Talk:Vibrissal afferents from trigeminus to cortices

REVIEW OF SCHOLARPEDIA ARTICLE by Martin Deschenes Title: Vibrissal afferents from trigeminus to cortices by Martin Deschenes

1. Title is not clear: How about something like “Vibrissal pathways to sensory-motor cortex.” to reflect the multiple pathways. 2. Pg. 5, the dorsal pathway: Are the multiwhisker cells in PrV actually large in size (large diameter cell bodies) and are the multiwhisker dorsal “head” cells in VPM large in diameter as well? This point is not clear. 3. Pg. 5, the dorsal pathway, paragraph 2: where exactly was the lesion in the paralemniscal and lemniscal pathways that had the effects described? It matters. 4. The fig. legend for fig. 1 is incomplete. There is no A or C panel described, and the description doesn’t describe all of the components in the diagram. Also the details cannot be seen in the histology at the magnification used. 5. There is a 'disconnect' for me in the new view of the pathways to septa. If the large RF POm pathway, which receives an input from SpVi and projects to the septa, and doesn’t generate the RFs in septal cells, then how do VPMhead cells, which similar to POm receives inputs from large, multiwhisker RF cells in PrV and in turn project to the septa interact with POm inputs? This scenario suggests that POm projects to the septa, but is a silent partner in driving the septal neurons, except under special circumstances, such as some sort of sensory-motor integration. Is this what is actually being proposed? Also several labs have shown that cutting the SpV inputs to the thalamus reduces VPM cells to 1-2 whisker receptive fields. Is this because none of these studies has recorded in VPMhead that receives multiwhisker inputs from large cells in PrV (i.e., several groups unknowingly only recorded from core barreloid cells)? or did the loss of the multiwhisker input from SpVi leave only the small RF PrV neurons driving the VPM neurons? The logic seems inescapable that single VPM neurons receive convergent PrV and SpVi inputs unless I am missing something. 6. Page4: undistinguishable should be indistinguishable 7. The PO pathway: I find it hard to visualize a “shell-like” shape of PO around VPM. It is dorsomedial, but not anterior, posterior, or lateral to VPM in a 'shell-like' distribution. Is there a better descriptor? 8. Pg 6, second paragraph: change ‘send branches in’ to ‘send branches to’. 9. Pg. 7, middle: Is it possible to say what cells in ZIv (local or projection GABAergic cells) receive the inputs from the ascending trigeminal fibers? If it is known, it should be mentioned. 10. Pg. 9, middle: In the topographic projections from cortex to PrV and SpV, do layer V cells beneath one barrel send collaterals to barrelette cells in both PrV and SpV divisions of the trigeminal complex? If this is known it would be good to include it. 11. Fig. 4, fig legend: There is no reference to panel ‘A’.

Ford Ebner January 13, 2009

COMMENTS on the MS for Scholarpedia by Deschenes M. "Vibrissal afferents from trigeminus to cortices"

The aim of this review article is to describe structural organization and functional interactions between different vibrissal afferent pathways starting from the trigeminal nuclei at the brainstem and finishing at the cerebral cortex. The contents, and the analysis of the sources involved into the MS, reflect current knowledge about vibrissal ascending pathways. The paper is, in general, well written, and the figures clearly illustrate most of the described features. However, there are some comments for the author to consider.

