New discoveries made concerning the brains of bats: 'What we have found instead is that brain areas represent common synergies of muscles'

A new study shows how the brains of Egyptian fruit bats are highly specialized for echolocation and flight, with motor areas of the cerebral cortex that are dedicated to sonar production and wing control.

Research is being done at the UC Davis Center for Neuroscience under the direction of Professor Leah Krubitzer on the influence of evolution and development on the brain organization of a wide range of mammals, such as primates, rodents, tree shrews, and opossums. In a recent study, the researchers investigated the motor cortex of the Egyptian fruit bat, a species that does echolocation using its tongue rather than its larynx. They discovered evidence for complicated motions involving a variety of the animal's body parts. The investigators found that the motor cortex of the bat contains a substantial region that depicts movements of the tongue. This is far more than what is found in the motor cortex of other species, such as primates and rodents.

"What we have found instead is that brain areas represent common synergies of muscles, rather than individual muscles," Krubitzer said. 

The whole motor cortex of any bat has never before been mapped, as noted by the study's first author, Andrew Halley, a postdoctoral researcher working in Krubitzer's group. The researchers gave the bats anesthesia and then used electrodes to activate various parts of the motor cortex in order to observe the muscle and limb movements that were elicited as a result of the stimulation. They discovered that regions of the brain represent shared synergies of muscles rather than individual muscles. This finding contradicts traditional notions of the formation of the motor cortex.

The study showed that the motor cortex of the bat represented coordinated movements of the shoulder and hindlimbs. This finding was significant because it reflected the fact that the power for wing movement comes from the muscles in the shoulder, while the fine adjustments that are necessary for flying come from coordinated movements of the shoulder and hindlimb muscles. Only a few regions of the motor cortex were responsible for representing forelimb movement on its own. Other regions only caused movements in the muscles of the bat's hindlimbs, which suggests that these muscles are engaged in the bat's locomotor behaviors.

According to Professor Krubitzer, one of the most effective methods for drawing extrapolations to the human predicament is to examine the brain organization of different species. The research was carried out in conjunction with academics from the University of California, Berkeley, Simon Fraser University, and the University of California, Davis. It was made possible by grants from the McDonnell Foundation, the National Institutes of Health, and other organizations.