The synapsins are a phosphoprotein family located in nerve terminals where they are involved in synaptic vesicle trafficking. Synapsin I/II double knock-out mice (DKO-mice) develop sensory provoked seizures previously described as grand mal like attacks with arched backs, inability to stay upright and post-seizure grooming. The animals show no other behavioral abnormalities or any gross anatomical deficiencies. At a cellular level, the mice appear functionally normal except for some deviant properties of synaptic short- term plasticity. It has generally been assumed that the synapsins are present in all nerve terminals in the brain, but studies of thalamocortical circuitry (Kielland et al. 2006) have demonstrated a lack of synapsin I/II in terminals of primary afferents to thalamocortical neurons. In this study we made simultaneous behavioral observations (video recordings), and electrophysiological registrations of cortical EEG and thalamic field potentials of awake, freely moving DKO-mice. Seizure morphology show a much greater variance than previously reported, with pronounced orofacial, forelimb and combined orofacial/forelimb myoclonies. Myoclonic phases occur alongside low-frequency spike-wave EEG complexes in synchrony with large-amplitude thalamic field potentials, suggesting a role for the thalamocortical circuitry in the myoclonic pathophysiology. The neuronal mechanisms of myoclonies in man are largely unknown, and to our knowledge no murine model for such epilepsies is available today. With its varied myoclonic seizures, its well-defined genetic defect, and its specific deviation of synaptic transmission, the DKO-mouse may be a valuable tool in the study of myoclonic epilepsies. Reference: Kielland, A., et al. 2006. Journal of Neuroscience 26, 5786–93.