Abstract
Electrophysiological studies have revealed that a large proportion of the mouse primary visual cortex (V1) receives input also from the ipsilateral eye. This is surprising as most optic nerve fibers cross at the optic chiasm in mice. Inactivating V1 of one hemisphere has recently demonstrated a strong contribution of one hemisphere's activity on binocularity of single units and visually evoked potentials of V1 in the other hemisphere of young rats and of single units in young adult mice. Here we used intrinsic signal optical imaging to quantitatively study the influence of cortico-cortical connections on the magnitude of neuronal activation in the entire binocular zone of adult mouse V1. We simultaneously measured V1-activity of both hemispheres in adult C57BL/6J mice before and after blocking sensory-driven activity in one hemisphere with muscimol. In V1 contralateral to the inactivation, ipsilateral eye evoked activity was reduced by on average 18% while contralateral eye evoked activity did not change. Our results clearly show that cortico-cortical interactions exert a global amplification of ipsilateral eye evoked activity in adult mouse V1.
Highlights
One important characteristic of neurons in the mammalian primary visual cortex (V1) is their binocularity, i.e. they get activated by both eyes
Cortico-cortical interactions have recently been shown to play an important role in ocular dominance and its plasticity in juvenile rats (P16-31): Inactivating one hemisphere decreased ipsilateral eye evoked responses in V1 of the opposite hemisphere and had a strong influence on ocular dominance [8,9]
We demonstrated that inactivating one hemisphere in adult mouse V1 significantly reduced ipsilateral eye evoked activity in the entire binocular part of V1 of the opposite hemisphere. These data emphasize that in adult mouse V1, cortico-cortical interactions play a major role for determining ocular dominance, and significantly extend previous knowledge about callosal influences on binocularity in juvenile rats [8,9,10]
Summary
One important characteristic of neurons in the mammalian primary visual cortex (V1) is their binocularity, i.e. they get activated by both eyes. Cortico-cortical interactions have recently been shown to play an important role in ocular dominance and its plasticity in juvenile rats (P16-31): Inactivating one hemisphere decreased ipsilateral eye evoked responses in V1 of the opposite hemisphere and had a strong influence on ocular dominance [8,9]. In vivo extracellular recordings in PD35-90 mice have recently shown that the ipsilateral eye’s response was reduced by removing the callosal input in a total of nine cells [10]. It is – – not yet known whether the callosal input has a global and homogeneous effect on ipsilateral eye activity throughout mouse V1 or not. We could show that corticocortical interactions exert a global amplification of ipsilateral eye evoked activity in the primary visual cortex of adult mice
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