Cortical and thalamic connectivity of occipital visual cortical areas 17, 18, 19 and 21 of the domestic ferret (Mustela putorius furo).

Abstract

The present study describes the ipsilateral and contralateral cortico-cortical and corticothalamic connectivity of the occipital visual areas 17,18, 19 and 21 in the ferret using standard anatomical tract-tracing methods. In line with previous studies of mammalian visual cortex connectivity, substantially more anterograde and retrograde label was present in the hemisphere ipsilateral to the injection site compared to the contralateral hemisphere. Ipsilateral reciprocal connectivity was the strongest within the occipital visual areas, while weaker connectivity strength was observed in the temporal, suprasylvian and parietal visual areas. Callosal connectivity tended to be strongest in the homotopic cortical areas, and revealed a similar areal distribution to that observed in the ipsilateral hemisphere, although often less widespread across cortical areas. Ipsilateral reciprocal connectivity was observed throughout the visual nuclei of the dorsal thalamus, with no contralateral connections to the visual thalamus being observed. The current study, along with previous studies of connectivity in the cat, identified the posteromedial lateral suprasylvian visual area (PMLS) as a distinct network hub external to the occipital visual areas in carnivores, implicating PMLS as a potential gateway to the parietal cortex for dorsal stream processing. These data will also contribute to the Ferretome (www.ferretome.org), a macro connectome database of the ferret brain, providing essential data for connectomics analyses and cross-species analyses of connectomes and brain connectivity matrices, as well as providing data relevant to additional studies of cortical connectivity across mammals and the evolution of cortical connectivity variation.

Cortical and thalamic connectivity of posterior parietal visual cortical areas PPc and PPr of the domestic ferret (Mustela putorius furo)

“…While the observed differences may be methodological (e.g., different tract tracers used), there are certain differences that are unlikely to be explained methodologically, specifically the connectivity of PPc with PMLS and the various laminae of the LGN in the ferret. In our previous study of the connectivity of the occipital visual area of the ferret (Dell, Innocenti, Hilgetag, & Manger, ), we noted that PMLS appears to form a hub in the network processing visual information in the ferret, and this is supported in the current study. In addition, we noted that when comparing the connectivity of the visual cortex with the LGN in the ferret and cat, that the LGN appears to be more strongly connected with visual areas early in the processing hierarchy in the cat, whereas the LGN is more strongly connected with visual areas later in the hierarchy in the ferret, and this pattern appears to continue into the posterior parietal cortex.…”

“…The second difference is the extended connectivity of the LGN to the posterior parietal cortex of the ferret, which appears to be absent in the cat (Figure ; Robertson & Cunningham, ; Raczkowski & Rosenquist, ; Scannell et al, ). This underscores a potential emphasis in the ferret on higher order visual stimuli detection compared to lower order visual stimulus detection emphasis in the cat, similar to that seen for the occipital visual areas (Dell et al, ). As discussed previously (Dell et al, ), these differences may relate to the larger brain size of the cat compared to the ferret, the extensive phylogenetic independence of the two species, anatomical differences related to eye position (lateral in the ferret, frontal in the cat), or their specific strategies for acquiring nutrition.…”

“…This underscores a potential emphasis in the ferret on higher order visual stimuli detection compared to lower order visual stimulus detection emphasis in the cat, similar to that seen for the occipital visual areas (Dell et al, ). As discussed previously (Dell et al, ), these differences may relate to the larger brain size of the cat compared to the ferret, the extensive phylogenetic independence of the two species, anatomical differences related to eye position (lateral in the ferret, frontal in the cat), or their specific strategies for acquiring nutrition. Further studies of species within the two major lineages of the carnivores are required to determine which of these possibilities explains the observed differences.…”

Cortical and thalamic connectivity of temporal visual cortical areas 20a and 20b of the domestic ferret (Mustela putorius furo)

“…Thus, although area 20a in the ferret and the cat share numerous similarities in connectivity patterns (Figure ), the connections with the anterior and dorsal lateral suprasylvian visual areas and with most of the lateral geniculate nucleus observed in the ferret are absent in the cat (Figure ). These differences reiterate our previous findings in the occipital and parietal visual areas of ferret as compared to the cat, where the higher order visual areas of the ferret are under a stronger influence of lateral geniculate input compared to the cat, potentially emphasizing differences in the extraction of visual information in the two species possibly related to life history and morphological differences (Dell, Innocenti, Hilgetag, & Manger, ; Dell, Innocenti, Hilgetag, & Manger, ).…”

“…The posterior parietal cortex has been identified as an integral component of the visual dorsal stream, maintaining direct connections with the prefrontal cortex, as well as numerous direct and indirect connections with the occipital cortex. This has been illustrated in numerous animal studies (Baizer, Ungerleider, & Desimone, ; Kaas & Stepniewska, ; Remple, Reed, Stepniewska, Lyon, & Kaas, ) as well as in the ferret (Dell et al, , ). Similarly, the visual temporal cortex is integral to visual ventral stream information processing; thus, direct connections with the prefrontal cortex are anticipated (Cloutman, ; Goodale & Milner, ; Webster et al, ).…”