The latest work by Karl Farrow and his team zooms in on the organization of neurons in the superior colliculus, a midbrain structure that mediates attention and orientation responses to visual cues. In today’s edition of Current Biology, the team reports that nearby direction-selective neurons tend to prefer the same motion direction, and that there is a sharp transition in the preference for nasal versus temporal motion at the border where visual information from both eyes meets.
To understand how visual information guides behavior, we need to know how these responses are orchestrated in brain areas important for behavior. One such structure is the superior colliculus: a layered structure of the midbrain that plays a role in the orienting responses of the eye, head and body towards objects of interest in our environment.
To characterize the functional properties of neurons in the superficial layers of the mouse superior colliculus, Daniel de Malmazet, first author and PhD student in the Farrow lab, performed in-vivo two-photon calcium imaging in awake, head-fixed mice that viewed visual stimuli on a screen.
The researchers classified collicular neurons according to their direction selectivity, orientation selectivity and retinotopic location. “Neurons that responded best to a particular direction of motion were considered to be direction-selective cells, those that responded best to a particular orientation of the moving visual cue—independent of the direction of motion—were considered to be orientation-selective,” explains de Malmazet.
Putting this information together, the team found that direction-selective neurons cluster anatomically by preferred direction. But what is the biological meaning of this grouping?
Sensory neurons often display an ordered spatial arrangement that enhances the encoding of specific features on different sides of natural borders in the visual field. In central visual areas, one prominent natural border is formed by the confluence of information from the two eyes: the monocular-binocular border.
Along this border, the researchers identified a sharp transition in the local preference of direction-selective neurons. “We found that the border between the monocular and binocular zone acts to partition nasally and temporally tuned direction-selective neurons,” explains Karl Farrow.
Together, these results illustrate the important connection between the spatial organization of our visual field and the response properties within the visual system. “They also suggest we may need to re-analyze receptive field organization within the superior colliculus from an ecological perspective,” says de Malmazet. “We tend to think of how we process visual information based on our own experiences, but the way neurons are organized in the brain is very much linked to how animals interact with their world.
Retinotopic Separation of Nasal and Temporal Motion Selectivity in the Mouse Superior Colliculus
de Malmazet et al. 2018, Current Biology