Talk:Vibrissal midbrain loops

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    The article is well written, thorough and comprehensive.

    comments: the paper Vibrissal midbrain loops should describe the sensory-motor loops running through the midbrain. while information about the various connections appear in the text in several places, the summary diagram (Figure 1) does not include the entire loop(s) and thus creates a (sensory) biased picture. It is recommented to: 1. include the connections from the midbrain to the motor end in Figure 1. 2. include the connections of the relevant components with M1 in Figure 1 3. include other midbrain stations, such as the red nucleus, in Figure 1. the authors can use dashed lines or other markers to indicate the level of confidence about various connections.

    round 2:

    This article is becoming an excellent source of knowledge about midbrain loops, although currently still strongly biased towards SC related circuits. As this bias reflects the bias in current knowledge, I assume that the authors will update other midbrain information in the future as it will become available. In order to complete the current article as a thorough reference on midbrain loops, I recommend a few more additions: 1. Provide the list of references for the entire set of descending output pathways 2. Describe the non-SC pathways (mostly descending ones) also in the text, with appropriate references. Where appropriate, mention what information is still missing (to help guiding future studies) 3. Since the PO (shouldn’t it be POm?) – ZI circuit is described, it is important to add the connections of both with the motor cortex.

    Response: 1 and 2. We have added references and details in the first paragraph about non-SC pathways. SC input and output pathways are fully described in the article with references. 3. There are many pathways that are not included in the diagram, including the many targets of M1 outputs. The diagram is already very busy and mostly includes midbrain related connections. We feel that additional connections (outside midbrain) would make it too complex.

    Reviewer 3 This is a nice, comprehensive, in depth review about the structure and function of midbrain vibrissal loop. I just have a few comments and a question

    1) The incertotectal pathway. For the trigeminal synaptic input to zona incerta Lavalle et al., 2005 is a better citation than Veinante 2000 since it actually shows trigeminal contacts on GABAergic ZI cells at the EM level. For the ZI-Po pathway Bartho et al 2002 is the correct citation.

    2)The tectoincertal pathway. It may be worth to mention that the tectoincertal pathway target different part of ZI (dorsal ZI) than the origin of the incertotectal pathway (ventral ZI).

    3)The term cuneiform nucleus is rarely used in rodents use DpMe.

    4)I miss a brief evolutinonary account of the superior colliculus. Namely in lower vertabrates without significant cortical organization (e.g amphibians) SC acts like the highest brain center and control escape and approach. With the evolution of neocortex these and more complex functions were relocated to the cortex but SC still retains many of these ancient functions, which is widely discussion here. You may consider to put it in this evolutionary perspective.

    5)Finally I was thinking about the potential problems of facial nerve stimulation to judge the relationship between whisker movement and SC activity. The nerve stimulation backfire the motor nucleus which projects widely in the brainstem. The SC response may be the consequence of this activity rather than the whisker movements. Since recordings are available in freely moving preparations as well isn’t possible to correlate whisker movement and SC activity in these animals?

    RESPONSE to Reviewer 3: 1. We have changed the reference as suggested. 2. We have mentioned this point. 3. We have pointed this out. 4. We have added a brief evolutionary account in the functions section. 5. In these experiments, the motor nerve is cut between the stimulating electrode and the motorneurons; so the electrical stimulation does not backfire motorneurons. We are currently doing those experiments in animals that have implanted EMG electrodes to monitor whisker movements.

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