It is also well known that parvocellular systems

code certain luminance signals by virtue of their spatially opponent mode of function (Ingling & Martinez-Uriegas, 1983). Human EEG data show that at > 8% contrast it is not possible to discount the interplay of multiple channels in coding luminance while contrasts Z-VAD-FMK cost < 8% do indeed bias processing of low-frequency stimuli towards the magnocellular stream (Rudvin et al., 2000). Furthermore, chromatic differences between red and green should not be equated with L – M isolating, parvocellular-driven processing; in fact, colors typically considered as ‘red’ and ‘green’ actually contain a significant S – (L + M) decrement (Wuerger et al., 2005). Here we compared the luminance and chromatic-based visual pathways, which are more readily and unambiguously defined in terms of their preferred driving stimuli. Although the nature of a specialized cortical pathway for color processing originating in V1 is still debated (Conway et al., 2010), there is abundant evidence that suggests a prominent involvement of ventral occipitotemporal cortices in color processing

(Conway, 2009). Both these occipitotemporal cortices and more posterior pericalcarine areas possess bi-directional connections with the bilateral amygdaloid nuclei in the macaque monkey brain (Amaral H 89 clinical trial et al., 1992). Imaging work using fluorescent tracers demonstrates, however, that the neuronal populations within the

basal nucleus of the amygdala that are bi-directionally connected with low-level visual cortex (V1 and V2) do not greatly overlap with the populations connected with the more ventral visual areas. Re-entrant projections find more originating in basal nucleus layers with larger (magno-) neurons tend to have their targets in primary and secondary visual cortex, whereas higher-order occipitotemporal visual areas receive afferents from layers characterized by intermediate and small (parvo-) cell bodies (Amaral et al., 2003). Assuming a similar neuroarchitecture in the human brain, this would imply that luminance-defined Gabor patches readily benefit from strong amygdalofugal re-entry into retinotopic visual areas when the CS+ becomes reliably paired with threat. The present data suggest that, when viewing chromatic stimuli, the visual cortex cannot establish such a flexible link with structures providing modulatory input into pericalcarine regions, at least not in ways that would affect rapidly oscillating excitations of visual neuron populations (i.e. ssVEPs). It is well established that the ssVEP is confined to lower-tier areas in the visual hierarchy, particularly with stimulation frequencies > 7 Hz (Müller et al., 2006; Wieser & Keil, 2011).