Spatiotemporal specificity of contrast adaptation in mouse primary visual cortex

Optogenetic Activation of Interneuron Subtypes Modulates Visual Contrast Responses of Mouse V1 Neurons

Interneurons are critical for information processing in the cortex. In vitro optogenetic studies in mouse primary visual cortex (V1) have sketched the connectivity of a local neural circuit comprising excitatory pyramidal neurons and distinct interneuron subtypes that express parvalbumin (Pvalb+), somatostatin (SOM+), or vasoactive intestinal peptide (VIP+). However, in vivo studies focusing on V1 orientation tuning have ascribed discrepant computational roles to specific interneuron subtypes. Here, we sought to clarify the differences between interneuron subtypes by examining the effects of optogenetic activation of Pvalb+, SOM+, or VIP+ interneurons on contrast tuning of V1 neurons while also accounting for cortical depth and photostimulation intensity. We found that illumination of the cortical surface produced a similar spectrum of saturating additive photostimulation effects in all 3 interneuron subtypes, which varied with cortical depth rather than light intensity in Pvalb+ and SOM+ cells. Pyramidal cell modulation was well explained by a conductance-based model that incorporated these interneuron photostimulation effects.

Adaptation to stimulus orientation in mouse primary visual cortex

Information processing in the visual system is shaped by recent stimulus history, such that prolonged viewing of an adapting stimulus can alter the perception of subsequently presented test stimuli. In the tilt-after-effect, the perceived orientation of a grating is often repelled away from the orientation of a previously viewed adapting grating. A possible neural correlate for the tilt-after-effect has been described in cat and macaque primary visual cortex (V1), where adaptation produces repulsive shifts in the orientation tuning curves of V1 neurons. We investigated adaptation to stimulus orientation in mouse V1 to determine whether known species differences in orientation processing, notably V1 functional architecture and proportion of tightly tuned cells, are important for these repulsive shifts. Unlike the consistent repulsion reported in other species, we found that repulsion was only about twice as common as attraction in our mouse data. Furthermore, adapted responses were attenuated across all orientations. A simple model that captured key physiological findings reported in cats and mice indicated that the greater proportion of broadly tuned neurons in mice may explain the observed species differences in adaptation.

Specificity and timescales of cortical adaptation as inferences about natural movie statistics

Adaptation is a phenomenological umbrella term under which a variety of temporal contextual effects are grouped. Previous models have shown that some aspects of visual adaptation reflect optimal processing of dynamic visual inputs, suggesting that adaptation should be tuned to the properties of natural visual inputs. However, the link between natural dynamic inputs and adaptation is poorly understood. Here, we extend a previously developed Bayesian modeling framework for spatial contextual effects to the temporal domain. The model learns temporal statistical regularities of natural movies and links these statistics to adaptation in primary visual cortex via divisive normalization, a ubiquitous neural computation. In particular, the model divisively normalizes the present visual input by the past visual inputs only to the degree that these are inferred to be statistically dependent. We show that this flexible form of normalization reproduces classical findings on how brief adaptation affects neuronal selectivity. Furthermore, prior knowledge acquired by the Bayesian model from natural movies can be modified by prolonged exposure to novel visual stimuli. We show that this updating can explain classical results on contrast adaptation. We also simulate the recent finding that adaptation maintains population homeostasis, namely, a balanced level of activity across a population of neurons with different orientation preferences. Consistent with previous disparate observations, our work further clarifies the influence of stimulus-specific and neuronal-specific normalization signals in adaptation.

Adaptive Processes in Thalamus and Cortex Revealed by Silencing of Primary Visual Cortex during Contrast Adaptation

