title: Reentrainment Impairs Spatial Working Memory until Both Activity Onset and Offset Reentrain.
abstract: Compression of the active phase (α) during reentrainment to phase-shifted light-dark (LD) cycles is a common feature of circadian systems, but its functional consequences have not been investigated. This study tested whether α compression in Siberian hamsters (Phodopus sungorus) impaired their spatial working memory as assessed by spontaneous alternation (SA) behavior in a T-maze. Animals were exposed to a 1- or 3-h phase delay of the LD cycle (16 h light/8 h dark). SA behavior was tested at 4 multiday intervals after the phase shift, and α was quantified for those days. All animals failed at the SA task while α was decompressing but recovered spatial memory ability once α returned to baseline levels. A second experiment exposed hamsters to a 2-h light pulse either early or late at night to compress α without phase-shifting the LD cycle. SA behavior was impaired until α decompressed to baseline levels. In a third experiment, α was compressed by changing photoperiod (LD 16:8, 18:6, 20:4) to see if absolute differences in α were related to spatial memory ability. Animals performed the SA task successfully in all 3 photoperiods. These data show that the dynamic process of α compression and decompression impairs spatial working memory and suggests that α modulation is a potential biomarker for assessing the impact of transmeridian flight or shift work on memory.
authors.affiliation: Biology Department, Stanford University, Stanford, California ruby@stanford.edu.
authors.forename: Norman F
authors.initials: NF
authors.lastname: Ruby
authors.affiliation: Biology Department, Stanford University, Stanford, California.
authors.forename: Danica F
authors.initials: DF
authors.lastname: Patton
authors.affiliation: Biology Department, Stanford University, Stanford, California.
authors.forename: Shalmali
authors.initials: S
authors.lastname: Bane
authors.affiliation: Biology Department, Stanford University, Stanford, California.
authors.forename: David
authors.initials: D
authors.lastname: Looi
authors.affiliation: Biology Department, Stanford University, Stanford, California.
authors.forename: H Craig
authors.initials: HC
authors.lastname: Heller
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D002940:Circadian Rhythm / Q000502:physiology*; D006224:Cricetinae; D005260:Female; D008027:Light; D008297:Male; D018782:Maze Learning / Q000502:physiology* / Q000528:radiation effects; D008570:Memory, Short-Term / Q000502:physiology*; D009043:Motor Activity / Q000502:physiology / Q000528:radiation effects; D017111:Phodopus; D017440:Photoperiod; D013997:Time Factors
keywords: alpha; biomarker; circadian; jet lag; phase shift; sex differences; shift work; spontaneous alternation