title: Phase matters: responding to and learning about peripheral stimuli depends on hippocampal θ phase at stimulus onset.
abstract: Hippocampal θ (3-12 Hz) oscillations are implicated in learning and memory, but their functional role remains unclear. We studied the effect of the phase of local θ oscillation on hippocampal responses to a neutral conditioned stimulus (CS) and subsequent learning of classical trace eyeblink conditioning in adult rabbits. High-amplitude, regular hippocampal θ-band responses (that predict good learning) were elicited by the CS when it was timed to commence at the fissure θ trough (Trough group). Regardless, learning in this group was not enhanced compared with a yoked control group, possibly due to a ceiling effect. However, when the CS was consistently presented to the peak of θ (Peak group), hippocampal θ-band responding was less organized and learning was retarded. In well-trained animals, the hippocampal θ phase at CS onset no longer affected performance of the learned response, suggesting a time-limited role for hippocampal processing in learning. To our knowledge, this is the first study to demonstrate that timing a peripheral stimulus to a specific phase of the hippocampal θ cycle produces robust effects on the synchronization of neural responses and affects learning at the behavioral level. Our results support the notion that the phase of spontaneous hippocampal θ oscillation is a means of regulating the processing of information in the brain to a behaviorally relevant degree.
authors.affiliation: Department of Psychology, University of Jyvaskyla, FI-40014 Jyväskylän, Finland miriam.nokia@jyu.fi.
authors.forename: Miriam S
authors.initials: MS
authors.lastname: Nokia
authors.affiliation: Department of Psychology, University of Jyvaskyla, FI-40014 Jyväskylän, Finland.
authors.forename: Tomi
authors.initials: T
authors.lastname: Waselius
authors.affiliation: Department of Psychology, University of Jyvaskyla, FI-40014 Jyväskylän, Finland Centre for Interdisciplinary Brain Research, University of Jyvaskyla, FI-40014 Jyväskylän, Finland.
authors.forename: Jarno E
authors.initials: JE
authors.lastname: Mikkonen
authors.affiliation: Department of Psychology, University of Jyvaskyla, FI-40014 Jyväskylän, Finland Centre for Interdisciplinary Brain Research, University of Jyvaskyla, FI-40014 Jyväskylän, Finland.
authors.forename: Jan
authors.initials: J
authors.lastname: Wikgren
authors.affiliation: Department of Psychology, University of Jyvaskyla, FI-40014 Jyväskylän, Finland.
authors.forename: Markku
authors.initials: M
authors.lastname: Penttonen
mesh_terms: D000818:Animals; D003215:Conditioning, Eyelid / Q000502:physiology*; D005260:Female; D006624:Hippocampus / Q000502:physiology*; D011817:Rabbits; D013826:Theta Rhythm