Why don’t we remember specific events during those crucial first few years, when our brains worked overtime to learn so much? A new Yale study finds evidence that we do form memories, but can’t retrieve them.
If you try to think back to your earliest memory, chances are it’s not from before you were about three years old. Scientists call the memory murkiness surrounding this crucial period of our lives “infantile amnesia,” but exactly why it happens remains largely unknown. One leading hypothesis suggests that the part of our brain responsible for memory – the hippocampus – is underdeveloped at that stage of life and isn’t ready to store memories.
A new study at Yale investigated this theory, developing a new memory test for infants. The team placed 26 children, aged between four months and two years, in an fMRI machine to monitor their brain activity while they viewed a series of images of faces, objects and scenes. All were things the children had never seen before, but after a while one would appear for a second time.
“When babies have seen something just once before, we expect them to look at it more when they see it again,” said Nick Turk-Browne, senior author of the study. “So in this task, if an infant stares at the previously seen image more than the new one next to it, that can be interpreted as the baby recognizing it as familiar.”
The team noticed an intriguing correlation between brain activity and memory behavior. They found that babies tended to stare longer at a repeated image if their hippocampus activity was strong when they saw that image the first time around. This suggests that the information is being better encoded as a memory, priming them to recognize it next time.
This correlation applied to all 26 infants in the study, but the effect was found to be strongest for the half of the group that was more than 12 months old. This implies that this kind of memory does start in some form earlier than we may have thought, but solidifies around the time of a child’s first birthday.
Most importantly, this study was testing for a version called episodic memory – the ability to recall specific events. It’s thought that this is a more advanced form of memory that doesn’t emerge until later, hence why we all suffer from infantile amnesia. All that important learning we do during this time is instead associated with statistical learning, a form of memory that focuses on more general patterns in our experiences.
“Statistical learning is about extracting the structure in the world around us,” said Turk-Browne. “This is critical for the development of language, vision, concepts, and more. So it’s understandable why statistical learning may come into play earlier than episodic memory.”
Both statistical learning and episodic memory occur in the hippocampus, but in different areas. During this test the fMRI scans detected brain activity towards the back of the head – a region associated with episodic memory.
So, if we do start storing these memories earlier than expected, why can’t we recall them? The researchers suggest that they might not be converted into long-term memories, so they fade away by the time we hit puberty. Another possibility is that they’re still in there, we just didn’t develop the right framework to be able to access them anymore. Figuring out which it is will require more research.
“We’re working to track the durability of hippocampal memories across childhood and even beginning to entertain the radical, almost sci-fi possibility that they may endure in some form into adulthood, despite being inaccessible,” said Turk-Browne.
The research was published in the journal Science.
Source: Yale University
