Reentrainment Impairs Spatial Working Memory until Both Activity Onset and Offset Reentrain

Compression of the active phase () 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 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 was quantified for those days. All animals failed at the SA task while was decompressing but recovered spatial memory ability once returned to baseline levels. A second experiment exposed hamsters to a 2-h light pulse either early or late at night to compress without phase-shifting the LD cycle. SA behavior was impaired until decompressed to baseline levels. In a third experiment, was compressed by changing photoperiod (LD 16:8, 18:6, 20:4) to see if absolute differences in were related to spatial memory ability. Animals performed the SA task successfully in all 3 photoperiods. These data show that the dynamic process of compression and decompression impairs spatial working memory and suggests that modulation is a potential biomarker for assessing the impact of transmeridian flight or shift work on memory.