Good Horsemanship

Left or Right Brain

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We can, perhaps, take some of this information and see how it may apply to horses.

When fish get emotional

07 July 2007
NewScientist.com news service
Nora Schultz

WHO ever heard of a fish being in two minds about something? Yet it seems that like humans, fish process information - and perhaps emotions - on different sides of the brain.

Fish growing up in the wild among predators use their left eye to look at novel objects, while their offspring raised in captivity use the right eye.

This suggests that life experiences can affect which side of the brain fish use, and even, says Victoria Braithwaite of the University of Edinburgh, UK, that they have emotional mindsets, since different sides of the brain may correspond to a curious or suspicious attitude.

"The lab-reared fish could process information about novel objects in the left brain [which means they are looking at things with their right eye] because they feel more comfortable, whereas their parents are more cautious."

"Lab-reared fish could process information about novel objects in the left brain because they feel more comfortable."

Humans use their left and right brain lobes differently, the most well-known consequence being handedness. Brain lateralisation has been found in an increasing number of other species in recent years.

"Especially for animals that have to cope with many predators, it is an advantage if they can use one hemisphere to keep an eye on predators while they use the other hemisphere to do other things," says Culum Brown, now at Macquarie University in Sydney, Australia.

Brown and his team caught bishop fish (Brachyraphis episcopi), which are similar to guppies (see Photo), from areas with high and low predation rates in Panama. The team bred the fish in the lab and then tested the behaviour of both the wild parents and their offspring. Fish swam towards a slatted barrier through which they could see either a novel object (a yellow cross), nothing, or another bishop fish. They could then swim past the barrier either to the left or to the right. Exiting to the left meant the fish had kept its right eye on the barrier, and vice versa.

Neither fish from areas of low predation nor their young showed much of a preference for a left or right exit, suggesting their brains were not very lateralised. However, fish that had to deal with a lot of predators in the wild favoured one eye, as did their lab-born offspring, especially when viewing the novel object (Animal Behaviour, DOI: 10.1016/j.anbehav.2006.08.014).

"This shows that a tendency for brain splitting can be inherited," says Braithwaite. "But amazingly, the captive-born offspring preferred the right eye when their parents preferred the left. So the way the fish then use this brain division is a learned thing."

Giorgio Vallortigara from the University of Trieste, Italy, who studies lateralisation in vertebrates, says that the left side of the brain directs approach behaviour and the right side withdrawal. Dogs wag their tail to the right when they see a friendly human but to the left when faced with a scary dominant dog, he found (Current Biology, vol 17, p R200). "The wild fish could similarly use their left eye here because they are frightened and more likely to withdraw," he says.

But there is another explanation, says Brown. Left-eye preference for novel objects in wild fish could mean they have learned to take better advantage of their innate ability to lateralise: "Using the left lobe could simply be the default in this context," Brown says. Indeed, fish from low-predation areas showed a slight tendency to use the right eye in all tasks. Lab-born fish of parents from high-predation areas could be exaggerating this default right-eye bias because they have inherited strong lateralisation. However, since they've never met a predator, they haven't learned to pay special attention to novel objects using their right brain and left eye.

Whether humans with differing life experience also vary in which brain side they use to deal with certain emotive stimuli is not yet known, but the researchers agree that such processing plasticity is likely in all lateralised species: "We know, for example, that stroke patients with damage to one hemisphere can learn to compensate with the other lobe," says Brown. And Vallortigara adds: "I would expect a dog who has never seen a human would feel more sceptical and wag its tail to the left."

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