A. Del Felice

13. Cortical modularity breakdown in the epileptic brain

Sleep and deprivation of it are known methods to increase the yield of epileptic abnormalities. Whereas neurophysiological mechanisms underlying discharges increase were suggested, less is known of the topographical distribution patterns in wake and sleep. We compared interictal epileptic discharges (IEDs) scalp distribution using 256-channels EEG recordings in wake and sleep in people with pharmaco-resistant temporal lobe epilepsy (TLE). 14 adults with Right TLE, identified through clinical data, 3T-MRI, PET and electrical source imaging, recorded during a daytime-nap were included. IEDs were identified in wake and S2. A mean of 21 IEDs in wake and 39 in sleep were selected ( p =0.024) and processed to obtain the averaged spike. Digital signals from the averaged wake traces were then subtracted to the sleep ones (Geodesic-EGI, Oregon, USA) and a t -test between the two conditions run. Single subjects traces localized IEDs over the right temporal regions (rare zygomatic projection), topographically more circumscribed in sleep. EEG digital subtraction showed higher amplitude IEDs limited to the temporal mesio-posterior right areas, with a dipole inversion over the contralateral zygomatic leads. Student t -test confirmed a statistically significant signal increase over the same topographic region, with a slight posterior shift on temporal leads ( p =0.039). This is the first report of a progressive breaking up of cortical modularity during sleep, even S2 stage, in a pathologically hyperactive brain. A similar phenomenon has been previously described (Massimini et al., 2005) using TMS during sleep in healthy subjects. Our data exploit naturally occurring interfering stimuli (IEDs) in a naturally sleeping epileptic brain, demonstrating how they reverberate differently in sleep and in wake, with a sleep related amplitude increase. Interestingly, such phenomenon tends to be constrained to a cortical area partially overlapping with the waking one, as to point to the progressive disconnection of integrated areas.

P 152. Phosphene threshold and 256 channels EEG in MCI patients as a measure of cognitive decline

Question Since phosphene has been considered as a measure of cortical excitability (Brigo et al., 2012; Abrahamyan et al., 2011) and EEG is a measure of the brain rhythms development in MCI (Mild Cognitive Impairment) patients (Babiloni et al., 2011), it has been described the correlation between motor and phosphene threshold compared with alpha posterior rhythms amplitude. The Aim of the study was to correlate the phosphene threshold with the alpha posterior rhythms in patients affected by MCI who were involved in a cognitive decline. Methods A single pulse TMS stimulation (MX6000 Transcranial Magnetic Stimulator. Ates Biomedica Italy) was performed for each patient on the occipital right and left cortex. The frequency of stimulation was administered randomly. We marked stimulation sites on posterior regions as O1, O2 and OZ and P3, P4 positions. The Focal coil (figure of eight) was handled in a vertical position. Each patient was trained to say if he would have some bright sensation on his eyes i.e. phosphene. The basic stimulation was set at 30% of the simulators output increasing it at rates of 10% until 100% considered as maximum. A resting state 256 channels EEG was performed in order to evaluate the alpha brain activity of each patient. Results Only 20% (5 patients) saw phopshenes. Two of them at low intensity (46% stimulators output), 3 of them at high intensity (90–100% stimulators output). All our controls presented a phosphene threshold of 60–70% with motor threshold of 40–50% showing always a difference of 20% in the stimulators output between the former and latter.Most of the patients presented a borderline pathological EEG dealing with decrease of alpha brain rhythms in occipital regions instead of a progressive spreading over the frontal areas, or in few cases an increase of theta rhythms over the temporal EEG derivations T3/T4; T5/T6. Conclusions In MCI patients phosphene threshold can be considered as a measure of visual cortical excitability. Only a small percentage of patients were involved in phosphene (20%) and the major of them with a high intensity output stimulators (60%), while the majority did not perceived any posphene. This finding is associated with a decrease in alpha rhythms and could be related to the degenerative involvement of cortical layers typical of such disease. These preliminary data suggest that changes in EEG rhythms associated with reduction of phosphene evoked by TMS could be a signature of cognitive decline.

PTMS5 How sleep and sleep deprivation modulate juvenile myoclonic epilepsy: a combined EEG TMS study

Results: The rMT and aMT mean values were significantly reduced when comparing half sine and biphasic stimulations to the monophasic stimulation. As MEP amplitude was greater with half sine and biphasic pulse, MEP onset latencies were lower. iSPT mean values were also significantly lower for half sine and biphasic pulses compared to monophasic pulses, whereas iSP frequency was greatly increased. Mean iSPOL values were significantly reduced for biphasic pulses only, with no change of iSPD, whereas TCT values remained within the same range. Conclusions: iSP parameters are affected by the TMS pulse waveform. Our results suggest that biphasic, more than monophasic and half sine TMS waveforms, seems to be more efficient in evoking the iSP.

PTMS20 Perturbational approach to sleep deprivation: an EEG TMS study

Objectives: To investigate inter-individual variation in the efficiency of BST with regard to the stimulation site. Methods: We studied 31 healthy subjects, using a right hand muscle as a recording site. Three stimulation sites were compared: BST over the inion (inion BST), and BST over the midpoint between the inion and the right (ipsilateral BST) or left (contralateral BST) mastoid process. Five suprathreshold BSTs were performed for each stimulation site using the same stimulation intensity. The mean peak-to-peak amplitudes of MEP were compared. The active motor threshold (AMT) and onset latency for inion BST and ipsilateral BST were also measured and compared. Results: Contralateral BST did not evoke discernible MEPs in most subjects. In 21 subjects (67.7%), ipsilateral BST elicited larger MEPs than inion BST, and AMT for ipsilateral BST was lower than or equal to the AMT for inion BST in all subjects. Ipsilateral BST elicited shorter latency in such subjects, when MEP amplitudes were adjusted. Conclusions: The suitable stimulation site for BST differed among subjects. About two-thirds showed larger MEP to ipsilateral BST. Efficient stimulation site needs to be searched before the main examination.