The Venus of Hohle Fels. (Credit: Photo by H. Jensen; Copyright: Universität Tübingen)
Wednesday, May 20, 2009
The Venus of Hohle Fels.
The Venus of Hohle Fels. (Credit: Photo by H. Jensen; Copyright: Universität Tübingen)
Wednesday, May 6, 2009
Good News for Night Owls
Good News for Night Owls
By Elsa Youngsteadt
ScienceNOW Daily News
23 April 2009
Night owls seem to have a cognitive edge over early risers--at least when they're on their natural sleep schedule. That's one upshot of a new brain-imaging study that also gives surprising new insights into how the brain manages the urge to sleep and wake. The results, sleep researchers say, may improve predictions of when people are most at risk for drowsy accidents.
Two factors control our bedtime. The first is hardwired: A master clock in the brain regulates a so-called circadian rhythm, which synchronizes activity patterns to the 24-hour day. Some people's clocks tell them to go to bed at 9 p.m., others' at 3 a.m., (ScienceNOW, 24 June 2003). The second factor--called sleep pressure--depends not on time of day but simply on how long someone has been awake already.
Because sleep pressure accumulates during waking hours, logic suggests that we should be most alert--and hence sharpest--shortly after we get up versus right before we go to bed, regardless of whether we're night owls or larks.
But that's not what Christina Schmidt found. The doctoral student at the University of Liège in Belgium and her collaborators, led by sleep researcher Philippe Peigneux, recruited 16 morning people and 15 night people to take alertness tests in a brain scanner. Subjects had to pay attention to numbers on a computer screen and hit a button whenever the numbers began to change. To control for the effect of the circadian clock, the subjects were allowed to sleep on their own natural schedules and take the test 1.5 hours and 10.5 hours after waking, regardless of the actual time of day.
Both groups performed equally well on the test when they took it 1.5 hours after waking. But after 10.5 hours without sleep, the night owls pulled ahead. Their reaction times improved by about 6% relative to the morning people and to their own earlier performance, the researchers report in tomorrow's issue of Science. This suggests that once they wake up, sleep pressure builds up faster in early birds, says Peigneux, and that this hurts their cognition over time.
It's a result with "real-world consequences," says sleep researcher David Dinges of the University of Pennsylvania School of Medicine in Philadelphia. Current risk analyses use the time of day and hours worked to predict when people are in greatest danger of accidents--such as aviation errors. But now, Dinges says, they may need to take into account that morning people tend to lose their concentration faster. At the very least, according to sleep researcher Amita Sehgal, also at the University of Pennsylvania School of Medicine, this is a new and "intriguing" explanation for larks' and owls' different habits.
But the really provocative result, adds Dinges, came from the brain imaging. The night owls showed greater activity in the master-clock region of their brains--a cluster of cells known as the suprachiasmatic nucleus--than the larks when taking the later test. That suggests that sleep pressure and the circadian clock can influence each other directly--bringing together two systems that, for decades, had been thought to operate separately.
By Elsa Youngsteadt
ScienceNOW Daily News
23 April 2009
Night owls seem to have a cognitive edge over early risers--at least when they're on their natural sleep schedule. That's one upshot of a new brain-imaging study that also gives surprising new insights into how the brain manages the urge to sleep and wake. The results, sleep researchers say, may improve predictions of when people are most at risk for drowsy accidents.
Two factors control our bedtime. The first is hardwired: A master clock in the brain regulates a so-called circadian rhythm, which synchronizes activity patterns to the 24-hour day. Some people's clocks tell them to go to bed at 9 p.m., others' at 3 a.m., (ScienceNOW, 24 June 2003). The second factor--called sleep pressure--depends not on time of day but simply on how long someone has been awake already.
Because sleep pressure accumulates during waking hours, logic suggests that we should be most alert--and hence sharpest--shortly after we get up versus right before we go to bed, regardless of whether we're night owls or larks.
