title: Neurochemical Modulation in Posteromedial Default-mode Network Cortex Induced by Transcranial Magnetic Stimulation.
abstract: BACKGROUND
  The Default Mode Network (DMN) is severely compromised in several psychiatric and neurodegenerative disorders where plasticity alterations are observed. Glutamate and GABA are the major excitatory and inhibitory brain neurotransmitters respectively and are strongly related to plasticity responses and large-scale network expression.
  
  
  OBJECTIVE
  To investigate whether regional Glx (Glutamate + Glutamine) and GABA could be modulated within the DMN after experimentally-controlled induction of plasticity and to study the effect of intrinsic connectivity over brain responses to stimulation.
  
  
  METHODS
  We applied individually-guided neuronavigated Theta Burst Stimulation (TBS) to the left inferior parietal lobe (IPL) in-between two magnetic resonance spectroscopy (MRS) acquisitions to 36 young subjects. A resting-state fMRI sequence was also acquired before stimulation.
  
  
  RESULTS
  After intermittent TBS, distal GABA increases in posteromedial DMN areas were observed. Instead, no significant changes were detected locally, in left IPL areas. Neurotransmitter modulation in posteromedial areas was related to baseline fMRI connectivity between this region and the TBS-targeted area.
  
  
  CONCLUSIONS
  The prediction of neurotransmitter modulation by connectivity highlights the relevance of connectivity patterns to understand brain responses to plasticity-inducing protocols. The ability to modulate GABA in a key core of the DMN by means of TBS may open new avenues to evaluate plasticity mechanisms in a key area for major neurodegenerative and psychiatric conditions.
authors.affiliation: Department of Psychiatry and Clinical Psychobiology, Faculty of Medicine, University of Barcelona, Spain.
authors.forename: Dídac
authors.initials: D
authors.lastname: Vidal-Piñeiro
authors.affiliation: Department of Psychiatry and Clinical Psychobiology, Faculty of Medicine, University of Barcelona, Spain.
authors.forename: Pablo
authors.initials: P
authors.lastname: Martín-Trias
authors.affiliation: Medical Imaging Group, University of Barcelona, CIBER-BBN, Spain.
authors.forename: Carles
authors.initials: C
authors.lastname: Falcón
authors.affiliation: Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Spain; Neuroradiology Section, Radiology Service, Centre de Diagnòstic per la Imatge, Hospital Clinic de Barcelona, Spain.
authors.forename: Núria
authors.initials: N
authors.lastname: Bargalló
authors.affiliation: Department of Psychiatry and Clinical Psychobiology, Faculty of Psychology, University of Barcelona, Spain.
authors.forename: Imma C
authors.initials: IC
authors.lastname: Clemente
authors.affiliation: EMG Unit, Neurology Service, Hospital Clínic de Barcelona, Barcelona, Spain.
authors.forename: Josep
authors.initials: J
authors.lastname: Valls-Solé
authors.affiliation: Department of Psychiatry and Clinical Psychobiology, Faculty of Medicine, University of Barcelona, Spain; Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Spain.
authors.forename: Carme
authors.initials: C
authors.lastname: Junqué
authors.affiliation: Berenson-Allen Center for Noninvasive Brain Stimulation, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA; Institut Universitari de Neurorehabilitació Guttmann, Universitat Autònoma de Barcelona, Badalona, Spain.
authors.forename: Alvaro
authors.initials: A
authors.lastname: Pascual-Leone
authors.affiliation: Department of Psychiatry and Clinical Psychobiology, Faculty of Medicine, University of Barcelona, Spain; Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Spain. Electronic address: dbartres@ub.edu.
authors.forename: David
authors.initials: D
authors.lastname: Bartrés-Faz
mesh_terms: D063132:Connectome; D005260:Female; D018698:Glutamic Acid / Q000378:metabolism*; D006801:Humans; D008297:Male; D010296:Parietal Lobe / Q000378:metabolism / Q000502:physiology*; D013826:Theta Rhythm; D050781:Transcranial Magnetic Stimulation; D055815:Young Adult; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
chemical_list: D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid
keywords: Default-mode network; GABA; Magnetic resonance spectroscopy; Plasticity; Transcranial magnetic stimulation; fMRI connectivity