Beyond identifying specific functions of individual brain regions, there has been significant interest in understanding how multiple regions interact to perform various functions. However, there are many theories but few conclusions regarding how regions of the brain coordinate to underlie attention and consciousness.
In a study published in the Nature journal Scientific Reports Feb. 1, Johns Hopkins Medicine researchers analyzed brain activity recorded through electrodes placed on or beneath the brain surface and examined coherence changes during cognitive tasks used to terminate afterdischarges (ADs), seizure-like electrical brain activities that can progress to actual seizures. They found a mechanism wherein all of the cortex changed simultaneously, which suggested the presence of a widespread matrix that the researchers propose is critical to human attention and possibly consciousness.
“Specific cortical regions are important for attention and consciousness,” says Ronald Lesser, Professor Emeritus of Neurology and Neurological Surgery. “However, in addition, we propose that there are widespread changes in coherence that occur as emergent properties of the entire cortex, and that may underlie attention and consciousness.”
A standard part of evaluating some patients with epilepsy who need surgery to help manage seizure activity is to record and electrically stimulate the brain to locate regions important for movement, sensation, vision, speech and other functions so that the regions would be avoided during surgical removal of brain tissue. ADs are a known possible side effect of brain stimulation, and in this study, cognitive interventions — in particular, arithmetic or spelling tasks (ASTs) — were used to abort the ADs. The researchers posit that a variety of cognitive activities that require attention, including ASTs, can end ADs. This occurs because such activities affect brain cells throughout the cortex, including in the more limited region where a patient’s ADs occur.
Researchers reviewed recordings of 15 participants who had intracranial electrode contacts placed for evaluation of intractable seizures and had undergone clinical stimulation testing. None of the study participants reported seizures precipitated by calculation, spelling or similar mental activities. An AST was associated with AD termination in 50 trials among 12 of the 15 patients, six males and six females, ages 12–53 years. Session durations ranged from 47 to 177 minutes, with the average duration being 111 minutes.
Researchers assessed coherence, a measure of synchronization, between pairs of brain sites. When ADs stopped, brain recordings showed a decrease in coherence. Brain coherence changes were present whether ADs occurred at individual brain sites, regardless of whether the sites were thought important for math or spelling, and no matter how far apart the sites were from each other. Notably, coherence changes weren’t occurring in one or a few parts of the brain, but rather across the entirety of the outer part of the brain.
Because findings indicated the possibility that the cortex can act as a single matrix, the researchers theorize that examining this matrix while study participants engage in various activities may lead to better understanding of the intricacies of attention and consciousness. However, researchers need to learn more about what specific kinds of attention or thinking might be more likely to end ADs and seizures in general, or affect other brain patterns.
The results of these studies also suggest future therapies might benefit from considering both localized and widespread brain interactions. Advancements could potentially lead to more effective management of intractable epilepsy and other neurological conditions.
“A lot is known about the parts of the brain that are important for things like movement, sensation and language, and about how these parts communicate with each other,” says Lesser. “Much also is known about individual brain cells, the parts inside the cells, and the chemicals that are inside and around the cells that help them to function and to communicate with each other. Our research suggests that, along with studies of parts of the brain, there should be more studies about how the brain acts as a whole.”
Other researchers involved in this study are Bob Webber at Johns Hopkins and Diana Miglioretti at University of California, Davis.
Portions of this study were supported by the Dr. Charles R. Fields Epilepsy and Neuroscience Fund and by financial gifts from patients and their families.
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