Abstracts

Rationale: Electrodermal activity (EDA) reflects sympathetic activation within the autonomic nervous system. Activity within prefrontal cortices and limbic structures strongly influence ipsilateral EDA (Critchley HD Neuroscientist 2002;8:132-42). This relationship suggests that unilateral dysfunction of cortical activity may affect the direction of EDA lateralization. We hypothesized that hemispheric location of seizure onset in patients with epilepsy may be related to ipsilaterally increased sympathetic skin response as evidenced by EDA asymmetry. Methods: EDA of 22 patients undergoing long-term video/EEG monitoring were recorded continuously from the ventral side of bilateral distal forearms using custom-built skin conductance sensors for 1-4 days. EDA recordings were lowpass filtered (1024 points, Hamming window, cutoff 0.016 Hz) to obtain skin conductance levels (SCL). Right/left differences were calculated in order to determine f_R>L, the frequency of right-sided EDA lateralization (R > L), f_L>R, the frequency of left-sided EDA lateralization (L > R) and f_R=L, the frequency of EDA symmetry (R = L). Differences less than 0.05 μS were considered as R = L. The frequency of right/left EDA lateralization was compared within patients with a right (n = 6) and left-sided (n = 12) irritative zone or seizure onset zone respectively. To examine the role of handedness on EDA lateralization, the frequency of right/left EDA lateralization was also compared within both right (n = 13) and left-handed (n = 3) patients (handedness of 2 patients was unknown). Statistics were computed with MATLAB using the Wilcoxon rank sum test. Results: 18 patients (11 males, 7 females) between ages 4-20 years with unilateral irritative zone or unilateral seizure onset on scalp EEG as determined by long-term video/EEG monitoring were included. 13 patients were right-handed, 3 were left-handed, and in 2 handedness was undetermined. There were 12 and 6 patients with a left and right-sided ictal onset/irritative zone respectively. For patients with a left-sided seizure onset zone or irritative zone, the mean f_R>L (0.43 ± 0.23) was not significantly different from the mean f_L>R (0.46 ± 0.23). However, for patients with a right-sided seizure onset, the mean f_R>L (0.58 ± 0.22) was higher than the mean f_L>R (0.28 ± 0.20) (p < 0.05). Neither right nor left-handed patients nor patients with right or left MRI lesions displayed significantly different frequency of right/left EDA lateralization.