Major comments

1. The introduction refers only to the lemniscal system, without explicitly saying it. It is recommended to include reference to all pathways in the introduction. 2. There is some inconsistency in the names of the pathways – some are by pathway name and some by thalamic nuclei. It is suggested to choose a consistent framework. 3. There is inconsistency in referring to functional roles of the pathways. At the outset it is stated that "it would be premature to refer to these pathways in functional terms (i.e., touch, proprioception, motion, etc). " But later on functional roles are referred to ("They likely use the same sensory inputs to inform the brain about whisker motion, texture and shape, and object location in the whisking space, or again different pathways may operate in different behavioral contexts (e.g., the exploratory and object recognition modes discussed by Curtis and Kleinfeld, 2006)." Thus, either the latter is removed, or the former is removed and other functional suggestions made in the literature should be mentioned. 4. Differences between pathways in spatial RFs are described, but those in temporal RFs (e.g., frequency) are ignored. 5. Po vs POm. Perhaps this is the right place to step towards consistency in the literature. What is needed is a term for the whisker-recipient zone in Po. It would be excellent if the author explains in this article what's wrong with the term POm, and suggests another name instead ("Po" does not refer specifically to the whisker-recipient zone in it). 6. The projections from Po to sub-cortical targets (SC, red nucleus; e.g., Cadusseau J , Roger M, J Hirnforsch 1990 , 31:459-465) are not mentioned. 7. The legend to Figure 1 is not giving an account of the figure properly. The figure contains three panels (A, B, and C), but in the legend, only two of them are mentioned, and in both cases in an irrelevant way: "A" should mention a "diagram", not a "photomicrograph"; "B" should include a thalamic "photomicrograph", not a "brainstem" slice; and "C" should refer to a "brainstem" slice, but it is absent in the legend. Panels "B" and "C" should be provided with the information about spatial orientation and size. 8. Figure 2 needs a special attention. a) Panel "A" was already published in 2000 (Pierret, Lavallee, Deschenes, J Neurosci 20:7455-7462), as a b/w version, but the scales supplying the same slice in this and in published figures are not consistent. b) Both panels represent inverted images of cortical slices. It should be mentioned in the legend, what kind of transformation of the original image was performed. c) The legend should be rephrased: the first sentence looks like a textual explanation instead of giving a name to the figure. 9. The MS contains many abbreviations for anatomical structures. It is the Author's prerogative of choosing abbreviations. However, in this case, the article is designated for a wide audience that is usually familiar with the general anatomical sources, such as atlases. In his previous publications, the Author was using terminology and abbreviations that corresponded to those used in the atlases by Paxinos and Watson (Deschenes et al, Brain Res Rev, 1998, 28:286-308; Pinault and Deschenes, J Comp Neurol, 1998, 391:180-203). For example, reticular thalamic nucleus was abbreviated in mentioned atlases and in previous Author papers as "Rt". In this MS, it appeared as "(nRT; Harris, 1987)" (p.3, para 4, line 22). By the way, Harris used another abbreviation, "TRN", for this nucleus. I suppose that in this MS, the abbreviations should correspond to those used in most frequently used atlases. Maybe, it is reasonable to unify the abbreviations in all the articles of the "Encyclopedia of touch".

Minor comments

1. Last section of the MS is called "Crosstalk between the vibrissal pathways". Meanwhile, it contains mainly morphological data, and it looks reasonable to add to the title something like "Anatomical basis for …". 2. "Posterior thalamic nuclear group" was abbreviated as "Po" (p.1, para 2, lines 6-7). However, in the MS, another abbreviation ("Pom" which is known as "medial division" of the Po) for the same structure appeared without any explanation (p. 2, legend to Figure 2; p.4, para 7, line 4; p.5, para 2, line3). 3. Figure 3 contains too much free space at the top. 4. P. 5, para 4: the paper by "Sosnik et al., 2001" is mentioned in the text, but it is absent in the References. 5. P. 3, para 3, line 7. Cite: Haidarliu S, Yu C, Rubin N, Ahissar E, Front Neuroanat 2, 4 (2008), for atlas-like definition of VPMdm-VPMvl border. 6. P. 4, para 4, line 2 – "other regions of the brainstem" should it be brainstem or thalamus? 7. P. 4, para 4, line 7-8 – do head and core receive feedback from layer 6 of S2? 8. P. 4, para 4, line 10-12 – "S2 cells derive their response properties directly from the VPMvl" – what about Po? 9. P. 4, para 5, line 4-5 – Pom axons terminate only in the shell over VPM? What about the region dorso-medial to VPM along the border? 10. P. 5, para 1 – Add: Groh et al, J Neurosci 28, 9652-63 (2008). 11. P. 6, para 1, - Cite: S. Lee, G. E. Carvell, D. J. Simons, Nat Neurosci (2008). 12. P. 6, last para – the sentence "…and there is no good reason to believe that this information must be conveyed to the cerebral cortex through the lemniscal pathway." doesn't come out so clear. Perhaps use something like: "and thus might be gated out from the lemniscal input in these conditions". 13. There are also small language or style errors, for example: a) p. 3, para 4, line 17: it is written "barreloids", instead of "barreloid"; b) references for the figures should be given in a similar way: abbreviated, as "(Fig. 1)" on p. 2, para 3, line 8, or not abbreviated (p. 3, para 4, line24; p. 5, para 1, line3; p. 5, para4, line 28; p. 6, para 2, line3).

S.Haidarliu & E.Ahissar

November 19 2008–11–22