Knowing which way is up is a pretty useful skill, without which we’d probably be forever spilling our drinks and failing miserably at pretty much all sports. While most people rarely worry themselves over how the brain orients itself in space, researchers at Johns Hopkins University have identified the neurons responsible for this vital task, providing new insights into how we keep track of our position in the world.
According to the most widely-held current theories, visual stimuli are processed by the brain cells of two distinctive pathways, known as the dorsal and ventral visual streams. The ventral pathway in particular is thought to be responsible for object perception and recognition, containing neurons that become activated in response to the appearance of specific identifiable shapes.
However, recent research has indicated that some of these neurons – particularly those found in a region known as the anterior inferotemporal cortex (AIT) – are more responsive to scenes than objects. To learn more about how these cells react to different elements within a scenic image, the researchers designed an experiment using rhesus macaques, since the organization of neurons in the brains of these monkeys is very similar to that of humans.
Monkeys were shown 3D images on a computer screen while the researchers tracked the electrical activity of neurons in their AITs. Each macaque was presented with between 400 and 600 different images, allowing the study authors to gain a thorough appreciation of the neural responses to different features of these scenes.
The results – which appear in the journal Current Biology – reveal that these neurons react to the appearance of large horizontal planes, particularly those “in the orientation range of ground surfaces,” meaning those located where the floor normally appears in relation to the eye. Other horizontal planes in the orientation range of ceilings also generated a strong response, while vertical surfaces such as walls produced a slightly weaker reaction.
Based on these findings, the researchers suggest that the neurons of the AIT play a role in establishing where the ground is, enabling us to keep track of which way is up even as we rotate our field of vision. This, in turn, allows us to predict the movement of objects through our environment by maintaining a sense of the direction of gravity.
Commenting on this research, senior author Charles E. Connor explained that the “results show how the direction of gravity can be derived from visual cues, providing critical information about object physics as well as additional cues for maintaining posture and balance.”