Person: Ahmed, Omar Jamil
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Omar Jamil
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Ahmed, Omar Jamil
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Publication Finding synchrony in the desynchronized EEG: the history and interpretation of gamma rhythms(Frontiers Media S.A., 2013) Ahmed, Omar Jamil; Cash, SydneyNeocortical gamma (30–80 Hz) rhythms correlate with attention, movement and perception and are often disrupted in neurological and psychiatric disorders. Gamma primarily occurs during alert brain states characterized by the so-called “desynchronized” EEG. Is this because gamma rhythms are devoid of synchrony? In this review we take a historical approach to answering this question. Richard Caton and Adolf Beck were the first to report the rhythmic voltage fluctuations in the animal brain. They were limited by the poor amplification of their early galvanometers. Thus when they presented light or other stimuli, they observed a disappearance of the large resting oscillations. Several groups have since shown that visual stimuli lead to low amplitude gamma rhythms and that groups of neurons in the visual cortices fire together during individual gamma cycles. This synchronous firing can more strongly drive downstream neurons. We discuss how gamma-band synchrony can support ongoing communication between brain regions, and highlight an important fact: there is at least local neuronal synchrony during gamma rhythms. Thus, it is best to refer to the low amplitude, high frequency EEG as an “activated”, not “desynchronized”, EEG.Publication Mixed Effects of Deep Brain Stimulation on Depressive Symptomatology in Parkinson’s Disease: A Review of Randomized Clinical Trials(Frontiers Media S.A., 2014) Gökbayrak, N. Simay; Piryatinsky, Irene; Gavett, Rebecca A.; Ahmed, Omar JamilAlthough ~50% of patients with Parkinson’s disease (PD) experience depression, treatment for this important and debilitating comorbidity is relatively understudied. Deep brain stimulation (DBS) has been increasingly utilized for the management of tremors in progressive PD. Several preliminary studies have shown the potential benefit of DBS for non-motor PD symptoms such as depression. Here, we critically evaluate seven recent randomized clinical trials of the effectiveness of DBS in reducing depressive symptomatology among individuals with PD. Findings are mixed for the effectiveness of DBS as a treatment for depression in PD. Our review suggests that this is due, in large part, to the anatomical and methodological variation across the DBS studies. We provide a comprehensive discussion of these variations and highlight the need to conduct larger, more controlled studies aimed specifically at evaluating the treatment of depression in PD patients.Publication Inhibitory single neuron control of seizures and epileptic traveling waves in humans(BioMed Central, 2014) Ahmed, Omar Jamil; Kramer, Mark A; Truccolo, Wilson; Naftulin, Jason S; Potter, Nicholas S; Eskandar, Emad; Cosgrove, Garth R; Blum, Andrew S; Hochberg, Leigh; Cash, SydneyPublication A Biologically Constrained, Mathematical Model of Cortical Wave Propagation Preceding Seizure Termination(Public Library of Science, 2015) González-Ramírez, Laura R.; Ahmed, Omar Jamil; Cash, Sydney; Wayne, C. Eugene; Kramer, Mark A.Epilepsy—the condition of recurrent, unprovoked seizures—manifests in brain voltage activity with characteristic spatiotemporal patterns. These patterns include stereotyped semi-rhythmic activity produced by aggregate neuronal populations, and organized spatiotemporal phenomena, including waves. To assess these spatiotemporal patterns, we develop a mathematical model consistent with the observed neuronal population activity and determine analytically the parameter configurations that support traveling wave solutions. We then utilize high-density local field potential data recorded in vivo from human cortex preceding seizure termination from three patients to constrain the model parameters, and propose basic mechanisms that contribute to the observed traveling waves. We conclude that a relatively simple and abstract mathematical model consisting of localized interactions between excitatory cells with slow adaptation captures the quantitative features of wave propagation observed in the human local field potential preceding seizure termination.Publication Optogenetic Delay of Status Epilepticus Onset in an In Vivo Rodent Epilepsy Model(Public Library of Science, 2013) Sukhotinsky, Inna; Chan, Alexander M.; Ahmed, Omar Jamil; Rao, Vikram Ramnath; Gradinaru, Viviana; Ramakrishnan, Charu; Deisseroth, Karl; Majewska, Ania K.; Cash, SydneyEpilepsy is a devastating disease, currently treated with medications, surgery or electrical stimulation. None of these approaches is totally effective and our ability to control seizures remains limited and complicated by frequent side effects. The emerging revolutionary technique of optogenetics enables manipulation of the activity of specific neuronal populations in vivo with exquisite spatiotemporal resolution using light. We used optogenetic approaches to test the role of hippocampal excitatory neurons in the lithium-pilocarpine model of acute elicited seizures in awake behaving rats. Hippocampal pyramidal neurons were transduced in vivo with a virus carrying an enhanced halorhodopsin (eNpHR), a yellow light activated chloride pump, and acute seizure progression was then monitored behaviorally and electrophysiologically in the presence and absence of illumination delivered via an optical fiber. Inhibition of those neurons with illumination prior to seizure onset significantly delayed electrographic and behavioral initiation of status epilepticus, and altered the dynamics of ictal activity development. These results reveal an essential role of hippocampal excitatory neurons in this model of ictogenesis and illustrate the power of optogenetic approaches for elucidation of seizure mechanisms. This early success in controlling seizures also suggests future therapeutic avenues.