Summary:Purpose: A strong relation exists between lateralization of seizure onset in temporal-lobe epilepsy and atrophic mesial structures measured by volumetric magnetic resonance imaging (MRI). We examined whether this relation extended to subregions of the mesial temporal lobe and whether the trend for seizures to spread contralaterally could be related to the localization of atrophy.Methods: We analyzed 362 seizures (with and without clinical signs) from 23 patients having bitemporal epilepsy in whom intracerebral electrodes were implanted for presurgical evaluation. Patients had measurements of hippocampal and amygdala volumes, including comparison with normal controls. We assessed on EEG the laterialization and localization of seizure onset and the trend to spread to the contralateral side (proportion of seizures that spread for each patient). We included all seizures, independent of the presence of clinical manifestations. These features were related to presence and localization of atrophy.Results: Among the 19 patients with mesial atrophy, agreement between side of prevalent seizure onset and predominant atrophy was found in 10 (53%). From 99 seizures starting in a temporal lobe with atrophy limited to the hippocampus, 67% started simultaneously in amygdala and hippocampus, 20% in hippocampus, and 13% in amygdala. From 137 seizures starting in a temporal lobe with amygdala and hippocampal atrophy, 47% started in amygdala and hippocampus, 48% in hippocampus, and 5% in amygdala. The trend to spread was 45% to the most atrophic side and 62% to the normal or less atrophic side.Conclusions: When examining amygdala and hippocampus in this group of patients with bitemporal epilepsy, regions of seizure onset did not correspond to regions of predominant atrophy. The likelihood that seizures spread contralaterally was not influenced by atrophy in the region targeted by the spread. Precise relation between mesial temporal atrophy and seizures remain to be elucidated. Key Words: Seizure morphologyInterhemispheric spread-Mesial atrophy.Mesial temporal sclerosis is the most common pathologic substrate in patients with temporal lobe epilepsy (TLE; 1 4 ) . Volumetric magnetic resonance imaging (MRI) measurement is an efficient noninvasive method of identifying amygdala (AM) and hippocampus (HF) atrophy (5-7), and MRI demonstration of HF atrophy is highly predictive of medial temporal lobe sclerosis verified by pathology and of epileptogenicity verified by depth EEG (8,9). It is reasonable to assume that the morphology of the EEG seizure discharge, which reflects neuronal activity, is related to the pathologic changes. The relation between mesial temporal sclerosis and EEG morphology during temporal-lobe seizures has indeed been examined by several authors. Spencer et al. (10) found that, in patients investigated with intracranial EEG, mesial temporal seizure onset had a significantly Accepted April 11, 1997. Address correspondence and reprint requests to Dr. J. Gotman at Montreal Neurological Institute, 3801 Universi...

Transcranial magnetic stimulation (TCS) was applied to both hemispheres of 16 patients affected by criptogenic focal epilepsy to evaluate the interhemispheric symmetry of the motor cortex excitability. The amplitude of the motor evoked potentials (MEPs) and the duration of the post-MEP silent period (SP) were measured at threshold (THR) and at increasing TCS stimulation intensities. The THR was significantly higher in patients than in 16 age-matched control subjects (p < 0.01). No interhemispheric differences were found in MEP amplitude. In controls, the correlation between SP duration and increasing TCS stimulus intensity was linear with a symmetrical progression of the SP duration over the two hemispheres. In patients this linear SP progression was lacking on the 'epileptic' hemisphere: the SP duration did not increase following TCS > 40% above THR, indicating abnormal interhemispheric asymmetry. This finding suggests a selective dysfunction of inhibition in the epileptic hemisphere as signaled by an abnormal SP duration in response to progressively higher TCS intensities.

Computerized EEG study was performed on 39 healthy elderly subjects (50-90 years), divided into two cohorts of increasing age (old, older) and on a group of 21 young controls. The EEG was recorded at rest, with eyes closed (EC) and during blocking reaction (BR), fixation (FIX) and mental arithmetic (MA) tasks. At rest with EC, the only significant variation was an increase of beta 1 relative power in old subjects which was positively correlated with age. During the performance of the mental tasks, in the elderly population when compared to young controls, the slow activity decreased slightly or was not significantly modified, while the alpha reactivity progressively decreased, showing a negative correlation with age in the older group. Beta 2 increased significantly in elderly subjects during BR and FIX but such change was less consistent with increasing age. Data show that at rest, the EEG in the elderly population differs only from that of young controls by showing a more pronounced fast activity, while only during mental processes is it possible to evidence changes that can be utilized as physiological "markers" of normal aging.

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