Abstracts

Naming disturbances may be caused by lesions in different dominant hemisphere regions, e.g., the temporal pole and the lateral temporal cortex. In left temporal lobe epilepsy (TLE), naming deficits have been often interpreted as lexical-semantic disturbances and have been usually associated with hippocampal sclerosis. On this basis, questions have been raised whether naming impairment consistently reflects semantic memory impairment and may be caused by temporal lobe lesions of different nature and location.
Eighty-two TLE patients with lateral (12 left, nine right) or mesial temporal lesions (30 left, 31 right) were compared with 35 healthy controls. Hippocampal sclerosis was determined in 16 left and 18 right TLE patients; low-grade gliomas, cavernous angiomas, and neural migration disorders were documented in the other patients. Picture naming (PN)required to name line-drawings of 40 living and 40 non-living things. Verbal and visual Pyramid and palm trees test (PPTT) assessed material-specific semantic memory.
Separate Mann-Whitney tests comparing left TLE patients and controls revealed significant deficits in the cortical lateral (PN: U=95, p=0.0047; verbal PPTT: U=129.5, p=0.015) and mesial lesion subgroups (PN: U=162, p=0.0003; verbal PPTT: U=372, p=0.018; visual PPTT: U=325.5, p=0.0059). Subsequent comparisons showed that left hippocampal sclerosis patients were impaired in all three tests (PN: U=162, p=0.0038; verbal PPTT: U=225, p=0.040; visual PPTT: U=190, p=0.012), while patients with other hippocampal lesions were only impaired in PPTT (verbal: U=126, p=0.031; visual: U=111, p=0.020). Compared to controls, right TLE patients with cortical lateral lesions were impaired in visual PPTT (U=78.5, p=0.013), whereas patients with mesial lesions did not show any deficits. In left TLE patients, PN scores were significantly related with PPTT scores.
The data suggest that left TLE associated with either lateral or mesial temporal lobe lesions may significantly affect naming and that naming deficits reflect semantic memory impairment. The association of naming deficits and material-specific semantic deficits with lateral temporal lobe lesions is in accord with the role played by the temporal cortex in semantic storage and retrieval. By contrast, the impairment of both verbal and visual semantic memory in patients with left mesial temporal lobe lesions suggests implication of particular left hippocampal functions (e.g., the processing of semantically meaningful verbal or visual stimuli). The significant naming impairment in patients with left hippocampal sclerosis (in contrast with normal performances in patients with other hippocampal lesions) suggests that this type of lesion plays a specific causal role: it could interfere with the functions of distant brain areas through hippocampal [ndash] cortical pathways involved in lexical retrieval, in line with its effects on other cortical cognitive functions.