Temporal Seizure Onset Research Articles

Electroclinical Analysis of Postictal Noserubbing

Postictal noserubbing (PIN) has been identified as a good, albeit imperfect, lateralizing and localizing sign in human partial epilepsy, possibly related to ictal autonomic activation. PIN was studied prospectively in a group of consecutive patients admitted for video-EEG monitoring, with the laterality of noserubbing correlated with electrographic sites of seizure onset, intra- and interhemispheric spread, and sites of seizure termination. PIN was significantly more frequent in temporal than extratemporal epilepsy (p<0.001; 23/41 (56%) patients and 41/197 (21%) seizures in temporal lobe epilepsy compared with 4/34 (12%) patients and 12/167 (7%) seizures in extratemporal epilepsy). The hand used to rub the nose was ipsilateral to the side of seizure onset in 83% of both temporal and extratemporal seizures. Seizures with contralateral PIN correlated with spread to the contralateral temporal lobe on scalp EEG (p<0.04). All extratemporal seizures with PIN showed spread to temporal lobe structures. One patient investigated with intracranial electrodes showed PIN only when ictal activity spread to involve the amygdala: seizures confined to the hippocampus were not associated with PIN. PIN was not observed in 63 nonepileptic events in 17 patients. Unexpectedly, one patient with primary generalized epilepsy showed typical PIN after 1/3 recorded absence seizures. This study confirms PIN as a good indicator of ipsilateral temporal lobe seizure onset. Instances of false lateralization and localization appear to reflect seizure spread to contralateral or ipsilateral temporal lobe structures, respectively. Involvement of the amygdala appears to be of prime importance for induction of PIN.

Neuromagnetic recordings in temporal lobe epilepsy.

The introduction of whole-head magnetoencephalography (MEG) systems facilitating simultaneous recording from the entire brain surface has established MEG as a clinically feasible method for the evaluation of patients with temporal lobe epilepsy (TLE). In mesial TLE, two types of MEG spike dipoles could be identified: an anterior vertical and an anterior horizontal dipole. Dipole orientations can be used to attribute spike activity to temporal lobe subcompartments. Whereas the anterior vertical dipole is compatible with epileptic activity in the mediobasal temporal lobe, the anterior horizontal dipole can be explained by epileptic activity of the temporal tip cortex. In nonlesional TLE, medial and lateral vertical dipoles were found which could distinguish between medial and lateral temporal seizure onset zones as evidenced from invasive recordings. In lesional TLE, MEG could clarify the spatial relationship of the structural lesion to the irritative zone. Evaluation of patients with persistent seizures after epilepsy surgery may represent another clinical important application of MEG because magnetic fields are less influenced than electric fields by the prior operation. Simultaneous MEG and invasive EEG recordings indicate that epileptic activity restricted to mesial temporal structures cannot reliably be detected on MEG and that an extended cortical area of at least 6 to 8 cm2 involving also the basal temporal lobe is necessary to produce a reproducible MEG signal. In lateral neocortical TLE MEG seems to be more sensitive than scalp-EEG which further underlines the potential role of MEG for the study of nonlesional TLE. Whole-head MEG therefore can be regarded as a valuable and clinically relevant noninvasive method for the evaluation of patients with TLE.

Localizing value of epileptic visual auras

It is difficult to differentiate between seizures of occipital or temporal lobe origin in patients with focal epileptic seizures associated with visual aura. These are often suspected to originate from the visual cortex, which causes reluctance to propose resection as treatment for the affected patient. To determine the value of localizing different types of visual auras, we report on 20 patients experiencing visual aura from a series of 878 surgically treated patients suffering from intractable focal seizures. In all of these patients, a morphological abnormality was identified on MRI (n = 18) or cranial CT (n = 2). These abnormalities were shown to represent the morphological correlate of the epileptogenic zone in each case, as demonstrated by intracranial ictal EEG recordings and/or seizure freedom after focal resective surgery. Elementary hallucinations, illusions and visual loss were reported not only by all patients with occipital lobe epilepsy, but also by patients with occipitotemporal and anteromedial temporal seizure onset. Complex hallucinations never occurred in occipital lobe seizures but were present in the two other groups. The same correlation was found for concentric changes of visual field (tunnel vision), a newly described ictal phenomenon. We conclude that elementary hallucinations, illusions and visual loss, although typical for occipital lobe epilepsy, can also occur in anteromedial temporal or occipitotemporal seizures and are therefore not a discordant feature in presurgical evaluation of patients with suspected temporal lobe epilepsy. Complex hallucinations and tunnel vision, however, should be considered concordant only with the assumption of an anteromedial temporal or occipitotemporal seizure onset.

