Abstracts

Rationale: The chromosome-20-Ring is a rare chromosomal disorder associated to epilepsy, arrest of mental development, and to a specific EEG pattern characterized by trains of theta waves bursts in fronto-temporal regions. To investigate the neural correlates of the theta waves bursts in Ring-20 syndrome simultaneous recording of EEG and fMRI was performed. EEG-fMRI is an innovative procedure that studies the hemodynamic changes happening to the brain in coincidence with EEG events, and it could be useful to recognize the epileptic network involved in this syndrome.Methods: Three patients with chromosome-20-Ring (aged 19, 32 and 61 years old) were investigated with EEG-fMRI co-registration (30-minutes long for patient n.1, 20-minutes long for patient n. 2 and n.3). EEG was inspected for bursts of sharp theta waves with bilateral midtemporal predominance, which represented the events of interest for the fMRI analysis. Scalp EEG was recorded by means of a 32 channels MRI-compatible EEG recording system (Micromed S.p.A, Italy). Functional data were acquired with a 3T Philips Achieva system (TR=3000 ms) from 30 axial contiguous 4 mm slices (64 x 64 matrix). Event-related analysis was performed on functional data with SPM5 software, using standard hemodynamic response function and its time-derivates. Events were represented as variable-duration blocks beginning at the onset of theta-bursts and ending upon their cessation. Motion realignment parameters were included as covariates of no interest. Results: Eight events were recorded in patient n. 1 (mean duration 2.4 seconds); nine in patient n. 2 (mean duration of 3.7 seconds); 39 events in the third patient (4.3 seconds). Events were always bilateral in distribution with a frequency peak around 5 Hz. EEG-related analysis showed increases of BOLD signal (p<0.001) in clusters localized in the pre-central and post-central gyri with a maximum significance on the left hemisphere. BOLD decreases (p<0.001) were observed bilaterally in the default mode network regions.Conclusions: Our results, even if in a small patients sample, underline the possible role of the sensory-motor cortex in the generation of theta waves trains in this chromosomal disorder. The increased BOLD signal in this region could represent a specific dysfunction of Ring-20 syndrome causing its peculiar EEG features. Finally, the deactivation of the brain s Default Mode Network in these patients is similar to that observed in relationship to interictal or ictal discharges in either generalized and focal epilepsies syndromes due to a suspension of the brain resting state caused by epileptiform activities.