Abstract
PurposeImpairment of cognitive functions is commonly observed in temporal lobe epilepsy (TLE). The aim of this study was to assess visuospatial memory functions and memory-related networks using an adapted version of Roland’s Hometown Walking (RHWT) functional MRI (fMRI) task in patients with TLE.MethodsWe used fMRI to study activation patterns based on a visuospatial memory paradigm in 32 TLE patients (9 right; 23 left) and also within subgroups of lesional and non-lesional TLE. To test for performance, a correlational analysis of fMRI activation patterns and out-of-scanner neuropsychological visuospatial memory testing was performed. Additionally, we assessed memory-related networks using functional connectivity (FC).ResultsGreater contralateral than ipsilateral mesiotemporal (parahippocampal gyrus/hippocampus) activation was observed in left (n = 23)/right (n = 9) TLE. In lesional left TLE (n = 17), significant activations were seen in right more than left mesiotemporal areas (parahippocampal gyrus), while non-lesional left TLE patients (n = 6) showed significant bilateral (left>right) activations in mesiotemporal structures (parahippocampal gyrus). In left TLE, visuospatial cognitive testing correlated with fMRI activations in left (parahippocampal gyrus) and right mesiotemporal structures (hippocampus), characterized by greater fMRI activation being associated with better memory scores. In right TLE, higher scores in visuospatial memory testing were associated with greater fMRI activations in left and right insular regions. FC patterns of memory-related networks differ in right and left TLE.ConclusionWhile TLE in general leads to asymmetrical mesiotemporal activation, lesion-induced and non-lesional TLE patients reveal different memory fMRI activation patterns. In right TLE, insular regions try to compensate for impaired right mesiotemporal structures during the performance of visuospatial tasks. Underlying functional visuospatial memory networks differ in right and left TLE.
Highlights
Temporal lobe epilepsy (TLE) is the most frequent type of focal epilepsy [1] and remains drug resistant in 30% of the cases [2].If remission of temporal lobe seizures is not achievable by antiepileptic drug treatment, epilepsy-surgery might be an alternative treatment option [1, 3]
While TLE in general leads to asymmetrical mesiotemporal activation, lesion-induced and non-lesional TLE patients reveal different memory functional magnetic resonance imaging (MRI) (fMRI) activation patterns
In right TLE, insular regions try to compensate for impaired right mesiotemporal structures during the performance of visuospatial tasks
Summary
Temporal lobe epilepsy (TLE) is the most frequent type of focal epilepsy [1] and remains drug resistant in 30% of the cases [2]. If remission of temporal lobe seizures is not achievable by antiepileptic drug treatment, epilepsy-surgery might be an alternative treatment option [1, 3]. A detailed pre-surgical assessment using prolonged video-electroencephalography (EEG) monitoring, neuropsychological and neuropsychiatric evaluation, structural magnetic resonance imaging (MRI), and functional MRI (fMRI) provide important information on the localization of the epileptogenic zone, which has to be removed and essential brain regions [4, 5], which have to be spared during epilepsy-surgery. Jokeit et al used fMRI and an adapted version of the Roland’s Hometown Walking task (RHWT) [6], in order to investigate hemispheric activation asymmetries in TLE patients [7]. TLE patients showed reduced fMRI activations on the side of the seizure focus [7]. The same paradigm provided valuable results for the prediction of visual memory impairment after right-sided temporal lobe resection [8]
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