What is it about?
"Social brain networks," such as the default mode network, of bats have not been studied due to a lack of brain imaging studies in these animals. Our brain imaging study found connections between the bat's version of the default mode network and the parts of the cerebral cortex that process sound. These connections are stronger and more widespread for sound processing areas on the left side of the bat's brain than on the right side.
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Photo by Todd Cravens on Unsplash
Why is it important?
Bats represent ~20% of all mammalian species. They live very close together in large colonies and are very "talkative." Their brains have relatively large social, emotional, and sound processing areas. Their hearing is so high frequency that they cannot hear the loud, noxious sounds of MRI scanners. This makes them ideal for MRI-based brain imaging studies, especially studies of audition and social processing. There is also previous evidence that bats use the left sides (more than the right sides) of their brains to hear other bats "talk." The links between the bat version of the social brain (default mode) network and left auditory cortex suggests that the left auditory cortex has a greater role in socialization than the right auditory cortex. Similarities between mammalian brains suggests that these results are highly comparable to humans, who also known to preferentially use their left auditory cortices to process speech and language.
Perspectives
Bat neuroscience research has proven to be highly informative yet somewhat overly cautious. Studies employing classic electrophysiological and behavioral techniques in bats have formed the foundations of many discoveries related to auditory processing, especially echolocation. However, since bats are wild-caught and do not readily breed in captivity, their use in neuroscience research is more limited than rodents. As a result, their use in modern neuroimaging techniques, such as functional MRI, has been limited too. This study represents (to our knowledge) the first *complete* fMRI study of a bat species. It reports a default mode-like network (DMLN, similar to the default mode network humans and other mammals) in bats, shows DMLN's strong connectivity with auditory cortex, and shows that those connections are preferentially left hemispheric. It must also be noted that the loudest components of MRI gradient noise fall below the hearing range of pale spear-nosed bats (Phyllostomus discolor). This study's results have wide implications for bat research and neuroimaging in general. Specifically, this study: 1. Reveals a focal basal-ganglia resting-state network in a species that has a clear caudate and putamen separated by an internal capsule, a feature that is more characteristic of humans and other primates than rodents and other animals. 2. Reports a network that includes one of the largest amygdalae (i.e., a nuclear complex responsible for processing fear and other emotions) relative to brain size amongst mammals, with the potential for seed-based analyses, and even future neural/behavioral stimulation experiments. 3. Bolsters already existing evidence for hemispheric asymmetry in the auditory cortex of a non-primate mammalian species (namely pale spear-nosed and mustached bats), which may have implications for aphasia, specific language impairment, and other communication disorders affecting humans. 4. Provides a means of acquiring fMRI data with little interference from gradient noise, which has important implications for auditory fMRI research. Each of these four bullet points represents a different “holy grail” long sought after by auditory neuroscientists and/or neuroimaging researchers.
Stuart Washington
Howard University
Read the Original
This page is a summary of: Auditory cortical regions show resting-state functional connectivity with the default mode-like network in echolocating bats, Proceedings of the National Academy of Sciences, June 2024, Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.2306029121.
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