Spatial integration in mouse primary visual cortex

Abstract

Responses of many neurons in primary visual cortex (V1) are suppressed by stimuli exceeding the classical receptive field (RF), an important property that might underlie the computation of visual saliency. Traditionally, it has proven difficult to disentangle the underlying neural circuits, including feedforward, horizontal intracortical, and feedback connectivity. Since circuit-level analysis is particularly feasible in the mouse, we asked whether neural signatures of spatial integration in mouse V1 are similar to those of higher-order mammals and investigated the role of parvalbumin-expressing (PVϩ) inhibitory interneurons. Analogous to what is known from primates and carnivores, we demonstrate that, in awake mice, surround suppression is present in the majority of V1 neurons and is strongest in superficial cortical layers. Anesthesia with isoflurane-urethane, however, profoundly affects spatial integration: it reduces the laminar dependency, decreases overall suppression strength, and alters the temporal dynamics of responses. We show that these effects of brain state can be parsimoniously explained by assuming that anesthesia affects contrast normalization. Hence, the full impact of suppressive influences in mouse V1 cannot be studied under anesthesia with isoflurane-urethane. To assess the neural circuits of spatial integration, we targeted PVϩ interneurons using optogenetics. Optogenetic depolarization of PVϩ interneurons was associated with increased RF size and decreased suppression in the recorded population, similar to effects of lowering stimulus contrast, suggesting that PVϩ interneurons contribute to spatial integration by affecting overall stimulus drive. We conclude that the mouse is a promising model for circuit-level mechanisms of spatial integration, which relies on the combined activity of different types of inhibitory interneurons.

Visual Cortex Modulates the Magnitude but Not the Selectivity of Looming-Evoked Responses in the Superior Colliculus of Awake Mice

“…In contrast, cortical cells may gradually integrate modest inputs from increasing larger areas within their receptive fields when the stimulus looms, and the response reaches its peak when the stimulus gets to a certain size. The weaker surround suppression, as reported in deep layer cortical cells (Nienborg et al, 2013; Vaiceliunaite et al, 2013), might allow the response to build up during a relatively long period.…”

Photons and neurons

“…Either way the frequency of spontaneous seizures were reduced significantly. Optogenetics is also widely employed in neocortex for network activities (Favero and Castro-Alamancos, 2013), motor cortex for optical control of type-specific neural activities (Aravanis et al, 2007) and corticocortical connections (Hira et al, 2013), and visual cortex for the studies such as multisensory integration (Olcese et al, 2013), spatial integration (Vaiceliunaite et al, 2013) and neurovascular coupling (Pisauro et al, 2013). …”

Time to wake up: Studying neurovascular coupling and brain-wide circuit function in the un-anesthetized animal

“…This distortion will have implications for neuroimaging-based mapping experiments since the activated area following sensory stimulation may be much larger in the awake animal (Ferezou et al, 2007). However, in the visual cortex, anesthesia seems to increase the spatial spread and prolong the duration of the response to visual input (Haider et al, 2013; Vaiceliunaite et al, 2013). In the olfactory bulb, odor evoked responses are larger in the anesthetized animal (Kato et al, 2013; Rinberg et al, 2006).…”