Spitting automatism in complex partial seizures: a nondominant temporal localizing sign?

Spitting as an ictal automatism has been rarely reported. We aimed to establish its potential lateralizing and localizing significance. Review of patients undergoing surgery for intractable epilepsy at two comprehensive epilepsy centers. Five patients were found who had spitting as a stereotyped automatism of their complex partial seizures. All had evidence of right temporal ictal onset and underwent resective surgery. Two had tumors; one, a cavernous angioma; one, hippocampal gliosis, and one, hippocampal sclerosis. We found no instances of ictal spitting in patients with left hemisphere onset. Spitting as an automatism in complex partial seizures, although uncommon, may be a localizing sign to the nondominant temporal lobe.

Paired pulse suppression and facilitation in human epileptogenic hippocampal formation.

Paired pulse stimulation has commonly been employed to investigate changes in excitability in epileptic hippocampal tissue employing the in vitro slice preparation. We used paired pulse stimulation in the intact temporal lobe of patients with temporal lobe seizures to compare the excitability of pathways in the epileptogenic hippocampus (located in the temporal lobe in which seizures arise) with those in the non-epileptogenic hippocampus of the contralateral temporal lobe (in the hemisphere to which seizures spread). A total of 20 patients with temporal lobe seizure onsets were studied during chronic depth electrode monitoring for seizure localization. Intracranial in vivo stimulation and recording sites included the hippocampus, entorhinal cortex, subicular cortex and parahippocampal gyrus. A comparison of all hippocampal pathways located in the temporal lobe where seizures typically started (n = 37) with those in temporal lobes contralateral to seizure onset (n = 53) showed significantly greater paired pulse suppression of population post-synaptic potentials on the epileptogenic side (F(1,87) = 6.1, P < 0.01). Similarly, mean paired pulse suppression was significantly greater for epileptogenic perforant path responses than for contralateral perforant path responses (F(1,13) = 7.5, P < 0.01). In contrast, local stimulation activating intrinsic associational pathways of the epileptogenic hippocampus showed decreased paired pulse suppression in comparison to the epileptogenic perforant path. These results may be a functional consequence of the formation of abnormal recurrent inhibitory and recurrent excitatory pathways in the sclerotic hippocampus. Enhanced inhibition may be adaptive in suppressing seizures during interictal periods, while abnormal recurrent excitatory circuits in the presence of enhanced inhibition may drive the hypersynchronization of principal neurons necessary for seizure genesis.

Time–frequency analysis using the matching pursuit algorithm applied to seizures originating from the mesial temporal lobe

Objectives: The ability to analyze patterns of recorded seizure activity is important in the localization and classification of seizures. Ictal evolution is typically a dynamic process with signals composed of multiple frequencies; this can limit or complicate methods of analysis. The recently-developed matching pursuit algorithm permits continuous time–frequency analyses, making it particularly appealing for application to these signals. The studies here represent the initial applications of this method to intracranial ictal recordings. Methods: Mesial temporal onset partial seizures were recorded from 9 patients. The data were analyzed by the matching pursuit algorithm were continuous digitized single channel recordings from the depth electrode contact nearest the region of seizure onset. Time–frequency energy distributions were plotted for each seizure and correlated with the intracranial EEG recordings. Results: Periods of seizure initiation, transitional rhythmic bursting activity, organized rhythmic bursting activity and intermittent bursting activity were identified. During periods of organized rhythmic bursting activity, all mesial temporal onset seizures analyzed had a maximum predominant frequency of 5.3–8.4 Hz with a monotonic decline in frequency over a period of less than 60 s. The matching pursuit method allowed for time–frequency decomposition of entire seizures. Conclusions: The matching pursuit method is a valuable tool for time–frequency analyses of dynamic seizure activity. It is well suited for application to the non-stationary activity that typically characterizes seizure evolution. Time–frequency patterns of seizures originating from different brain regions can be compared using the matching pursuit method.

