http://cvrl.ucl.ac.uk/people/Stockman/pubs/2000%20L%20&%20M%20cone%20spectral%20sensitivities%20SS.pdf

The spectral sensitivities of the middle- and long-wavelength-sensitive cones derived from measurements in observers of known genotype.

Calcium entry through voltage-gated calcium channels can activate either large- (BK) or small- (SK) conductance calcium-activated potassium channels. In hippocampal neurons, activation of BK channels underlies the falling phase of an action potential and generation of the fast afterhyperpolarization (AHP). In contrast, SK channel activation underlies generation of the slow AHP after a burst of action potentials. The source of calcium for BK channel activation is unknown, but the slow AHP is blocked by dihydropyridine antagonists, indicating that L-type calcium channels provide the calcium for activation of SK channels. It is not understood how this specialized coupling between calcium and potassium channels is achieved. Here we study channel activity in cell-attached patches from hippocampal neurons and report a unique specificity of coupling. L-type channels activate SK channels only, without activating BK channels present in the same patch. The delay between the opening of L-type channels and SK channels indicates that these channels are 50-150 nm apart. In contrast, N-type calcium channels activate BK channels only, with opening of the two channel types being nearly coincident. This temporal association indicates that N and BK channels are very close. Finally, P/Q-type calcium channels do not couple to either SK or BK channels. These data indicate an absolute segregation of coupling between channels, and illustrate the functional importance of submembrane calcium microdomains.

Selective activation of Ca2+ : activated K+ channels by co-localized Ca2+ channels in hippocampal neurons

A multi-stage color model.

The primate retina contains three classes of cones, the L, M and S cones, which respond preferentially to long-, middle- and short-wavelength visible light, respectively. Colour appearance results from neural processing of these cone signals within the retina and the brain. Perceptual experiments have identified three types of neural pathways that represent colour: a red–green pathway that signals differences between L- and M-cone responses; a blue–yellow pathway that signals differences between S-cone responses and a sum of L- and M-cone responses; and a luminance pathway that signals a sum of L- and M-cone responses1,2,3. It might be expected that there are neurons in the primary visual cortex with response properties that resemble these three perceptual pathways, but attempts to find them have led to inconsistent results4,5,6,7. We have therefore used functional magnetic resonance imaging (fMRI) to examine responses in the human brain to a large number of colours. In visual cortical areas V1 and V2, the strongest response is to red–green stimuli, and much of this activity is from neurons receiving opposing inputs from L and M cones. A strong response is also seen with blue–yellow stimuli, and this response declines rapidly as the temporal frequency of the stimulus is increased. These responses resemble psychophysical measurements, suggesting that colour signals relevant for perception are encoded in a large population of neurons in areas V1 and V2.

/pdf/colour-tuning-in-human-visual-cortex-measured-with-y74qd2ax96.pdf

Colour tuning in human visual cortex measured with functional magnetic resonance imaging.

Transient chromatic adaptation produced by an abrupt change of background color permits an easier and closer approach to cone isolation than does steady-state adaptation. Using this technique, we measured middle-wave-sensitive (M)-cone spectral sensitivities in 11 normals and 2 protanopes and long-wavelength-sensitive (L-) cone spectral sensitivities in 12 normals and 4 deuteranopes. Although there is great individual variation in the adapting intensity required for effective isolation, there is little variation in the shape of the M- and L-cone spectral-sensitivity functions across subjects. At middle and long wavelengths, our mean spectral sensitivities agree extremely well with dichromatic spectral sensitivities and with the M- and L-cone fundamentals of Smith and Pokorny [Vision Res. 15, 161 (1975)] and of Vos and Walraven [Vision Res. 11, 799 (1971)], both of which are based on the CIE (Judd-revised) 2 degrees color-matching functions (CMF's). But the agreement with the M-cone fundamentals of Estevez [Ph.D. dissertation, Amsterdam University (1979)] and of Vos et al. [Vision Res. 30, 936 (1990)], which are based on the Stiles-Burch 2 degrees CMF's, is poor. Using our spectral-sensitivity data, tritanopic color-matching data, and Stile's pi 3, we derive new sets of cone fundamentals. The consistency of the proposed fundamentals based on either the Stiles-Burch 2 degrees CMF's or the CIE 10 degrees large-field CMF's with each other, with protanopic and deuteranopic spectral sensitivities, with tritanopic color-matching data, and with short-wavelength-sensitive (S-) cone spectral-sensitivity data suggests that they are to be preferred over fundamentals based on the CIE 2 degrees CMF's.

Spectral sensitivities of the human cones

http://www.cvrl.org/people/Stockman/pubs/1991%20S%20cone%20SMD.pdf

Derryl D. DePriest

Papers

The temporal properties of the human short-wave photoreceptors and their associated pathways.