Parietal Lobe May Control how the Brain Reacts During Anesthesia

A new study has found that anesthesia induction and emergence are distinct neurobiological processes, possibly assimilated by the parietal lobe.

Researchers at the University of Michigan (Ann Arbor, USA) conducted a study involving 20 healthy young males who were given intravenous (IV) infusions of the anesthetic propofol, while their brain activity was recorded with electroencephalography EEG). The researchers succeeded in isolating two brain network properties--the structure of brain networks, and the connection strength of brain networks. Loss of consciousness was consistently associated with sudden structural disruption of brain networks, rather than with the strength of connections. Recovery of consciousness, however, was often associated with a sudden increase in the strength of connections after the structural changes had returned to normal.

The researchers also investigated how propofol affects different sections of the brain, particularly the frontal and parietal lobes. They found that network structure was maintained in the frontal region, but significantly disrupted in the parietal region. Connection strength decreased somewhat in the frontal region, but it was more significantly affected in the parietal region. The researchers therefore concluded that network structure might be more reliable in monitoring changes in the anesthetic state, since connection strength appeared to have a variable behavior, showing two distinct responses in the population studied. The study was presented at the annual meeting of the American Society of Anesthesiologists, held during October 2010 in San Diego (CA, USA).

"Our data support recent evidence suggesting that anesthetic induction and emergence are not mirror images of one another, as previously thought, but rather have a distinct underlying neurobiology,” said lead author and study presenter George Mashour, M.D., Ph.D., of the department of anesthesiology. "It has been suggested that the parietal lobe is a critical point of integration for neural information and that its disruption is important for anesthetic-induced consciousness; our data support this hypothesis.”

According to the researchers, resolving the question of how states of consciousness are induced and revoked would help anesthesiologists detect or predict return to consciousness in the operating room (OR), and would aid in the development of more sophisticated brain function monitors.

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