Abstract
SummaryPurposeIn patients with left temporal lobe epilepsy (TLE) due to hippocampal sclerosis (HS) decreased naming ability is common, suggesting a critical role for the medial left temporal lobe in this task. We investigated the integrity of language networks with functional MRI (fMRI) in controls and TLE patients.Experimental designWe performed an fMRI verbal fluency paradigm in 22 controls and 66 patients with unilateral mesial TLE (37 left HS, 29 right HS). Verbal fluency and naming ability were investigated as part of the standard presurgical neuropsychological assessment. Naming ability was assessed using a visual confrontation naming test.ResultsLeft TLE patients had significantly lower naming scores than controls and those with right TLE. Right TLE patients performed less well than controls, but better than those with left TLE. Left TLE had significantly lower scores for verbal fluency than controls.In controls and right TLE, left hippocampal activation during the verbal fluency task was significantly correlated with naming, characterised by higher scores in subjects with greater hippocampal fMRI activation. In left TLE no correlation with naming scores was seen in the left hippocampus, but there was a significant correlation in the left middle and inferior frontal gyri, not observed in controls and right TLE. In left and right TLE, out of scanner verbal fluency scores significantly correlated with fMRI activation for verbal fluency in the left middle and inferior frontal gyri.ConclusionGood confrontation naming ability depends on the integrity of the hippocampus and the connecting fronto-temporal networks. Functional MRI activation in the left hippocampus during verbal fluency is associated with naming function in healthy controls and patients with right TLE. In left TLE, there was evidence of involvement of the left frontal lobe when naming was more proficient, most likely reflecting a compensatory response due to the ongoing epileptic activity and/or underlying pathology.
Highlights
Temporal lobe epilepsy (TLE) is commonly associated with impairment in cognitive function, in particular memory and language function
There was a significant difference in naming scores between controls, left and right TLE patients, with patients showing significantly lower scores than controls (ANOVA left: p < 0.001; right: p < 0.001, Bonferroni corrected for multiple comparisons) and left TLE patients demonstrating significantly lower naming scores than right TLE patients (ANOVA p < 0.01, Bonferroni corrected for multiple comparisons)
There was no significant correlation between age of epilepsy onset and naming test scores in left or right TLE patients
Summary
Temporal lobe epilepsy (TLE) is commonly associated with impairment in cognitive function, in particular memory and language function. The impairment of language function in patients with TLE in contrast is less well understood. Up to 40% of patients with TLE and a speech dominant focus have a clinically significant deficit in naming abilities (Bell et al, 2003; Loring et al, 1994) which is often aggravated following anterior temporal lobe resection (ATLR) of the language dominant hemisphere (Davies et al, 1998). FMRI studies using simple phonemic verbal fluency paradigms reliably lateralise language dominance in healthy controls and TLE patients by showing left frontal lobe activation corresponding to Broca’s area, and less prominent activation in the medial temporal lobes (Friedman et al, 1998; Phelps et al, 1997)
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