Infantile amnesia is a common phenomenon that occurs during our earliest years, when we learn rapidly.
Science published a new study on Thursday that challenges the assumptions made about infant memory. It shows that young minds form memories. However, the question remains as to why these memories are difficult to recall later in life.
Nick Turk-Browne is a professor of psychology and the senior author of the study. He said: “I have always been fascinated by that mysterious blank space we have in our personal history.”
Around age one, children are extraordinary learners. They learn to speak, walk, recognize objects, understand social bonds, and much more. “Yet, we don’t remember any of those experiences – so there is a mismatch between our incredible plasticity and ability to learn,” he said.
Sigmund Freud, the founder and father of psychoanalysis, believed that early memories were suppressed. However, science has since largely rejected the idea of active suppression. Modern theories instead focus on the hippocampus – a brain region critical for episodic memories but not fully developed during infancy.
Turk-Browne was, however, intrigued by clues gleaned from prior behavioral research. As babies are unable to verbally communicate their memories until they learn language, the tendency of them to stare longer at familiar objects can provide important clues.
Recent studies on rodents have shown that engrams – patterns of cells that contain memories – form in the infant’s hippocampus, but they become inaccessible with time. However, these engrams can be artificially reawakened by using a technique that uses light to stimulate neuronal activity.
The ability to combine brain imaging with observations of infants was previously impossible because babies are notoriously difficult to sit still in a Functional Magnetic Resonance Imaging machine (fMRI), which tracks blood flow and “sees” brain activity.
Turk-Browne’s team overcame this challenge by using methods that his lab has developed over the years. They worked with families and included pacifiers and blankets; they held babies still with pillows and used psychedelic patterns as background patterns.
The team ran hundreds of sessions to account for the inevitable wiggling that led to blurry pictures.
The brains of 26 infants- half younger than a year, and half older- were scanned as they performed a memory test adapted from studies on adults.
Initially, images of objects, scenes, or faces were displayed. After viewing several images, the participants were shown a previous image along with a brand new one.
Turk-Browne said, “We measure how long they spend looking back at an old image. That’s a measurement of their memory.”
Researchers confirmed the importance of the hippocampus in memory encoding by comparing brain activity between successful memory formation and forgotten images.
It was the case for 11 out of 13 babies older than a year, but not for those younger. The researchers also discovered that the babies who did best in memory tests showed more hippocampal activation.
Turk-Browne said, “What we have concluded accurately is that babies can encode episodic memory in the hippocampus as early as one year old.”
In an accompanying editorial in Science, Adam Ramsaran & Paul Frankland write: “Their experimental approach is a marvel of ingenuity.”
What remains to be resolved is what becomes of these early memories. They may never be fully stored in long-term memory, or they might persist but not be accessible.
Turk-Browne suspects this and is leading a study to test whether infants and toddlers can recognize videos recorded from their perspective as babies.
These memories may persist up to age three before they fade. Turk-Browne was particularly interested in the possibility that these fragments might one day be activated later in life.
