Robust effects of corticothalamic feedback and behavioral state on movie responses in mouse dLGN
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Evaluation Summary:
Spacek et al. study the corticothalamic feedback of different visual stimuli on visual thalamus. With optogenetic suppression of visual cortex feedback and simultaneous multi-channel recordings in visual thalamus, the authors succeeded to acquire important data about this essential feedback loop in awake, behaving animals. The authors impressively show that the cortical feedback acts as a gain factor in thalamus for the transmission of signals from retina to cortex, specifically for natural scenes. These careful measurements performed in a well-defined circuit also advance our understanding of the role of feedback more generally in the brain.
(This preprint has been reviewed by eLife. We include the public reviews from the reviewers here; the authors also receive private feedback with suggested changes to the manuscript. The reviewers remained anonymous to the authors.)
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Abstract
Neurons in the dorsolateral geniculate nucleus (dLGN) of the thalamus receive a substantial proportion of modulatory inputs from corticothalamic (CT) feedback and brain stem nuclei. Hypothesizing that these modulatory influences might be differentially engaged depending on the visual stimulus and behavioral state, we performed in vivo extracellular recordings from mouse dLGN while optogenetically suppressing CT feedback and monitoring behavioral state by locomotion and pupil dilation. For naturalistic movie clips, we found CT feedback to consistently increase dLGN response gain and promote tonic firing. In contrast, for gratings, CT feedback effects on firing rates were mixed. For both stimulus types, the neural signatures of CT feedback closely resembled those of behavioral state, yet effects of behavioral state on responses to movies persisted even when CT feedback was suppressed. We conclude that CT feedback modulates visual information on its way to cortex in a stimulus-dependent manner, but largely independently of behavioral state.
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Author Response
Reviewer #1 (Public Review):
In this paper, the authors examine the role of feedback from primary visual cortex (V1) to the dorsolateral geniculate nucleus of the thalamus (dLGN) under a variety of visual stimulus conditions. This is a well-defined circuit originating from a specific population of Layer 6 cells in the cortex, and the authors test the role of this projection by recording in dLGN during silencing of V1 via ChR2 expression in PV inhibitory cells. This is a well-established technique for strong silencing of cortex. However, because there are other disynaptic pathways from V1 to thalamus, they also perform a similar set of experiments using more targeted optogenetic inhibition of a genetically-defined class of Layer 6 (NTSR1) cells that make up most of the L6 corticothalamic projections. The fact that …
Author Response
Reviewer #1 (Public Review):
In this paper, the authors examine the role of feedback from primary visual cortex (V1) to the dorsolateral geniculate nucleus of the thalamus (dLGN) under a variety of visual stimulus conditions. This is a well-defined circuit originating from a specific population of Layer 6 cells in the cortex, and the authors test the role of this projection by recording in dLGN during silencing of V1 via ChR2 expression in PV inhibitory cells. This is a well-established technique for strong silencing of cortex. However, because there are other disynaptic pathways from V1 to thalamus, they also perform a similar set of experiments using more targeted optogenetic inhibition of a genetically-defined class of Layer 6 (NTSR1) cells that make up most of the L6 corticothalamic projections. The fact that these experiments elicit similar results supports their interpretation that these direct projections are largely responsible for the observed results. While previous studies have manipulated corticothalamic projections pharmacologically, via V1 lesions, or via optogenetics, the authors rightly point out that most previous studies have focused on simple parametric stimuli and/or have been performed in anesthetized animals. The results of this study suggest feedback during natural visual stimuli and locomotion reveal effects that are distinct from these previous studies.
Overall, these are important and carefully-performed experiments that significantly advance our understanding of the role of corticothalamic feedback to the dLGN.
We thank the reviewer for the appreciation of our methods and results.
The authors suggestion that the different effects observed during simple and complex stimuli may be due to increased surround suppression during the full-field gratings seems reasonable, but I didn’t understand how the analysis of blank periods during these two conditions supported this argument. It wasn’t clear to me what mechanisms would be expected to support the alternative outcome, where suppressing feedback during the blank periods interleaved with the two different stimuli would have different effects - unless they are testing whether natural movies elicit some longer-lasting state change that would change the results observed during blank periods. This seems somewhat implausible, and unless the authors wish to expand the study to include different stimulus sizes, I think the interpretation regarding surround suppression is best left to the discussion, where it is already treated well.
