Abstract
Purpose
The site specific effects of two different types of electrical stimulation of the thalamus on electroencephalic epileptic activity as generated in the cortico-thalamo-cortical system were investigated in genetic epileptic WAG/Rij rats, a well characterized and validated absence model.
Methods
First, 12 male rats received low frequency (double-pulse pairs of 2.5 Hz, 150 μA intensity and 30 s inter-pair-interval) open-loop stimulation to either the Ventral-Postero-Medial (VPM) or the Anterior Thalamic Nucleus (ATN) for 8 h. Second, rats received high frequency (130 Hz, pulse train of 1 s) closed-loop stimulation applied to either VPM or ATN whenever a spike-wave discharge (SWD) was automatically detected.
Results
Low frequency stimulation induced 8 Hz SWD-like afterdischarges (AD). AD were frequently seen in VPM but rarely in ATN stimulated rats. AD, recorded in cortex and thalamus, showed a strong temporal coherence (visually assessed) and opposite spike polarities. Properties of AD and spontaneous SWD were equally affected by the stimulation. Closed-loop high frequency stimulation disrupted spontaneous SWD with no difference between ATN and VPM stimulated rats. 89% of SWD could be disrupted leading to a decrease in average SWD duration from 9 to 1.5 s.
Conclusion
Low frequency stimulation induced AD, which strongly mimic SWD. Moreover, the effects were site-specific. High frequency thalamic stimulation disrupts ongoing SWD probable by interfering with the slow firing pattern of cortico-thalamo-cortical neurons seen during SWD cycle. The absence of stimulation site specificity for high frequency stimulation might be due to the fact that stimulation only started on average 1 s after SWD onset when SWD are already fully expressed in the bidirectional cortico-thalamo-cortical resonance system.
