepsy

The mechanisms underlying mesial temporal lobe epilepsy (MTLE) remain uncertain. Putative mechanisms should account for several features characteristic of the clinical presentation and the neurophysiological and neuropathological abnormalities observed in patients with intractable MTLE. Synaptic reorganization of the mossy fiber pathway has received considerable attention over the past two decades as a potential mechanism that increases the excitability of the hippocampal network through the formation of new recurrent excitatory collaterals. Morphological plasticity beyond the mossy fiber pathway has not been as thoroughly investigated. Recently, plasticity of the CA1 pyramidal axons has been demonstrated in acute and chronic experimental models of MTLE. As the hippocampal formation is topographically organized in stacks of slices (lamellae), synaptic reorganization of CA1 axons projecting to subiculum appears to increase the connectivity between lamellae, providing a mechanism for translamellar synchronization of cellular hyperexcitability, leading to pharmacologically intractable seizures.

Independent component analysis identifies ictal bitemporal activity in intracranial recordings at the time of unilateral discharges

OBJECTIVE

To apply independent component analysis (ICA) in intracranial recordings to analyze interactions during temporal lobe seizures.

METHODS

Seizures from 20 patients with bitemporal implantation were classified as unilateral or bilateral and analyzed with ICA. During the period preceding bilateral activity, correlation coefficients were calculated between ICA components having ictal activity during the unilateral seizure phase (early ICA components) and every channel of the original EEG. ICA components were classified as unilateral if the correlation was >0.2 exclusively with channels in one hemisphere; and bilateral if both hemispheres were involved.

RESULTS

One hundred twenty-three seizures were analyzed. Thirty-two percent of visually classified unilateral seizures and 64% of bilateral seizures (during the unilateral phase) had bilateral ICA components. The proportion of early ICA components that were bilateral and the proportion of channels contralateral to the visually identified seizure with correlation higher than 0.2 with at least one early ICA component were significantly lower in seizures that stayed unilateral than in seizures that later became bilateral by visual inspection (11 and 10%, respectively, in unilateral seizures; 33 and 28% in bilateral seizures; P=0.001).

CONCLUSIONS

In patients with bitemporal epilepsy, approximately 20% of the components extracted using ICA have a bitemporal distribution even at the time when the seizures are apparently unilateral. The presence of early contralateral ictal activity is more frequent and extensive in seizures that later become evidently bilateral.

SIGNIFICANCE

Minimal contralateral seizure activity is present even when the discharge appears unilateral and this is more frequent in seizures which later spread to the contralateral temporal lobe.

Neuronal plasticity in memory and learning abilities: theoretical position and selective review

Neural plasticity of modality-nonspecific and modality-specific memory and learning abilities pertains to fluid intelligence and crystallized intelligence, respectively. The limbic system with the novelty neurons of the hippocampus interacts with the prefrontal cortex optimization of the orienting reflex and voluntary attention. Brain-derived neurotrophic factor produced by novelty neurons of the hippocampus contributes to long-term memory formation and improves learning abilities in a wide range of disciplines. Synergistic combination of stimulation with "analytical-specific visual perceptual patterns" and "optimally high" physiological activation of the bilateral electrodermal system optimizes the limbic system and prefrontal cortex activity as demonstrated by enhanced prefrontal N450 ERPs to a memory workload paradigm. This is accompanied by improvements in auditory retention tasks, word memorization, higher school achievement and marks, and an amelioration of "analytical-specific perceptual skills" as measured by the Mangina-Test. Intracerebral ERPs to a memory workload paradigm contributed to the elucidation of limbic structures and neocortical sites involved in memory workload processes. The progressive degeneration of these same structures causes the gradual decline of memory functions observed in early Alzheimer's disease. Research findings indicate that ERPs elicited by a memory workload paradigm are sensitive markers for diagnosis, treatment and clinical follow-up of early Alzheimer's patients. In addition, ERPs provide objective measurement of cholinergic medication effects on cerebral functions involved in memory processes through neuropsychophysiological parameters.

