Double Dissociation of Parahippocampal and Amygdalar fMRI Activation in Patients with Mesial Temporal Lobe Epilepsy

Functional MRI of limbic mesial temporal lobe structures may help to tailor epilepsy surgery in patients with refractory mesial temporal lobe epilepsy (MTLE). We have shown earlier that fMRI well lateralizes the side of MTLE by activation of the parahippocampal gyri. In addition, information about the integrity or dysfunction of the amygdala may influence the decision about the anterior extension of the resection. The amygdala is involved in several processes like emotion, memory enhancement, attention modulation and social cognition. Although only in a minority of surgical patients, postoperative deficits in social and emotional cognition and behavior occur. Five male patients (aged 25–45 years) with refractory MTLE (3 left) were investigated. Three patients had hippocampal sclerosis, the others a neoplasia or cavernoma. We measured (i) language-related activity by a verbal fluency task, (ii) parahippocampal activity by Roland's Home Town Walking Task, and (iii) amygdala activity. Amygdala activation was induced by presentation of scenes from movies showing animated fearful faces. This paradigm was validated in 15 healthy controls showing bilateral amygdala activation (p<0.001). Reproducibility was demonstrated by restudying 6 of the control subjects. All patients had activated left hemisphere regions during a verbal fluency task and demonstrated significant parahippocampal and amygdala activity. In 3 patients contralateral amygdalar and parahippocampal activity was higher compared to ipsilateral activity. In one patient with right-sided MTLE and questionable hippocampal sclerosis, a comparable activity of both amygdala was detected while parahippocampal activity was asymmetrical corresponding to the side of MTLE. In one patient with left-sided MTLE and a paraamygdala neoplasia, only contralateral activity of the amygdala was detected while parahippocampal activity was symmetrical. In 3 out of 5 patients parahippocampal and amygdalar activity were asymmetrical corresponding to the side of MTLE. Two patients demonstrated a double dissociation of amygdala and parahippocampal activation. In patients with MTLE, the use of two simple paradigms allows an individual dissociation of amygdalar and parahippocampal activation within MTL structures. The prognostic value of this information for surgery and counselling of patients has to be evaluated in prospective studies. Studies of limbic mesial temporal lobe structures may help to tailor epilepsy surgery in patients with refractory MTLE.