Intracranial EEG substrates of scalp ictal patterns from temporal lobe foci.

To determine the intracranial EEG features responsible for producing the various ictal scalp rhythms, which we previously identified in a new EEG classification for temporal lobe seizures. In 24 patients, we analyzed simultaneous intracranial and surface ictal EEG recordings (64 total channels) obtained from a combination of intracerebral depth, subdural strip, and scalp electrodes. Four of four patients with Type 1 scalp seizure patterns had mesial temporal seizure onsets. However, discharges confined to the hippocampus produced no scalp EEG rhythms. The regular 5- to 9-Hz subtemporal and temporal EEG pattern of Type 1a seizures required the synchronous recruitment of adjacent inferolateral temporal neocortex. Seizure discharges confined to the mesiobasal temporal cortex produced a vertex dominant rhythm (Type 1c) due to the net vertical orientation of dipolar sources located there. Ten of 13 patients with Type 2 seizures had inferolateral or lateral, temporal neocortical seizure onsets. Initial cerebral ictal activity was typically a focal or regional, low voltage, fast rhythm (20-40 Hz) that was often associated with widespread background flattening. Only an attenuation of normal rhythms was reflected in scalp electrodes. Irregular 2- to 4-Hz cortical ictal rhythms that commonly followed resulted in a comparably slow and irregular scalp EEG pattern (Type 2a). Type 2C seizures showed regional, periodic, 1- to 4-Hz sharp waves following intracranial seizure onset. Seven patients had Type 3 scalp seizures, which were characterized by diffuse slowing or attenuation of background scalp EEG activity. This resulted when seizure activity was confined to the hippocampus, when there was rapid seizure propagation to the contralateral temporal lobe, or when cortical ictal activity failed to achieve widespread synchrony. Type 1, 2, and 3 scalp EEG patterns of temporal lobe seizures are not a reflection of cortical activity at seizure onset. Differences in the subsequent development, propagation, and synchrony of cortical ictal discharges produce the characteristic scalp EEG rhythms.

Language function in patients with left dominant mesial versus regional/lateral temporal seizure onset determined by chronic corticography

Language function is impaired in patients with left, speech-dominant temporal ictal onset compared to those with non-speech-dominant onset, even though the pathology in most cases is mesial temporal. In patients with intractable epilepsy undergoing chronic invasive electroencephalography (EEG) with subdural electrodes, ictal onset was classified as mesial temporal (MT) when only the mesial contacts of the subtemporal electrode were initially involved, lateral temporal (LT) when only the contacts of the lateral temporal electrode were involved, and regional temporal (RT) when the contacts of all temporal electrodes were involved. We hypothesized that preoperative language function assessed by neuropsychological parameters would be worse in the patients with RT or LT onset compared with patients in whom ictal onset was MT. Fifty-two patients were studied. Thirty-nine patients had MT onset, 10 had RT onset, and 3 had LT onset. Language function was assessed by a standard aphasia battery and no significant differences were found between the two groups. All patients underwent anterior temporal lobectomy. All LT patients and 40% RT patients had evidence of lateral temporal lobe pathology. None of the MT patients had lateral temporal pathology, 29 had hippocampal sclerosis (HS) and 10 had normal hippocampus. LT or RT ictal onset do not appear to confer additional language deficits compared with patients with MT onset.

Neuropsychological evaluation in epilepsy surgery.