Ictal dystonic posturing in mesial versus neocortical temporal lobe seizures

PURPOSE

Ictal contralateral dystonic posturing is a frequently observed clinical feature in temporal lobe seizures. It is generally interpreted as the result of spread of the ictal discharge into basal ganglia structure. In previous reports, analysing ictal behavior, a precise definition and description of the upper limb ictal dystonia is often lacking or contradictory. In our study we aimed to determine whether different subtypes of dystonia and their latency from the clinical onset of seizure might be of value for the differentiation between mesial temporal lobe epilepsy (MTLE) and neocortical temporal lobe epilepsy (NTLE).

METHODS

Eighty seizures (51 MTLE and 29 NTLE) and 30 patients (20 MTLE and 10 NTLE) were analyzed with regard to dystonic posturing of the upper limb. Ictal dystonia was subdivided into different subtypes according to distinct clinical features. Their frequency and latency from the clinical onset of seizure were assessed.

RESULTS

Frequencies of all subtypes were similar in MTLE and NTLE. Concerning the latencies contralateral dystonic posturing characterized by sustained muscle contractions with flexion of the wrist and fist closure, a frequently appearing feature, occurred significantly earlier in NTLE than in MTLE seizures.

CONCLUSIONS

This difference between the two groups may provide a differentiation between an epileptic focus of mesial from neocortical temporal lobe origin.

Combined MEG/EEG analysis of the interictal spike complex in mesial temporal lobe epilepsy

We studied the functional organization of the interictal spike complex in 30 patients with mesial temporal lobe epilepsy (MTLE) using combined magnetoencephalography (MEG)/electroencephalography (EEG) recordings. Spikes could be recorded in 14 patients (47%) during the 2- to 3-h MEG/EEG recording session. The MEG and EEG spikes were subjected to separate dipole analyses; the MEG spike dipole localizations were superimposed on MRI scans. All spike dipoles could be localized to the temporal lobe with a clear preponderance in the medial region. Based on dipole orientations in MEG, patients could be classified into two groups: patients with anterior medial vertical (AMV) dipoles, suggesting epileptic activity in the mediobasal temporal lobe and patients with anterior medial horizontal (AMH) dipoles, indicating involvement of the temporal pole and the anterior parts of the lateral temporal lobe. Whereas patients with AMV dipoles had strictly unitemporal interictal and ictal EEG changes during prolonged video-EEG monitoring, 50% of patients with AMH dipoles showed evidence of bitemporal affection on interictal and ictal EEG. Nine patients underwent epilepsy surgery so far. Whereas all five patients with AMV dipoles became completely seizure-free postoperatively (Class Ia), two out of four patients with AMH dipoles experienced persistent auras (Class Ib). This difference, however, was not statistically significant. We therefore conclude that combined MEG/EEG dipole modeling can identify subcompartments of the temporal lobe involved in epileptic activity and may be helpful to differentiate between subtypes of mesial temporal lobe epilepsy noninvasively.

Fast Contralateral Propagation of After-Discharges Induced by Stimulation of Medial Temporal Lobe

In a patient with unilateral hippocampal sclerosis, stimulation of the contralateral anterior perirhinal cortex triggered after-discharges in the sclerotic hippocampus, followed in one case by a seizure. The spatial and temporal characteristics of these responses reveal fast interconnections between the two medial temporal lobes.

Unilateral Hippocampal Sclerosis with Contralateral Temporal Scalp Ictal Onset

PURPOSE

To investigate the clinical characteristics and surgical outcomes in patients with unilateral hippocampal sclerosis whose scalp ictal EEG recordings localize to the opposite temporal lobe.

METHODS

We retrospectively reviewed the data of all adult patients who had undergone depth electrode implantation for suspected temporal lobe epilepsy (TLE) at UCLA (1993-2000) or the Montreal Neurological Institute (1991-1998) to identify patients who had (a) unilateral hippocampal atrophy, and (b) surface ictal recordings in which the majority of seizures appeared to initiate in the opposite temporal lobe, with few or none that were concordant with the hippocampal atrophy.

