What are the effects of severe visual impairment on the cortical organization and connectivity of primary visual cortex?

Abstract

The organization and connections of the primary visual area (V1) were examined in mice that lacked functional rods (Gnat−/−), but had normal cone function. Because mice are nocturnal and rely almost exclusively on rod vision for normal behaviors, the Gnat−/− mice used in the present study are considered functionally blind. Our goal was to determine if visual cortex is reorganized in these mice, and to examine the neuroanatomical connections that may subserve reorganization. We found that most neurons in V1 responded to auditory, or some combination of auditory, somatosensory, and/or visual stimulation. We also determined that cortical connections of V1 in Gnat−/− mice were similar to those in normal animals, but even in normal animals, there is sparse input from auditory cortex (AC) to V1. An important observation was that most of the subcortical inputs to V1 were from thalamic nuclei that normally project to V1 such as the lateral geniculate (LG), lateral posterior (LP), and lateral dorsal (LD) nuclei. However, V1 also received some abnormal subcortical inputs from the anterior thalamic nuclei, the ventral posterior, the ventral lateral and the posterior nuclei. While the vision generated from the small number of cones appears to be sufficient to maintain most of the patterns of normal connectivity, the sparse abnormal thalamic inputs to VI, existing inputs from AC, and possibly abnormal inputs to LG and LP may be responsible for generating the alterations in the functional organization of V1.

Cortical and subcortical projections to primary visual cortex in anophthalmic, enucleated and sighted mice

“…Multiple connections between the primary visual cortex and non‐sensory visual cortical areas were also reported in other studies (Garrett et al. , 1992; Wang & Burkhalter, 2007; Larsen et al. , 2009; Laramée et al.…”

“…, 2002), cats (Hall & Lomber, 2008), ferrets (Allman et al. , 2008) and mice (Larsen et al. , 2009; Laramée et al.…”

Long, intrinsic horizontal axons radiating through and beyond rat barrel cortex have spatial distributions similar to horizontal spreads of activity evoked by whisker stimulation

“…In rat barrel cortex, horizontal projections have generally been described as extending only one or two barrel diameters in any given direction for pyramidal neurons in barrel columns, and for two to four barrel diameters in any given direction for neurons in septal columns, although evidence for a sparser projection beyond this extent often has been present in photomicrographs (Chapin et al 1987; Koralek et al 1990, Bernardo et al 1990; Fabri and Burton 1991; Hoeflinger et al 1995; Gottlieb and Keller 1997; Kim and Ebner 1999; Broser et al 2008; Oberlaender et al 2011; Lee et al 2011; Kim and Lee 2013; Narayanan et al 2015). Prior studies in rats (Miller and Vogt 1984; Paperna and Malach 1991) and other rodents (Budinger et al 2006; Larsen et al 2009; Campi et al 2007; 2010; Charbonneau et al 2012; Laramée et al 2013; Henschke et al 2015) resulted in reports of sparse projections from somatosensory cortex to other primary sensory cortices, but most of these studies employed retrograde neuronal tracers and therefore could not have appreciated that the axons involved coursed diffusely through gray matter, branching along the way. Although neurons in the barrel field are known to have long projections to the dysgranular zone of the somatosensory cortex and to the posterior parietal cortex (Kim and Ebner 1999; Oberlaender et al 2011; Lee et al 2011; Kim and Lee 2013), these axons typically are not discussed as being abundant in other associational cortices posterior to PMBSF.…”

“…The existence of long, horizontal axons radiating diffusely from the barrel field into other sensory cortices may be relevant to cross-modal responses to whisker stimulation that can be recorded in visual and auditory cortices of rats and other rodents (Wallace et al 2004; Campi et al 2007; Frostig et al 2008; Larsen et al 2009; Vasconcelos et al 2011) and to the modulatory influence that whisker stimulation can have on responses to visual stimuli in rodent visual cortex (Iurilli et al 2012). Horizontal projections also may contribute to the ability of stimuli from one modality to evoke activity in cortices corresponding to another modality following associative learning (Cahill et al 1996).…”

Nonlinear Electroencephalographic Correlates of Auditorymotor Integration in Boys With Obtained Visual Dysfunction

“…Встановлено [13], що більшість нейронів первинної зорової кори мишей з частковою зоровою депривацією (блокування функції паличок) відповідають на звукову стимуля-цію. Анатомічним підґрунтям цього можуть бути нещодавно виявлені у зрячих приматів прямі гетеромодальні зв'язки між первинною слуховою та зоровою зонами кори [14,15].…”