One hertz stimulation to the corpus callosum quenches seizure development and attenuates motor map expansion

Novel Optogenetic Approaches in Epilepsy Research

Epilepsy is a major neurological disorder characterized by repeated seizures afflicting 1% of the global population. The emergence of seizures is associated with several comorbidities and severely decreases the quality of life of patients. Unfortunately, around 30% of patients do not respond to first-line treatment using anti-seizure drugs (ASDs). Furthermore, it is still unclear how seizures arise in the healthy brain. Therefore, it is critical to have well developed models where a causal understanding of epilepsy can be investigated. While the development of seizures has been studied in several animal models, using chemical or electrical induction, deciphering the results of such studies has been difficult due to the uncertainty of the cell population being targeted as well as potential confounds such as brain damage from the procedure itself. Here we describe novel approaches using combinations of optical and genetic methods for studying epileptogenesis. These approaches can circumvent some shortcomings associated with the classical animal models and may thus increase the likelihood of developing new treatment options.

Deep brain stimulation for epilepsy

Deep brain stimulation for seizures has been applied to cerebellum, caudate, locus coeruleus, subthalamic nucleus, mammillary bodies, centromedian thalamus, anterior nucleus of thalamus, hippocampus and amygdala, hippocampal commissure, corpus callosum, neocortex, and occasionally to other sites. Animal and clinical studies have primarily investigated seizure prevention and, to a lessersmaller extent, seizure interruption. No studies have yet shown stimulation able to cure epilepsy. A wide variety of stimulation parameters have been employed in multiple different combinations of frequencies, amplitudes, and durations. Literature review identifies at least 52 clinical studies of brain stimulation for epilepsy in 817 patients. Two studies were large, randomized, and controlled, one in the anterior nucleus of thalamus and another at the cortical or hippocampal seizure focus; both of these studies showed efficacy and tolerability of stimulation. Many questions remain. We do not know the mechanisms, the best stimulation parameters, the best patient population, or how to predict benefit in advance. We do not know why benefit of neurostimulation for epilepsy seems to increase over time or whether there are long-term deleterious effects. All of these questions may be answerable with a combination of laboratory research and clinical experience.

Neocortical movement representations are reduced and reorganized following bilateral intrastriatal 6-hydroxydopamine infusion and dopamine type-2 receptor antagonism

The neurophysiologic model of Parkinson's disease predicts nigrostriatal dopamine depletion leads to increased inhibitory basal ganglia output resulting in frontal neocortical hypoactivity. The nature of this hypoactivation is not well understood and modeled predominantly by a unilateral representation. Intracortical microstimulation (ICMS) was used to probe topographic movement representations of the left forelimb motor area 2 weeks following sham, unilateral left hemisphere or bilateral intrastriatal 6-hydroxydopamine (6-OHDA) infusion and under acute dopamine receptor antagonism with haloperidol in non-lesioned rats. 6-OHDA infusions induced a significant loss of substantia nigra pars compacta (SNc) dopamine neurons. Bilateral SNc lesions and haloperidol significantly reduced map area which was preserved in unilateral lesions. All lesion conditions and haloperidol induced significant map reorganization, characterized by increased representation of distal forelimb movements. Results suggest basal ganglia dopamine deficiency can affect the topographic organization of sensorimotor neocortex and lead to significant reduction in the size of motor representations. We conclude that the neurophysiologic model is supported but that bilateral loss of dopamine is required to see a reduction in the size of motor maps.