Figure 1.
The melanopic sensitivity function accounts for the spectral sensitivity of LGN responses in rodless/coneless mice.
(A) Spectral profile of the 3 test stimuli and the melanopic sensitivity function (Vzλ: shaded area). (B) Example response of an rd/rd cl LGN neuron to the three test stimuli presented at a range of different irradiances (numbers above traces indicate log light intensity relative to the maximum achievable: 3.4 log m-lux). (C) Mean ± SEM responses to the three stimuli (and below in overlay) at maximum irradiance (n = 30 cells; each unit's response normalised to the largest change in firing rate across all stimuli). (D–F) Irradiance response relationship for rd/rd cl LGN responses to the three stimuli. A single curve best explains all the data (F-test) when irradiances are expressed in melanopic lux (D; P = 0.641), but not number of photons between 470–480 nm (E; P = 0.04), photopic lux (F; P = 0.001), total photons or total optical power (not shown).
Figure 2.
The melanopic sensitivity function accounts for the impact of long wavelength conditioning stimuli on pupillary responses in rodless/coneless mice.
(A) Sensitivity of rd/rd cl pupil responses to shortwavelength (<500 nm) flash (100 ms) is not altered by 30 min pretreatment with short (498 nm) or long (644 nm) wavelength conditioning stimuli matched for melanopic illuminance (0.4 m-lux; F-test, P = 0.931). (B) Sensitivity of rd/rd cl pupil responses to <500 nm flicker (1 Hz; ON duration = 71 ms), alternating with with short (<500 nm) or long (>600 nm) wavelength background illumination can be predicted when time-averaged irradiance is expressed in m-lux (F-test; P = 0.256).
Figure 3.
The temporal profile of melanopsin-dependent responses is equivalent under short and long wavelength adaptation.
(A) Mean firing rate (± SEM) around a 10 s step of 470 nm (3.8 log m-lux; 10 repeats; interstimulus interval = 240 s) alternating with a background of 470 nm (blue line) or 630 nm (orange line). Backgrounds were calculated to provide −0.1 log m-lux, but differed in terms of total photons (10.6 and 14.6 log photons/m2/s, respectively). (B) Firing rate over the 10s stimulus was not significantly different between conditions (P = 0.34 two-sample T-test). (C) One-phase exponential decay curves were fitted to responses of each unit following light offset, and no significant difference was found in span, k-constant or plateau between the backgrounds (P = 0.40, P = 0.72 and P = 0.33, respectively, following two-sample T-test). (C&D) Long wavelength flashes (15.3 photons/cm2/s) calculated to produce a negligible change (∼1% increase) in melanopsin excitation drive no change in FR immediately following flash onset, and do not have any cumulative effects on ongoing responses (E&F).
Figure 4.
The melanopic sensitivity function accounts for OPN responses to spectrally modulated stimuli in rodless/coneless mice.
(A) Spectral profile of stimuli that differ in irradiance but not melanopic illuminance (4-fold difference in total photons between ‘dim’ and ‘bright’), termed ‘melanopsin silent’. (B) Mean (± SEM) firing rate of 131 PON neurons to transitions between the two melanopsin silent stimuli. These transitions evoked no significant change in firing activity (paired t-test, P = 0.944). (C) Spectral profile of stimuli which differ substantially in melanopic illuminance (21-fold between dim and bright) but not total photons (<1% difference), termed ‘melanopsin active’. (D) Mean (± SEM) firing rate of PON neurons to transitions between the two melanopsin active stimuli. Transitions to the melanopsin ‘bright’ condition evoked a significant increase firing activity (paired t-test, P = 0.014, n = 131). Yellow bar in C & D indicates presentation of the ‘bright’ stimulus, with dim stimulus present at all other times.
Figure 5.
The melanopic sensitivity function accounts for the spectral sensitivity of tonic LGN firing activity in mice with functional rods/cones.
(A) Example response of an Opn1mwR ‘sustained’ LGN neuron to the three test stimuli depicted in Fig. 1A at a range of irradiances (numbers above traces indicate log light intensity relative to the maximum achievable-3.4 log m-lux). (B) Mean ± SEM response to the three stimuli (and below in overlay) at maximum irradiance (n = 46 cells; each unit's response normalised to the largest change in firing rate across all stimuli). (C–E) Irradiance response relationship for Opn1mwR LGN sustained firing responses (20–30 s after stimulus onset) to the three stimuli. Sensitivity could be explained by a single linear function (F-test) when irradiances were expressed in melanopic lux (C; 0.432), but not in effective photon flux for L- or S-cones (D & E; P = 0.001 & 0.022 respectively).