Neuropsychology has played a prominent role throughout the modern era of epilepsy surgery. Neuropsychology, including the Wada test, has been of benefit in documenting dysfunction associated with a lateralized temporal lobe seizure onset. In addition, neuropsychological results have some predicative power regarding seizure outcome following anterior temporal lobectomy. The current status of neuropsychology in patient evaluation and outcome prediction will be presented. Differences between the Wada test, an inactivation procedure, and functional magnetic resonance imaging, which is an activation procedure, will be discussed. This paper will also present preliminary information about the Wechsler Adult Intelligence Scale-III, the recent revision of the most commonly used test of intellectual function, and its effects on neuropsychological performance results.

Wada memory and timing of stimulus presentation.

We compared Wada memory performance for stimuli presented at two timing intervals following amobarbital injection in 47 non-lesional patients with complex partial seizures (L = 26; R = 21). A significant interaction between seizure focus and timing of presentation was present (P < 0.03). Memory performance for objects whose presentation began approximately 50-55 s following amobarbital administration differed as a function of ipsilateral vs. contralateral injection at a very high level of statistical significance (P < 0.00001). Items presented approximately 4 min, 30 s post injection were also related to seizure onset literality, but at a lower statistical level (P < 0.01). Presentation of Wada memory stimuli earlier during hemispheric anaesthesia yields results that are more sensitive to lateralized temporal lobe seizure onset than does presentation of items later during the procedure.

Is 11C-flumazenil PET superior to 18FDG PET and 123I-iomazenil SPECT in presurgical evaluation of temporal lobe epilepsy?

OBJECTIVE: To determine the contribution of 18FDG PET, 11C-flumazenil PET, and 123I-iomazenil SPECT to the presurgical evaluation of patients with medically intractable complex partial seizures. METHODS: Presurgical evaluation was performed...

Temporal lobectomy for intractable epilepsy: Correlation of ictal onset determined by chronic electrocorticography and seizure outcome with degree of hippocampal sclerosis

This study sought to determine whether hippocampal sclerosis (HS) can be predicted from the results of electrocorticography (ECoG). One hundred seven patients underwent anterior temporal lobectomy (ATL) (44 R, 63 L) for epilepsy in the absence of a structural lesion and had the degree of HS graded pathologically from 0 to 4. Preoperative evaluation included ictal chronic ECoG with subdural strip electrodes, which showed a temporal onset in each case. Twenty-seven (25%) specimens were grade 0, 15 (14%) were grade 1–2, and 65 (61%) were grade 3–4. ECoG showed a unilateral mesial temporal seizure onset in 70% of grade 0, 73% of grade 1–2, and 78% of grade 3–4 patients ( p > 0.5). A unilateral regional onset, i.e., involving all temporal electrodes, occurred in 15% of grade 0, 13% of grade 1–2, and 12% of grade 3–4 patients ( p > 0.5). Bilateral independent onset occurred in 11% of grade 0, 13% of grade 1–2 ( p > 0.5), and none of grade 3–4 patients ( p p p p

Comparison of Mesial Versus Neocortical Onset Temporal Lobe Seizures: Neurodiagnostic Findings and Surgical Outcome

We compared historical features, surface EEG findings, results of intracarotid sodium amobarbital memory testing (IAT), and outcome after anterotemporal lobectomy (ATL) in patients with mesiotemporal lobe seizure onset with those with more diffuse temporal lobe seizure onset (intracranial EEG). Forty-eight patients evaluated consecutively between July 1985 and October 1991 with both scalp/sphenoidal and intracranial EEG were shown to have seizures originating in one temporal lobe. No patients had temporal lobe tumor or vascular malformation. Thirty-seven of the 48 patients had seizure onset in the amygdala/hippocampus (amyg/hipp). Eleven of the 48 had either temporal neocortical onset or simultaneous amyg/hipp and neocortical onset. Patients with mesial onset seizures were more likely to have lateralized memory impairment on IAT (p = 0.05). We noted a trend toward a difference in age of first risk for epilepsy between the two groups (p = 0.09) but not for a difference in any specific risk factor. There were no significant differences in surface EEG interictal findings. Unlike in previous studies, comparison of outcome between the two groups showed no difference in seizure-free outcome. Sudden unexpected death (SUD) was more frequent in neocortical seizure patients who were not seizure-free (p < 0.05).

