Evaluate the impact of temporal lobe epilepsy surgery on a regional functional MRI (fMRI) measure of spontaneous neural activity, fractional amplitude of low frequency fluctuations (fALFF)

fALFF indirectly assesses spontaneous neural activity via resting state functional MRI (fMRI) blood-oxygen level dependent (BOLD) signal, in the range of 0.01 – 0.08 Hz. It has been investigated as a measure of regional brain integrity in temporal lobe epilepsy. There is a paucity of literature on post-operative changes in fALFF or other regional BOLD measures after epilepsy surgery. We investigated changes in fALFF after temporal lobe surgery for epilepsy to further understand the physiological significance of this noninvasive measure of neural activity.

Twenty-two patients with temporal lobe epilepsy, who had epilepsy surgery at Vanderbilt University Medical Center after consensus epilepsy surgery conference, and also obtained resting-state functional imaging, were analyzed. The majority of patients underwent selective amygdalohippocampectomy. Sixteen had right and six had left temporal lobe epilepsy. After standard fMRI preprocessing, fALFF maps were calculated for each participant pre- and post-operatively. The maps were parcellated into regions for each participant via a pre-defined multi-atlas approach.

Postoperatively, patients with temporal lobe epilepsy had significantly increased fALFF (p < 0.05, pairwise t-tests) in left central operculum, left angular gyrus, left supramarginal gyrus, left inferior occipital gyrus, left superior temporal gyrus, and left post-central gyrus.

Patients with temporal lobe epilepsy had increased fALFF in a group of primarily left parietal regions of interest postoperatively, which may imply an improvement in regional brain integrity. These changes should be correlated with standardized postoperative neuropsychological measures, particularly those related to semantic fluency, in a larger dataset. The data support the need for further investigation into fALFF as a noninvasive measure of neural activity, as well as its significance in different epilepsy subtypes.