Introduction: It is well known that epilepsy is likely to cause atypical language organization and this phenomenon is clinically relevant in the epilepsy surgery to spare the language function. The purpose of this study is to investigate the precise definition of the connectivity associated with the reorganized language network in patients with temporal lobe epilepsy (TLE) using cortico-cortical evoked potential (CCEP), which reveals the brain networks.
Methods: Six patients with intractable TLE who underwent chronic intracranial electrode placement and revealed an atypical distribution of posterior language areas (Wernicke’s areas) were studied. Alternating 1 Hz electrical stimuli were delivered to the anterior language areas (Broca’s areas). CCEPs were recorded by averaging electrocorticograms time-locked to stimuli from the subdural electrodes. We calculated the root mean square (RMS) of CCEP responses between 10 and 300 ms (1 ms slide) to evaluate the distribution of the anterior–posterior language network. Thereafter, the posterior language areas identified by the electrical cortical mapping and CCEP distributions were compared.
Results: CCEP responses were observed in various areas within the temporal, temporo-parietal and temporo-occipital area, including the temporal pole, inferior temporal gyrus and temporo-occipital junction. The posterior language area was located within CCEP distribution in two patients, whereas parts of the language areas were outside CCEP-positive areas in four patients. In addition, larger CCEP responses were observed in the surrounding cortices rather than in posterior language areas in two patients.
Conclusions: Our results suggest that the posterior language areas can shift to the cortices within or outside the anterior–posterior language network. Language reorganization might be associated with a functional shift to the surrounding cortices outside of the anterior–posterior language network as well as re-routing the language network.
Patient Care: Although there is a limitation and discrepancy, This method can be used as approximate guide of language mapping.
Learning Objectives: 1. This is a cortical stimulaion study to investigate the language reorganization.
2. Language areas can be relocated outside of the anterior–posterior language network.
3. Language reorganization can be caused by functional shift to the surrounding areas.