Unveiling the Neural Innovators: How Crabs Revolutionized Neuroscience

In the early 1970s, computers emerged as a ubiquitous presence, capturing the imagination of people worldwide. Coincidentally, neuroscientists saw an intriguing similarity between the wiring of the human nervous system and these marvels of technology. Our neurons, like computer circuits, received inputs, passed electrical messages, and generated outputs, leading scientists to perceive the brain as a vast network of "hardwired" circuits. However, this neat one input, one circuit, one output analogy soon proved insufficient to explain the astounding complexity and adaptability of our nervous system.

Amidst this puzzle, Eve Marder, an innovative neuroscientist, offered an alternative theory for how our nervous systems truly function. To prove her groundbreaking hypothesis, she turned to an unexpected source: crab stomachs. Yes, those crustaceans' stomachs revealed fascinating insights into the inner workings of the human brain.

Consider the act of walking—a seemingly simple behavior. The muscles in our legs, ankles, and feet perform intricate movements to adjust to the terrain and maintain balance. Understanding how such behaviors are produced becomes vital when it comes to identifying and addressing anomalies.

Early on, neuroscientists believed that brain activity relied on electricity traveling through neural circuits, similar to how currents flow in a circuit board. Anatomists observed networks of nerves connecting to muscles throughout the body, reinforcing the notion of neural circuitry. The brain would generate an instruction, the "wires" (neurons) would transmit the signal, and the result would be a behavior. This view dominated neuroscience in the 1970s.

However, this simplistic model began to crumble as researchers delved deeper into neuroanatomy. It became apparent that the human body didn't have enough neurons to support the notion of one circuit per behavior. Additionally, individual differences in neural connections didn't significantly impact behavioral outcomes. Moreover, neurons, while durable, still needed replacements for certain parts, which contradicted the idea of a fixed circuit.

Eve Marder set out to explore the stomatogastric ganglion (STG), a cluster of approximately 30 neurons connected to crustaceans' stomachs. These STG neurons controlled a unique form of "chewing" in crabs and lobsters. Rather than chewing with their mouths and swallowing, these creatures used their stomach muscles to grind their dinner into digestible pieces. The STG neurons proved ideal for research, as they continued to function even when isolated from the organism.

Marder's research focused on how neuromodulators—molecules influencing neuronal behavior, like dopamine—affected the STG neurons. At the time, most scientists believed neuromodulators influenced individual neurons in a sequential manner. However, Marder made a remarkable discovery—neuromodulators influenced the entire group of STG neurons collectively. Each neuron responded differently to the same molecule, leading to a variety of outcomes.

This finding was revolutionary and suggested that a single neural circuit could produce multiple behavioral outcomes with the influence of neuromodulators. The implications for our own nervous systems were profound. Marder's work demonstrated how our brains achieved fine-tuned behaviors, like different walking patterns, without requiring an astronomical number of unique neural connections. It also explained how different individuals could produce the same behaviors despite differences in neural connections.

Her research further addressed the adaptability of the nervous system as individual neurons underwent replacement. The brain could still produce the same outcomes using different circuits or parts of a circuit. Marder's insights opened new avenues for investigating various neurological issues. For instance, understanding how neuromodulators create flexibility in the nervous system could be crucial for stroke treatment. After a stroke, the brain can establish new connections to compensate for lost functions, allowing it to adapt without having to rebuild the same circuits.

As Marder's research continues, she also explores how wild-caught animals are affected by climate change. Her work exemplifies how nervous systems both change and stay the same, earning her the prestigious 2016 Kavli Prize in Neuroscience.

In the grand scheme of science, Eve Marder's journey mirrors the mysteries of the nervous system. By embracing new perspectives and challenging traditional models, entirely new pathways of understanding are revealed—opening the door to groundbreaking discoveries that revolutionize neuroscience and reshape our comprehension of the human brain.