The utility of the warrington recognition memory test for temporal lobe epilepsy: Pre- and postoperative results

We wished to examine the ability of the Warrington Recognition Memory Test (RMT) to distinguish epilepsy of left versus right temporal lobe origin during preoperative testing and to assess pre- to postoperative changes in memory function after anterior temporal lobectomy (ATL). Seventy-seven patients were assessed preoperatively and 6–8 months postoperatively. Patients' performance for verbal (Words) and nonverbal (Faces) material was examined with raw, scaled, and discrepancy scores, as well as with more formal diagnostic efficiency statistics and receiver operating characteristics (ROC) curves. Preoperatively, no aspect of the RMT could reliably distinguish left from right temporal lobe epilepsy groups. Examination of pre- to postoperative memory change showed declines in Word recognition memory after left ATL and less consistent declines in Face recognition memory after right ATL. Diagnostic efficiency statistics demonstrated poor classification ability preoperatively and improved classification ability postoperatively. We conclude that the RMT is not insensitive to lateralized temporal lobe lesions (as demonstrated by the pre- to postoperative performance changes), but it is of extremely limited clinical utility in identifying laterality of temporal lobe seizure onset preoperatively. The reasons for this interesting pattern of results are discussed.

Analysis of mesial temporal seizure onset and propagation using the directed transfer function method

The directed transfer function (DTF) method, a multichannel parametric method of analysis based on an autoregressive model, is a newly developed tool that permits determination of patterns of flow of activity. The DTF method of analysis was applied to seizures originating from mesial temporal structures in 3 patients recorded by combined subdural grid and depth electrode arrays. These first applications to human intracranial recordings demonstrated that the DTF method can accurately determine patterns of seizure onset and propagations. In addition the DTF method can provide evidence regarding patterns of flow of seizure activity that are not readily apparent from visual inspection of the EEG recording. Important considerations for appropriate application of the DTF method for the analysis of intracranial ictal recording are discussed.

Do dichotic word listening asymmetries predict side of temporal lobe seizure onset?

Dichotic word listening asymmetries are thought to be useful in predicting side of temporal lobe dysfunction. However, little direct evidence exists to support this assumption in practice, especially in patients with subtle epileptogenic lesions. To determine if word listening ear asymmetries are valid predictors of side of temporal lobe seizure onset, we examined the preoperative dichotic word listening performance of 80 patients with either left ( N = 41) or right ( N = 39) temporal lobe (TL) seizure foci. On a group level, patients showed a statistically significant ‘lesion effect’ as evidenced by a relative deficit in the ear contralateral to the side of lesion. Prediction of side of seizure focus in individual cases, however, was poor: depending upon the criteria used, 61% to 80% of epileptics with unilateral temporal lobe foci did not show the expected contralateral ear deficit. Results suggest that caution be exercised when inferring side of temporal lobe seizure focus through dichotic word listening asymmetries in individual temporal lobe epilepsy cases.

Electrophysiology of bimanual-bipedal automatisms.

To determine the localizing value and electrophysiology of bimanual-bipedal automatisms (BBAs), we studied these behaviors in 54 seizures of 8 patients with temporal or frontal lobe seizure onset. BBAs occurred with a frequency of 27% in frontal lobe epilepsy (FLE) and of 7% in temporal lobe epilepsy (TLE). The distribution of electrode sites showing ictal activity during these automatisms was significantly different in the two patient groups (0.0001 Chi-square). Mesio- and/or laterotemporal plus orbital frontal areas were involved areas when the behaviors appeared in patients with TLE; dorsolateral and mesiofrontal regions were the most commonly involved when the behaviors occurred during the course of frontal lobe seizures. We concluded that BBAs represent activation of frontal lobe circuitry but are not unique to seizures of frontal lobe origin. Eyelid flutter and repetitive body movements in either the axial or sagittal plane were significantly associated with the frontal lobe group whereas oral-alimentary automatisms were associated with the temporal lobe group. Thus, these associated behaviors may help indicate whether a frontal or temporal lobe seizure onset has occurred when BBAs are observed. A new concept of ictal expression is proposed to conform with the results as well as with other apparently disparate ictal behaviors that may have localizing value.

