Abstracts

Rationale: Studies of evoked responses (visual and auditory) in patients with epilepsy have determined that these patients have longer cortical response latencies than other patient populations (Major, 2011). This investigation examines cortical response latencies to median nerve stimulation using magnetoencephalography. Prior research sample (Wikström et al., 1997) with a normal population identified primary somatosensory responses at 20, 35 and 60 ms. We sought to determine whether cortical response latencies would be different within a sample of patients with intractable epilepsy. Methods: Using planar gradiometers and working at the sensor level, 22 patients (mean age 26.8, 13 males) had median nerve stimulation as part of the clinical protocol for MEG. 4 members of the group had been indicated as having bilateral seizure loci while 8 were noted to have left hemisphere lateralization. Left and right median nerves were alternately stimulated at the wrist with the electrodes and voltage adjusted until a thumb twitch was elicited. Data were processed and analyzed with the BrainStorm software package and response latencies along with demographic information were entered into an SPSS database for analysis. Data from a control sample (Wikström et al., 1997) were used to compare latencies. Results: In this pilot study, intragroup analysis found a significant negative correlation between epilepsy duration and speed of cortical response in the left hemisphere; meaning that patients who had epilepsy longer had shorter response latencies. In addition, males had longer response latencies but not significantly so. There were no significant correlations with age, but the group is small and this was not to be expected. In contrast to expected latencies in a normal population, this sample differed significantly by having significantly shorter response latencies for the 20, 35 and 60 ms responses. Conclusions: Patients with intractable epilepsy show a difference in the speed with which information reaches the somatosensory cortex. Further research with a larger group could provide information regarding the effects of certain medications, age, gender, the degree to which seizure focus has an effect on cortical response and the influence of interictal activity on response latency.