Projection from Visual Areas V2 and Prostriata to Caudal Auditory Cortex in the Monkey

Abstract

Studies in humans and monkeys report widespread multisensory interactions at or near primary visual and auditory areas of neocortex. The range and scale of these effects has prompted increased interest in interconnectivity between the putatively ''unisensory'' cortices at lower hierarchical levels. Recent anatomical tract-tracing studies have revealed direct projections from auditory cortex to primary visual area (V1) and secondary visual area (V2) that could serve as a substrate for auditory influences over low-level visual processing. To better understand the significance of these connections, we looked for reciprocal projections from visual cortex to caudal auditory cortical areas in macaque monkeys. We found direct projections from area prostriata and the peripheral visual representations of area V2. Projections were more abundant after injections of temporoparietal area and caudal parabelt than after injections of caudal medial belt and the contiguous areas near the fundus of the lateral sulcus. Only one injection was confined to primary auditory cortex (area A1) and did not demonstrate visual connections. The projections from visual areas originated mainly from infragranular layers, suggestive of a ''feedback''-type projection. The selective localization of these connections to peripheral visual areas and caudal auditory cortex suggests that they are involved in spatial localization.

Auditory–Visual Multisensory Interactions in Humans: Timing, Topography, Directionality, and Sources

“…That is, auditory responses in all of the regions where we observed nonlinear interactions could begin before the arrival of visual responses. The requisite anatomy for such interactions has been well documented (Falchier et al, 2002(Falchier et al, , 2010Rockland and Ojima, 2003;Cappe and Barone, 2005) and may even include a corticothalamocortical loop (Cappe et al, 2007a(Cappe et al, , 2009cHackett et al, 2007). When considered in conjunction with functional studies showing multisensory interactions in low-level cortices and/or at early latencies (Ghazanfar and Schroeder, 2006;Bizley et al, 2007;Cappe et al, 2007b;Martuzzi et al, 2007;Romei et al, 2007Romei et al, , 2009Bizley and King, 2008;Kayser et al, 2008;Wang et al, 2008;Raij et al, 2010), we consider it probable that the present phenomena are supported by direct interconnections that at a functional level are likely a combination of feedforward as well as feedback activity.…”

“…In the case of auditory-visual (AV) interactions, primates possess the requisite anatomy (Falchier et al, 2002(Falchier et al, , 2010Rockland and Ojima, 2003;Cappe and Barone, 2005;Cappe et al, 2009a) and exhibit the predicted neurophysiology (Kayser et al, 2007(Kayser et al, , 2008Wang et al, 2008) for AV convergence and interactions at early poststimulus latencies and in low-level brain regions, including primary cortices. In humans, however, embracing this new model is challenged by methodological criticisms that in turn dramatically impact the purported timing of nonlinear interactions and limit the neurophysiologic interpretability of the results.…”

Looming Signals Reveal Synergistic Principles of Multisensory Integration

“…Structurally, monosynaptic projections identified between unisensory (including primary) cortices raise the possibility of interactions during early stimulus processing stages (Falchier et al, 2002(Falchier et al, , 2010Rockland and Ojima, 2003;Cappe and Barone, 2005;Cappe et al, 2009a; see also Beer et al, 2011). In agreement, functional data support the occurrence of multisensory interactions within 100 ms poststimulus onset and within low-level cortical areas (Giard and Peronnet, 1999;Molholm et al, 2002;Martuzzi et al, 2007;Romei et al, 2007Romei et al, , 2009Cappe et al, 2010;Raij et al, 2010;Van der Burg et al, 2011).…”

A Defense of an Amodal Number System

“…As Cappe and colleagues point out, the mentioned communication between different sensory systems is the result of strong neural connections between them [39]. For instance, there have been found direct projections from the auditory cortex to the primary visual cortex V1, as well as projections from extrastriate visual area V2 to the auditory area TPT (temporoparietal temporal area) in the superior temporal gyrus [40,41]. This implies that, unlike information processing within modules, visual processing is not localized but highly distributed.…”