Octopuses are known for their remarkable intelligence and abilities, such as solving puzzles, escaping from tanks, and even using tools. But what makes these creatures so smart? A new study by researchers from the Hebrew University of Jerusalem and Harvard University has shed some light on the neural architecture that governs the learning processes of the common octopus (Octopus vulgaris).
The vertical lobe: a key structure for learning and memory
The researchers focused on the vertical lobe of the octopus’s central nervous system, which is crucial for learning and memory. The vertical lobe is composed of about 25 million interneurons that are divided into two distinct groups: simple amacrine cells (SAMs) and complex amacrine cells (CAMs). The SAMs, which make up about 92% of the interneurons, specialize in learning visual characteristics through synaptic reinforcement. The CAMs, which make up the remaining 8%, are involved in more complex cognitive functions, such as associative learning and memory consolidation.
Using a robotic system and a sophisticated computational algorithm, the researchers were able to reconstruct a three-dimensional representation of the structural elements that comprise the network. They used an electron microscope to achieve a resolution of about four millionths of a millimeter, which allowed them to trace the intricate synaptic connections among the neural elements.
A simple yet efficient network for learning
The researchers found that the vertical lobe has a simple yet efficient network structure that enables fast and flexible learning. The SAMs form a dense network that can quickly adapt to new stimuli and store short-term memories. The CAMs form a sparse network that can integrate information from different sources and store long-term memories. The CAMs also have a unique feature: they can form synapses with themselves, creating loops that may enhance memory retention and retrieval.
The researchers also discovered that the octopus’s network shares some similarities with the mammalian hippocampus, which is also responsible for learning and memory. Both networks have recurrent connections that can strengthen synaptic plasticity and memory formation. Both networks also have inhibitory interneurons that can regulate the activity of the network and prevent overstimulation.
Implications for understanding memory processes across species
The study reveals how the octopus, which diverged from humans by 700 million years of evolution, has developed a sophisticated neural system that supports its cognitive abilities. The study also provides a promising model for studying memory networks in other animals and humans, by comparing the neural mechanisms and principles that underlie learning and memory across species.
The study was published in the journal eLife under the title “Connectomics of the Octopus vulgaris Vertical Lobe Provides Insight into Conserved and Novel Principles of a Memory Acquisition Network.”
