The brain is made of networks of neurons that send information to each other via spikes. Sleep and wake are the most clearly definable brain states and each exerts unique effects upon neural network spiking activity. We used large-scale recordings in the frontal cortex of mice and rats to examine the activity of neurons during wake/sleep cycles and found that a novel form of homeostatic action is taken by sleep: homogenization of firing rates. Whereas it was previously believed that sleep simple decreased firing rates, we found that this was much more true of the most active neurons only, thereby reducing the variance of the population.
To extend this observation of homeostatic forced during sleep we also examine how sleep and wake states interact with learning and performance, which is also facilitated by sleep. We have therefore begun to record before, during and after learning sessions to determine how learning interacts with the usual homeostatic effects of sleep. Further we can also record how waking changes in brain states such as motivation and attention modulate firing and information processing by neurons during behavior itself.
Finally, our end-goal to translate these kinds of basic neurobiologic observations in healthy rodents to states of stress or treatments of stress. Unfortunately the chronic stress states of relevance to psychiatric disease do not last seconds but days and weeks. We have therefore begun to build new long-term recording environments to enable future experiments over these time-spans.
Dr. Watson is an assistant professor in psychiatry at the University of Michigan. He grew up in Ann Arbor and then obtained his BA from Cornell University and his M.D. and Ph.D. degrees from Columbia University. During his Ph.D. he used two-photon microscopy to study the behavior of neurons in local cortical microcircuits. During his doctoral work he also participated in technical development of multi-beam two photon imaging techniques. Upon graduation from medical school, Dr. Watson pursued a residency in Psychiatry at Weill Cornell Medical College as well postdoctoral work at New York University. He received the National Institute for Mental Health’s Outstanding Resident Award, the American Psychiatric Association’s Lilly Research Fellowship and the Leon Levy Neuroscience Fellowship. He did a fellowship with Dr. Gyorgy Buzsaki at NYU to record ongoing activity in naturally behaving and sleeping animals wherein he showed that sleep reorganizes neuronal firing architecture in the neocortex in previously unknown ways. He is now combining his electrical recordings with behavioral tools to deepen his understanding of both use and regulation of cortical brain circuits.