Chinese study reveals key overnight shift in memory formation

Chinese researchers have uncovered new clues about how the brain transforms newly learned information into long-term memories, according to a study published online in the journal Neuron on June 15.

The study, conducted by a neurosurgery research team at Xinqiao Hospital of the Army Medical University, provides direct evidence that after a single night of sleep, the brain's "memory commander" begins a quiet change of guard, shifting responsibility for newly learned information from the hippocampus to the neocortex.

To investigate the process, the team monitored 14 patients with drug-resistant epilepsy over six consecutive days. Using stereoelectroencephalography (SEEG), researchers recorded high-frequency brain activity while participants repeatedly learned and recalled images.

The researchers found that memory formation involves a dynamic handover between different parts of the brain. On the first day of learning, the hippocampus — a brain region crucial for forming new memories — acts like a commander, guiding the neocortex through brief bursts of synchronized neural activity known as ripples.

After a night's sleep, however, a quiet "change of guard" begins. From the second day onward, ripple activity in the neocortex becomes more active than in the hippocampus and continues to play a leading role during memory recall. Communication between the two regions also becomes stronger, with information flow shifting from the hippocampus to the neocortex.

The process can be compared to learning how to drive, said Wang Lukang, the study's first author. On the first day, a driving instructor closely guides every move. After a good night's sleep, however, the brain's cortical networks take over, allowing the skill to become more automatic and stable.

The findings suggest that a key stage of memory consolidation may occur much earlier than previously thought — during the very first night after learning. Researchers say the discovery could also provide new clues for treating memory-related disorders, including Alzheimer's disease, traumatic brain injury and epilepsy-associated cognitive impairment.

Source(s): Science and Technology Daily; Neuron