We thank the reviewer for the recommendation. We fully agree that explaining the difference in CT feedback across blanks, gratings, and movies will require more experiments. We have followed the recommendation of the reviewer and removed the interpretation related to differences in surround suppression from the results section and treat it now in the discussion only.
The paper would benefit from more clearly highlighting results that agree or disagree with previous studies, with a brief mention of how the authors interpret these similarities or differences. For example the results of Olsen et al 2012 seem to be consistent with what the authors observe here with gratings but not with natural movies, and although Olsen et al performed some awake recordings, I think the LGN recordings were all under anesthesia. Specifically highlighting these differences (and suggesting an interpretation for them) would help emphasize the novelty of the study.
We thank the reviewer for the recommendation and now highlight throughout the results and discussion where our results agree or disagree with previous studies. As mentioned by the reviewer, we have similar results for gratings to the results obtained by Olsen et al. (2012), although in our study we have not explicitly centered the full field gratings on the RFs and we have not measured surround suppression. The results for the blank stimuli and the movies, however, are different, at least in terms of how CT feedback affects ring rate. A key insight of our study, at least in our view, is that CT feedback effects might well differ for different stimuli, and understanding the underlying mechanism (e.g., differential engagement of the excitatory and indirect inhibitory CT feedback pathway) will be an important avenue of research in the future.
The authors should comment more on the spatial extent of V1 silencing and potential effects of the variability observed across mice, especially given that they appear to have made only a single injection of ChR2 to label PV cells. While silencing with this method extends beyond the injection site, it probably doesn’t cover all of V1. Was any analysis done of variability across mice based on the size or location of the ChR2 expression measured post-hoc?
Unfortunately, we did not preserve enough slices to precisely quantify the extent of expression across animals. However, visual inspection of the slices revealed that even a single injection typically resulted in a widespread pattern of expression. In fact, we think that activation of PV neurons was determined in its spatial extent not so much by the virus expression but rather by the photoactivation light. With a distance of 0.5 0.1 mm of the optical fibre from the cortical surface, most of V1 was covered by light. A previous study performing a quantitative characterization of the lateral spread of optogenetic suppression by PV activation demonstrates that pyramidal neuron ring can be suppressed 2 3 mm from the laser center Li et al. (2019). Hence, we think that variability in opsin expression across mice is unlikely to have a substantial impact on our results.
The decrease in reliability and sparseness during running is attributed partially to increased eye movements. In cortex this has been studied in awake animals with natural movies in a variety of studies where the opposite effects are observed including Froudarakis et al 2014 where there was a small increase in both metrics during running, and Reimer et al 2014 where reliability strongly increased during pupil dilation. If there is enough data to condition on running periods where eye movements are stable or dilation outside of running to measure the effects of feedback suppression during these periods, this would be useful information.
We thank the reviewer for bringing up this interesting issue. We fully agree that our results recorded in dLGN are different from those measured by Froudarakis et al. (2014) and Reimer et al. (2014) in V1.
As suggested by the reviewer, we have repeated the analysis proposed by Reimer et al. (2014) to identify periods in the movie with the most rapid pupil dilation / constriction in face of continuous changes in overall luminance. Besides the effects of pupil dilation / constriction on ring rate, we have computed reliability both according to what we had used throughout our manuscript and in the way proposed in Reimer et al. (2014), which resembles our measure of SNR. We find that both measures of reliability are unaffected by pupil dilation.
Interestingly, in the meantime other studies have also reported that reliability might be differently affected by behavioral state in V1 compared to dLGN. For instance, Nestvogel and McCormick (2022) found that consistent with our results variability of membrane potential in visual thalamic neurons was not significantly altered by locomotion or whisker movement.
Reviewer #2 (Public Review):
Spacek et al. study the corticothalamic feedback of different visual stimuli on visual thalamus. With optogenetic suppression of visual cortex feedback and simultaneous multi-channel recordings in visual thalamus, the authors succeeded to acquire important data about this essential feedback loop in awake, behaving animals. The authors show in detail that the cortical feedback acts as a gain factor in thalamus for the transmission of signals from retina to cortex. They also show that naturalistic scenes result in robust feedback from cortex. As expected from anatomy, the authors find that modulatory feedback from cortex and modulatory input from brain stem act rather independently on thalamus. The paper is technically very impressive and the results are important for a wide range of readers.
