title: Neurochemical modulation of repetition suppression and novelty signals in the human brain.
abstract: The repeated processing of a sensory stimulus, such as a picture or sound, leads to a decrement in response in neurons that fired to the initial presentation. These effects are well known from single cell recordings in the inferior temporal cortex in monkeys, and functional neuroimaging in humans on large-scale neural activity could show similar effects in extrastriate, frontal and medial temporal lobe (MTL) regions. The role of specific neurotransmitters in repeated processing of information is, however, less clear. In the first part of this article, we will introduce the two concepts of repetition suppression and novelty signals, which is followed by a brief overview of pharmacological neuroimaging in humans. We will then summarize human studies suggesting that gamma-aminobutyric-acid (GABA) and acetylcholine (ACh) play an important role in modulating behavioral priming and associated repetition suppression in extrastriate and frontal brain regions. Finally, we review studies on neural novelty signals in the dopaminergic mesolimbic system, and conclude that dopamine (DA) regulates the temporal aspects of novelty processing and closely relates to long-term memory encoding rather than behavioral priming. As such, this review describes differential roles of GABA, ACh and DA in repeated stimulus processing, and further suggests that repetition suppression and neural novelty signals may not be two sides of the same coin but rather independent processes.
authors.affiliation: Department of Psychology, University of Lübeck, Lübeck, Germany; Department of Systems Neuroscience, University Medical Center Hamburg-Eppendorf, Hamburg, Germany. Electronic address: nico.bunzeck@uni-luebeck.de.
authors.forename: Nico
authors.initials: N
authors.lastname: Bunzeck
authors.affiliation: Biological Psychology, Department of Psychology, European Medical School, Carl von Ossietzky University Oldenburg, Oldenburg, Germany; Cluster of Excellence "Hearing4all" and Research Center Neurosensory Science, Carl von Ossietzky University Oldenburg, Oldenburg, Germany.
authors.forename: Christiane
authors.initials: C
authors.lastname: Thiel
mesh_terms: D000818:Animals; D001921:Brain / Q000502:physiology*; D001931:Brain Mapping; D006801:Humans; D008279:Magnetic Resonance Imaging; D008568:Memory / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods; D011930:Reaction Time / Q000502:physiology
keywords: Acetylcholine; Dopamine; GABA; Novelty; Repetition suppression