I briefly reviewed this study published in Nature two mths ago. At the time, I was intrigued by the results and totally overlooked the revolutionary contributions of the research methods to the categorization of electrophysiologic sleep/wake states. This is also most likely because I was still in a circadian rhythms lab at the time. Regardless, we reviewed this article published by a friendly lab at Wisconsin (Tononi and Cirelli) in today’s (Morehouse School of Medicine) journal club. As a recap, more neurons in various brain cortices enter an offline state characterized by high-amplitude, low-frequency EEG with increasing wake, and transition to a frenzied, highly active state with increasing sleep. However, the innovation and impact of this study manifests from the collection of invasive, local neuron recording techniques done at a multi-cellular level through the utility of local field potentials, which involves the implantation of a deep, cortical electrode to characterize EEG with minimal artifact from a large population of neurons, and at a singular and few-cell level via the real-time recording of neuron firing. As shown in this figure, there is a precise time-course of rapid transitions in neuron onlining and off-lining unveiled (and with limited artifact!!!) which has never been accomplished before.
Such frequent neuron transitions from an online to off-line state is very problematic for accurate analyses of frequency power. Therefore, us electrophysiologists need to revise our current categorical criteria of wake and sleep states, because there is more leakage of sleep-indicative frequencies across time awake and more wake-indicative frequencies across time asleep. Our lab technicians who score sleep records will not be thrilled, but such work needs to be considered because clearly many previous interpretations of the effects of sleep loss on electrophysiologic output characteristic of sleep depth may be highly confounded.
Vyazovskiy VV, Olcese U, Hanlon EC, Nir Y, Cirelli C, & Tononi G (2011). Local sleep in awake rats. Nature, 472 (7344), 443-7 PMID: 21525926