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.
Highlights
The importance of sensory input to the developing brain is manifest in individuals with congenital loss of a sensory system, such as deafness or blindness
In the present investigation we examined the consequences of visual impairment on the cortical organization and connectivity of primary visual cortex in a mouse model that lacks rod-mediated vision
We found that there was a functional reorganization of V1 in that neurons responded mostly to auditory, somatosensory stimulation, or some combination of stimulation of these modalities
Summary
The importance of sensory input to the developing brain is manifest in individuals with congenital loss of a sensory system, such as deafness or blindness. Studies in blind humans indicate that auditory localization tasks activate occipital cortex in regions normally involved in visual localization and motion detection (Weeks et al, 2000), and that occipital cortex is activated with electrotactile stimulation of the tongue (Ptito et al, 2005), Braille reading and vibrotactile stimulation (Sadato et al, 1996; Burton et al, 2002, 2004) While all of these studies demonstrate dramatic cross-modal plasticity, the anatomical substrate for this plasticity is not completely understood (see Karlen et al, 2010 for review). Animal models of congenital blindness generally examine the effects of complete loss of activity, or loss of the sensory apparatus, on cortical and subcortical structures These studies have shown that the neocortex undergoes dramatic organizational changes in that cortex normally devoted to processing visual input is taken over by the spared sensory systems Studies of connections indicate that the primary visual area (V1) receives inputs from a variety of non-visual cortical and subcortical structures associated with the spared modalities (Izraeli et al, 2002; Karlen et al, 2006)
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