Episodic memory in left temporal lobe epilepsy: a functional MRI study

Left medial temporal lobe epilepsy (MTLE) is associated with verbal memory impairment usually related to hippocampal damage. We used functional MRI (f MRI) to investigate the patterns of functional activity in healthy voluntee rs and MTLE patients engaged in verbal episodic memory tasks to look for ev idence of a reallocation of verbal memory in epileptic patients. fMRI data were collected from seven MTLE patients with left-sided hippocampal scleros is and 10 healthy right-handed control subjects on a 3T scanner. Subjects w ere instructed to learn a list of 17 words (encoding) and then to recall th em (retrieval) on successive trials. Healthy volunteers and patients both e xhibited bilateral activation (right higher than left) of the parahippocamp al gyrus during the retrieval. This effect was more marked in the control s ubjects. In contrast to the control subjects, patients exhibited consistent and extensive left prefrontal activations in all the memory tasks. These f indings show that verbal memory tasks did not involve the same functional p atterns in patients and healthy volunteers. This may be interpreted as a dy sfunctional response due to the epilepsy and left hippocampal sclerosis, an d could reflect the early onset and progressive course of the disease.