But that's not what Christina Schmidt found. The doctoral student at the University of Liège in Belgium and her collaborators, led by sleep researcher Philippe Peigneux, recruited 16 morning people and 15 night people to take alertness tests in a brain scanner. Subjects had to pay attention to numbers on a computer screen and hit a button whenever the numbers began to change. To control for the effect of the circadian clock, the subjects were allowed to sleep on their own natural schedules and take the test 1.5 hours and 10.5 hours after waking, regardless of the actual time of day.
Both groups performed equally well on the test when they took it 1.5 hours after waking. But after 10.5 hours without sleep, the night owls pulled ahead. Their reaction times improved by about 6% relative to the morning people and to their own earlier performance, the researchers report in tomorrow's issue of Science. This suggests that once they wake up, sleep pressure builds up faster in early birds, says Peigneux, and that this hurts their cognition over time.
It's a result with "real-world consequences," says sleep researcher David Dinges of the University of Pennsylvania School of Medicine in Philadelphia. Current risk analyses use the time of day and hours worked to predict when people are in greatest danger of accidents--such as aviation errors. But now, Dinges says, they may need to take into account that morning people tend to lose their concentration faster. At the very least, according to sleep researcher Amita Sehgal, also at the University of Pennsylvania School of Medicine, this is a new and "intriguing" explanation for larks' and owls' different habits.
But the really provocative result, adds Dinges, came from the brain imaging. The night owls showed greater activity in the master-clock region of their brains--a cluster of cells known as the suprachiasmatic nucleus--than the larks when taking the later test. That suggests that sleep pressure and the circadian clock can influence each other directly--bringing together two systems that, for decades, had been thought to operate separately.
Homeostatic Sleep Pressure and Responses to Sustained Attention in the Suprachiasmatic Area
Science 24 April 2009:
Vol. 324. no. 5926, pp. 516 - 519
DOI: 10.1126/science.1167337
Prev | Table of Contents | Next
Reports
Homeostatic Sleep Pressure and Responses to Sustained Attention in the Suprachiasmatic Area
Christina Schmidt,1,2,* Fabienne Collette,1,2 Yves Leclercq,1 Virginie Sterpenich,1 Gilles Vandewalle,1 Pierre Berthomier,3 Christian Berthomier,3 Christophe Phillips,1 Gilberte Tinguely,1 Annabelle Darsaud,1 Steffen Gais,1 Manuel Schabus,1 Martin Desseilles,1 Thien Thanh Dang-Vu,1 Eric Salmon,1 Evelyne Balteau,1 Christian Degueldre,1 André Luxen,1 Pierre Maquet,1 Christian Cajochen,4 Philippe Peigneux1,5,*
Throughout the day, cognitive performance is under the combined influence of circadian processes and homeostatic sleep pressure. Some people perform best in the morning, whereas others are more alert in the evening. These chronotypes provide a unique way to study the effects of sleep-wake regulation on the cerebral mechanisms supporting cognition. Using functional magnetic resonance imaging in extreme chronotypes, we found that maintaining attention in the evening was associated with higher activity in evening than morning chronotypes in a region of the locus coeruleus and in a suprachiasmatic area (SCA) including the circadian master clock. Activity in the SCA decreased with increasing homeostatic sleep pressure. This result shows the direct influence of the homeostatic and circadian interaction on the neural activity underpinning human behavior.
Vol. 324. no. 5926, pp. 516 - 519
DOI: 10.1126/science.1167337
Prev | Table of Contents | Next
Reports
Homeostatic Sleep Pressure and Responses to Sustained Attention in the Suprachiasmatic Area
Christina Schmidt,1,2,* Fabienne Collette,1,2 Yves Leclercq,1 Virginie Sterpenich,1 Gilles Vandewalle,1 Pierre Berthomier,3 Christian Berthomier,3 Christophe Phillips,1 Gilberte Tinguely,1 Annabelle Darsaud,1 Steffen Gais,1 Manuel Schabus,1 Martin Desseilles,1 Thien Thanh Dang-Vu,1 Eric Salmon,1 Evelyne Balteau,1 Christian Degueldre,1 André Luxen,1 Pierre Maquet,1 Christian Cajochen,4 Philippe Peigneux1,5,*
Throughout the day, cognitive performance is under the combined influence of circadian processes and homeostatic sleep pressure. Some people perform best in the morning, whereas others are more alert in the evening. These chronotypes provide a unique way to study the effects of sleep-wake regulation on the cerebral mechanisms supporting cognition. Using functional magnetic resonance imaging in extreme chronotypes, we found that maintaining attention in the evening was associated with higher activity in evening than morning chronotypes in a region of the locus coeruleus and in a suprachiasmatic area (SCA) including the circadian master clock. Activity in the SCA decreased with increasing homeostatic sleep pressure. This result shows the direct influence of the homeostatic and circadian interaction on the neural activity underpinning human behavior.
