Based on a study conducted on mouse models by the National Eye Institute (NEI) and the National Institute of Mental Health (NIMH). The light-sensing retina in the eyes taps different circuits. It depends on whether it is generating image-forming vision or carrying out a non-vision function. For example, regulation of pupil size and sleep/wake cycles. Moreover, our eyes also regulate our mood, sleep, digestion, and metabolism. The findings published in Cell Reports may also have implications for understanding them.
The senior author of the study, Johan Pahlberg, PhD, said,
We know a lot about pathways involved in image-forming vision, but until now it remained unknown if and how non-image-forming visual behaviours rely on these same pathways in the eye,
Pahlberg and colleagues studied groups of mice that had been genetically altered to turn off one or more pathway links, or synapses, between photoreceptors and their next downstream neuronal neighbours, known as bipolar cells. They did so to investigate the pathways used by image-forming versus non-image-forming functions in the retina. The team looked into the functions of three different types of bipolar cells, including rod bipolar cells, “on” cone bipolar cells, and “off” cone bipolar cells. Rod photoreceptors are sensitive to low light levels, whereas cone photoreceptors sense colour.
No functional connection between the rods and “on” bipolar cells was seen in some of the mice in the study. Other than that, connections between cones and bipolar cells or between rod and cone receptors also lacked.
The mice’s responses to visual stimuli were compared. Moreover, the pupillary light responses and the mice’s nocturnal wake/sleep cycle were also observed. They discovered that rod and cone photoreceptors, along with all varieties of bipolar cells, can be used in image-forming vision. However, the same does not apply to non-image-forming tasks.
Pahlberg said,
We were really surprised to find that animals with only ‘off’ bipolar cells can’t adjust to changes in the day/night cycle, but can still see and respond to visual events, meaning they have functional image-forming vision. It was really interesting to us that the non-imaging forming functions completely ignore information from the ‘off’ pathway,
We were equally surprised that rod photoreceptors, which are optimized for low light conditions, were still being used for the pupillary response even when light levels were high. We really thought the rods would be maxed out at that point.
