A stadium packed with fans hears the announcer’s voice for the first time, and instantly the whole place erupts. The message sounds again and again. Only a handful of people in nearby rows respond. That’s roughly how neural networks behave in brain organoids — tiny lab-grown replicas of the brain.

The researchers stimulated the organoids with electrical pulses and recorded the response using a microelectrode array. They expected a wave, like ripples on water. But the opposite happened. The response proved to be Neural Network Oscillations — a synchronous burst across the entire network, with no delays at the detectors. Biologists call this collective behavior of neurons.

The most interesting part emerged during repeat experiments. Organoids that were stimulated daily gradually reduced their activity: by the fifth session, the response encompassed only 10% of the electrodes, compared to 93% on the first day. The decisive argument came from the control group. One organoid received its first stimulus only on the seventh day of development, and showed a full response. This ruled out the influence of maturation. Thus it was confirmed: repeated experience rewires the network, making it stop responding to a familiar signal.

The organoid’s neurons learn to distinguish the important from the routine, like fans who stop jumping up at every announcement. These findings change the approach to organoid experiments. Now it’s clear: repeated stimulation alters the system itself. This must be taken into account in future research. Perhaps one day such models will help unravel the mechanisms of learning and memory.