Altered processing of visual memory in patients with mesial temporal sclerosis: an FMRI study.

Introduction: Hippocampal complex and neocortex play distinct, complementary roles in processing of memory, which is impaired in patients with mesial temporal sclerosis (MTS).

Method: Ten right-sided MTS patients and 10 controls were prospectively assessed by functional Magnetic Resonance Imaging (fMRI) using encoding and retrieval of visual memory tasks. Image analyses were done using SPM2 and voxels showing activity with T-score>4 were considered significant. Two-sample t-test was applied for equality of means and P<.01 was considered significant. Patterns of activity in both encoding and retrieval tasks were compared between the patients and controls.

Results: In normal controls, there was activation of bilateral tail of hippocampus, parahippocampal gyrus, occipital (right>left), right prefrontal, and inferior frontal region (T-score>9) during the encoding of memory and during the retrieval, there was activation of left inferior frontal region, bilateral parahippocampal gyrus, and occipital and parietal region (right>left) activity (T-score>4). In patients there was activation of bilateral prefrontal (left≫right), bilateral inferior parietal lobule (right≫left), and bilateral parieto-occipital lobe activity(T-score>4) during encoding and there was comparatively less activation (T-score>3) of bilateral inferior parietal lobule (left≫right) and bilateral prefrontal (right≫left) regions during retrieval.

Conclusion: Visual memory processing is affected and altered in patients with MTS. Reallocation of visual memory processing is observed in patients with MTS suggesting different networking.