Abstracts

Rationale: Voxel based analyses of resting-state fMRI BOLD signals can provide information regarding large-scale, spatial patterns of intrinsic activity throughout the brain including regions critical for important cognitive functions, such as memory and language. Such measures of intrinsic connectivity contrast (ICC) provide information on how well connected, functionally, any tissue element is and this provides a means of investigating the relationship between ICC and cognitive function. Cognitive changes are important co-morbidities of chronic temporal lobe epilepsy (TLE). This study aims to elucidate the neural correlates of cognitive impairment by analyzing the ICC in drug-resistant intractable TLE patients. We Hypothesized that ICC would demonstrate local changes in functional connectivity associated with changes in psychological test scores across subjects. Methods: 25 TLE patients underwent both resting-state fMRI and neuropsychological testing as part of presurgical evaluations, followed by standard temporal lobectomy with at least one year of postoperative follow-up. There were 12 left and 13 right TLE patients, 9 males and 16 females with mean age at surgery of 39.1 11.1 years old. Intrinsic connectivity contrast was calculated from BOLD fMRI data, using the network measure, degree, on a voxel basis, which reflects the number of voxels any particular voxel is connected to with a correlation coefficient greater than 0.25. In this work the degree measure was calculated for the whole-brain, an extended medial temporal mask, and a limited (hippocampus only) mask, for ipsi- (which measures only those connections within the hemisphere), and contra- (which measures only those connections to the opposite hemisphere). These ICC measures were then correlated with preoperative neuropsychological test scores including the verbal and non-verbal Selective Reminding Tests (SRT), the California Verbal Learning Test (CVLT), and the Boston Naming test (BNT).Results: Verbal SRT scores were positively correlated with ipsi-ICC in left hippocampus and contra-ICC in both hippocampi using medial temporal mask. Verbal SRT showed similar positive correlation with ipsi- and contra-ICC values with the whole brain mask in left middle and part of inferior temporal gyri. Impaired non-verbal SRT was correlated with decreased ipsi- and contra-ICC in right hippocampus, right superior temporal gyrus with medial/lateral temporal mask. Decreased CVLT scores were correlated with decreased ipsi- and contra-ICC in left middle temporal gyrus, and BNT showed similar positive correlation with left superior/middle temporal gyri.Conclusions: The findings suggest that impairments in cognitive function in TLE patients are reflected in the intrinsic functional organization of the brain as measured by ICC. Impairments of verbal learning and naming in TLE patients showed alterations in dominant temporal lobe structures while non-verbal learning abnormalities were associated with changes in non-dominant temporal structures, in agreement with the previous knowledge of memory and language networks.