Matthew A. Wilson, professor of brain and cognitive sciences at MIT's Picower Institute for Learning and Memory, and postdoctoral associate Daoyun Ji looked at what happens in rats' brains when they dream about the mazes they ran while they were awake.
In a landmark 2001 study, Wilson showed that rats formed complex memories for sequences of events experienced while they were awake, and that these memories were replayed while they slept--perhaps reflecting the animal equivalent of dreaming.
Because these replayed memories were detected in the hippocampus, the memory center of the brain, the researchers were not able to determine whether they were accompanied by the type of sensory experience that we associate with dreams--in particular, the presence of visual imagery.
In the latest experiment, by recording brain activity simultaneously in the hippocampus and the visual cortex, Wilson and Ji demonstrated that replayed memories did, in fact, contain the visual images that were present during the running experience.
"This work brings us closer to an understanding of the nature of animal dreams and gives us important clues as to the role of sleep in processing memories of our past experiences," Wilson said.
You'd think fish would not have that much on their minds to keep them up at night. But this week, Prober et al. describe transgenic zebrafish with a sleep disorder, a model system that may be useful in studies of sleep regulation. The authors first determined that hypocretin, the best characterized sleep wake regulator in mammals, is expressed in hypothalamic neurons of 5-d-old zebrafish in a pattern strikingly similar to that of mammals. The authors then engineered transgenic fish with a hypocretin promoter that could be induced by heat shock. Overexpression of the gene in zebrafish larvae promoted wakeful activity, hyperarousal, and inability to stay still, hallmarks of insomnia in humans. The effects of hypocretin overexpression were more dramatic in the absence of circadian cues, suggesting that the circadian system may normally antagonize hypocretin function.
Scientists have identified the first biochemical marker linked to sleep loss, an enzyme in saliva known as amylase, which increases in activity when sleep deprivation is prolonged. Researchers hope to make amylase the first of a panel of biomarkers that will aid diagnosis and treatment of sleep disorders and may one day help assess the risk of falling asleep at the wheel of a car or in other dangerous contexts.
Anone who has ever watched a sleeping dog paddle his feet, bark move his nose around as if smelling something, and move his eyes around under his closed lids will be pretty sure that dogs, at least, have dreams probably a lot like ours. Given the importance of a dog's strong sense of smell, I wouldn't be surprised if they have odors in their dreams, too.