Abstracts

Rationale: Pre-surgical functional mapping has become a regular tool in the planning of epilepsy surgeries. Magnetoencephalography (MEG) is now being used in a growing number of centers as a powerful tool for noninvasive cortical functional mapping. MEG has been proven to provide highly accurate localization of functions such as somatosensory, language, and motor control. However, when patients need sedation for the MEG procedures, functional mapping is limited by the patient’s inability to perform the necessary tasks. This is particularly true in pediatric cases, where young children or children with behavioral problems, may have difficulty being still for long periods of time. This has limited our ability to do noninvasive functional mapping in these cases. The field of rehabilitation has long used passive motor movements in its therapies to recover functional motor control. Research has shown that there is feedback from the peripheral motor system to the motor cortex. We hypothesized this feedback would make it possible for us to record responses to passive movements in the primary sensorimotor cortex. We present results of an ongoing evaluation of a method for mapping motor function, using passive movements, in children with seizures who were sedated during the motor mapping procedure. Methods: Three patients have undergone passive motor mapping, ranging in age from 3 to 6 years old. Sedation was achieved by giving 1.5 mcg/Kg of clonidine. Mapping began 45 min. after the clonidine was given. Sleep stage was confirmed using EEG. The task used to localize motor function involved having a technician manually manipulate the hand of the patient, using a fiber optic button device to signal each movement. A total of 250 passive movements were made. Data were filtered and averaged and the resulting evoked magnetic field waveform was analyzed using the equivalent current dipole model. To ensure reliability, the movements were also split and averaged separately. Each waveform was analyzed independently from the other and from the grand average. The source estimate of the peak of the response waveform was identified and plotted on an MRI image. Only the sources that were confirmed, temporally and spatially, by all three average waveforms were kept. Results: The localization of the motor cortex using this passive procedure has been compared to the results of cortical stimulation mapping in 2 of the patients. The stimulation mapping in these cases confirmed the localization by MEG. All of the patients who have undergone surgery to this point have no motor or somatosensory deficit and have been seizure free since their surgery. Conclusions: The successful surgical outcomes for the patients demonstrate clearly that it is possible to accurately localize the motor cortex in sedated patients using passive movements. This procedure greatly expands the utility of functional mapping with MEG for pediatric patients. Discussion of these results is in terms of the utility of this procedure in a pediatric setting and the mechanisms and pathways in the brain that make it possible to do passive mapping of the motor cortex.