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Frank Werblin is Professor of the Graduate School, Division of Neurobiology, at the University of California, Berkeley. [1]
Werblin earned his Ph.D. at Johns Hopkins University studying with Professor John Dowling. He was a Guggenheim Fellow, [2] and is noted for discovering the functional and morphological properties of the main retinal neural cell types underlying visual information processing in the retina and for developing the retina slice preparation that is now used universally by retinal researchers.
In 1969, Werblin and Dowling published their seminal studies of the electrophysiological response properties of all the major neuron types in the vertebrate retina. [3] This paper described, for the first time, the connections between all the major types of retina neurons and showed how interactions between these neurons created the visual code that was sent via the optic nerve to the brain. To accomplish this, the authors combined information about the electrical responses of the neurons with anatomical connectivity uncovered by electron microscopic identification of the neural pathways. The micropipette used to record from each cell contained a dye so that each physiologically identified cell could also be morphologically characterized within the layers of the retina. In 1978, Werblin published the first study of an isolated retinal slice preparation. Werblin invented and developed a clever slicing procedure that allowed for a quicker and easier means to access all of the neurons in the various layers of the retina, while leaving the cells largely intact with their supporting matrix and synaptic connections and electrical junctions. [4] This allowed, the researcher for the first time to target specific neurons in the retina for electrical recording. However, because the retinal slice was isolated from the supportive retinal pigment epithelium (PE) that enables the light responses of photoreceptors, light evoked responses were not reported until the retinal slices were constructed with PE still attached. [5] In this manner, whole cell patch recording of amacrine neurons in the salamander retina allowed light evoked excitatory post-synaptic currents (EPSCs) to be measured for the first time, as well as their light elicited spiking potentials, and voltage-gated currents. The new slice technique allowed, for the first time, a neuron to be characterized by its natural stimulus (light), and then to be fully characterized by its morphological, histological, electrophysiological (EPSCs, voltage gated currents, and graded and spike potentials), and chemical identity. [6] The new light-responsive slice methodology also allowed interplexiform cells to be identified and characterized for the first time, [7] as well as sustained and transient amacrine neurons. [8] Precise localization of synaptic inputs to the cell, and localization of functional receptors in the cell was achieved. [9] The slice technique would become a standard for retinal research and be developed for other animals with much smaller neurons, including the Zebrafish [10] and rat. [11] Werblin would then use these data to construct elegant models of visual information processing in the different layers of the retina. [12]
In 1990 Werblin was honored with the Friedenwald Award from the ARVO organization. In 2017, Werblin received the Pepose Award in Vision Science from Brandeis University. [13]
Werblin is also the inventor of Visionize a device/software that uses a smartphone to remap the visual world to help low-vision patients regain visual function. With this gained facility, patients who were functionally blind regain sight and re-enter the world of the sighted, recognizing faces, shopping at supermarkets, going to theater and sports events.. [14]
Werblin is also a Co-Founder, Chief Scientist of IrisVision, a more advanced technology device that connects clinicians with patients remotely through a portable vision laboratory that is located in the patient's home and controlled remotely by the clinician. Clinics can serve patients . [15]
The retina is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then processes that image within the retina and sends nerve impulses along the optic nerve to the visual cortex to create visual perception. The retina serves a function which is in many ways analogous to that of the film or image sensor in a camera.
A photoreceptor cell is a specialized type of neuroepithelial cell found in the retina that is capable of visual phototransduction. The great biological importance of photoreceptors is that they convert light into signals that can stimulate biological processes. To be more specific, photoreceptor proteins in the cell absorb photons, triggering a change in the cell's membrane potential.
A retinal ganglion cell (RGC) is a type of neuron located near the inner surface of the retina of the eye. It receives visual information from photoreceptors via two intermediate neuron types: bipolar cells and retina amacrine cells. Retina amacrine cells, particularly narrow field cells, are important for creating functional subunits within the ganglion cell layer and making it so that ganglion cells can observe a small dot moving a small distance. Retinal ganglion cells collectively transmit image-forming and non-image forming visual information from the retina in the form of action potential to several regions in the thalamus, hypothalamus, and mesencephalon, or midbrain.
