Anatomical Evidence of Multimodal Integration in Primate Striate Cortex

Abstract

The primary visual cortex (area 17 or V1) is not thought to receive input from nonvisual extrastriate cortical areas. However, this has yet to be shown to be the case using sensitive tracers in the part of area 17 subserving the peripheral visual field. Here we show using retrograde tracers that peripheral area 17 subserving the visual field at an eccentricity of 10-20 degrees receives projections from the core and parabelt areas of the auditory cortex as well as from the polysensory area of the temporal lobe (STP). The relative strength of these projections was calculated for each injection by computing the proportions of retrogradely labeled neurons located in the auditory and STP areas with respect to number of labeled neurons constituting the established projection from the superior temporal sulci (STS) motion complex (middle temporal area, medial superior temporal, fundus of the superior temporal area). In peripheral area V1 the projection from auditory cortex corresponds to 9.5% of that of the STS motion complex and STP to 35% of that from the STS motion complex. Compared to peripheral area 17, central and paracentral area 17 showed considerably weaker inputs from auditory cortex (0.2-0.8%) but slightly more from STP cortex (3.5-6.1%). The present results show that the connectivity of area 17 is eccentricity dependent. Direct projections from auditory and STP cortex to peripheral area 17 have important consequences for higher visual functions of area 17, including multimodal integration at early stages of the visual cortical pathway.

Multisensory anatomical pathways

“…Because both injections sites involved two areas (areas 1 and 3b), we cannot determine whether this reflects the preferential connections to either area. Similarly, auditory and multimodal projections to area V1 are prominent towards the representation of the peripheral visual field (Falchier et al, 2002), and only scattered neurons in the auditory cortex send a projection to foveal V1 (Fig. 1A).…”

“…However, no similar result had been observed in the monkey. But, very recently, the use of anterograde and retrograde tracers in the monkey made it possible to highlight direct projections of the auditory cortex to the primary visual cortex V1 (Falchier et al, 2002), as well as of the associative auditory cortex to the primary and secondary visual areas (Rockland and Ojima, 2003) (Fig. 1).…”

“…1). These direct connections arise in their majority from the parabelt auditory area located on the supratemporal gyrus (Falchier et al, 2002). We have estimated that about a third of the auditory projections originate from the anterior bank of the lateral sulcus, but only a small fraction of these projecting neurons are located in the primary auditory cortex.…”

“…For example, we estimated that these heteromodal projections constitute only a few percent of the total cortical inputs of the somatosensory cortex of the marmoset. However, the non-visual projections to the peripheral V1 can be as large as the projection arising from the motion visual area MT/V5 (Falchier et al, 2002), which is known to exert an influential impact on V1 responses (Hupé et al, 1998). In addition, all of these heteromodal connections do not consist in scattered projecting neurons, but rather have a topological organization (Batardiere et al, 1998) with a relatively compact projection zones probably linked to cortical functional modules.…”

Audiovisual Temporal Correspondence Modulates Human Multisensory Superior Temporal Sulcus Plus Primary Sensory Cortices

“…This was presented at the top of the MR bore via clusters of four optic fibers arranged into a rectangular shape and five interleaved fibers arranged into a cross shape, 2°above the horizontal meridian at an eccentricity of 18°. Visual stimuli were presented peripherally, which may maximize the opportunity for interplay between auditory and visual cortex (Falchier et al, 2002), and also allowed us to test for any contralaterality in effects for one visual field or the other. The peripheral fiber-optic endings could be illuminated red or green with a standard luminance of 40 cd/m 2 and were 1.5°in diameter (for schematics of the resulting colored "shapes," see Fig.…”