We thank the reviewer for the positive feedback.
It is advisable to revise the Introduction and Discussion to better integrate the new findings into the existing literature.
We thank the reviewer for this advice, and have revised the title, abstract, introduction and discussion to better integrate our new findings into the existing literature, and highlight our advances in relation to previous findings.
The authors distinguish between awake, resting state and running state. However, the awake, resting state in mice comprises a wide range of alertness levels. This range of alertness will most likely affect the bursting probability of thalamocortical neurons.
We thank the reviewer for this comment. So far, our manuscript had only taken locomotion as a proxy for behavioral state, as locomotion typically goes along with increased pupil size (Erisken et al., 2014; McGinley et al., 2015) and increased levels of arousal (McGinley et al., 2015; Vinck et al., 2015). To also study the effects of locomotion-independent arousal, we have now applied the analysis mentioned by the reviewer: following methods originally suggested by Reimer et al. (2014), we identified periods of the movie presentation without locomotion that corresponded to the upper or the lower quartile of pupil size change. Similar to the results that Reimer et al. (2014) found for primary visual cortex, we observed that ring rate in dLGN is enhanced during times when the pupil was dilating faster than usual vs. when it was constricting faster than usual. Like the effects of running, the modulations by pupil-indexed arousal persisted even with V1 suppression. We present these new results in Figure 5 - Supplement 2.
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Evaluation Summary:
Spacek et al. study the corticothalamic feedback of different visual stimuli on visual thalamus. With optogenetic suppression of visual cortex feedback and simultaneous multi-channel recordings in visual thalamus, the authors succeeded to acquire important data about this essential feedback loop in awake, behaving animals. The authors impressively show that the cortical feedback acts as a gain factor in thalamus for the transmission of signals from retina to cortex, specifically for natural scenes. These careful measurements performed in a well-defined circuit also advance our understanding of the role of feedback more generally in the brain.
(This preprint has been reviewed by eLife. We include the public reviews from the reviewers here; the authors also receive private feedback with suggested changes to the …
Evaluation Summary:
Spacek et al. study the corticothalamic feedback of different visual stimuli on visual thalamus. With optogenetic suppression of visual cortex feedback and simultaneous multi-channel recordings in visual thalamus, the authors succeeded to acquire important data about this essential feedback loop in awake, behaving animals. The authors impressively show that the cortical feedback acts as a gain factor in thalamus for the transmission of signals from retina to cortex, specifically for natural scenes. These careful measurements performed in a well-defined circuit also advance our understanding of the role of feedback more generally in the brain.
(This preprint has been reviewed by eLife. We include the public reviews from the reviewers here; the authors also receive private feedback with suggested changes to the manuscript. The reviewers remained anonymous to the authors.)
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Reviewer #1 (Public Review):
In this paper, the authors examine the role of feedback from primary visual cortex (V1) to the dorsolateral geniculate nucleus of the thalamus (dLGN) under a variety of visual stimulus conditions. This is a well-defined circuit originating from a specific population of Layer 6 cells in the cortex, and the authors test the role of this projection by recording in dLGN during silencing of V1 via ChR2 expression in PV inhibitory cells. This is a well-established technique for strong silencing of cortex. However, because there are other disynaptic pathways from V1 to thalamus, they also perform a similar set of experiments using more targeted optogenetic inhibition of a genetically-defined class of Layer 6 (NTSR1) cells that make up most of the L6 corticothalamic projections. The fact that these experiments …
Reviewer #1 (Public Review):
In this paper, the authors examine the role of feedback from primary visual cortex (V1) to the dorsolateral geniculate nucleus of the thalamus (dLGN) under a variety of visual stimulus conditions. This is a well-defined circuit originating from a specific population of Layer 6 cells in the cortex, and the authors test the role of this projection by recording in dLGN during silencing of V1 via ChR2 expression in PV inhibitory cells. This is a well-established technique for strong silencing of cortex. However, because there are other disynaptic pathways from V1 to thalamus, they also perform a similar set of experiments using more targeted optogenetic inhibition of a genetically-defined class of Layer 6 (NTSR1) cells that make up most of the L6 corticothalamic projections. The fact that these experiments elicit similar results supports their interpretation that these direct projections are largely responsible for the observed results. While previous studies have manipulated corticothalamic projections pharmacologically, via V1 lesions, or via optogenetics, the authors rightly point out that most previous studies have focused on simple parametric stimuli and/or have been performed in anesthetized animals. The results of this study suggest feedback during natural visual stimuli and locomotion reveal effects that are distinct from these previous studies.
