Feedback connections to ferret striate cortex: Direct evidence for visuotopic convergence of feedback inputs

Abstract

Interareal feedback connections are a fundamental aspect of cortical architecture, yet many aspects of their organization and functional relevance remain poorly understood. Previous studies have investigated the topography of feedback projections from extrastriate cortex to macaque area 17. We have extended this analysis to the ferret. We made restricted injections of cholera toxin B (CTb) into ferret area 17 and mapped the distribution of retrogradely labeled cells in extrastriate cortex. In addition to extensive label spreading within area 17, we found dense cell label in areas 18, 19, and 21 and the suprasylvian cortex and sparser connections from the lateral temporal and posterior parietal cortex. We made extensive physiological assessments of magnification factors in the extrastriate visual cortex and used these measures to convert the spread of labeled cortex in millimeters into a span in degrees of visual field. We also directly measured the visuotopic extents of receptive fields in the regions containing labeled cells in cases in which we made both CTb injections and physiological recordings in the same animals; we then compared the aggregate receptive field (ARF) of the labeled region in each extrastriate area with that of the injection site. In areas 18, 19, and 21, receptive fields of cells in regions containing labeled neurons overlapped those at the injection site but spanned a greater distance in visual space than the ARF of the injection site. The broad visuotopic extent of feedback connections is consistent with the suggestion that they contribute to response modulation by stimuli beyond the classical receptive field.

The role of multi-area interactions for the computation of apparent motion

“…The feed-forward connectivity was modeled to give a receptive field of b7 for 17/18 area neurons and 12°or 15°in 19/21 area neurons. These receptive field sizes are in accordance with the values for the center of the visual field reported by Manger et al (2002) and Cantone et al (2005) for the 19/21 area neurons. For a stimulus presented in the center of the field of view, the receptive field size in area 17/18 is twice the reported value, but a receptive field size at the 17/18 border at 5°eccentricity would be in accordance with published values (Manger et al, 2002;Cantone et al, 2005).…”

“…The larger receptive fields imply that even small objects flashed as much as 7 degrees apart may, in areas 19 and 21, induce neurons in between the mapping sites to fire. As the areas 19 and 21 have retinotopically ordered feedback axons to areas 18 and 17 (Cantone et al, 2005(Cantone et al, , 2006, the firing of the 19/21 neurons initiated by the offset of the first object can be transmitted as a feedback to area 17/18.…”

“…The two model areas are interconnected with retinotopically organized feed-forward and feedback connections (Cantone et al, 2005(Cantone et al, , 2006. We examine the hypotheses (1) whether short-range AM can be computed by the neurons in the primary visual area 17 only; (2) whether two interconnected areas are necessary for the computation of long-range AM.…”

Physiological and Anatomical Evidence for Multisensory Interactions in Auditory Cortex

“…Receptive field sizes and visual field representation vary among the cortical areas that project to auditory cortex (Law et al 1988;Manger et al 2002Manger et al , 2004Cantone et al 2005). In a limited number of recordings, we mapped the spatial extent of the visual receptive fields and found, in most cases, that these were broadly tuned to regions of space within the anterior contralateral quadrant.…”

Cortical feedback depolarization waves: A mechanism of top-down influence on early visual areas

“…One possibility is that the FBW may be produced by synaptic input to the dendrites in areas 21, 19, 18, and 17 from long-range feedback axons connecting area 21 with area 17 (27). Alternatively, spiking neurons in temporal and parietal lobe visual areas, by their long-range feedback axons, make multiple excitatory synapses in areas 21, 19, 18, and 17 produce the FBW.…”