In a world first, Johns Hopkins University (JHU) researchers used a tiny, wireless implant to record how bats’ brains process sensory information while flying freely and using echolocation.
According to their paper, now published in eLife, future investigations could use this pioneering technique of neural activity collection and analysis to illuminate how the brains of other mammals – including humans – focus on objects and activities in a real-world setting.
Previously, studies on what occurs in the brain as it interprets the external environment have been limited by reliance on restrained animals viewing the test stimuli on screens.
“If you want to understand how the brain operates in the real world, you have to have the animal moving through the world in a natural way,” said co-lead author Melville Wohlgemuth in a statement. “This idea of recording the brain without wires is brand new. And no one has used it to understand how an animal senses the world and reacts to that information.”
When choosing a study subject, the JHU team turned to bats, who, on top of being the only flying mammals, use echolocation to map their surroundings. By interpreting the delay between when they emit high-pitched vocalizations and when echoes from the sound waves reach their ears, bats can estimate the distance and position of objects relative to themselves.
The lightweight nerve signal-sensing probes were implanted in a midbrain area called the superior colliculus (SC) because earlier research had shown that clusters of neurons in the region are responsible for echolocation interpretation.
After many sessions of letting brain-linked big brown bats fly around a darkened lab, the team compared data on each bat's neural activity with records of their second-by-second location and when they produced echolocation vocalizations. The end result was a model that showed how different neurons fired as the bats moved through space and as their attention shifted to different objects in their paths.
As the authors predicted, the bat’s internal reconstruction of what the space around them “looked" like appears to be encoded by the firing of SC neurons.
Furthermore, when the bats shifted their attention to a particular object by emitting targeted clusters of vocalizations (which the authors compare to a person shifting from an undirected gaze to actively focusing their eyes on something), the spatial mapping neurons fired with more precision.
"To see signals in the brain when an animal is really looking at something and then to see a neuron fire was the holy grail for me,” said co-first author Ninad Kothari. “As this research goes forward, we can take the information we get from animals like bats, mice, and owls and put it into human terms to potentially help people with attention deficits.”