title: Disrupted Saccadic Corollary Discharge in Schizophrenia.
abstract: Disruptions in corollary discharge (CD), motor signals that send information to sensory areas and allow for prediction of sensory states, are argued to underlie the perceived loss of agency in schizophrenia. Behavioral and neurophysiological evidence for CD in primates comes largely from the saccadic double-step task, which requires participants to make two visually triggered saccadic eye movements in brief succession. Healthy individuals use CD to anticipate the change in eye position resulting from the first saccade when preparing the second saccade. In the current study with human participants, schizophrenia patients and healthy controls of both sexes performed a modified double-step task. Most trials required a saccade to a single visual target (T1). On a subset of trials, a second target (T2) was flashed shortly following T1. Subjects were instructed to look directly at T2. Healthy individuals also use CD to make rapid, corrective responses following erroneous saccades to T1. To assess CD in schizophrenia, we examined the following on error trials: (1) frequency and latency of corrective saccades, and (2) mislocalization of the corrective (second) saccade in the direction predicted by a failure to use CD to account for the first eye movement. Consistent with disrupted CD, patients made fewer and slower error corrections. Importantly, the corrective saccade vector angle was biased in a manner consistent with disrupted CD. These results provide novel and clear evidence for dysfunctional CD in the oculomotor system in patients with schizophrenia. Based on neurophysiology work, these disturbances might have their basis in medial thalamus dysfunction.
  
  
  CONCLUSIONS
  According to the World Health Organization, acute schizophrenia carries more disability weight than any other disease, but its etiology remains unknown. One promising theory of schizophrenia highlights alterations in a sense of self, in which self-generated thoughts or actions are attributed externally. Disruptions in corollary discharge (CD), motor signals sent to sensory areas that allow for the prediction of impending sensations, are proposed to underlie these symptoms. Direct physiological evidence, however, is limited. In nonhuman primates, inactivation of mediodorsal thalamic neurons disrupts CD associated with eye movements. Using the same task, we show similar impairments in schizophrenia patients, consistent with disrupted CD. These findings allow us to link clinical phenomenology to primate neurophysiology and interpret findings within a biological framework.
authors.affiliation: Department of Psychology, Vanderbilt University, Nashville, Tennessee 37240, Department of Psychiatry, University Medical Center Utrecht, 3584 CX Utrecht, The Netherlands, k.n.thakkar@umcutrecht.nl sohee.park@vanderbilt.edu.
authors.forename: Katharine N
authors.identifier: http://orcid.org/0000-0002-0026-2030
authors.initials: KN
authors.lastname: Thakkar
authors.affiliation: Department of Psychology, Vanderbilt University, Nashville, Tennessee 37240, Center for Integrative Cognitive Neuroscience and Vanderbilt Vision Research Center, Vanderbilt University, Nashville, Tennessee 37240, and.
authors.forename: Jeffrey D
authors.identifier: http://orcid.org/0000-0002-5248-943X
authors.initials: JD
authors.lastname: Schall
authors.affiliation: Department of Psychology, Vanderbilt University, Nashville, Tennessee 37240, Center for Integrative Cognitive Neuroscience and Departments of Psychiatry and Radiology and Radiological Sciences, Vanderbilt University, Nashville, Tennessee 37232.
authors.forename: Stephan
authors.identifier: http://orcid.org/0000-0003-3601-9910
authors.initials: S
authors.lastname: Heckers
authors.affiliation: Department of Psychology, Vanderbilt University, Nashville, Tennessee 37240, Center for Integrative Cognitive Neuroscience and Departments of Psychiatry and k.n.thakkar@umcutrecht.nl sohee.park@vanderbilt.edu.
authors.forename: Sohee
authors.identifier: http://orcid.org/0000-0003-3797-4776
authors.initials: S
authors.lastname: Park
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001921:Brain / Q000473:pathology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009474:Neurons / Q000502:physiology*; D015835:Ocular Motility Disorders / Q000209:etiology*; D010775:Photic Stimulation; D011569:Psychiatric Status Rating Scales; D011930:Reaction Time; D012438:Saccades / Q000502:physiology*; D012559:Schizophrenia / Q000473:pathology* / Q000503:physiopathology*
keywords: corollary discharge; double-step; efference copy; saccade; schizophrenia