RESULTS

Of 109 patients with suspected TLE who underwent depth electrode study at the two centers, five patients met the aforementioned criteria. Four of these five had very severe hippocampal atrophy, whereas the fifth had mild atrophy but extensive signal change on magnetic resonance imaging (MRI). Depth electrode recordings in four of the five patients yielded clear ictal onset in the mesial temporal lobe ipsilateral to the imaging abnormality (contralateral to apparent scalp ictal onset). One patient had an unusual bitemporal onset pattern, which was nonetheless suggestive of onset in the sclerotic hippocampus. No patient had intracranial ictal onset contralateral to the imaging abnormality. All patients underwent resection of the structurally abnormal temporal lobe. After follow-up of > or = 2 years, four (80%) of five patients were seizure free, while the fifth showed lesser improvement (class III).

CONCLUSIONS

Some patients with severe hippocampal sclerosis (sometimes called a "burned-out hippocampus") have atypical spread of ictal discharges, resulting in apparent gross discordance between imaging and scalp ictal recordings. These patients nonetheless have excellent surgical outcomes on the whole. Whether such patients may forego intracranial recordings requires further study.

Controversies in clinical neurophysiology. MEG is superior to EEG in the localization of interictal epileptiform activity: Con

OBJECTIVE

To assess whether MEG is superior to scalp-EEG in the localization of interictal epileptiform activity and to stress the 'con' part in this controversy.

METHODS

Advantages and disadvantages of the two techniques were systematically reviewed.

RESULTS

While MEG and EEG complement each other for the detection of interictal epileptiform discharges, EEG offers the advantage of long-term recording significantly increasing its diagnostic yield which is not feasible with MEG. Localization accuracies of EEG and MEG are comparable once inaccuracies for the solution of the forward problem are eliminated. MEG may be more sensitive for the detection of neocortical spike sources. EEG and MEG source localizations show comparable agreement with invasive electrical recordings, can clarify the spatial relationship between the irritative zone and structural lesions, guide the placement of invasive electrodes and attribute epileptic activity to lobar subcompartments in temporal lobe epilepsy and to a lesser extent in extratemporal epilepsy.

CONCLUSIONS

A clear superiority of MEG over EEG for the localization of interictal epileptiform activity cannot be derived from the studies presently available.

SIGNIFICANCE

The combination of EEG and MEG provides information for the localization of interictal epileptiform activity which cannot be obtained with either technique alone.

Wada memory performance predicts seizure outcome after epilepsy surgery in children

PURPOSE

Wada memory asymmetries were examined in children from four comprehensive epilepsy surgery centers who subsequently underwent epilepsy surgery to determine whether Wada memory performance could predict degree of seizure relief in children.

METHODS

One hundred fifty-six children (between ages 5 and 16 years) with intractable epilepsy underwent Wada testing before resective epilepsy surgery (93 within the left hemisphere, and 63 within the right hemisphere). Memory stimuli were presented soon after intracarotid amobarbital injection, and recognition memory for the items was assessed after return to neurologic baseline. Eighty-eight children underwent unilateral temporal lobe resection, and 68 had extratemporal lobe resections. One hundred four (67%) children were seizure free (Engel class I), and 52 (33%) were not seizure free (Engel classes II-IV) at follow-up (mean follow-up interval, 2.3 years).

RESULTS

Seizure-free children recalled 19.3% more Wada memory items after ipsilateral injection than did non-seizure-free children (p = 0.008). If analysis was restricted to youngsters with temporal lobectomies (TLs), seizure-free children recalled 27.7% more items after ipsilateral injection than did non-seizure-free TL children (p = 0.004). With regard to individual patient prediction, 75% of children who had memory score asymmetries consistent with the seizure focus were seizure free. In contrast, only 56% of children whose memory score asymmetries were inconsistent with the seizure focus were seizure free (p = 0.01).

CONCLUSIONS

Results suggest that Wada memory performance asymmetries are related to the degree of seizure relief after epilepsy surgery in children and adolescents.