Dr. Wolf M. Harmening from University Eye Hospital Bonn, together with American colleagues, studied color vision by probing individual sensory cells – photoreceptors – in the human eye. The results confirm that the photoreceptor cells of the retina are especially sensitive to colors corresponding to their visual pigments, even when stimulated in isolation. A new observation is that proximity effects play a key role: sensitivity of tested photoreceptors varied depending on which cell classes were located in their immediate neighborhood. The results have now been published in advance online and will soon be published in the Journal of Neuroscience.
It is a constant ‘aha’ effect: when the light is switched on in a dark room, color vision sets in. “This not only makes the world more colorful,” says Dr. Wolf M. Harmening, who heads an Emmy Noether research group at Bonn University Eye Hospital.
At the Adaptive Optics Scanning Laser Ophthalmoscope: Dr. Wolf M. Harmening (left) from University Eye Hospital Bonn and Dr. William S. Tuten (right) from the University of California, Berkeley.
© Photo: Rolf Müller/Ukom-UKB
“Color also allows spatial detail to become apparent that has proven vital for survival over the course of evolution.” Some predator camouflage can only be identified through color. Poisonous animals and plants also provide warning signals through color. That human color vision emerges from three independent channels within the retina is well established in the vision science literature.
By stimulating individual photoreceptor cells in living subjects, the lead authors Dr. Wolf M. Harmening from University Eye Hospital Bonn and Dr. William S. Tuten from the University of California, Berkeley, together with colleagues from the US universities in Seattle, Washington and Birmingham, Alabama, have now shown on a cellular scale how the human retina conveys color signals.
To do this, the researchers used an ophthalmoscope that can examine and stimulate the human retina non-invasively. The novel method – Adaptive Optics Scanning Laser Ophthalmoscopy – employs a combination of a laser and a very high-resolution microscope, which can even map individual sensory cells in the retina.
The research team has now used this ophthalmoscope to study vision in the retinas of two human subjects. According to common theory, all color stimuli can be formed by mixing the primary colors red, green, and blue. While rod photoreceptors are specialized for seeing in the dark, cone photoreceptors convey color vision. They carry light sensitive pigments specialized to absorb wavelengths near the primary colors, the basis of trichromatic vision.
Mapping of the retina
The researchers initially mapped the cone mosaic on the subjects’ retinas by measuring light absorption for certain wavelengths in each photoreceptor. In this way, they were able to determine the sensory cells’ identity, or class, within the framework of trichromacy. By reducing the intensity of the stimulation light, the researchers were then able to determine a detection threshold in each cone, at which light was just barely seen by the subjects. “This is important because we could use the sensitivity of each cell to determine how overall perception is governed by the contribution of individual cones,” reports Harmening.
Most notably, the sensitivity of single cells also depended on the immediate neighboring cells. “If a cone sensitive to red light is surrounded by cells that are more sensitive to green, this cone is more likely to behave like a green cone,” summarizes Harmening. Studying visual processing of color is complex, in part because the brain does not receive raw data from individual photoreceptors but rather an already preprocessed retinal signal. Harmening: “Spatial and color information of individual cones is modulated in the complex network of the retina, with lateral information spreading through what are known as horizontal cells.”
Their finding supports previous assumptions about color vision. “What’s new is that we can now study vision on the most elementary level, cell-by-cell,” says the scientist. Conventional tests of vision use stimuli that necessarily activate hundreds to thousands photoreceptor cells at the same time. Harmening emphasizes that cellular-scale retinal computation such as the proximity effect has important implications, for basic and clinical research. “When the basis of vision is understood better, we open avenues for new diagnoses and treatments in case of retinal disease,” says Harmening. The novel single cell approach offers access to new findings in ophthalmology.
Publication: William S. Tuten, Wolf M. Harmening, Ramkumar Sabesan, Austin Roorda, Lawrence C. Sincich: Spatiochromatic interactions between individual cone photoreceptors in the human retina, The Journal of Neuroscience, DOI: 10.1523/JNEUROSCI.0529-17.2017
Dr. Wolf M. Harmening
University Eye Hospital Bonn
Johannes Seiler | idw - Informationsdienst Wissenschaft
Usher syndrome: Gene therapy restores hearing and balance
25.09.2017 | Institut Pasteur
MRI contrast agent locates and distinguishes aggressive from slow-growing breast cancer
25.09.2017 | Case Western Reserve University
At the productronica trade fair in Munich this November, the Fraunhofer Institute for Laser Technology ILT will be presenting Laser-Based Tape-Automated Bonding, LaserTAB for short. The experts from Aachen will be demonstrating how new battery cells and power electronics can be micro-welded more efficiently and precisely than ever before thanks to new optics and robot support.
Fraunhofer ILT from Aachen relies on a clever combination of robotics and a laser scanner with new optics as well as process monitoring, which it has developed...
Plants and algae use the enzyme Rubisco to fix carbon dioxide, removing it from the atmosphere and converting it into biomass. Algae have figured out a way to increase the efficiency of carbon fixation. They gather most of their Rubisco into a ball-shaped microcompartment called the pyrenoid, which they flood with a high local concentration of carbon dioxide. A team of scientists at Princeton University, the Carnegie Institution for Science, Stanford University and the Max Plank Institute of Biochemistry have unravelled the mysteries of how the pyrenoid is assembled. These insights can help to engineer crops that remove more carbon dioxide from the atmosphere while producing more food.
A warming planet
Our brains house extremely complex neuronal circuits, whose detailed structures are still largely unknown. This is especially true for the so-called cerebral cortex of mammals, where among other things vision, thoughts or spatial orientation are being computed. Here the rules by which nerve cells are connected to each other are only partly understood. A team of scientists around Moritz Helmstaedter at the Frankfiurt Max Planck Institute for Brain Research and Helene Schmidt (Humboldt University in Berlin) have now discovered a surprisingly precise nerve cell connectivity pattern in the part of the cerebral cortex that is responsible for orienting the individual animal or human in space.
The researchers report online in Nature (Schmidt et al., 2017. Axonal synapse sorting in medial entorhinal cortex, DOI: 10.1038/nature24005) that synapses in...
Whispering gallery mode (WGM) resonators are used to make tiny micro-lasers, sensors, switches, routers and other devices. These tiny structures rely on a...
Using ultrafast flashes of laser and x-ray radiation, scientists at the Max Planck Institute of Quantum Optics (Garching, Germany) took snapshots of the briefest electron motion inside a solid material to date. The electron motion lasted only 750 billionths of the billionth of a second before it fainted, setting a new record of human capability to capture ultrafast processes inside solids!
When x-rays shine onto solid materials or large molecules, an electron is pushed away from its original place near the nucleus of the atom, leaving a hole...
19.09.2017 | Event News
12.09.2017 | Event News
06.09.2017 | Event News
25.09.2017 | Power and Electrical Engineering
25.09.2017 | Health and Medicine
25.09.2017 | Physics and Astronomy