Abstracts

Rationale: Influence of amygdala lesion in the right hemisphere on higher brain functions among intractable temporal lobe epilepsy (TLE) patients has not drawn much attention because (a) the right hemisphere is not language dominant, and (b) the majority of TLE patients come with hippocampal sclerosis (HS). Since amygdala is supposed to be related to emotions, drives, and other functions such as olfaction and autonomic control, effects of amygdala lesion on higher brain functions have not yet been reported in detail with certainty. This study intends to clarify effects of amygdala lesion in non-language dominant hemisphere on higher brain functions among intractable TLE patients in comparison with HS.Methods: The study evaluated the psychometric properties of 11 adult TLE patients with right amygdala lesion, and 15 adult TLE patients with right HS. Pre-surgical examinations included prolonged video-EEG monitoring with sphenoidal electrodes, MRI scans, Iomazenil-SPECT, and Wada test. Higher brain functions were tested using Wechsler Adult Intelligent Scale-III (WAIS-III), and Wechsler Memory Scale-R (WMS-R).Results: The overall ability of the two groups of TLE patients, which included full scale IQ, fell within the average range of normal subjects. Although the patients of both groups underwent surgical treatment during similar range of age, the average age of onset was significantly higher in the amygdala lesion group (20.4) compared with HS group (12.8) (p<0.05). Mean values of Verbal Memory Index and Visual Memory Index of amygdala lesion group were higher than those in HS group. Verbal IQ (VIQ) of amygdala lesion group was 4.2 point lower than that of HS group, and Attention/Concentration Index was 5.1 point lower. Performance IQ (PIQ) of both groups appeared the same on average. (Figure 1) Scaled scores of Digit Span and Letter Number Sequencing (in working memory category) in amygdala lesion group were apparently lower than those of HS group. (Table 2) Conclusions: The influence of amygdala lesion in the right hemisphere on higher brain functions among intractable temporal lobe epilepsy (TLE) patients appeared not as an overall impairment, but as distinctively differentiated effects among aggregated capabilities. The effects varied depending on the functional details. The scaled score of Digit Span subtest in WAIS-III exhibited statistically significant difference from that of HS group. (p < 0.05) Although not being proved with statistical significance, the mean score of Block Design of amygdala lesion group appeared lower, while the mean scores of Picture Arrangement and Symbol Search of this group appeared higher than those of HS group. Tasks that require working memory, Digit Span in particular, are negatively affected by amygdala lesion, indicating that amygdala may play an important role in these specific functions as well as its well-known role in emotional processing. The result may also suggest that pre-surgical examination must pay closer attention to these functions to prevent impairment after surgery.