麻豆淫院

The ability to quickly recognize sounds, particularly the vocalizations made by other animals, is known to contribute to the survival of a wide range of species. This ability is supported by a process known as categorical perception, which entails the transformation of continuous auditory input (e.g., gradual changes in pitch or tone) into distinct categories (i.e., vocalizations that mean something specific).

Various past studies have tried to shed light on the neural underpinnings of categorical perception and the categorization of vocalizations. While they broadly identified some brain regions that could play a part in these abilities, the precise processes through which animals categorize their peer's categorizations have not yet been fully elucidated.

Researchers at Johns Hopkins University recently carried out a study investigating how vocalizations are represented in the brain of big brown bats, which are scientifically known as Eptesicus fuscus. Their findings, in Nature Neuroscience, suggest that the categories of vocalizations are encoded in the bat midbrain.

"While categorical perception is thought to arise in the neocortex, humans and animals could benefit from a functional organization tailored to ethologically relevant sound processing earlier in the auditory pathway," wrote Jennifer Lawlor, Melville J. Wohlgemuth and their colleagues in their paper.

"We developed two-photon calcium imaging in the awake echolocating bat (Eptesicus fuscus) to study the representation of vocalizations in the inferior colliculus, which is as few as two synapses from the inner ear."

The species of bats examined by the team are echolocating. This essentially means that they rely on frequency-sweep-based vocalizations (i.e., sounds characterized by rapid changes in pitch) to navigate their surroundings and communicate with their peers.

To perform their experiments, the researchers used a technique known as two-photon calcium imaging, which leverages calcium ions to visualize the neural activity of animals in real-time. They applied this technique to awake echolocating brown bats, to better understand how their brain categorized and thus helped them make sense of their peers' vocalizations.

"Auditory playback experiments demonstrated that individual neurons responded selectively to social or navigation calls, enabling robust population-level decoding across categories," wrote the researchers. "When social calls were morphed into navigation calls in equidistant step-wise increments, individual neurons showed switch-like properties and population-level response patterns sharply transitioned at the category boundary."

Interestingly, the researchers observed that neurons in a midbrain structure known as the inferior colliculus that were activated when bats heard vocalizations belonging to specific categories formed spatial clusters. These clusters appeared to be independent of tonotopy (i.e., the strategy typically employed by the brain to organize sounds by frequency).

"These findings support a revised view of categorical processing in which specified channels for ethologically relevant sounds are spatially segregated early in the auditory hierarchy, enabling rapid subcortical organization into categorical primitives," wrote the researchers.

The findings gathered by this research group could reshape the present understanding of how animals process and categorize vocalizations. They could soon open new avenues for research, potentially leading to new interesting discoveries about the brain processes supporting echolocation and communication among animals.

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