Abstracts

Rationale: Idiopathic generalized epilepsy (IGE) is characterized by widespread cortical hyperexcitability without any detectable cortical or subcortical lesion. The excess neuronal synchrony may result from sodium or GABA channelopathies that alter thalamic activity or thalamo-cortical loops. Recent resting state studies in temporal lobe epilepsy have found disturbances in low frequency fluctuations (LFO) of the blood oxygen level dependent (BOLD) fMRI signal.(Zhang et al. Hum Brain Mapp 2010. Epub ahead of print.) The amplitude of such LFOs, in the range of 0.01-0.08 Hz gives insight into the nature and extent of spontaneous neuronal activity. (Zou et al. Neuroimage. 2010;49(2):1432-45) In the present resting state study, analysis of thalamic subregions was used to characterize regional differences of the amplitude of LFOs in patients with IGE compared to controls. Methods: Fourteen patients with IGE and 14 age- and sex-matched controls underwent fMRI 3T scans during which they were instructed to close their eyes for the entirety of the 6 min 38 second scan. Analysis of spontaneous BOLD fluctuations was performed with Resting-State fMRI Data Analysis Tool Kit. Images were bandpass-filtered at 0.01-0.08 Hz and co-registered to a common standard template. Within a probalistic mask of the thalamus, fractional amplitude of low frequency fluctuations (fALFF) estimates were generated for each voxel. (Behrens et al. Nat Neurosci. 2003;6(7):750-757) Unpaired t-tests were used to compare the average fALFF of controls and patients of the thalami and thalamic subdivisions. Results: The average of the fALFF over the entire left thalamus is decreased in IGE patients compared to normal controls. Additionally, we found a significant decrease in fALFF in patients in both left and right thalamic subdivisions that project to the prefrontal cortex. The subdivision on the right that projects to the premotor cortex also showed a statistically significant decrease in fALFF in IGE patients. Conclusions: Patients with idiopathic generalized epilepsy showed abnormal low-frequency BOLD activity in specific thalamic regions that project to the frontal lobes. These results may explain findings of maximal negative generalized discharges in bifrontal regions and impaired cognitive performance, such as executive functioning in these patients. (Piazzini et al. Epilepsia 2008;49(4):657-62) Disturbances in the spontaneous neuronal activity in the thalamus may account for generalized seizures or allow for seizure propagation in this group of epilepsy patients. In addition, this study shows that inter-ictal resting state fMRI can be used to detect functional abnormalities in patients with IGE while no anatomical abnormalities are identified.