Eon Systems Places Digitally Emulated Fly Brain Into a Virtual World

Complete fly brain emulation operates inside a virtual environment for the first time

Eon Systems has digitally replicated 125,000 neurons and 50 million synaptic connections of an adult fruit fly brain, then placed the resulting model into a simulated virtual environment. Co-founder Alex Wissner-Gross published video footage of the experiment.

The recording shows the virtual fly performing characteristic behaviors: moving its legs, rubbing them together, and drinking from a small bowl using its proboscis inside a digital sandbox.

Why this matters

Whole-brain emulation has remained one of the most ambitious goals in intelligence research for decades. Reproducing a brain neuron by neuron, synapse by synapse, and then running it — that is how Wissner-Gross framed the challenge. He described the experiment as the world's first whole-brain emulation capable of producing multiple types of behavior.

The critical breakthrough is the closing of a full sensorimotor loop: sensory signals flow into the model, neural activity propagates across the connectome, motor commands are sent outward, and a physically simulated body executes them. This marks the first time in the history of whole-brain emulation that the cycle from perception to action has been completed.

Scientific foundation

The experiment builds on work by Eon Systems senior researcher Philip Shiu and his colleagues. In 2024, the team constructed a complete computational model of the fruit fly brain to study neural circuits responsible for feeding and grooming behaviors.

The team leveraged Princeton University's FlyWire connectome project — a complete neural wiring diagram of the insect brain. Results demonstrated that the computational model predicts motor behavior of the simulated fly with approximately 95% accuracy. Activation of sugar- or water-sensitive neurons in the model accurately predicted the responses of taste-related nerve cells.

Road ahead: from fly to mouse to human

Wissner-Gross noted that Eon Systems' work extends earlier research, including a 2025 project by the DeepMind team that modeled fruit fly neural pathways using reinforcement learning.

Eon Systems intends to scale up its approach. The next milestone is a digital emulation of a mouse brain, with the ultimate goal being human brain emulation. The scale of the challenge is enormous: a mouse brain contains more than 500 times as many neurons as that of a fruit fly.

According to Wissner-Gross, if the sensorimotor loop was successfully closed in simulation for a fly, then achieving the same for a mouse is a matter of scale rather than principle.