Human brains on animal alert
It is a common showbiz adage that films about animals almost always draw an audience, but a new study proves this is not a myth - it is a function of the human brain.
At the sight of an adorable pet, in Hong Kong's case typically a poodle, most people would feel compelled to stop and stroke it while cooing: 'Oh ... so lovely.' If they see a snake, a crocodile or a spider they would usually show fear and back away.
Researchers discovered that these responses are prompted by a specific part of the human brain that is hard-wired to detect rapidly creatures of the non-human kind.
What is more, the same thing happens if people see images and movies or hear stories about such animals, which goes some way to explaining why films about animals - even animals talking to people and to each other in English - never fail to capture people's attention.
Researchers from the California Institute of Technology (Caltech) and the University of California, Los Angeles (UCLA) say that neurons throughout the amygdala - a centre in the brain known for processing emotional reactions - respond preferentially to images of animals.
Their findings appear online in the journal Nature Neuroscience.
The collaborative research team recruited 41 epilepsy patients at the Ronald Reagan UCLA Medical Centre who were already being monitored for brain activity related to seizures. Using electrodes already in place, the team recorded single-neuron responses in the amygdala as they showed the participants images of people, animals, landmarks and objects.
The amaygdalae are two almond-shaped clusters of neurons located in the medial temporal lobe of the brain. Neurons are cells that are core components of the nervous system.
'Our study shows that neurons in the human amygdala respond preferentially to pictures of animals, meaning that we saw the most amount of activity in cells when the patients looked at cats or snakes, versus buildings or people,' said Florian Mormann, lead author on the paper and a former postdoctoral scholar in Caltech's biology division.
'This preference extends to cute as well as ugly or dangerous animals, and appears to be independent of the emotional contents of the pictures,' he said. 'Remarkably, we find this response behaviour only in the right and not in the left amygdale.'
He said the hemispheric asymmetry helped strengthen previous findings supporting the idea that, early on in vertebrate evolution, the right hemisphere became specialised in dealing with expected and biologically relevant stimuli or with changes in the environment.
'In terms of brain evolution, the amygdala is a very old structure, and throughout our biological history, animals - which could represent either predators or prey - were a highly relevant class of stimuli,' he said.
'This is a pretty novel finding, since most amygdala research in the past was usually about faces of people and emotions related to fear, rather than pictures of animals,' said Ralph Adolphs, a co-author on the paper and Bren Professor of Psychology and Neuroscience and professor of biology at Caltech.
The neurons did not become more active when photos of human beings were shown, regardless of whether the photo was of a famous celebrity or a random stranger. Nor did it matter from what angle or distance the photos were taken.
'Nobody would have guessed that cells in the amygdala respond more to animals than they do to human faces, and in particular that they respond to all kinds of animals, not just dangerous ones,' he said. 'I think this will stimulate more research and has the potential to help us better understand phobias of animals.'
The study also shows how scientists doing basic research can benefit from working with collaborators in a clinical setting.
'This is a good example of how special situations in neurosurgery - in this case, patients who are treated in order to cure their epilepsy - can provide a unique window into the workings of the human mind,' said Itzhak Fried, a UCLA neurosurgeon and co-author of the study.
Using advances in neuroimaging technology, such as magnetic resonance imaging, scientists have made significant findings concerning the amygdala in the human brain.
A variety of data show the amygdala plays a substantial role in mental states, and is related to many psychological disorders.
The left amygdala has been linked to social anxiety, obsessive and compulsive disorders, and post-traumatic stress.
People with severe social phobia showed a correlation with increased response in the amygdala; depressed people showed exaggerated left amygdala activity when interpreting emotions for all faces, and especially for fearful faces.
Recent studies suggested possible correlations between brain structure and sexual orientation. Homosexual men tend to exhibit more female-like patterns in the amygdala than do heterosexual males, just as lesbians tend to show more male-like patterns than heterosexual women.
Studies in 2004 and 2006 showed that people who were shown images of frightened faces, or faces of people from another race, showed increased amygdale activity.
Two almond-shaped clusters of neurons - cells that are core components of the nervous system - deep in the brain's medial temporal lobe. Known to process emotional reactions and play a role in mental state and psychological disorders