Time rescaling reproduces EEG behavior during transition from propofol anesthesia-induced unconsciousness to consciousness

General anesthesia (GA) is a reversible manipulation of consciousness whose mechanism is mysterious at the level of neural networks leaving space for several competing hypotheses. We recorded electrocorticography (ECoG) signals in patients who underwent intracranial monitoring during awake surgery for the treatment of cerebral tumors in functional areas of the brain. Therefore, we recorded the transition from unconsciousness to consciousness directly on the brain surface. Using frequency resolved interferometry; we studied the intermediate ECoG frequencies (4-40 Hz). In the theoretical study, we used a computational Jansen and Rit neuron model to simulate recovery of consciousness (ROC). During ROC, we found that f increased by a factor equal to 1.62 ± 0.09, and δf varied by the same factor (1.61 ± 0.09) suggesting the existence of a scaling factor. We accelerated the time course of an unconscious EEG trace by an approximate factor 1.6 and we showed that the resulting EEG trace match the conscious state. Using the theoretical model, we successfully reproduced this behavior. We show that the recovery of consciousness corresponds to a transition in the frequency (f, δf) space, which is exactly reproduced by a simple time rescaling. These findings may perhaps be applied to other altered consciousness states.

Dry anaerobic digestion in batch mode: design and operation of a laboratory-scale, completely mixed reactor

A laboratory-scale (40 l) reactor was designed to investigate dry anaerobic digestion. The reactor is equipped with an intermittent paddle mixer, enabling complete mixing in the reactor. Three consecutive batch dry digestion tests of municipal solid waste were performed under mesophilic conditions and compared to operation results obtained on a pilot-scale (21 m(3)) with the same feedstock. Biogas and methane production at the end of the tests were similar (around 200 m(3) CH(4)STP/tVS), and the dynamics of methane production and VFA accumulation concurred. However, the maximal levels of VFA transitory accumulation varied between reactors and between runs in a same reactor. Ammonia levels were similar in both reactors. These results show that the new reactor accurately imitates the conditions found in larger ones. Adaptation of micro-organisms to the waste and operating conditions was also pointed out along the consecutive batches.

High-solids anaerobic digestion: comparison of three pilot scales

Two experiments were undertaken in three different experimental set-ups in order to compare them: an industrial 21-m3 pilot reactor, a new 40-l laboratory pilot reactor and bmp type plasma bottles. Three consecutive batch dry digestion tests of municipal solid waste were performed under mesophilic conditions with the same feedstock in all vessels. Biogas and methane production at the end of the tests were similar (around 200 m3 CH4STP/tVS) for both pilot reactors and were different from the bottle tests. The dynamics of methane production and VFA accumulation concurred. However, the maximal levels of VFA transitory accumulation varied between reactors and between runs in a same reactor. Ammonia levels were similar in both reactors. These results show that the new reactor accurately imitates the conditions found in the larger one. Adaptation of microorganisms to the waste and operating conditions was also pointed out along the consecutive batches. Thermophilic semi-continuous tests were performed in both reactors with similar conditions. The methane production efficiencies were similar.