A preview of our lab’s abstracts for this year’s SfN meeting in DC. Many of the usual suspects are there (neurogenesis, hippocampal, memories, forgetting) but there are also some newcomers (CLARITY and inhibitory) reflecting changes in our research-scape.
The Josselyn/Frankland lab is full of football sophisticates so, as the world cup begins, we surveyed the mood. First question, who do you want to win? Massive lab support for the Azzurri (7 out of 22)!
And second question, who is actually going to win it? There’s lots of obvious support for Spain, Germany, Brazil and Argentina. David picked England, proving that Americans know nothing about football. And some people don’t care (Gisella).
Congratulations to Afra who successfully defended her PhD yesterday. Her thesis explored how drug-associated memories reorganize over time (i.e., undergo systems consolidation). Above she is pictured post-defense with her PhD supervisory committee members Paul Fletcher and Sheena Josselyn.
Our knowledge of the world is based on the sum of our experiences, but it is not clear how multiple, distinct experiences are combined by the brain. Neuroscientists have hypothesized that the brain amalgamates different memories based on their commonalities, or patterns, long after the memories are formed, and possibly while we sleep (David Marr called this process the identification of statistical regularities across multiple experiences). This leads to the prediction that as time passes we lose the details from specific memories, but we gain a more accurate understanding of our cumulative experience.
To test this prediction, Blake Richards designed an experiment to measure how well mice remembered specific experiences versus a general pattern of experience. In these experiments, we trained the mice over many days to find a hidden platform in a pool of water. The location of this platform changed each day, though, according to a pattern, such that some locations were more likely than others. We then tested the mice by putting them in the pool without the platform. We found that if we tested them one day after training they spent most of their time searching in the last platform location, but if we gave them thirty days to rest and consolidate their memories, they spent more time searching for the more likely locations. Our study shows that the brain can ‘combine’ multiple memories even when an animal is not learning anything new and is simply resting.
Form the lab Frances Xia, Adam Santoro and Jana Husse contributed to this study. The paper is published in Nature Neuroscience, and a pdf is available here.
Last week the Keystone meeting on Adult Neurogenesis took place in Stockholm, Sweden. Bringing together leading neurogenesists from around the world, discussion focused on pattern separation (and pattern separation-like) processing in the dentate, neural stem cell lineage, human neurogenesis and even some forgetting. Looking like they are part of some weird parabiosis experiment, below are Rene Hen and Alejandro Schinder. More pictures from the meeting are posted here…
It’s been known now for a while that neurogenesis persists in the adult hippocampus. Since the hippocampus is important for memory, there have been lots of studies examining how new neurons might contribute to forming new memories. The typical result is that reducing levels of neurogenesis impairs the formation of new memories. But as new neurons integrate into the hippocampus, they may also impact existing memories. In particular, as new neurons integrate they necessarily remodel hippocampal circuits, and this remodeling may lead to degradation of information (memories) stored in those circuits. In a new paper we tested this idea by artificially elevating levels of neurogenesis after learning in adult mice. The key finding was that increasing neurogenesis after learning indeed led to forgetting.
So, what’s this got to do with infantile amnesia? Well, first what is infantile amnesia? Infantile amnesia refers the absence of memories for events that occurred in our earliest years—most people typically don’t remember much of what happened when they were only 2 or 3 years-old. But this doesn’t seem to be because children at this stage can’t make memories—when our daughter, for instance, was 3 years old she would enthusiastically recount in details trips to the zoo to see grandparents and so on. But she is now 5 and has no recollection of these events. These memories are rapidly forgotten. Since neurogenesis levels are highest during early postnatal development, we speculated that these high levels of hippocampal neurogenesis are essentially incompatible with stable memory storage—while infant mice (and human infants) are able to make memories, high levels of neurogenesis lead to the ‘overwriting’ of this information and forgetting. In our paper we provided evidence for this idea by showing that reducing neurogenesis in infant mice led to the relative preservation of memories that otherwise would have been forgotten.
This work was led by Katherine Akers, Alonso Martinez-Canabal and Leo Restivo.
There’s an accompanying Perspectives on our paper by Mongiat and Schinder.