Hummingbirds See Motion in an Unexpected Way

The brain area in question is known in birds as the lentiformis mesencephalic, or LM for short. (In mammals, it’s called the nucleus of the optic tract.) The LM is responsible for processing visual signals sent to the brain as images move across the retina.

The primary interest of the Altshuler lab is in understanding flight. To understand how birds fly, the researchers needed to understand how they see the world. Hummingbirds were of special interest because of their remarkable ability to zoom quickly and then stop to hover in place while sipping nectar in midair.

Earlier studies showed that the LM in hummingbirds is enlarged in comparison to that of other birds. Scientists also knew that hummingbirds monitor and correct for any minor drift in their position as they hover. Those findings had led researchers to suggest that the hummingbird brain might be specially attuned to pick up on slow movements.

To test that hypothesis in the new study, post-doc and first author of the new study Andrea Gaede recorded neural activity in the LMs of six Anna’s hummingbirds and ten zebra finches as the birds watched computer-generated dots move in various directions. Contrary to expectations, the recordings showed that hummingbirds are most sensitive to fast visual motion. What’s more, unlike other birds, the hummingbirds responded to movement in any direction about equally. That is, their LM neurons aren’t specially attuned to movements in the forward direction as in other animals. The researchers suggest that their visual abilities may play a role in dynamic behaviors, including competitive interactions, high-speed courtship displays, and insect foraging.

“This study provides compelling support for the hypothesis that the avian brain is specialized for flight and that hummingbirds are a powerful model for studying stabilization algorithms,” Gaede says.

Gaede says her next step is to investigate the response properties of other nuclei involved in this visual motion-processing pathway, with the ultimate goal of understanding how neural activity in the hummingbird brain is translated into specific flight behaviors.

This study was supported by grants from the Natural Sciences and Engineering Research Council of Canada and the Human Frontier Science Foundation.

Contacts and sources: