Interictal fast oscillations between 100 and 500 Hz have been reported in signals recorded from implanted microelectrodes in epileptic patients and experimental rat models. Oscillations between 250 and 500 Hz, or fast ripples (FR), appeared related to the epileptic focus whereas ripples (80-200 Hz) were not. We report high-frequency oscillations recorded with intracranial macroelectrodes in seven patients with refractory focal epilepsy during slow-wave sleep. We characterize the relation of fast oscillations to the seizure focus and quantify their concordance with epileptiform transients, with which they are strongly associated. The patients were selected because interictal spikes were found within and outside the seizure onset zone. Visual inspection was used to identify and classify the ripples and FRs according to their relation to epileptiform spikes. Continuous-time wavelet analysis was used to compute their power. Ripples were present in all patients while FRs where found in five of the seven patients. Most ripples and FRs occurred at the same time as epileptiform transients. The rate of occurrence of ripples was higher within the seizure onset zone than outside in four of seven patients. The rate of FRs was much higher within the seizure onset zone than outside in four of the five patients with FRs (in these four patients, FRs were almost inexistent outside the seizure onset zone). The power of ripples and FRs tended to be higher in the electrodes where their rate was also higher. These results indicate that FRs were more restricted to the electrodes located within the seizure onset zone, especially to the hippocampus, than ripples. In only one patient, FRs were more frequent outside the seizure onset zone; this patient was the only one with cortical dysplasia and the electrode with a high rate of FRs was inside the lesion. This study demonstrates that interictal ripples and FRs can be recorded with depth macroelectrodes in patients. Most occur at the time of epileptiform spikes but some are isolated. Ripples do not show a clear differentiation between the seizure onset zone and remote areas, whereas FRs have a higher rate and higher power in the seizure onset zone. Our results also suggest a special capacity of the abnormal hippocampus to generate FRs, although they were also recorded in other structures.

SUMMARYPurpose: We measured metabolic changes associated with temporal lobe (TL) spikes using combined electroencephalography (EEG) and functional magnetic resonance imaging (fMRI). We selected 18 patients with temporal lobe epilepsy (TLE) who underwent a 2-h simultaneous EEG-fMRI and had unilateral or bilateral independent TL spikes for interindividual group analysis, in order to identify consistent blood oxygenation level dependent (BOLD) responses to TL spikes. Methods: EEG was postprocessed and spikes were visually identified. fMRI data were preprocessed with motion correction, spatial smoothing, and removal of low frequency drifts. Spike timings were used as events for fMRI statistical analysis. Four hemodynamic response functions were used to account for variability in the BOLD response. Results: Group analysis revealed common areas of BOLD activations and deactivations. The hemodynamic response function (HRF) peaking 3 s after the spike showed activation involving ipsilaterally the mesial temporal structures (presumably the hippocampus), putamen/globus pallidus, inferior insula, and superior temporal gyrus. The HRF peaking at 5 s showed activations involving ipsiand contralaterally the superior temporal gyrus and inferior insula. Both HRFs showed bilateral posterior cingulate deactivations. Discussion: We disclosed involvement of a network of activated areas during unilateral TL spikes, including ipsilateral mesial temporal structures, basal ganglia, and bilateral neocortical temporal regions. Despite the low temporal resolution of fMRI we demonstrated that contralateral temporal involvement occurred later than ipsilateral activation. This contralateral change took place in the absence of visible EEG changes. The posterior cingulate deactivation may reflect the interconnections between this region and other limbic structures. It may also partially correspond to a suspension of the default mode network, as previously described for TL spikes.

