Amplitude of the transient visual evoked potential (tVEP) as a function of achromatic and chromatic contrast: Contribution of different visual pathways

Abstract

We investigated how the stimulation mode influences transient visual evoked potentials (tVEP) amplitude as a function of contrast of achromatic and isoluminant chromatic gratings. The chromatic stimulation probed only responses to the red-green axis. Visual stimuli were monocularly presented in a 5 degrees diameter circle, achromatic and chromatic horizontal gratings, 1 Hz pattern reversal stimulation, and achromatic and chromatic gratings, 300 ms onset per 700 ms offset stimulation. For the achromatic pattern reversal stimulation, a double slope function describes how the P100 amplitude varied as a function of log contrast which had a limb at low-to-medium contrasts and another limb at high contrasts. For the achromatic onset/offset stimulation, C2 amplitude saturated at the highest contrast tested and a single straight line described how it changed along most of the contrast range. Both presentation modes for chromatic gratings resulted in amplitude versus log contrast relations which were well described by single straight lines along most of the contrast range. The results may be interpreted as if at 2 cpd, achromatic pattern reversal stimulation evoked the activity of at least two visual pathways with high and low contrast sensitivity, respectively, while achromatic onset/offset stimulation favored the activity of a pathway with high contrast sensitivity. The neural activity in the M pathway is the best candidate to be the high contrast mechanism detected with pattern reversal and pattern onset/offset VEPs. The activity of color opponent pathways such as the P and K pathways either combined or in isolation seems to be responsible for VEPs obtained with isoluminant chromatic gratings at both presentation modes. When the amplitudes of chromatic VEPs were plotted in the same contrast scale as used for achromatic VEPs, chromatic contrast thresholds had similar values to those of the achromatic mechanism with high contrast sensitivity.

Contrast sensitivity of pattern transient VEP components: Contribution from M and P pathways.

“…By considering previous observations (Jeffreys, 1977;Shawkat & Kriss, 1998aPrevic, 1988;Ellemberg et al, 2001;Souza et al, 2007Souza et al, , 2008 and the present results, we may hypothesize that patternreversal P100 (lower limb) and N135 and pattern-onset/ offset C2 are mainly the result of M pathway activity. Conversely, pattern-reversal P100 (higher limb) and pattern-onset/offset C1 and possibly pattern-reversal N75 are the result of preferential activity along the P pathway, with a possible contribution from the activity of other pathways.…”

“…Several works found that pattern-reversal VEP component (P100) amplitude as a function of contrast can be described by two straight lines (Campbell & Maffei, 1970 Souza et al, 2007Souza et al, , 2008. The most accepted explanation for this is a contribution of different visual pathways to the VEP (Nakayama & Mackeben, 1982;Bobak et al, 1984;Valberg & Rudvin, 1997;Rudvin et al, 2000;Souza et al, 2007Souza et al, , 2008.…”

“…The way in which VEP changes with stimulus contrast has been used to distinguish between the cortical activity of different visual pathways (Campbell & Maffei, 1970;Nakayama & Mackeben, 1982;Bobak, Bodis-Wollner, Harnois, & Harnois, 1984;Previc, 1988;Valberg & Rudvin, 1997;Rudvin, Valberg, & Kilavik, 2000;Ellemberg, Hammarrenger, Lepore, Roy, & Guillemot, 2001;Gomes, Souza, Rodrigues, Saito, Silveira, & da Silva Filho, 2006;Gomes, Souza, Lima, Rodrigues, Saito, da Silva Filho, & Silveira, 2008;Souza, Gomes, Saito, da Silva Filho, & Silveira, 2007;Souza, Gomes, Lacerda, Saito, da Silva Filho, & Silveira, 2008). Visual evoked potential amplitude linearly depends on the logarithm of stimulus contrast, sometimes with saturation at high contrasts.…”

“…Although often only one straight line is sufficient to describe the data, depending on the spatial frequency, two separate straight lines may be needed (Campbell & Maffei, 1970;Nakayama & Mackeben, 1982;Bobak et al, 1984;Valberg & Rudvin, 1997;Rudvin et al, 2000;Souza et al, 1997Souza et al, , 1998. Zemon & Gordon (2006) and Souza et al (2007Souza et al ( , 2008 suggested that a function that relates VEP amplitude with stimulus contrast that linearly increases and then saturates at high achromatic contrasts is a signature of the activity of a single visual pathway, possibly the magnocellular (M) pathway, which is highly sensitive to contrast, reflected by single-cell recordings of M neurons in the retina and lateral geniculate nucleus (LGN) (Kaplan & Shapley, 1982, 1986Lee, Martin, & Valberg, 1989; Lee et al, 2000). Souza et al (2007) also suggested that a double-slope function indicates a contrast-dependent contribution of different visual pathways to VEP.…”

The Maximum Tolerated Dose of Gamma Radiation to the Optic Nerve during Gamma Knife Radiosurgery in an Animal Study

“…The pVEP adopted in this study, without normal individual variation of VEP induced by flash stimulation, has both powerful confidence and sensitivity to estimate abnormalities in the visual pathway. Variations in the latency and amplitude of the pVEP P100 wave are two main reference points for estimating abnormalities in the visual pathway [39,40,41,42]. …”