Microscopy image of an octopus cell (magenta). Image credit: Kreeger et al. (CC BY 4.0)
Imagine trying to listen to a friend in a busy coffee shop. Your brain helps to focus on their voice by distinguishing between the different sounds in the environment. This ability relies on specialized neurons in the auditory system called octopus cells, which detect when sound frequencies occur and change together.
Unlike most neurons in the auditory system, octopus cells can be activated by inputs from many different frequencies. However, they only reliably release an electrical signal after receiving these excitatory inputs simultaneously. This explains why these cells can respond at the beginning of a sound stimulus but not why they can also react to frequencies that change together over time, like in speech or music. This suggests that the cells’ computations may be more complex than previously thought. Rather than relying solely on excitatory inputs, alternative signals that reduce activity, known as inhibitory inputs, may also play a role.
To test this hypothesis, Kreeger et al. studied genetically modified mice to reveal the octopus cells’ activity using molecular fluorescent labels. They created a map of the incoming signals to the octopus cells, showing inhibitory inputs to the outer branched extensions of the cells. By using light to control cell activity and measuring electrical responses, Kreeger et al. showed that inhibition helps refine how excitatory signals travel through the neuron. This gives the octopus cell more time to process excitatory inputs, meaning that one cell can make computations both about the onset of sound and about frequencies that occur together during the sound.
These results provide a fuller picture of how the brain helps distinguish between sounds in noisy environments. Understanding the fine-tuning role of inhibitory signals in octopus cells may help researchers improve hearing aids and develop treatments for auditory processing disorders.
