Using hairlike microelectrodes and computer analysis, neurobiologists at Duke University Medical Center have demonstrated that they can see the detailed instant-to-instant electrical "brainscape" of neural activity across a living brain.
In their study on rats, they demonstrated that they could distinguish in unprecedented detail the patterns of brain activity -- including fleeting changes in communication among brain structures -- in awake animals, as they fall sleep and as they transition among different sleep stages.
The study is important, not only for its insight into the sleep process, but because neurobiologists have strong evidence that memory consolidation occurs during sleep, said the researchers.
More generally, they believe that their new analytical technique will enable unprecedented insights into function of both the healthy brain and those afflicted with neurological disease. Such insights could lead to new understanding and treatment if diseases including epilepsy, Alzheimer's disease and schizophrenia, they said.
Led by neurobiologist Dr. Miguel Nicolelis, M.D., Ph.D., the researchers published their findings in the December 8, 2004, Journal of Neuroscience. Nicolelis is professor of neurobiology and co-director of Duke's Center for Neuroengineering. Other co-authors were Damien Gervasoni, Shih-Chieh Lin, Sidarta Ribeiro, Ernesto Soares and Janaina Pantoja. The research was sponsored by the National Institutes of Health.
In their studies, Nicolelis and his colleagues implanted the microelectrodes, smaller than the diameter of a human hair, into regions of the brain responsible for a range of functions -- including sensory processing, motor function and memory formation. They then recorded and analyzed the electrical signals from the rats as the animals went through several days of sleep-wake cycling. Their analysis could detect activity patterns that marked waking, deep "slow wave" sleep and so-called "rapid-eye movement" sleep.
Importantly, said Nicolelis, their analysis could distinguish the fleeting changes in the brain as the animals transitioned from one sleep state from the other.
"We can actually predict such changes, because at that moment, these different structures fire together for a few hundred milliseconds to create a synchronous pattern of firing that is a signature of the change from the previous state to the next," said Nicolelis. A millisecond is one thousandth of a second.
"It's almost like two computers exchanging information over a modem, and they get synchronized in the process," he said.
"Our analysis revealed significant functional insights into sleep," said Nicolelis. "For example, we found that there are only a few physiologically possible transitions from state to state -- just as in chemistry there are only certain chemical reactions that are possible." For example, he said, the data distinguished the elusive transition called "intermediate sleep" between slow wave sleep and rapid-eye-movement sleep.
Importantly, said Nicolelis, the transitions they observed were the same from one animal to another, "suggesting that we have arrived at a major basic principle of how the brain actually operates."
The technology and analysis the researchers used is an extension of that used to enable monkeys to control a robot arm using only their brain signals, which Nicolelis and his colleagues reported in 2003.
"Now, however, we are recording broader brain signals -- hundreds, perhaps thousands," said Nicolelis. "By filtering and analyzing them, we can actually measure the global dynamic activity that tells us what behavioral states the animals are going through.
"Such capability is broadly important because it is the first physiological measurement that can reveal the global behavior of the brain, including the broad coordination of so many areas."
In contrast, said Nicolelis, magnetic resonance imaging and positron emission tomography -- the most widely used brain-scanning techniques -- can give only limited time-resolution of brain activity. Also, they give only indirect indications of brain activity by measuring blood flow as an indicator of activity.