P84. High-frequency anterior thalamus stimulation interrupts cortical midline theta rhythm during drowsiness in an epileptic patient. Issue 8 (August 2015) - Bucurenciu, I.
Abstract Deep brain stimulation (DBS) of anterior thalamic nuclei (ANT) reduces frequency and intensity of epileptic partial and secondarily-generalized seizures. However, exact mechanisms of action and the effects of ANT-DBS on cortical activity are unknown. Recently, we demonstrated in one of our patients who had non-lesional epilepsy the correlation of ANT-DBS with bilateral frontal epileptic patterns (Bucurenciu et al., 2014). We report the case of a 27-years old male epileptic patient with dyscognitive focal seizures, due to a left-hemispheric inoperable lesion, interpreted as focal cortical dysplasia and polymicrogyria, comprising the upper temporal lobe, the insula and the entire parietal lobe. At the age of 25, quadripolar DBS-electrodes (Model 3389, Medtronic®, Minneapolis, MN, USA), connected to a subclavicular dual-channel programmable stimulation device (Activa PC, Medtronic®), were stereotactically implanted in both ANTs. The stimulation parameters were 5 V and 5.5 V, 180 Hz, 150 μs pulse width, cycling mode with 1min on/3min off. Stimulation on-phases were identified based on periodical reduction of QRS-complex-amplitudes in electrocardiograms. A 20% reduction of seizure frequencies with no side effects were reported after initiation of ANT-DBS. In several long-term EEGs of the patient, prominent non-specific midline-theta frontal rhythms of uncertain significance were observed during drowsiness. During bilateral stimulation via the most upper (superior-lateral) electrode-contacts (3 and 11) a reliable interruption of midline-theta rhythm was observed in EEGs, density-spectral-arrays and power-spectra, similarly to the effect of activating the patient. When the lowest (inferio-medial) electrode contacts (0 and 8) were used for stimulation the midline-theta rhythm was less affected. Other cortical rhythms, such as occipital-alpha or sleep-spindles, were only unspecifically reduced in amplitude by stimulation of both the most upper and the lowest contact-pairs, respectively. The contact-specificity and the selective inhibition of midline-theta rhythm, associated with changes of the power-spectra shape, prove that the observed EEG-amplitude reduction during stimulation is a real desynchronization of midline-theta rhythm and not an artefact. This is the first direct proof of an acute, electrode-contact specific influence of high-frequency ANT-DBS with standard stimulation-parameters on a cortical rhythm and might be relevant for epilepsies involving frontal cortical regions.