gms | German Medical Science

Objective: To avoid neurologic dysfunction after surgery in eloquent areas we performed a preoperative fMRI measurement during language tasks. The cortical areas activated with speech-related paradigms are displayed in the navigation system during surgery. We also examined memory function to avoid memory loss due to surgery. Memory was separated into retrograde and anterograde memory. In retrograde memory, different parts of memory content can be distinguished. Besides episodic or autobiographic memory, which summarizes all sensations which were experienced during some time by the patient himself with his senses, there are memory entities, which are separated from a distinct experience, and specified in an abstract sense and called factual knowledge.

Methods: We conducted fMRI and MEG measurements of verbal memory. We examined episodic, short time and long time memory and memory of factual knowledge. In 68 patients, memory activity was localized with MEG and in 138 patients fMRI was measured with paradigms which engage verbal memory. Factual knowledge could be localized by fMRI in 53 patients. Paradigms used are capital cities of countries and multiplication tables. MEG measurements were carried out with a 2x37 channel biomagnetic system (Magnes II, 4-D Neuroimaging). Localization was performed by 1-dipole fit or beam former algorithm. For fMRI we used a 1.5 T MR scanner with echo planar imaging (Sonata, Siemens Medical Solutions) and a block paradigm with 180 measurements in 6 blocks (rest alternating with activation, 25 slices, 3 mm thickness & resolution TR=2470, TE=60). In addition we studied 11 patients with surgery close to or within the parahippocampal gyrus. In these we conducted testing of factual knowledge.

Results: Differentiated memory areas were separately localized in the dominant hippocampus during memorizing or remembering words with MEG and only in 10% of patients with fMRI. During memory testing, factual knowledge activity is found in the dominant parahippocampal gyrus lateral to the mesencephalon.

Conclusions: Localization of hippocampal memory activity is a useful tool for deciding whether the hippocampus can be resected. An area in the parahippocampal gyrus is essential for remembering factual knowledge. Resection of this area of the parahippocampal gyrus leads to distortion of factual knowledge, even if the hippocampus is spared. Localization of memory and use during navigation are thus useful tools to avoid memory loss.