Brain Mapping of Episodic Memory in Patients with Medial Temporal Lobe Epilepsy Using Activation Positron Emission Tomography

ABSTRACT

BACKGROUND: We aimed to study the regional cerebral PET activation patterns during memory tests in medial temporal lobe epilepsy (mTLE) patients and to see whether the activation study could lateralize memory dominance. METHODS: Participants included 6 right mTLE patients, 6 left mTLE patients, and 6 controls. Language was dominant in the left hemisphere in all the participants. PETs were performed while presenting a set of 30 line drawings of com-mon objects with 4 second intervals between each drawing. After 30 minutes, PETs were repeated while presenting a set of drawings with half of the obejcts changed. RESULTS: During the encoding, activated areas were dispersed in mTLE in the superior frontal gyrus, the primary sensory cortex, the premotor area, the supramarginal and angular gyri ipsilaterally or contralaterally, in addition to the inferior and middle frontal gyri activated in the controls. During the retrieval, activated areas were localized in the bilateral inferior frontal gyri and the right medial temporal area in the controls, but also in the premotor area, the primary sensory cortex, and the angular gyrus in mTLE. In the encoding and also in the retrieval, the activated fields of the prefrontal areas contralateral to the epileptogenic zone became wider compared to the controls and those ipsilateral to the epileptogenic zone became smaller. CONCLUSIONS: Cortical areas involved in the encoding and retrieval of the episodic memory are dispersed and contralaterally lateralized to the epileptogenic zone. Lateralization is most prominent in the prefrontal areas.