title: Chemosensory processing in children with attention-deficit/hyperactivity disorder.
abstract: BACKGROUND
  In attention-deficit/hyperactivity disorder (ADHD) not only deficits in dopamine-related cognitive functioning have been found but also a lower dopamine-sensitive olfactory threshold. The aim of the present study was to proof that only olfactory but not trigeminal sensitivity is increased in ADHD. Structural magnetic resonance imaging (MRI) was used to show increased olfactory bulb (OB) volume- a structure which is strongly shaped by olfactory performance through the mechanism of neuroplasticity (e.g. synaptogenesis). To elucidate whether cortical mechanisms are involved in altered olfaction in ADHD, functional MRI (fMRI) was introduced.
  
  
  METHODS
  A total of 18 boys with ADHD and 17 healthy controls (aged 7-12) were included in the study. Olfactory as well as trigeminal detection thresholds were examined. OB sizes were measured by means of structural MRI and an analysis of effective functional (fMRI) coupling of primary olfactory cortex was conducted. The frontal piriform cortex (fPIR) was chosen as seed region because of its importance in processing both trigeminal and olfactory stimuli as well as having profound influence on inner OB-signaling.
  
  
  RESULTS
  Increased olfactory sensitivity as well as an increase in OB volume was found in ADHD. There were no group differences in sensitivity towards a trigeminal stimulus. Compared to healthy controls, the fPIR in ADHD was more positively coupled with structures belonging to the salience network during olfactory and, to a lesser extent, during trigeminal stimulation.
  
  
  CONCLUSIONS
  Olfactory functioning is superior in subjects with ADHD. The observed increase in OB volume may relate to higher olfactory sensitivity in terms of neuroplasticity. During the processing of chemosensory stimuli, the primary olfactory cortex in ADHD is differently coupled to higher cortical structures which might indicate an altered top-down influence on OB structure and function.
authors.affiliation: Department of Child and Adolescent Psychiatry and Psychotherapy, University Hospital Schleswig-Holstein, Niemannsweg 147, 24105, Kiel, Germany. Electronic address: anna.lorenzen@med.uni-tuebingen.de.
authors.forename: Anna
authors.initials: A
authors.lastname: Lorenzen
authors.affiliation: Department of Child and Adolescent Psychiatry and Psychotherapy, University Hospital Schleswig-Holstein, Niemannsweg 147, 24105, Kiel, Germany. Electronic address: deborahscholz@outlook.de.
authors.forename: Deborah
authors.initials: D
authors.lastname: Scholz-Hehn
authors.affiliation: Department of Child and Adolescent Psychiatry and Psychotherapy, University Hospital Schleswig-Holstein, Niemannsweg 147, 24105, Kiel, Germany. Electronic address: c.d.wiesner@zip-kiel.de.
authors.forename: Christian D
authors.initials: CD
authors.lastname: Wiesner
authors.affiliation: Department of Neuroradiology, University Hospital Schleswig-Holstein, Arnold- Heller-Str. 3, 24105, Kiel, Germany. Electronic address: s.wolff@neurorad.uni-kiel.de.
authors.forename: Stephan
authors.initials: S
authors.lastname: Wolff
authors.affiliation: Department of Neurology & Stroke, and Hertie Institute for Clinical Brain Research, University of Tübingen, Ottfried-Müller-Str. 25, 72076, Tübingen, Germany; Institute for Medical Psychology and Behavioral Neurobiology, University of Tübingen, Ottfried-Müller-Str. 25, 72076, Tübingen, Germany; Institute of Psychology, Christian-Albrechts University of Kiel, Olshausenstr. 62, 24118, Kiel, Germany. Electronic address: til.bergmann@uni-tuebingen.de.
authors.forename: Til O
authors.initials: TO
authors.lastname: Bergmann
authors.affiliation: Department of Nuclear Medicine, University Hospital, Kerpenerstr. 62, 50937, Cologne, Germany; Department of Neurology, University Hospital, Kerpenerstr. 62, 50937, Cologne, Germany. Electronic address: thilo.van-eimeren@uk-koeln.de.
authors.forename: Thilo
authors.initials: T
authors.lastname: van Eimeren
authors.affiliation: Department of Child and Adolescent Psychiatry and Psychotherapy, University Hospital Schleswig-Holstein, Niemannsweg 147, 24105, Kiel, Germany. Electronic address: luisa.lentfer@gmail.com.
authors.forename: Luisa
authors.initials: L
authors.lastname: Lentfer
authors.affiliation: Department of Child and Adolescent Psychiatry and Psychotherapy, University Hospital Schleswig-Holstein, Niemannsweg 147, 24105, Kiel, Germany. Electronic address: lioba.baving@uksh.de.
authors.forename: Lioba
authors.initials: L
authors.lastname: Baving
authors.affiliation: Department of Child and Adolescent Psychiatry and Psychotherapy, University Hospital Schleswig-Holstein, Niemannsweg 147, 24105, Kiel, Germany. Electronic address: a.prehn@zip-kiel.de.
authors.forename: Alexander
authors.initials: A
authors.lastname: Prehn-Kristensen
mesh_terms: D000293:Adolescent; D001289:Attention Deficit Disorder with Hyperactivity / Q000150:complications* / Q000000981:diagnostic imaging*; D002648:Child; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D000857:Olfaction Disorders / Q000209:etiology*; D009830:Olfactory Bulb / Q000000981:diagnostic imaging*; D066194:Olfactory Cortex / Q000000981:diagnostic imaging*; D010100:Oxygen / Q000097:blood; D012684:Sensory Thresholds / Q000502:physiology
chemical_list: D010100:Oxygen
keywords: ADHD; Olfactory bulb; Olfactory processing; Sensory threshold; Trigeminal processing; fMRI