There was once a time that people thought that when we sleep, our brains also shut down for the night, so that sleep was a sort of coma. Since that time, scientific study has proven otherwise, but that doesn’t mean that we still fully understand exactly what is going on when we fall asleep. To that point, a new study conducted by neurologist Dr. Josef Parvizi of Stanford University has shown that not only is the brain active during the time that we’re sleeping, but that the activity that is going on is specific and targeted. The finding is providing valuable information about the enormous amount of energy that the brain uses each night while we are sleeping.
Dr. Parvizi says, “There is something that’s going on in a very structured manner during rest and during sleep, and that will, of course, require energy consumption.”
The collected information has been made possible by the advent of functional MRI scans, or fMRI, which track the brain’s electrical activity. Where it was once thought that the brain’s activity during rest and sleep were just random “noise,” the latest studies are showing that the activity is replicating patterns of coordinated activity that are also being seen in patients while they are awake.
The study conducted by Parvizi and his team followed a cohort of patients who were preparing for surgery for the treatment of epileptic seizures. In the lead up to their operations, the patients submitted to a series of tests that they took while electrodes were monitoring their brain activity. The goal was to find the source of their seizures, and to do so by monitoring various groups of brain cells to determine when seizures occurred and what activity within those cells might serve as a catalyst. “We wanted to know exactly what’s going on during rest,” Parvisi said, “and whether or not it reflects what went on during the daytime when the subject was not resting.”
The group observed the patients both while they were awake and asleep, and during waking hours tracked their brain activity in response to simple questions that required that they engage in actively probing their recent memories for recent actions. The questions were specifically about activities that the patients had engaged in over the previous week. “In order to answer yes or no, you retrieve a lot of facts; you retrieve a lot of visualized memories.”
What the team found was that the response to the questions created activity in two separate brain areas that have already been established as active in episodic memories, and that the activity between the two brain areas appeared to be highly coordinated. But unexpectedly, the researchers found the same signals continued to fire in the participants’ brains after they had gone to sleep, in the same coordinated way. Parvizi believes that the brain may continue the relationship between the brain centers that had previously worked together.
The study’s results were published in the journal Neuron.