title: NMDA Receptor Antagonist Ketamine Distorts Object Recognition by Reducing Feedback to Early Visual Cortex.
abstract: It is a well-established fact that top-down processes influence neural representations in lower-level visual areas. Electrophysiological recordings in monkeys as well as theoretical models suggest that these top-down processes depend on NMDA receptor functioning. However, this underlying neural mechanism has not been tested in humans. We used fMRI multivoxel pattern analysis to compare the neural representations of ambiguous Mooney images before and after they were recognized with their unambiguous grayscale version. Additionally, we administered ketamine, an NMDA receptor antagonist, to interfere with this process. Our results demonstrate that after recognition, the pattern of brain activation elicited by a Mooney image is more similar to that of its easily recognizable grayscale version than to the pattern evoked by the identical Mooney image before recognition. Moreover, recognition of Mooney images decreased mean response; however, neural representations of separate images became more dissimilar. So from the neural perspective, unrecognizable Mooney images all "look the same", whereas recognized Mooneys look different. We observed these effects in posterior fusiform part of lateral occipital cortex and in early visual cortex. Ketamine distorted these effects of recognition, but in early visual cortex only. This suggests that top-down processes from higher- to lower-level visual areas might operate via an NMDA pathway.
authors: Department of Brain and Cognition, University of Amsterdam, Amsterdam 1018 XA, The Netherlands Amsterdam Brain and Cognition, University of Amsterdam, Amsterdam 1018 WS, The Netherlands Department of Cognitive Psychology, VU University, Amsterdam 1081 BT, The Netherlands.
authors: Anouk M
authors: AM
authors: van Loon
authors: Department of Cognitive Psychology, VU University, Amsterdam 1081 BT, The Netherlands.
authors: Johannes J
authors: JJ
authors: Fahrenfort
authors: Department of Brain and Cognition, University of Amsterdam, Amsterdam 1018 XA, The Netherlands.
authors: Bauke
authors: B
authors: van der Velde
authors: Department of Anesthesiology, Academic Medical Center, University of Amsterdam, Amsterdam 1105 DD, The Netherlands.
authors: Philipp B
authors: PB
authors: Lirk
authors: Department of Psychiatry, Academic Medical Center, University of Amsterdam, Amsterdam 1105 AZ, The Netherlands.
authors: Nienke C C
authors: NC
authors: Vulink
authors: Department of Anesthesiology, Academic Medical Center, University of Amsterdam, Amsterdam 1105 DD, The Netherlands.
authors: Markus W
authors: MW
authors: Hollmann
authors: Department of Brain and Cognition, University of Amsterdam, Amsterdam 1018 XA, The Netherlands Amsterdam Brain and Cognition, University of Amsterdam, Amsterdam 1018 WS, The Netherlands.
authors: H Steven
authors: HS
authors: Scholte
authors: Department of Brain and Cognition, University of Amsterdam, Amsterdam 1018 XA, The Netherlands Amsterdam Brain and Cognition, University of Amsterdam, Amsterdam 1018 WS, The Netherlands.
authors: Victor A F
authors: VA
authors: Lamme
mesh_terms: D000328:Adult; D001931:Brain Mapping; D025461:Feedback, Physiological / Q000187:drug effects*; D005260:Female; D006801:Humans; D007649:Ketamine / Q000008:administration & dosage*; D008279:Magnetic Resonance Imaging; D008297:Male; D010364:Pattern Recognition, Visual / Q000187:drug effects / Q000502:physiology*; D010775:Photic Stimulation; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors / Q000502:physiology*; D021641:Recognition, Psychology / Q000187:drug effects / Q000502:physiology*; D014793:Visual Cortex / Q000187:drug effects / Q000502:physiology*; D055815:Young Adult
chemical_list: D016194:Receptors, N-Methyl-D-Aspartate; D007649:Ketamine
keywords: MVPA; Mooney; fMRI; object; perception; top-down