Locomotion modulates specific functional cell types in the mouse visual thalamus

The visual system is composed of diverse cell types that encode distinct aspects of the visual scene and may form separate processing channels. Here we present further evidence for that hypothesis whereby functional cell groups in the dorsal lateral geniculate nucleus (dLGN) are differentially modulated during behavior. Using simultaneous multi-electrode recordings in dLGN and primary visual cortex (V1) of behaving mice, we characterized the impact of locomotor activity on response amplitude, variability, correlation and spatiotemporal tuning. Locomotion strongly impacts the amplitudes of dLGN and V1 responses but the effects on variability and correlations are relatively minor. With regards to tunings, locomotion enhances dLGN responses to high temporal frequencies, preferentially affecting ON transient cells and neurons with nonlinear responses to high spatial frequencies. Channel specific modulations may serve to highlight particular visual inputs during active behaviors

Behavioral and neural effects of visual masking and optogenetic V1 suppression in mice

The necessary condition for sensory information to enter consciousness remains an open question. Studies on humans and non-human primates indicate the need for reverberant neural activity lasting for 10s-100s of milliseconds. Properties of this reverberant activity, especially the involvement of early sensory areas, are heavily debated. Here, we addressed these issues using behavior and causal circuit manipulation in mice. Using visual backward masking, we first tested whether visual perception in mice requires reverberant neural activity. Mice were trained to discriminate between locations (± 45 deg eccentricity) of a briefly presented target (grating, 16 ms duration, 10 contrast). After reaching threshold discriminability (d’ > 2), bilateral masks (plaids, 16 ms, 100 contrast) were introduced at various delays to target onset. Mice performed at chance up to stimulus onset asynchronies (SOAs) of 66.7 ms. Together with the results of rats (Watanabe et al. SfN 2014), the capacity of the mask to render the target invisible beyond the time of target offset indicates the necessity of reverberant activity for rodent visual perception. Next, to investigate whether V1 takes part in the crucial circuitry for perception, we replaced the visual mask with optogenetic suppression of V1. Unlike the visual mask eliciting activity throughout the visual system, optogenetic suppression acts locally and is ideal for testing the necessity of activity in distinct processing stages. We trained mice with ChR2 expression targeted at V1 PV+ inhibitory interneurons in the position discrimination task, in which we replaced the visual mask by bilateral optogenetic suppression of V1 activity. We induced suppression by activation of inhibitory interneurons (1.5 s duration) at various delays. Behavioral performance was at chance when V1 was suppressed before the onset of target evoked activity, but was significantly above chance when suppressed later (> 32 ms). Since only the initial transient V1 response, and not the later sustained V1 activity, is required for perception, V1 seems to function as an initial supplier of visual information to the reverberant loop, but does not play a crucial role in its maintenance. Finally we investigated visual forward masking where a visual mask (16 ms, 100 contrast) precedes the target (16 ms, 10 contrast). Behavioral results showed extended SOA ranges of invisibility (16-150 ms). Interestingly, neural responses to high contrast masks (16 ms duration) resulted in a prolonged neural suppression effect (150 ms) that matched the SOAs of invisibility. The results indicate that forward masking blocks relaying of visual information as early as area V1

Corticothalamic feedback sculpts visual spatial integration in mouse thalamus.

En route from the retina to the cortex, visual information passes through the dorsolateral geniculate nucleus (dLGN) of the thalamus, where extensive corticothalamic (CT) feedback has been suggested to modulate spatial processing. How this modulation arises from direct excitatory and indirect inhibitory CT feedback pathways remains enigmatic. Here, we show that in awake mice, retinotopically organized cortical feedback sharpens receptive fields (RFs) and increases surround suppression in the dLGN. Guided by a network model indicating that widespread inhibitory CT feedback is necessary to reproduce these effects, we targeted the visual sector of the thalamic reticular nucleus (visTRN) for recordings. We found that visTRN neurons have large RFs, show little surround suppression and exhibit strong feedback-dependent responses to large stimuli. These features make them an ideal candidate for mediating feedback-enhanced surround suppression in the dLGN. We conclude that cortical feedback sculpts spatial integration in the dLGN, likely via recruitment of neurons in the visTRN

Mouse primary visual cortex in not part of the reverberant neural circuitry critical for visual perception

Attention allows our brain to focus its limited resources on a given task. It does so by selective modulation of neural activity and of functional connectivity (FC) across brain-wide networks. While there is extensive literature on activity changes, surprisingly few studies examined brain-wide FC modulations that can be cleanly attributed to attention compared to matched visual processing. In contrast to prior approaches, we used an ultra-long trial design that avoided transients from trial onsets, included slow fluctuations (< 0.1 Hz) that carry important information on FC, and allowed for frequency-segregated analyses. We found that FC derived from long blocks had a nearly two-fold higher gain compared to FC derived from traditional (short) block designs. Second, attention enhanced intrinsic (negative or positive) correlations across networks, such as between the default-mode network (DMN), the dorsal attention network (DAN), and the visual system (VIS). In contrast attention de-correlated the intrinsically correlated visual regions. Third, the de-correlation within VIS was driven primarily by high frequencies, whereas the increase in DAN-VIS predominantly by low frequencies. These results pinpoint two fundamentally distinct effects of attention on connectivity. Information flow increases between distinct large-scale networks, and de-correlation within sensory cortex indicates decreased redundancy