Pupil size says a lot about the type of memories we hold on to: What should we know

Our eyes are more than just windows to the world—they’re also mirrors to our minds. Here is an interesting fact that you will know today, the size of our pupils reveals a lot about the memories we store and even how we process them during sleep. There has been a discovery recently. Scientists have found a connection between pupil size and the way our brain balances new and old memories, particularly in the quiet depths of non-REM sleep. Here is how this discovery unfolds and why it matters.

What is the connection between pupils and memory?

Have you ever noticed that your pupils change in size in response to emotions or light? In addition to these normal responses, your pupils also change when you sleep, showing how your brain processes memories. A study that was published in Nature claims that these alterations are not at all random. Your pupils’ rotation between smaller and larger sizes as you sleep is a reflection of how your brain reviews prior experiences and reinforces new information.

According to neuroscientists, this oscillation lessens “

catastrophic forgetting

,” a phenomenon in which new memories remove old ones, by assisting the brain in better organising memories. Your pupils serve as microscopic windows into how your mind reconciles the past and present.

Non-REM sleep

The brain functions in the background during non-REM sleep, which is essential for memory consolidation. The pupils exhibit minor changes throughout this phase, but the eyes remain mostly still. The brain concentrates on creating new memories, such recent experiences or lessons learnt, while your pupils contract.

These micro-adjustments, which last only milliseconds, are critical for arranging our mental archives. They avoid interference between new and old knowledge, helping us to remember what is vital without losing earlier knowledge.

But do you know what REM and Non-REM sleep mean?

When we sleep we go through two primary stages: rapid eye movement (REM) sleep and non-rapid eye movement (non-REM) sleep. These stages play distinct roles in physical restoration and memory consolidation.
Non-REM sleep occurs first and has three stages, each progressively deeper. It’s during this phase that the body repairs tissues, strengthens the immune system, and consolidates memories. According to neuroscientist Azahara Oliva, “Non-REM sleep is when the actual memory consolidation happens. These moments are very short, like 100 milliseconds, but crucial for organizing new and old memories.” Non-REM sleep ensures our mental archives remain intact, processing new knowledge while preserving the old.

REM sleep, which follows, is the dream stage. Characterized by rapid eye movements, increased brain activity, and muscle paralysis, REM sleep supports emotional regulation and creative problem-solving. During REM, the brain synthesizes information, linking old experiences with new insights. As per a study done in 2018, REM sleep is essential for learning complex skills and fostering creativity.
For a healthy sleep cycle, both phases are equally important. REM adds emotional and cognitive experiences, whereas non-REM concentrates on memory storage and restoration. They demonstrate the complex mechanisms of sleep’s restorative ability and together serve as the cornerstone of a healthy body and mind.

What is the science behind pupil fluctuations?

To better understand this, researchers tracked mice’s brain activity and pupil size while they slept. The mice were taught activities such as exploring mazes to find food or water. Later, they were assigned new tasks. During sleep, the pupil size reflected whether the brain was processing new or old memories.
When researchers disturbed the mice’s sleep during specific pupil stages, the mice had difficulty recalling tasks associated with those stages. This confirmed the relationship between

pupil size and memory

type.
– Smaller pupils: Concentrate on new memories.
– Larger pupils: Revisiting old memories.

These findings suggest that pupil size could be a window into understanding how humans process memories, too.

Dreams and reactions: What pupils reveal about memory

Dreams feel like a jumbled mix of the past and present. Pupil size during non-REM sleep may also explain why. When your brain revisits old memories (larger pupils), you might dream of past events. Similarly, when consolidating new memories (smaller pupils), your dreams could reflect recent experiences.

This fluctuation could explain why dreams sometimes blend past knowledge with new ones. It’s the brain’s way of organising and synthesizing memories, helping you wake up with a clearer understanding of what to retain.