Scientists at NTNU’s Kavli Institute for Systems Neuroscience in Norway have made a groundbreaking discovery regarding the brain’s ability to organize sequential experiences. The researchers have identified a pattern of activity, which they describe as a fundamental algorithm intrinsic to the brain and independent of experience. The findings have been published in the journal Nature.
The brain’s capacity to arrange elements into sequences is a crucial biological function that is essential for various cognitive tasks, including communication, time perception, spatial navigation, and memory consolidation. Without the ability to organize experiences into a temporal order, the world would appear as a chaotic and disjointed series of events.
According to Professor Edvard Moser, memories should be more accurately likened to videos rather than snapshots. Every experience we have unfolds over time, with one event following another. The brain possesses the remarkable ability to capture and organize selected events in the order they occurred, creating meaningful experiences. This process occurs on the timescale in which we interact with the environment and takes time to replay when recalling the memory.
However, the question remains as to how the brain is capable of generating and storing lengthy and unique sequences of information in real-time. The researchers at NTNU sought to uncover the foundational mechanism responsible for sequence formation, specifically focusing on the medial entorhinal cortex (MEC) in the brain. This region plays a vital role in brain functions related to navigation and episodic memory, which occur over longer timescales.
To investigate how neurons coordinate at these slow timescales, the researchers designed an experimental environment in which sensory inputs were minimized. They allowed a mouse to freely run in complete darkness without any specific task or reward, while simultaneously monitoring the activity in the mouse’s entorhinal cortex. What the researchers discovered was a distinct pattern of neural activity characterized by slow oscillations traveling through the network in a coordinated manner, reminiscent of rhythms in a symphony.
These ultra-slow sequences took two minutes to travel throughout the neural network before repeating the cycle, which could last for the duration of the test session. The researchers observed that as each cell oscillated, the cells also organized themselves into distinct sequences, firing in a specific order, before returning to the initial cell and starting the process again. This coordinated activity aligned with the timescale at which events are encoded into episodic memories, suggesting that these sequences serve as a template for constructing the sequential structure of memories.
The activity patterns observed in the MEC were found to be transmitted through synaptic connections between cells in the network. While it may be challenging to observe this coordinated activity without proper visualization techniques, the researchers were able to identify the pattern using a raster plot, which revealed the rhythmic waves traveling through the network.
When examining the raster plot, a distinct spiral pattern emerged, representing the network’s activity over time. The sequence of firing cells in the network formed a ring-like structure, where each cell had a designated firing time distributed across the ring’s surface. The signal traveled through the entire ring structure before returning to the same cell, indicating repetitive sequence patterns.
The researchers believe that this discovery opens up new possibilities for understanding the brain and its coordination patterns. The notion that cells with different properties can coordinate and work together on different timescales challenges current understanding and may revolutionize our understanding of brain functioning. This fundamental brain algorithm for sequencing experiences may have significant implications for various fields, including neuroscience, psychology, and artificial intelligence.
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