Summary: Researchers have identified three distinct stages of brain development that occur before an episodic memory can form.
How and when the ability to form and store memories arises are topics of great interest to neuroscientists. Now Yale researchers have identified three distinct stages in brain development that occur before episodic memories can form.
Yale scientists measured brain activity in the hippocampus of newborn rats and found at the beginning of third week of postnatal life there was no evidence of neural activity that would allow the animal to link sequential events either in time or space.
“They are constantly in the present,” explains George Dragoi, assistant professor of psychiatry and neuroscience and senior author of the new study. This stage corresponds to the human state of infantile amnesia — or the inability to properly encode and store episodic memories of events in infancy and early development so that they can be recalled in adulthood.
The Yale team also identified changes in brain architecture later in the third week of rodent life that would allow the brain to encode distinct experiences using innate patterns of neuronal activity. However, no evidence of lasting changes in these neural patterns was found from those experiences. Early in the fourth week of postnatal life, the rat brains showed beginnings of network activity that would allow them to record “the singularity of an experience in space and time for long-term,” Dragoi said.
Source: Bill Hathaway – Yale
Publisher: Organized by NeuroscienceNews.com.
Image Source: NeuroscienceNews.com image is adapted from the Yale news release.
Original Research: Abstract for “Emergence of preconfigured and plastic time-compressed sequences in early postnatal development” by U. Farooq, and G. Dragoi in Science. Published January 11 2019.
Emergence of preconfigured and plastic time-compressed sequences in early postnatal development
When and how hippocampal neuronal ensembles first organize to support encoding and consolidation of memory episodes, a critical cognitive function of the brain, are unknown. We recorded electrophysiological activity from large ensembles of hippocampal neurons starting on the first day after eye opening as naïve rats navigated linear environments and slept. We found a gradual age-dependent, navigational experience–independent assembly of preconfigured trajectory-like sequences from persistent, location-depicting ensembles during postnatal week 3. Adult-like compressed binding of adjacent locations into trajectories during navigation and their navigational experience–dependent replay during sleep emerged in concert from spontaneous preconfigured sequences only during early postnatal week 4. Our findings reveal ethologically relevant distinct phases in the development of hippocampal preconfigured and experience-dependent sequential patterns thought to be important for episodic memory formation.