Summary:Purpose: In patients with reflex epilepsy, it is sometimes possible to evoke interictal spikes predictably, thus providing an uncommon but important experimental paradigm for examining the physiological changes produced by epileptiform discharges.Methods. To examine the changes in regional cerebral blood flow (rCBF) and glucose consumption (rCMRglc) produced by interictal spikes, we performed positron emission tomography (PET) scans with the blood-flow tracer ['50]H,0 and with [ iXF]tluorodeoxyglucose in a patient with fixation-off epilepsy. The scans were performed in states of high and low spike frequency produced by eye closure and opening, respectively.Results: The rCBF study revealed a focal increase in blood flow associated with the state of increased interictal spiking. The focus was in the posterior portion of the left superior parietal lobule (Talairach coordinates: x: -36, y: -71, z: 39; t = 4.5; p < 0.05) and corresponded to the site of maximal ictal EEG abnormality recorded with implanted electrodes. In a volume of interest of 10-mm diameter centered on the t statistic peak in the rCBF study, the mean rCMRglc was 39.1 pmo1/100 g/min with eyes open and 44. I pmo1/100 g/min (13% increase) with eyes closed. An identical activation paradigm was used in six normal subjects studied with functional magnetic resonance imaging. In the normal subjects, no significant activation was observed in the parieto-occipital region, indicating that the changes observed in the patient were due to interictal spiking rather than to task performance alone.Conclusions: Interictal spiking produces focal increases in cerebral blood flow and glucose metabolism. Key Words: Epilepsy -1nterictal spikes-PET-Glucose-Ener g y .The energy requirements of interictal spike discharges remain incompletely understood. In the majority of cases of adult temporal lobe epilepsy, interictal ["F]fluorodeoxyglucose (FDG) uptake is reduced (1-S), despite the presence of interictal spikes. However, a number of patients with increased focal glucose metabolism during interictal spike activity have now been reported (2,9,10). Additionally, in some animal models, interictal spikes have been shown to increase the regional metabolic rate for glucose (rCMRglc; 11). In general, it is difficult to study the metabolic effects of interictal spike discharges in humans because spike frequency can rarely be manipulated to suit a scanning schedule.We describe a patient with fixation-off epilepsy in whom interictal spike frequency was modulated by eye closure. Positron emission tomography (PET) was used

A consecutive series of 170 patients who have been submitted to intracranial depth electrode recordings is reviewed to assess the overall morbidity of the technique. Most patients had bitemporal and frontal electrodes inserted and were monitored for an average period of 18 days. A surgically amenable focus was found in 85% of the cases. There were 4 cases of infection including 2 cerebral abscesses which required surgical evacuation. One patient with frontal lobe atrophy developed an acute subdural hematoma after electrode implantation. There was no death or neurological deficit in the entire series. Morbidity was encountered mainly in the neuropsychological sphere, several patients having developed transient postictal psychosis after repetitive seizures. Our recording technique has been associated with low surgical morbidity. Patients undergoing depth electrode recordings should be closely monitored to minimize the occurrence of psychotic episodes associated with drug withdrawal and increased seizure frequency.

The objective of this study was to assess which features of temporal lobe proton magnetic resonance spectroscopic imaging (1H-MRSI) are associated with satisfactory surgical outcome in patients with intractable temporal lobe epilepsy and bilateral hippocampal atrophy. We studied 21 patients with intractable temporal lobe epilepsy and bilateral hippocampal atrophy defined by magnetic resonance imaging volumetric measurements who underwent surgical treatment. 1H-MRSI was used to determine the relative resonance intensity ratio of the neuronal marker N-acetylaspartate to creatine + phosphocreatine (NAA/Cr) for mid and posterior temporal lobe regions of the left and right hemisphere, as well as an asymmetry index. Values lower than 2 SDs below the normal mean were considered abnormal. We used Engel's classification to assess surgical outcome with respect to seizure control. Eleven patients (52%) were in class I-II and 10 (48%) were in class III-IV. All 21 were operated on the side of maximal electroencephalographic (EEG) lateralization. Concordant lateralization of decreases in NAA/Cr to the side of surgery and normal NAA/Cr values in the contralateral posterior-temporal region were significantly associated with good surgical outcome: 11 (69%) of 16 patients with 1H-MRSI abnormalities concordant with EEG lateralization and none of the 5 patients with nonconcordant 1H-MRSI had a good outcome (class I-II); 10 (77%) of 13 patients with normal NAA/Cr contralateral to the EEG lateralization versus 1 (12.5%) of 8 of those with NAA/Cr reduction contralateral to EEG lateralization were in class I-II. Regression correlation analysis showed significant linear correlation between the midtemporal NAA/Cr relative asymmetry ratio and surgical outcome; the greater the asymmetry, the better the outcome. We conclude that discriminant 1H-MRSI features associated with favorable surgical outcome in patients with temporal lobe epilepsy and bilateral hippocampal atrophy were (1) concordant 1H-MRSI lateralization, (2) a greater side-to-side asymmetry of NAA/Cr, and (3) an absence of contralateral posterior NAA/Cr reduction.

MRI signal changes within the hippocampal sulcus have been attributed to a dilated Virchow-Robin space within that sulcus, but no clinical correlates have previously been described. We present a 64-year-old man who developed right temporal seizures. MRI revealed an unusually enlarged Virchow-Robin space within the hippocampus, suggesting space-occupying effect. Such an abnormality should be considered a possible etiology in patients with late-onset temporal lobe epilepsy.