Fish that prefer to inspect predators with their left eye and mates with their right. Emotional processing is lateralized even in animals without a corpus callosum.
Art of Pogrebnoj-Alexandroff, CC BY-SA 3.0, via Wikimedia Commons
A brain of two halves
The idea that the left and right hemispheres of the brain are specialized for different tasks is a familiar concept for humans. For decades, this functional division was thought to be a unique feature of the human brain, linked to complex behaviors like language. Research over the past 20 years, much of it centered at the University of Padua, shows this assumption is wrong. Brain lateralization is a characteristic of all vertebrates, and studies on fish provide some of the clearest examples.
At the University of Padua, researchers like Angelo Bisazza have extensively documented how fish exhibit strong preferences for using one eye over the other depending on the situation. Because the optic nerves in most fish almost completely cross over, the left eye sends information primarily to the right brain hemisphere, while the right eye communicates with the left hemisphere. This anatomical arrangement allows scientists to infer which side of the brain is processing information simply by observing which eye the fish uses to view a stimulus.
Left for threats, right for tasks
Experiments reveal a consistent pattern of brain specialization. The right hemisphere, which receives input from the left eye, deals with novelty and danger. It controls responses to unexpected stimuli and potential predators. When a fish spots a potential threat, it will preferentially use its left eye to monitor the situation. Strongly lateralized fish have been shown to have superior escape abilities compared to non-lateralized individuals, suggesting a direct survival advantage.
Conversely, the left hemisphere, fed by the right eye, manages learned behaviors and routine tasks. This includes activities like foraging for food or inspecting a potential mate. Studies on several species, including the eastern mosquitofish (Gambusia holbrooki) and the goldbelly topminnow (Girardinus falcatus), have confirmed these preferences. This division of labor allows a fish to perform two tasks simultaneously; for example, it can search for food with its right eye while its left eye remains vigilant for predators. This parallel processing capability is an evolutionary benefit of having a lateralized brain. This holds true even in fish that lack a corpus callosum, the structure that connects the two hemispheres in mammals, indicating that brain lateralization is an ancient vertebrate trait.
💡Fun Facts
Some fish species, like the Bahamas mosquitofish (*Gambusia hubbsi*), show a stronger degree of brain lateralization in environments with high predation pressure.
The heritability of eye preference in some fish, like the goldbelly topminnow, can be over 0.5, indicating a strong genetic basis for the trait.
The scale-eating cichlid fish (*Perissodus microlepis*) from Lake Tanganyika has an asymmetric mouth, and individuals consistently use the eye on their mouth-opening side to aim their attacks on prey.
Unlike mammals where the optic nerves only partially cross, in most teleost fishes, they decussate (cross over) completely at the optic chiasm.
The coordinates point to the University of Padua's Department of General Psychology, which is an active research institution and not a public tourist venue. The exterior can be viewed from public streets at any time.
Admission
Free to view from the outside.
Accessibility
The area around the university buildings is accessible via paved city sidewalks.