Tuesday, May 5, 2009
2 micron plasmid hitchhikes on mitotic mechanism of Saccharomyces cerevisiae to maintain equal distribution in host
Published online April 13, 2009
doi:10.1083/jcb.200810130
The Journal of Cell Biology, Vol. 185, No. 2, 251-264
The Rockefeller University Press, 0021-9525 $30.00
© 2009 Cui et al.
The selfish yeast plasmid uses the nuclear motor Kip1p but not Cin8p for its localization and equal segregation
Hong Cui, Santanu K. Ghosh, and Makkuni Jayaram
Section of Molecular Genetics and Microbiology, University of Texas at Austin, Austin, TX 78712
Correspondence to Makkuni Jayaram: jayaram@icmb.utexas.edu
The 2 micron plasmid of Saccharomyces cerevisiae uses the Kip1 motor, but not the functionally redundant Cin8 motor, for its precise nuclear localization and equal segregation. The timing and lifetime of Kip1p association with the plasmid partitioning locus STB are consistent with Kip1p being an authentic component of the plasmid partitioning complex. Kip1–STB association is not blocked by disassembling the mitotic spindle. Lack of Kip1p disrupts recruitment of the cohesin complex at STB and cohesion of replicated plasmid molecules. Colocalization of a 2 micron reporter plasmid with Kip1p in close proximity to the spindle pole body is reminiscent of that of a CEN reporter plasmid. Absence of Kip1p displaces the plasmid from this nuclear address, where it has the potential to tether to a chromosome or poach chromosome segregation factors. Exploiting Kip1p, which is subsidiary to Cin8p for chromosome segregation, to direct itself to a "partitioning center" represents yet another facet of the benign parasitism of the yeast plasmid.
doi:10.1083/jcb.200810130
The Journal of Cell Biology, Vol. 185, No. 2, 251-264
The Rockefeller University Press, 0021-9525 $30.00
© 2009 Cui et al.
The selfish yeast plasmid uses the nuclear motor Kip1p but not Cin8p for its localization and equal segregation
Hong Cui, Santanu K. Ghosh, and Makkuni Jayaram
Section of Molecular Genetics and Microbiology, University of Texas at Austin, Austin, TX 78712
Correspondence to Makkuni Jayaram: jayaram@icmb.utexas.edu
The 2 micron plasmid of Saccharomyces cerevisiae uses the Kip1 motor, but not the functionally redundant Cin8 motor, for its precise nuclear localization and equal segregation. The timing and lifetime of Kip1p association with the plasmid partitioning locus STB are consistent with Kip1p being an authentic component of the plasmid partitioning complex. Kip1–STB association is not blocked by disassembling the mitotic spindle. Lack of Kip1p disrupts recruitment of the cohesin complex at STB and cohesion of replicated plasmid molecules. Colocalization of a 2 micron reporter plasmid with Kip1p in close proximity to the spindle pole body is reminiscent of that of a CEN reporter plasmid. Absence of Kip1p displaces the plasmid from this nuclear address, where it has the potential to tether to a chromosome or poach chromosome segregation factors. Exploiting Kip1p, which is subsidiary to Cin8p for chromosome segregation, to direct itself to a "partitioning center" represents yet another facet of the benign parasitism of the yeast plasmid.
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