Difference between revisions of "On-Off Direction-Selective Ganglion Cell"

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[File:onoffdsgc.png|thumb|right|400px|Reconstructed by [[Omni Desktop]] from Helmstaedter's skeleton<ref name="briggman2011">{{cite journal  | author=K. L. Briggman, M. Helmstaedter, and W. Denk|title=€œWiring specificity in the direction-selectivity circuit of the retina|journal=Nature |volume=471|pages=183–188 |year=2011 |doi=10.1038/nature09818}} [[media:10.1038_nature09818.pdf|(PDF Download)]]</ref>]]]
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[[[File:onoffdsgc.png|thumb|right|400px|Reconstructed by [[Omni Desktop]] from Helmstaedter's skeleton<ref name="briggman2011">{{cite journal  | author=K. L. Briggman, M. Helmstaedter, and W. Denk|title=€œWiring specificity in the direction-selectivity circuit of the retina|journal=Nature |volume=471|pages=183–188 |year=2011 |doi=10.1038/nature09818}} [[media:10.1038_nature09818.pdf|(PDF Download)]]</ref>]]]
  
 
Direction selective (DS) cells in the retina are defined as neurons that respond differentially to the direction of a visual stimulus. The term is used to describe a group of neurons that preferrentially "gives a vigorous discharge of impulses when a (bright) stimulus object is moved through its receptive field in one direction" <ref name="barlow1965">{{cite journal  | author=H. B. Barlow and W. R. Levick|title=The Mechanism of Directionally Selective Units in Rabbit's Retina |journal=J. Physiol. |volume=178|pages=477-504 |year=1965}} [http://jp.physoc.org/content/178/3/477.full.pdf (PDF Download)]</ref>. There are three known types of DS cells in the vertebrate retina of the mouse, ON/OFF DS ganglion cells, [[ON DS Ganglion Cells]] (which respond to the leading edge of a bright stimulus) and [[OFF DS Ganglion Cells]] (which respond only to the trailing edge of a bright stimulus).  Each has a disntinctive physiology and anatomy<ref>"Motion Sensing in Vision." Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/wiki/Motion_Sensing_in_Vision (Accessed April 02, 2012).</ref>. The rest of this page will only apply to ON/OFF DS Ganglion Cells.
 
Direction selective (DS) cells in the retina are defined as neurons that respond differentially to the direction of a visual stimulus. The term is used to describe a group of neurons that preferrentially "gives a vigorous discharge of impulses when a (bright) stimulus object is moved through its receptive field in one direction" <ref name="barlow1965">{{cite journal  | author=H. B. Barlow and W. R. Levick|title=The Mechanism of Directionally Selective Units in Rabbit's Retina |journal=J. Physiol. |volume=178|pages=477-504 |year=1965}} [http://jp.physoc.org/content/178/3/477.full.pdf (PDF Download)]</ref>. There are three known types of DS cells in the vertebrate retina of the mouse, ON/OFF DS ganglion cells, [[ON DS Ganglion Cells]] (which respond to the leading edge of a bright stimulus) and [[OFF DS Ganglion Cells]] (which respond only to the trailing edge of a bright stimulus).  Each has a disntinctive physiology and anatomy<ref>"Motion Sensing in Vision." Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/wiki/Motion_Sensing_in_Vision (Accessed April 02, 2012).</ref>. The rest of this page will only apply to ON/OFF DS Ganglion Cells.

Revision as of 20:37, 30 April 2012

[[[File:onoffdsgc.png|thumb|right|400px|Reconstructed by Omni Desktop from Helmstaedter's skeleton[1]]]]

Direction selective (DS) cells in the retina are defined as neurons that respond differentially to the direction of a visual stimulus. The term is used to describe a group of neurons that preferrentially "gives a vigorous discharge of impulses when a (bright) stimulus object is moved through its receptive field in one direction" [2]. There are three known types of DS cells in the vertebrate retina of the mouse, ON/OFF DS ganglion cells, ON DS Ganglion Cells (which respond to the leading edge of a bright stimulus) and OFF DS Ganglion Cells (which respond only to the trailing edge of a bright stimulus). Each has a disntinctive physiology and anatomy[3]. The rest of this page will only apply to ON/OFF DS Ganglion Cells.

Physiology

ON/OFF DS ganglion cells act as local motion detectors. They fire at the onset and offset of a bright 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. The classical receptive field of the ON–OFF DSGC exhibits center-surround structure, with the size of the receptive field center matching well with its dendritic diameter [6–8]. When presented with a moving bar visual stimulus, both the ON and OFF components of the spike response are direction-selective over a wide range of movement velocities [2]. Furthermore, motion stimuli restricted to a small fraction (<20% in rabbit) of the receptive field can produce directional spiking of ON–OFF DSGCs, indicating that direction-selective mechanisms are present in local dendritic computational subunits that repeat in an array over the DSGC dendritic arbor [4].

The 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.

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.

Moving visual stimuli that crossed the cell’s receptive field elicited strong spiking when moving in a particular ‘preferred’ direction but little or no response when moving in the opposite ‘null’ direction.

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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.

The colored objects in panel a are six DSGCs reconstructed by the researchers. The circles are representations of the cell bodies, and the lines are "skeletons" of the dendrites. Each DSGC is said to be "bistratified," which means that its dendrites branch out in two sublayers ("strata") of the IPL. The total number of strata in the IPL is estimated to be around ten. A view of the bottom of the sandwich (panel b) shows the branching of the DSGC dendrites.