Visual adaptation illusions indicate that our perception is influenced not only by the current stimulus but also by what we have seen in the recent past. Adaptation to stimulus contrast (the relative luminance created by edges or contours in a scene) induces the perception of the stimulus fading away and increases the contrast detection threshold in psychophysical tests [1, 2]. Neural correlates of contrast adaptation have been described throughout the visual system including the retina [3], dorsal lateral geniculate nucleus (dLGN) [4, 5], primary visual cortex (V1) [6], and parietal cortex [7]. The apparent ubiquity of adaptation at all stages raises the question of how this process cascades across brain regions [8]. Focusing on V1, adaptation could be inherited from pre-cortical stages, arise from synaptic depression at the thalamo-cortical synapse [9], or develop locally, but what is the weighting of these contributions? Because contrast adaptation in mouse V1 is similar to classical animal models [10, 11], we took advantage of the optogenetic tools available in mice to disentangle the processes contributing to adaptation in V1. We disrupted cortical adaptation by optogenetically silencing V1 and found that adaptation measured in V1 now resembled that observed in dLGN. Thus, the majority of adaptation seen in V1 neurons arises through local activity-dependent processes, with smaller contributions from dLGN inheritance and synaptic depression at the thalamo-cortical synapse. Furthermore, modeling indicates that divisive scaling of the weakly adapted dLGN input can predict some of the emerging features of V1 adaptation.

Contrast-dependent orientation discrimination in the mouse

As an important animal model to study the relationship between behaviour and neural activity, the mouse is able to perform a variety of visual tasks, such as orientation discrimination and contrast detection. However, it is not clear how stimulus contrast influences the performance of orientation discrimination in mice. In this study, we used two task designs, two-alternative forced choice (2AFC) and go/no-go, to examine the performance of mice to discriminate two orthogonal orientations at different contrasts. We found that the performance tended to increase with contrast, and the performance at high contrast was better when the stimulus set contained a single contrast than multiple contrasts. Physiological experiments in V1 showed that neural discriminability of two orthogonal orientations increased with contrast. Furthermore, orientation discriminability of V1 neurons at high contrast was higher in the single than in the multiple contrast condition, largely due to smaller response variance in the single contrast condition. Thus, the performance of mice to discriminate orientations at high contrast is adapted to the contrast range in the stimuli, partly attributed to the contrast-range dependent capacity of V1 neurons to discriminate orientations.

Contrast adaptation is spatial frequency specific in mouse primary visual cortex

Contrast adaptation, generated by prolonged viewing of a high contrast spatial pattern, is known to reduce perceptual sensitivity to subsequently presented stimuli of similar spatial frequency (SF). Neural correlates of this pattern-specific contrast adaptation have been described in several classic studies in cat primary visual cortex (V1). These results have also recently been extended to mice, which is a genetically manipulable animal model. Here we attempt to parse the potential mechanisms contributing to this phenomenon by determining whether the SF specificity of contrast adaptation observed in mouse V1 neurons depends on the spike rate elicited by the adapting gratings. We found that adapting stimuli that drove a neuron more strongly generally produced more adaptation, implicating an intrinsic or fatigue-like process. Importantly, we also observed that slightly stronger contrast adaptation was produced when the adapting SF matched the test SF even when matched and nonmatched adapting gratings elicited similar spike rates indicating extrinsic or network processes contribute as well.

GABA-ergic interneurons involved in transcallosal inhibition of the visual cortices in vivo in mice

In the current study we investigated the role of the corpus callosum, particularly the gamma-aminobutyric acid-ergic (GABAergic) projection neurons involved in interhemispheric inhibition (IHI). In order to explore IHI in primary visual cortices, we adopted a protocol whereby we performed a direct current lesion of the unilateral primary visual cortex with or without posterior callosotomy, and used two-photon Ca(2+)in vivo imaging on the opposite unaffected region to detect neural activities in mice. Following this procedure, the numbers of vesicular GABAergic transporters (VGATs) and GABAergic interneurons in the unaffected primary cortex were determined using immunofluorescence staining. Results indicated that following unilateral visual cortical lesioning without callosotomy, the neuronal Ca(2+) activities in the opposite side were significantly increased. However, the neuronal activities of the unaffected visual cortex in animals with unilateral cortical lesion with callosotomy were not significantly different. Additionally, there was no significant difference in the numbers of GABAergic interneurons in the unaffected region between each group, while the number of VGATs in the unaffected region was significantly decreased following unilateral visual cortical lesion without callosotomy, which was unchanged once with callosotomy. Finally, callosotomy alone without cortical lesioning produced no change in neuronal activities, the number of GABAergic interneurons or VGATs. Our results demonstrate that IHI between the homologous primary visual cortices occurs via the corpus callosum, and further indicate the important involvement of long-range GABAergic interneurons in transcallosal inhibition.