title: A network centred on the inferior frontal cortex is critically involved in levodopa-induced dyskinesias.
abstract: Levodopa-induced dyskinesias are disabling motor complications of long-term dopamine replacement in patients with Parkinson's disease. In recent years, several alternative models have been proposed to explain the pathophysiological mechanisms underlying this hyperkinetic motor disorder. In particular, our group has shed new light on the role of the prefrontal cortex as a key site of interest, demonstrating that, among other areas, the inferior frontal cortex is particularly characterized by altered patterns of anatomical and functional changes. However, how neural activity varies depending on levodopa treatment in patients with dyskinesias and whether the reported prefrontal abnormalities may have a critical role in dyskinesias is debated. To answer these questions we performed independent functional magnetic resonance imaging and repetitive transcranial magnetic stimulation studies. In the first experiment we applied resting state functional magnetic resonance imaging on 12 patients with Parkinson's disease with levodopa-induced dyskinesias and 12 clinically matched patients without dyskinesias, before and after administration of levodopa. Functional connectivity of brain networks in the resting state was assessed in both groups. We chose the right inferior frontal cortex as the seed region given the evidence highlighting the role of this region in motor control. In a second experiment, we applied different forms of repetitive transcranial magnetic stimulation over the right inferior frontal cortex in a new group of dyskinetic patients who were taking a supramaximal dose of levodopa, to verify the clinical relevance of this area in controlling the development of hyperkinetic movements. The resting state functional imaging analysis revealed that in patients with levodopa-induced dyskinesias connectivity of the right inferior frontal cortex was decreased with the left motor cortex and increased with the right putamen when compared to patients without levodopa-induced dyskinesias. This abnormal pattern of connectivity was evident only during the ON phase of levodopa treatment and the degree of such alteration correlated with motor disability. The repetitive TMS experiments showed that a session of continuous but not intermittent or sham theta burst stimulation applied over the inferior frontal cortex was able to reduce the amount of dyskinesias induced by a supramaximal single dose of levodopa, suggesting that this area may play a key role in controlling the development of dyskinesias. Our combined resting state functional magnetic resonance and transcranial magnetic stimulation studies demonstrate that pathophysiological mechanisms underlying levodopa-induced dyskinesias may extend beyond the 'classical' basal ganglia dysfunctions model, including the modulation performed by the neural network centred on the inferior frontal cortex.
authors.affiliation: 1 Consiglio Nazionale delle Ricerche, IBFM, 88100, Catanzaro, Italy a.cerasa@unicz.it g.koch@hsantalucia.it.
authors.forename: Antonio
authors.initials: A
authors.lastname: Cerasa
authors.affiliation: 2 Non-Invasive Brain Stimulation Unit, Neurologia Clinica e Comportamentale, Fondazione Santa Lucia IRCCS, Rome, Italy 3 Stroke Unit, Policlinico Tor Vergata, Rome, Italy a.cerasa@unicz.it g.koch@hsantalucia.it.
authors.forename: Giacomo
authors.initials: G
authors.lastname: Koch
authors.affiliation: 1 Consiglio Nazionale delle Ricerche, IBFM, 88100, Catanzaro, Italy.
authors.forename: Giulia
authors.initials: G
authors.lastname: Donzuso
authors.affiliation: 1 Consiglio Nazionale delle Ricerche, IBFM, 88100, Catanzaro, Italy.
authors.forename: Graziella
authors.initials: G
authors.lastname: Mangone
authors.affiliation: 4 Università degli studi 'Magna Graecia', Clinica Neurologica, 88100, Catanzaro, Italy.
authors.forename: Maurizio
authors.initials: M
authors.lastname: Morelli
authors.affiliation: 5 UOC Neurologia, Ospedale Sant'Eugenio, Rome, Italy.
authors.forename: Livia
authors.initials: L
authors.lastname: Brusa
authors.affiliation: 2 Non-Invasive Brain Stimulation Unit, Neurologia Clinica e Comportamentale, Fondazione Santa Lucia IRCCS, Rome, Italy 3 Stroke Unit, Policlinico Tor Vergata, Rome, Italy.
authors.forename: Mario
authors.initials: M
authors.lastname: Stampanoni Bassi
authors.affiliation: 2 Non-Invasive Brain Stimulation Unit, Neurologia Clinica e Comportamentale, Fondazione Santa Lucia IRCCS, Rome, Italy.
authors.forename: Viviana
authors.initials: V
authors.lastname: Ponzo
authors.affiliation: 2 Non-Invasive Brain Stimulation Unit, Neurologia Clinica e Comportamentale, Fondazione Santa Lucia IRCCS, Rome, Italy.
authors.forename: Silvia
authors.initials: S
authors.lastname: Picazio
authors.affiliation: 1 Consiglio Nazionale delle Ricerche, IBFM, 88100, Catanzaro, Italy.
authors.forename: Luca
authors.initials: L
authors.lastname: Passamonti
authors.affiliation: 1 Consiglio Nazionale delle Ricerche, IBFM, 88100, Catanzaro, Italy.
authors.forename: Maria
authors.initials: M
authors.lastname: Salsone
authors.affiliation: 1 Consiglio Nazionale delle Ricerche, IBFM, 88100, Catanzaro, Italy.
authors.forename: Antonio
authors.initials: A
authors.lastname: Augimeri
authors.affiliation: 2 Non-Invasive Brain Stimulation Unit, Neurologia Clinica e Comportamentale, Fondazione Santa Lucia IRCCS, Rome, Italy.
authors.forename: Carlo
authors.initials: C
authors.lastname: Caltagirone
authors.affiliation: 1 Consiglio Nazionale delle Ricerche, IBFM, 88100, Catanzaro, Italy 4 Università degli studi 'Magna Graecia', Clinica Neurologica, 88100, Catanzaro, Italy.
authors.forename: Aldo
authors.initials: A
authors.lastname: Quattrone
mesh_terms: D000368:Aged; D000978:Antiparkinson Agents / Q000009:adverse effects*; D004409:Dyskinesia, Drug-Induced / Q000503:physiopathology*; D004525:Efferent Pathways / Q000503:physiopathology; D005260:Female; D006801:Humans; D007980:Levodopa / Q000009:adverse effects*; D008297:Male; D008875:Middle Aged; D009483:Neuropsychological Tests; D017397:Prefrontal Cortex / Q000503:physiopathology*; D013826:Theta Rhythm / Q000187:drug effects; D050781:Transcranial Magnetic Stimulation
chemical_list: D000978:Antiparkinson Agents; D007980:Levodopa
keywords: Parkinson’s disease; TMS; inferior frontal cortex; levodopa-induced dyskinesias; resting state functional MRI