Physiology: Dueling Brain Waves Anchor or Erase Learning During Sleep

Quanta Magazine said:

The brain collects far more memories than it can keep. We absorb new information throughout the day, but retain only some overnight and beyond. Sleep seems crucial to this balance of learning and forgetting, solidifying some memories and eroding others through the brain’s patterns of electrical signaling, but the mechanisms at work have been unclear. Research reported earlier this month, however, has chipped away at the mystery by isolating the opposing functions of two kinds of brain waves: one that strengthens memories and one that weakens them.

Simply by distinguishing these brain waves from each other, the researchers began to form an explanation that reconciles competing theories about how the brain processes memories to retain some and lose others. There was a gap in our understanding of how sleep could be important both for remembering and forgetting, said Karunesh Ganguly, an associate professor of neurology at the University of California, San Francisco, and the senior author on the study.

Theories about memory consolidation generally fall into one of two camps, and some evidence supports each of them. One attributes long-term learning to patterns of brain activity that are reenacted during sleep. These ensembles of neural firing mimic the signals involved in the original learning, and that repetition strengthens the synaptic connections between the neurons to ingrain the memory. Without reactivation, other connections are in theory not fortified, and those memories should wither away.

As an alternative, many researchers put stock in the idea of “synaptic downscaling,” in which the brain more actively clears itself of less useful memories. Because learning involves neural activity that strengthens brain connections, it becomes an energy drain. During sleep, less energy goes into the connections, allowing those with less long-term importance to weaken. Removing this background noise from unneeded memories clarifies the brain’s signals and keeps it more efficient.

The new research bridges the divide between these theories by looking at the roles in memory retention of different brain wave patterns associated with sleep.

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