The Butterfly Brain Reveals the Subtleties Necessary for Cognitive Innovation

19.10.2024

A species of tropical butterfly with unusually expanded brain structures reveals a fascinating mosaic of neural expansion associated with cognitive innovation.

The study, published in Current Biology, examines the neural basis of behavioral innovation in Heliconius butterflies, the only genus known to feed on both nectar and pollen. As part of this behavior, they demonstrate a remarkable ability to learn and remember spatial information about food sources—skills previously associated with an expansion of a brain structure called the mushroom body, which is responsible for learning and memory.

Lead author Dr Max Farnworth, from the School of Biological Sciences at the University of Bristol, explained: “There is huge interest in how a larger brain might support improved cognition, behavioral precision or flexibility. But during brain expansion, it is often difficult to separate the effects of increases in overall size from changes in internal structure.”

To answer this question, the study authors delved into changes that occurred in the neural circuits that support learning and memory in Heliconius butterflies. Neural circuits are very similar to electrical circuits in that each cell has specific targets that it connects to and assembles a network with its connections. This network then calls certain functions, creating a circuit.

Through detailed analysis of the butterfly’s brain, the team discovered that certain groups of cells, known as Kenyon cells, expanded at different rates. This change has led to a pattern called mosaic brain evolution, where some parts of the brain expand while others remain unchanged, similar to mosaic tiles that are all very different from each other.

Dr Farnworth explained: “We predict that as we see these mosaic patterns of neural changes, they will be associated with specific shifts in behavioral performance – consistent with a number of learning experiments that show Heliconius outperforms its closest relatives only in very specific ways.” contexts such as long-term visual memory and model learning.”

To feed on pollen, Heliconius butterflies need efficient feeding routes because pollen-bearing plants are quite rare.

Project leader and co-author Dr Stephen Montgomery said: “Rather than following a random foraging route, these butterflies appear to take fixed routes between floral resources – akin to bus routes. The planning and memory processes required for this behavior are carried out by collections of neurons within the mushroom bodies, which is why we are so interested in the internal circuitry throughout it all.”

“Our results suggest that certain aspects of these circuits have been modified to provide enhanced capabilities to Heliconius butterflies.”

This research contributes to the understanding of how neural circuits change to reflect cognitive innovation and change. Studying neural circuits in tractable model systems such as insects promises to reveal genetic and cellular mechanisms common to all neural circuits, thereby potentially bridging the gap, at least at the mechanistic level, with other organisms such as humans.

Looking ahead, the team plans to explore neural circuits beyond the learning and memory centers of the butterfly brain. They are also aiming to increase the resolution of their brain mapping to visualize how individual neurons connect at an even more granular level.

Dr Farnworth said: “I’m really fascinated by the fact that we see such a high degree of conservatism in the anatomy and evolution of the brain, yet there are very noticeable but distinct changes.”

“This is really exciting and a great example of a layer of biodiversity that we don’t usually see, the diversity of brain and sensory systems, and the ways in which animals process and use the information provided by their environment,” Dr Montgomery concluded.

Author Vladislav Kulach

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