Reconstructed ganglion and amacrine cells.


Location

Shape

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Image of an On-Off Direction-Selective Ganglion Cell[5].

Connections

File:DSGC Brigmann.jpg
Cells and synapses reconstructed from serial block face electron microscopy data. A single starburst amacrine cell (yellow, note synaptic varicosities) and two direction-selective ganglion cells (green). Even though there is substantial dendritic overlap with both cells, all connections (magenta) go to the right ganglion cell. ©Kevin Briggman. New microscope decodes complex eye circuitry: Retinal ganglion cells can recognise directions thanks to amacrine cells[1]

TODO: DS ON/OFF ganglion cells receive excitatory input from bipolar cells but also from the previously mentioned starburst cells (Figure 5A), which are also known as cholinergic amacrine cells (Famiglietti, 1983,Masland and Mills, 1979). Besides ACh, starburst amacrine cells (SACs) also release GABA (Brecha et al., 1988,Masland et al., 1984b,Vaney and Young, 1988) and provide DS ganglion cells with inhibition as well (Figure 5A). In addition, the DS ganglion cells receive both GABA and glycinergic inhibition from other amacrine cell types (reviewed in Dacheux et al., 2003).

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Connections to SAC

Molecules

As described above, ON/OFF DS ganglion cells can be divided into 4 subtypes differing in their directional preference, ventral, dorsal, nasal, or temporal. Recent research has identified markers for distinguishing between the different subtypes, and for separating ON/OFF DSGCs from other retinal ganglion cells. These markers are independent of experience, and suggest a method for how these cells obtain different inputs.

Recent research has lead to the development of transgenic mouse lines that selectively mark ON/OFF DSGCs that prefer ventral or nasal motion and another line that marks ventral and dorsal preferring DSGCs. These lines were used to identify cell surface molecules (including Cadherin 6, CollagenXXV1, and Matrix metalloprotease 17), that allow each of the four types of ON/OFF DSGCs to be differentiated. A neuropeptide, CART (cocaine and amphetamine regulated transcript) has been found to differentiate ON/OFF DSGCs from all other retinal ganglion cells. Strikingly, these patterns of molecular differentiation occur before animal eye-opening, and demonstrate that these differences are experience-independent. Therefore, the molecular differences may help to explain the differing functionality between subtypes [6].

Figure showing how ON/OFF DSGCs can be distinguished from other RGCs. As described in the text, this is accomplished using CART; a careful morphological analysis confirms that this marker correctly identifies the ON/OFF DSGCs with no false positives. [7]

Models

The firing pattern of On-Off Direction-Selective Ganglion cells is time-dependent and is supported by the Reichardt- Hassenstain model, which detects spatiotemporal correlation between the two adjacent points <wiki>.

The model consists of two symmetrical subunits. Both subunits have a receptor that can be stimulated by an input (light in the case of visual system). In each subunit, when an input is received, a signal is sent to the other subunit. At the same time, the signal is delayed in time within the subunit, and after the temporal filter, is then multiplied by the signal received from the other subunit. Thus, within each subunit, the two brightness values, one received directly from its receptor with a time delay and the other received from the adjacent receptor, are multiplied. The multiplied values from the two subunits are then subtracted to produce an output. The direction of selectivity or preferred direction is determined by whether the difference is positive or negative. The direction which produces a positive outcome is the preferred direction.

In order to confirm that the Reichardt-Hassenstain model accurately describes the directional selectivity in the retina, the study was conducted using optical recordings of free cytosolic calcium levels after loading a fluorescent indicator dye into the fly tangential cells. The fly was presented uniformly moving gratings while the calcium concentration in the dendritic tips of the tangential cells was measured. The tangential cells showed modulations that matched the temporal frequency of the gratings, and the velocity of the moving gratings at which the neurons respond most strongly showed a close dependency on the pattern wavelength. This confirmed the accuracy of the model both at the cellular and the behavioral level [8].


History

Levick and Barlow performed many of the early experiments related to direction selectivity during the 1960s using rabbit retina [2]. Many additional experiments have been performed during the past fifty years in organisms as diverse as the turtle (e.g., Marchiafava 1979) and the mouse (Briggman 2011).

Open questions / status / relevance to eyewire

Cells will be available for tracing in Eyewire, although these cells are not currently available (March 2012). See http://wiki.eyewire.org/wiki/E2198

Reading List

K. L. Briggman, M. Helmstaedter, and W. Denk, €œWiring specificity in the direction-selectivity circuit of the retina., Nature, vol. 471, no. 7337, pp. 183-8, Mar. 2011.

A. Borst and T. Euler, €œReview Seeing Things in Motion : Models, Circuits and Mechanisms,€ Neuron, vol. 71, no. 6, pp. 974-994, 2011.

D. I. Vaney, B. Sivyer, and W. R. Taylor, Direction selectivity in the retina: symmetry and asymmetry in structure and function,€ Nature reviews. Neuroscience, vol. 13, no. 3, pp. 194-208, Jan. 2012.

W. R. Levick and H. B. Barlow, €œThe Mechanism of Directionally Selective Units in Rabbit's Retina, pp. 477-504, 1965.

References

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  3. "Motion Sensing in Vision." Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/wiki/Motion_Sensing_in_Vision (Accessed April 02, 2012).
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