Neurobiologists characterize nerve cells that detect motion by light changes

[Jim__]

From phys.org:

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The ability to see the direction in which something is moving is vital for survival. Only in this way is it possible to avoid predators, capture prey or, as humans in a modern world, cross a road safely. However, the direction of motion is not explicitly represented at the level of the photoreceptors but rather must be calculated by subsequent layers of nerve cells. Scientists from the Max Planck Institute of Neurobiology in Martinsried have now discovered that, in fruit flies, four classes of nerve cell are involved in calculating directionally selective signals. This is strikingly different from mathematical models of motion detection discussed in the literature so far.

...

Alexander Borst and his team at the Max Planck Institute of Neurobiology have unravelled cell by cell how the brain calculates motion from light changes. Their model is the fruit fly, a master in motion vision, possessing a relatively small brain. Although there are more than 50,000 nerve cells in the area of the fruit fly brain responsible for motion vision, the researchers believe that the network is "simple" enough to allow them to understand the circuitry at the cellular level. In previous studies, they have shown that in flies, similar to vertebrates, motion is detected in two parallel pathways, one for moving bright edges (ON-pathway) and one for moving dark edges (OFF-pathway).

The scientists have now succeeded in identifying the first nerve cells in the fruit flies' OFF-pathway, known as T5 cells, which perceive the direction of motion. These cells receive input from four upstream cells, called Tm cells. A whole series of experiments based on two-photon microscopy, electrophysiology and behavioural analyses have shown that Tm cells are activated specifically by "light OFF" brightness changes. In contrast, T5 cells are only activated by motion of OFF-edges in a specific direction. The signals of all four Tm cells are required for a directionally selective signal to arise in a T5 cell. "That was a surprising finding, because mathematical models for motion detection only involved two input cells," reports Etienne Serbe, one of the two lead authors of the study. "Another exciting finding is that the visual system of vertebrates deviates from these models in a similar way," says Matthias Meier, the other lead author.

a little bit more ...

[DhhD]

1. Then, we have better vision if the darker side/edge is moving forward, helping us see predators.

[Jim__]

2. My understanding is that there is an ON-Pathway and an OFF-Pathway and they studied the OFF-Pathway.

The full article is behind a pay-wall, but here's the summary from Neuron:

Estimating motion is a fundamental task for the visual system of sighted animals. In Drosophila, direction-selective T4 and T5 cells respond to moving brightness increments (ON) and decrements (OFF), respectively. Current algorithmic models of the circuit are based on the interaction of two differentially filtered signals. However, electron microscopy studies have shown that T5 cells receive their major input from four classes of neurons: Tm1, Tm2, Tm4, and Tm9. Using two-photon calcium imaging, we demonstrate that T5 is the first direction-selective stage within the OFF pathway. The four cells provide an array of spatiotemporal filters to T5. Silencing their synaptic output in various combinations, we find that all input elements are involved in OFF motion detection to varying degrees. Our comprehensive survey challenges the simplified view of how neural systems compute the direction of motion and suggests that an intricate interplay of many signals results in direction selectivity.

In the picture accompanying the article they show a diagram of the T5 cell, but they don't show the T4.