As a part of the retina, bipolar cells exist between photoreceptors and ganglion cells. They act, directly or indirectly, to transmit signals from the photoreceptors to the ganglion cells.
Motion perception is the process of inferring the speed and direction of elements in a scene based on visual, vestibular and proprioceptive inputs. Although this process appears straightforward to most observers, it has proven to be a difficult problem from a computational perspective, and difficult to explain in terms of neural processing.
Electroretinography measures the electrical responses of various cell types in the retina, including the photoreceptors, inner retinal cells, and the ganglion cells. Electrodes are placed on the surface of the cornea or on the skin beneath the eye to measure retinal responses. Retinal pigment epithelium (RPE) responses are measured with an EOG test with skin-contact electrodes placed near the canthi. During a recording, the patient's eyes are exposed to standardized stimuli and the resulting signal is displayed showing the time course of the signal's amplitude (voltage). Signals are very small, and typically are measured in microvolts or nanovolts. The ERG is composed of electrical potentials contributed by different cell types within the retina, and the stimulus conditions can elicit stronger response from certain components.
In the study of visual perception, scotopic vision is the vision of the eye under low-light conditions. The term comes from the Greek skotos, meaning 'darkness', and -opia, meaning 'a condition of sight'. In the human eye, cone cells are nonfunctional in low visible light. Scotopic vision is produced exclusively through rod cells, which are most sensitive to wavelengths of around 498 nm and are insensitive to wavelengths longer than about 640 nm. Under scotopic conditions, light incident on the retina is not encoded in terms of the spectral power distribution. Higher visual perception occurs under scotopic vision as it does under photopic vision.
Visual phototransduction is the sensory transduction process of the visual system by which light is detected by photoreceptor cells in the vertebrate retina. A photon is absorbed by a retinal chromophore, which initiates a signal cascade through several intermediate cells, then through the retinal ganglion cells (RGCs) comprising the optic nerve.
In the anatomy of the eye, amacrine cells are interneurons in the retina. They are named from Greek a– 'non' makr– 'long' and in– 'fiber', because of their short neuronal processes. Amacrine cells are inhibitory neurons which project their dendritic arbors onto the inner plexiform layer (IPL). They interact with retinal ganglion cells and bipolar cells.
Horizontal cells are the laterally interconnecting neurons having cell bodies in the inner nuclear layer of the retina of vertebrate eyes. They help integrate and regulate the input from multiple photoreceptor cells. Among their functions, horizontal cells are believed to be responsible for increasing contrast via lateral inhibition and adapting both to bright and dim light conditions. Horizontal cells provide inhibitory feedback to rod and cone photoreceptors. They are thought to be important for the antagonistic center-surround property of the receptive fields of many types of retinal ganglion cells.
Intrinsically photosensitive retinal ganglion cells (ipRGCs), also called photosensitive retinal ganglion cells (pRGC), or melanopsin-containing retinal ganglion cells (mRGCs), are a type of neuron in the retina of the mammalian eye. The presence of an additional photoreceptor was first suspected in 1927 when mice lacking rod and cone cells still responded to changing light levels through pupil constriction; this suggested that rods and cones are not the only light-sensitive tissue. However, it was unclear whether this light sensitivity arose from an additional retinal photoreceptor or elsewhere in the body. Recent research has shown that these retinal ganglion cells, unlike other retinal ganglion cells, are intrinsically photosensitive due to the presence of melanopsin, a light-sensitive protein. Therefore, they constitute a third class of photoreceptors, in addition to rod and cone cells.
A retinal implant is a visual prosthesis for restoration of sight to patients blinded by retinal degeneration. The system is meant to partially restore useful vision to those who have lost their photoreceptors due to retinal diseases such as retinitis pigmentosa (RP) or age-related macular degeneration (AMD). Retinal implants are being developed by a number of private companies and research institutions, and three types are in clinical trials: epiretinal, subretinal, and suprachoroidal. The implants introduce visual information into the retina by electrically stimulating the surviving retinal neurons. So far, elicited percepts had rather low resolution, and may be suitable for light perception and recognition of simple objects.
