Natural disasters such as earthquakes, volcanoes, floods, and fires can have devastating effects on the lives of animals.
However, some mammals have evolved remarkable ways to cope with these environmental challenges by changing their brains.
A new study shows in real-time what helps mammals survive a natural disaster by using advanced imaging techniques to monitor the brain activity of wild rodents during simulated seismic events.
Earthquakes trigger brain plasticity in rodents
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The study, published in the journal Nature Communications, was conducted by a team of researchers from the University of California, Berkeley, the University of Chile, and the Pontifical Catholic University of Chile.
They used miniature wireless devices to record the electrical activity of neurons in the hippocampus, a brain region involved in learning and memory, of wild degus, a rodent species native to Chile.
The researchers exposed the degus to different levels of vibration, mimicking the intensity and duration of real earthquakes that occurred in Chile in the past decade.
The degus showed increased neuronal activity and synaptic plasticity, the ability of neurons to form new connections, in response to the vibration. The higher the intensity and duration of the vibration, the more plasticity the degus exhibited.
The researchers also tested the degus' spatial memory and anxiety levels before and after the vibration.
According to the researchers, it experienced higher levels of vibration performed better in a maze task, indicating improved memory, and showed less anxiety in an open field test, indicating reduced stress.
The researchers suggested that these behavioral changes are adaptive responses that help the degus cope with the unpredictable and threatening environment caused by earthquakes.
The degus have relatively large and complex brains for their body size, similar to other social rodents such as squirrels and prairie dogs.
The researchers argued that sociality, the tendency to form groups and cooperate with others, is a key factor that drives the evolution of brain size and complexity in mammals.
Social animals need to process more information and communicate more effectively with their group members, which requires more brain power.
Living in earthquake-prone regions may have further selected larger and more complex brains in the degus, as they need to adapt to frequent environmental disturbances.
Moreover, brain size and complexity vary widely across different mammal groups and that these variations are influenced by several factors, such as diet, habitat, and body size.
For example, carnivores tend to have larger and more complex brains than herbivores, as they need to hunt and catch their prey.
Arboreal animals tend to have more complex brains than terrestrial animals, as they need to navigate and balance in the trees.
Larger animals tend to have smaller brains relative to their body size than smaller animals, as they need to conserve energy and resources.
The researchers used three different measures of brain complexity: the Brillouin index, which measures the diversity of vertebrae types in the spinal column; the evenness index, which measures the distribution of vertebrae types across the spinal column; and the T:L ratio, which measures the proportion of thoracic to lumbar vertebrae.
They found that these measures correlate well with each other and with other indicators of brain complexity, such as the number of neurons and the degree of folding in the cerebral cortex.
The researchers concluded that their study provides new insights into the neural and behavioral adaptations of mammals to natural disasters and the evolutionary patterns and processes of brain size and complexity in mammals.
They hoped that their findings will inspire further research on the effects of environmental stress on the brain and behavior of animals, and the factors that shape the diversity and complexity of life on Earth.
