Timed, sustained, attention-demanding performance reorganizes or dampens multiple circadian rhythms.

Gritton et al (2009) reported that rats practicing daily a sustained attention task (SAT) at ZT4 exhibit inverted activity patterns, such that the majority of activity as measured by movement occurs during the light phase. This shift was not apparent in animals trained under several other control conditions, including an operantly similar simple reaction task that requires less cognitive vigilance performed at the same time of day. Here we report that the SAT performance also alters circadian running wheel activity at ZT4 in a similar manner. Furthermore, the SAT performance causes phase advances (diurnality) at ZT4, a smaller phase advance at ZT10 and small phase delays at ZT16. Core body temperatures (Tb) are consistent with running wheel records for training at ZT10 and ZT16. However, at ZT4 the Tb is no longer synchronized with running wheel records, and contain elements of both daily training and LD effects. Acetylcholine (ACh) release in the prefrontal cortex, as measured via microdialysis, anticipates and remains entrained for at least 3 days after the last training session at ZT4. Entrainment to the time of daily training also occurs at ZT16, but the anticipatory rise is absent. In contrast, an operant schedule of reinforcement devoid of explicit demands on cognitive processes (FI-9) did not shift activity at ZT4 also did not entrain ACh release. Animals practicing at ZT4 the SAT, but not the FI-9, exhibit dampened food intake, stool output, and corticosterone rhythms in addition to the noted changes in activity rhythms and ACh release. Finally, the per2 rhythm in the colon also had a dampened level of expression. These data suggest that attention-demanding tasks may act to attenuate SCN-control of peripheral oscillators.