Animal Rights Amygdala

Your right amygdala can't
 resist the pygmy marmoset.

When you see a human face, neurons in your amygdala wake up and take note. But when you see an animal, whether cute or menacing, the amygdala in your right hemisphere jumps to its feet and starts to dance. Caltech and UCLA neuroscientists found that while pictures of humans evoked strong neuronal responses in the amygdalas of 41 human research subjects, the responses were far stronger, and faster, to images of animals. The amygdala, a two-lobed part of the limbic system buried deep in the medial temporal lobes of each brain hemisphere, is a key player in emotional reaction and processing emotional memory.

The researchers, led by Caltech postdoc Florian Mormann, suggests that we are hard-wired to respond emotionally--and thus pay close attention to--animals of all kinds. This may reflect the important role animals have played throughout human history as predators, prey, and potential allies.

The response to images of animals was especially marked in the right amygdala, perhaps reflecting the  right hemisphere's commitment to processing "unexpected and biologically relevant stimuli, or with changes in the environment," according to Mormann in the Caltech press release.

The research is open to all kinds of interpretation, but it makes one thing clear: animals are important to us. We knew that already, but still, it's interesting to see it reflected in the deepest, most primal reflexes of the old brain.

The study, like so many at the coolest edges of neuroscience today, was conducted in the brains of epilepsy patients. These generous men and women were already wired up with single-neuron-reading intra-cortical electrodes in preparation for surgery and volunteered their brains for study while they were at it.  Itzak Fried, the surgeon who installed the electrodes for this study, uses them to find the foci of his patients' seizures and to conduct other research in the meantime. He has been the key to  several other important studies, including the identification of the first human mirror neurons.

The paper was published in the August 28, 2011 issue of Nature Neuroscience.