In neurobiology, lateral inhibition is the capacity of an excited neuron to reduce the activity of its neighbors. Lateral inhibition disables the spreading of action potentials from excited neurons to neighboring neurons in the lateral direction. This creates a contrast in stimulation that allows increased sensory perception. It is also referred to as lateral antagonism and occurs primarily in visual processes, but also in tactile, auditory, and even olfactory processing. Cells that utilize lateral inhibition appear primarily in the cerebral cortex and thalamus and make up lateral inhibitory networks (LINs). Artificial lateral inhibition has been incorporated into artificial sensory systems, such as vision chips, hearing systems, and optical mice. An often under-appreciated point is that although lateral inhibition is visualised in a spatial sense, it is also thought to exist in what is known as "lateral inhibition across abstract dimensions." This refers to lateral inhibition between neurons that are not adjacent in a spatial sense, but in terms of modality of stimulus. This phenomenon is thought to aid in colour discrimination.
A bipolar neuron, or bipolar cell, is a type of neuron characterized by having both an axon and a dendrite extending from the soma in opposite directions. These neurons are predominantly found in the retina and olfactory system. The embryological period encompassing weeks seven through eight marks the commencement of bipolar neuron development.
The ribbon synapse is a type of neuronal synapse characterized by the presence of an electron-dense structure, the synaptic ribbon, that holds vesicles close to the active zone. It is characterized by a tight vesicle-calcium channel coupling that promotes rapid neurotransmitter release and sustained signal transmission. Ribbon synapses undergo a cycle of exocytosis and endocytosis in response to graded changes of membrane potential. It has been proposed that most ribbon synapses undergo a special type of exocytosis based on coordinated multivesicular release. This interpretation has recently been questioned at the inner hair cell ribbon synapse, where it has been instead proposed that exocytosis is described by uniquantal release shaped by a flickering vesicle fusion pore.
Non-spiking neurons are neurons that are located in the central and peripheral nervous systems and function as intermediary relays for sensory-motor neurons. They do not exhibit the characteristic spiking behavior of action potential generating neurons.
Retinal waves are spontaneous bursts of action potentials that propagate in a wave-like fashion across the developing retina. These waves occur before rod and cone maturation and before vision can occur. The signals from retinal waves drive the activity in the dorsal lateral geniculate nucleus (dLGN) and the primary visual cortex. The waves are thought to propagate across neighboring cells in random directions determined by periods of refractoriness that follow the initial depolarization. Retinal waves are thought to have properties that define early connectivity of circuits and synapses between cells in the retina. There is still much debate about the exact role of retinal waves. Some contend that the waves are instructional in the formation of retinogeniculate pathways, while others argue that the activity is necessary but not instructional in the formation of retinogeniculate pathways.
Communication between neurons happens primarily through chemical neurotransmission at the synapse. Neurotransmitters are packaged into synaptic vesicles for release from the presynaptic cell into the synapse, from where they diffuse and can bind to postsynaptic receptors. While most presynaptic cells are historically thought to release one vesicle at a time per active site, more recent research has pointed towards the possibility of multiple vesicles being released from the same active site in response to an action potential.
Douglas G. McMahon is a professor of Biological Sciences and Pharmacology at Vanderbilt University. McMahon has contributed several important discoveries to the field of chronobiology and vision. His research focuses on connecting the anatomical location in the brain to specific behaviors. As a graduate student under Gene Block, McMahon identified that the basal retinal neurons (BRNs) of the molluscan eye exhibited circadian rhythms in spike frequency and membrane potential, indicating they are the clock neurons. He became the 1986 winner of the Society for Neuroscience's Donald B. Lindsley Prize in Behavioral Neuroscience for his work. Later, he moved on to investigate visual, circadian, and serotonergic mechanisms of neuroplasticity. In addition, he helped find that constant light can desynchronize the circadian cells in the suprachiasmatic nucleus (SCN). He has always been interested in the underlying causes of behavior and examining the long term changes in behavior and physiology in the neurological modular system. McMahon helped identifying a retrograde neurotransmission system in the retina involving the melanopsin containing ganglion cells and the retinal dopaminergic amacrine neurons.
AII (A2) amacrine cells are a subtype of amacrine cells. Amacrine cells are neurons that exist in the retina of mammals to assist in interpreting photoreceptive signals. AII amacrine cells serve the critical role of transferring light signals from rod photoreceptors to the retinal ganglion cells.
