Is it harder to change your ways as you get older? Axel Guskjolen addressed this question in a new paper published in The Neurobiology of Learning and Memory. He trained different aged mice in the water maze to find a platform in a fixed location, and first showed that ability to retain spatial memories increases with age: Infant mice forget within a day or two, whereas older mice can remember up to a month. He then went onto ask whether forgetting would allow younger mice to behave more flexibly. When the platform was moved to a different location in the pool, younger mice could learn this conflicting platform position more readily.
Poster day at U of T. Undergrad Moriam presenting her summer’s work.
Violet Ha presenting her summer’s work at the SickKids summer student poster session. A big thanks to Violet and the other students for all their industry this summer.
The Hardt lab at McGill recently published a paper that identified a role for AMPA trafficking in forgetting. Axel Guskjolen (pictured here at the recent neurogenesis meeting with Amar Sahay and Diano Marrone) has written a commentary on the paper. Axel’s commentary appears as a ‘journal club’ article in The Journal of Neuroscience, and you can read it here.
A big thank you to the undergrads who chose to spend their summer in the J/F lab in 2016. Top row (L to R): Violet, Tiange, Matt and Rouzbeh. Bottom row (L to R): Moriam, Phyllis, Catherine and Sean.
Some memories seem to naturally go together. For instance, if you think of an important experience in your life (exchanging your vows at the church, for example), you may also be likely to think about another experience that happened around that time (later on your friend drank too much wine at the reception). These two memories seem to be somehow linked in your mind. In a new study, our labs have figured out how memories how this might happen in the brain.
Our memories are thought to be represented in the brain by small collections of cells (neurons). In recent years, our labs have identified collections of neurons (or engrams) in the brain’s amygdala that store specific memories. But there are many thousands of neurons in the amygdala. How does the brain decide which collections of neurons encode a particular memory? Sheena’s lab found that the activity (or excitability) of neurons in the amygdala fluctuates, and only the neurons that are most excitable when an event occurs are likely to ‘grab’ the memory.
In the new paper, we take this one step further and ask how are memories for separate events linked in the brain. We find that after encoding a memory, these ‘engram’ cells remain active for a few hours before their excitability levels fall back in line with their neighbors. We show that if a second event occurs within this window (i.e., <6 hours), then the memory for that event is encoded in exactly the same collection of neurons as the first memory. These two memories have been encoded in the same population of cells and have become linked.
In contrast, if the second event occurs outside of this window (e.g., a day later) then these cells are no longer excitable, and the memory for that event is encoded in a different population of cells. These two memories are not linked.
We went onto to prove that a neuron’s excitability was the key factor determining whether two memories were linked or not. By artificially manipulating neuron excitability we could link two memories that would normally be encoded in separate populations of amygdala neurons. Conversely, they could separate two memories that would normally be encoded in the same population of neurons.
Asim Rashid (in Sheena’s lab) is the lead author on this work. His contributions to the lab selfie project are above, and his paper is available here.
One of the best things about the adult neurogenesis field is that we meet about every 3 months. This time in Bordeaux. Huge thanks to Nora Abrous and Sophie Tronel for organizing a terrific meeting! Many more pictures from the meeting can be found here.
At the meeting and then on the streets of Bordeaux.
In nearly two decades of work, neuroscientist Todd Sacktor has argued that the protein PKM-ζ regulates memory maintenance in rodents. However, 3 years ago two papers (here and here) showed that mice lacking PKM-ζ could remember normally, and severely undermined PKM-ζ’s status as preeminent memory molecule. In response to these papers, a new study by Sacktor’s group reveals that another isoform of the protein acts as backup when PKM-ζ is knocked out. We have written a commentary on this new chapter in the PKM-ζ controversy.
Some pictures from last week’s NYU Frontiers in Memory meeting in Florence, featuring Mark Mayford and Cristina Alberini.