Direction Selective Ganglion Cell

Direction selective (DS) cells in the retina are defined as neurons that respond differentially to the direction of a visual stimulus. According to Barlow and Levick (1965), the term is used to describe a group of neurons that “gives a vigorous discharge of impulses when a stimulus object is moved through its receptive field in one direction.”[3] This direction in which a set of neurons respond most strongly to is their “preferred direction.” In contrast, they do not respond at all to the opposite direction, “null direction.” The preferred direction is not dependent on the stimulus- that is, regardless of the stimulus’ size, shape, or color, the neurons respond when it is moving in their preferred direction, and do not respond if it is moving in the null direction. There are three known types of DS cells in the vertebrate retina of the mouse, ON/OFF DS ganglion cells, ON DS ganglion cells, and OFF DS ganglion cells. Each has a distinctive physiology and anatomy.

Introduction
This wiki will only apply to ON/OFF DS Ganglion Cells. There are also ON DS Ganglion cells (which respond to the leading edge of a stimulus) and OFF DS Ganglion cells (which respond only to the trailing edge of a stimulus).

Physiology
ON/OFF DS ganglion cells act as local motion detectors. They fire at the onset and offset of a stimulus (a light source). If a stimulus is moving in the direction of the cell’s preference, it will fire at the leading and the trailing edge. Their firing pattern is time-dependent and is supported by the Reichardt- Hassenstain model, which detects spatiotemporal correlation between the two adjacent points.

Anatomy
The anatomy of ON/OFF cells is such that the dendrites extend to two sublaminae of the inner plexiform layer and make synapses with bipolar and amacrine cells. They have four subtypes, each with own preference for direction.

Shape
There are four subtypes, each with a preference for direction.

Connections
Synapses with bipolar and amacrine cells.



Molecules
ON/OFF DS ganglion cells can be divided into 4 subtypes differing in their directional preference, ventral, dorsal, nasal, or temporal. The cells of different subtypes also differ in their dendritic structure and synaptic targets in the brain. The neurons that were identified to prefer ventral motion were also found to have dendritic projections in the ventral direction. Also, the neurons that prefer nasal motion had asymmetric dendritic extensions in the nasal direction. Thus, a strong association between the structural and functional asymmetry in ventral and nasal direction was observed. With a distinct property and preference for each subtype, there was an expectation that they could be selectively labeled by molecular markers. The neurons that were preferentially responsive to vertical motion were indeed shown to be selectively expressed by a specific molecular marker. However, molecular markers for other three subtypes have not been yet found.[8] (NEED TO ADD SPECIFIC MARKER)

History
Levick 1966 rabbit experiments are a good place to start.

Open questions / status / relevance to eyewire
TBD