Overall, these are important and carefully-performed experiments that significantly advance our understanding of the role of corticothalamic feedback to the dLGN.
The authors suggestion that the different effects observed during simple and complex stimuli may be due to increased surround suppression during the full-field gratings seems reasonable, but I didn't understand how the analysis of blank periods during these two conditions supported this argument. It wasn't clear to me what mechanisms would be expected to support the alternative outcome, where suppressing feedback during the blank periods interleaved with the two different stimuli would have different effects - unless they are testing whether natural movies elicit some longer-lasting state change that would change the results observed during blank periods. This seems somewhat implausible, and unless the authors wish to expand the study to include different stimulus sizes, I think the interpretation regarding surround suppression is best left to the discussion, where it is already treated well.
The paper would benefit from more clearly highlighting results that agree or disagree with previous studies, with a brief mention of how the authors interpret these similarities or differences. For example the results of Olsen et al 2012 seem to be consistent with what the authors observe here with gratings but not with natural movies, and although Olsen et al performed some awake recordings, I think the LGN recordings were all under anesthesia. Specifically highlighting these differences (and suggesting an interpretation for them) would help emphasize the novelty of the study.
The authors should comment more on the spatial extent of V1 silencing and potential effects of the variability observed across mice, especially given that they appear to have made only a single injection of ChR2 to label PV cells. While silencing with this method extends beyond the injection site, it probably doesn't cover all of V1. Was any analysis done of variability across mice based on the size or location of the ChR2 expression measured post-hoc?
The decrease in reliability and sparseness during running is attributed partially to increased eye movements. In cortex this has been studied in awake animals with natural movies in a variety of studies where the opposite effects are observed including Froudarakis et al 2014 where there was a small increase in both metrics during running, and Reimer et al 2014 where reliability strongly increased during pupil dilation. If there is enough data to condition on running periods where eye movements are stable or dilation outside of running to measure the effects of feedback suppression during these periods, this would be useful information.
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Reviewer #2 (Public Review):
Spacek et al. study the corticothalamic feedback of different visual stimuli on visual thalamus. With optogenetic suppression of visual cortex feedback and simultaneous multi-channel recordings in visual thalamus, the authors succeeded to acquire important data about this essential feedback loop in awake, behaving animals. The authors show in detail that the cortical feedback acts as a gain factor in thalamus for the transmission of signals from retina to cortex. They also show that naturalistic scenes result in robust feedback from cortex. As expected from anatomy, the authors find that modulatory feedback from cortex and modulatory input from brain stem act rather independently on thalamus. The paper is technically very impressive and the results are important for a wide range of readers.
It is advisable …
Reviewer #2 (Public Review):
Spacek et al. study the corticothalamic feedback of different visual stimuli on visual thalamus. With optogenetic suppression of visual cortex feedback and simultaneous multi-channel recordings in visual thalamus, the authors succeeded to acquire important data about this essential feedback loop in awake, behaving animals. The authors show in detail that the cortical feedback acts as a gain factor in thalamus for the transmission of signals from retina to cortex. They also show that naturalistic scenes result in robust feedback from cortex. As expected from anatomy, the authors find that modulatory feedback from cortex and modulatory input from brain stem act rather independently on thalamus. The paper is technically very impressive and the results are important for a wide range of readers.
It is advisable to revise the Introduction and Discussion to better integrate the new findings into the existing literature.
The authors distinguish between awake, resting state and running state. However, the awake, resting state in mice comprises a wide range of alertness levels. This range of alertness will most likely affect the bursting probability of thalamocortical neurons.
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