What Are Memories Made Of?

CNS 2024 guest post by Julia Cardarelli

Preparing to write this post about new memory research presented at CNS 2024 in Toronto required me to search my own memories for what I found most salient. A lot of my recall from the event comes down to certain factors that affect how we form memories, how emotion can alter how we remember events, as well as the physiological state of my brain since the event. These factors seem to boil down to a simple yet consequential question: What are memories made of?

“Memory may be defined as the retention over time of internal representations gained through experience, and the capacity to reconstruct these representations at later times.” -Sheena Josselyn, 2024

Well, maybe it depends on who you ask. To me, a memory is something I have to remind myself of an experience I’ve lived or it can be a consequence of learning information and storing it for later use. I believe that anyone you ask might have a similar answer, because we all know the universal concept of autobiographical and procedural memory.

However, if you ask a neuroscientist, you might find a more specific answer. Indeed, at CNS 2024, researchers approached memory from a myriad of different perspectives, ranging from their physical representation in the brain, to efforts to demystify the neural basis of memory, to the impact emotion has on memory consolidation.

Physical representation

Sheena Josselyn, the CNS 2024 keynote speaker and professor in physiology and psychology of The Hospital for Sick Children and The University of Toronto, discussed how the physical manifestation of memories allows us to study them in new ways, showing us in the audience how specific sets of neurons working together to form a representation of memories known as engrams. This was a new way for me to think about memories and what they are made of, and I found the possibility of identifying neural circuits that represent specific memories exciting.

Josselyn’s work has focused on memory expression in rodent models using genetics, optogenetics, and surgical procedures to alter the animal’s neural expression of memories. Physical alterations are sometimes studied in tandem with behavioral conditions, such as administering cocaine or foot shocks, to generate a learned behavior through operant conditioning.

Together, these tools have given Josselyn and her team the ability to target and identify specific groups of neurons in the rodent brain, associated with a memory she has taught the animal. An engram is just one piece of the puzzle attempting to explain what memories are made of.

The emotional role

Beyond the physical representations of memories in the brain, emotions play a huge role in what we remember and how. In a symposium entitled “Reconciling the Impact of Emotion On Episodic Relational Memory,” Daniela Palombo, an associate professor of psychology at The University of British Columbia, discussed how neutral versus negative emotion alters how we remember information. This topic is of especial importance in the context of fear and PTSD associated emotion dysregulation.

Using a short movie clip, Palomba exposed her participants to both neutral and negative scenes and asked the participants to recall the information. She and colleagues discovered that emotion enhances temporal order but not free-recall.

Palomba explained that their methods are unique, as many researchers may avoid using movie clips because they often have conflicting information causing interference with task instructions. Her lab devised a way to generate a movie clip that minimized information conflict by splicing scenes together. What I learned from Palomba is that emotion helps us to remember events in sequence, as if we use our feelings as a timestamp to recall the order of an event at a later time.

The physical-emotional interplay

In work that tied together physical representations of human memory with the effects of emotion in recall, Hannah Piccirilli, an honors student of Westminster College, presented research that uses EEG to measure recall in a word recognition task. She specifically targeted the Late Positive Potential (LPP) an Event Related Potential (ERP) which is associated with emotion.

Piccirilli was able to highlight the correlation between LPP amplitude and memory recall of emotional words over time. She hypothesizes that the LPP has implications in memory consolidation that are related to emotional valence. Piccirilli explained to me how her findings could suggest that the LPP could represent a neural mechanism employed to tag emotional stimuli for memory consolidation.

Piccirilli’s findings reminded me of the discussions from both Josselyn and Palomba about why negative emotion is so prevalent in memory research. Specifically, fear is thought to be an important factor for creating long-term memory because survival is dependent on avoiding dangerous situations and learning to avoid these fearful and dangerous situations aids in that endeavor.

What lies ahead

Prior to CNS 2024, an uncharted territory lay ahead of me. Amid the four days worth of poster sessions, symposia, and invited lectures, I was not sure what themes would emerge. But reflecting on my own memories, I can clearly see how memory research continues to captivate the minds of cognitive neuroscience, challenging our views of what memories are and how they can change over time.

Memory is perceived to be part of what makes us who we are. If not for memories, who would you be? It is important to understand the neural mechanisms that represent memories, how emotion can manipulate the formation of memories, and how brain dysfunction can teach us what brain regions are most strongly associated with memory.

Each method used to study memory generates an important piece of the puzzle. A memory engram is a group of neurons working together to retain and recall information. However, the story doesn’t stop there: memory is implicated by emotion. Strong emotion is generally thought to be a factor which makes memories more vivid and easily recalled.

Discovering neural signatures that represent memory formation and recall is a hallmark of neuroscience. Each of these methods provide evidence that several systems work together to digest the perceptual information of our environment resulting in a long lasting change to our brain architecture, known as a memory.

The interplay between memory formation, recall, and emotions is surely a topic that will continue to evolve, and I cannot wait to see what is next on tap at CNS 2025 and beyond!

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Julia Cardarelli, B.A., is a research assistant at the University of Hawaii at Manoa. On a volunteer basis, she has studied human perception and attention in the Brain & Behavior Laboratory and Perception and Attention Research Laboratory with Jonas Vibell and Scott Sinnett, respectively. In the future, she aims to study emotional memory implicated by PTSD and brain injury subjects.