Characteristics of medial temporal lobe epilepsy: I. Results of history and physical examination

In order to more precisely define a syndrome of medial temporal lobe epilepsy, histories and physical findings were evaluated in 67 patients studied with intracranial electrodes who had medial temporal seizure onset and became seizure free following temporal lobectomy. Patients with circumscribed, potentially epileptogenic mass lesions were excluded. Fifty-four patients (81%) had histories of convulsions during early childhood or infancy, 52 of which were associated with fever. Complicated febrile seizures occurred in 33 (94%) of the 35 patients in whom detailed descriptions of the febrile seizures were available. Bacterial (5) or viral (2) central central nervous system infections were present in 7 patients with seizures and fevers. Other less common, but probably significant, risk factors included head trauma (10%) and birth trauma (3%). Only 5 patients had no apparent risk factors. The mean age at habitual seizure onset was 9 years. All patients had complex partial seizures, with half having only complex partial seizures. The other half also had secondarily generalized tonic-clonic seizures, but these were never the predominant seizure type. Only 3 patients had histories of convulsive status epilepticus and no patient had a history of nonconvulsive status epilepticus. All but 3 patients reported auras before some or all of their seizures, with an abdominal visceral sensation being by far the most common type of aura (61%). Of the 60 patients with identified risk factors, all but 2 had an interval between the presumed cerebral insult and the development of habitual seizures, with a mean seizure-free interval of 7.5 years.(ABSTRACT TRUNCATED AT 250 WORDS)

Diagnosis of medial temporal lobe seizure onset

Measurement of hippocampal volume by MRI is a new technique with potential value in the localization of epileptic regions, but whether reduced hippocampal volume predicts the location of electrical seizure onset in mixed patient groups is not known. We examined the sensitivity and specificity of this technique among 56 refractory epileptic patients for the diagnosis of medial temporal lobe epilepsy as judged by intracranial EEG recording of spontaneous seizure onset. Since these patients had intracranial EEG because of inconsistent or insufficient localization by noninvasive electrophysiologic, functional, and structural assessment, this patient population can be considered the most difficult to localize. Hippocampal atrophy by MRI volumetry was 75% sensitive to, and 64% specific for, ipsilateral medial temporal lobe seizure onset in this group. Hippocampal atrophy was significantly correlated with longer duration of epilepsy. MRI compared favorably with all other noninvasive means of localization, which had 41 to 73% sensitivity and 45 to 65% specificity to medial temporal ictal onset; of these, none had as acceptable a combination of both adequate sensitivity and specificity. We conclude that MRI volumetry of the hippocampus is a valuable, noninvasive localization method in chronic epilepsy, with a yield and accuracy surpassing all other noninvasive studies used to predict the presence of medial temporal seizure onset.

Temporal lobe epilepsy in early childhood.

To explore the electroclinical features of temporal lobe epilepsy (TLE) in early childhood, we studied results of video-EEG and other tests of 14 children aged 16 months to 12 years selected by seizure-free outcome after temporal lobectomy. Four children had mesiotemporal sclerosis, 1 had cortical dysplasia, and 9 had low-grade temporal neoplasms. The children had complex partial seizures (CPS) with symptomatology similar to that of adults with TLE, including decreased responsiveness and automatisms. Automatisms tended to be simpler in the younger children, typically limited to lip smacking and fumbling hand gestures. Scalp/sphenoidal EEG showed anterior/inferior temporal interictal sharp waves and unilateral temporal seizure onset in the 4 children with mesiotemporal sclerosis and in the child with cortical dysplasia, but EEG findings in 9 children with low-grade temporal tumors were complex, including multifocal interictal sharp waves or poorly localized or falsely lateralized EEG seizure onset. In children without tumors, video-EEG was critical to localization of the epileptogenic zone for resection, but in patients with tumors video-EEG was less localizing and its main value was to confirm that the reported behaviors were epileptic seizures with semiology typical of temporal lobe onset.