Talk:Vibrissal basal ganglia circuits
Hi Kevin, great article, however (why is there always a 'however' ?) there are a few points you might like to consider before I push the 'accept' button. I will put them under the same headings as used in the article.
Introduction 1) The article is called ‘vibrissal basal ganglia circuits’ and then deals almost exclusively with the cortico-basal ganglia vibrissal circuits – “…information processed by the vibrissal circuit comes mainly form the primary somatosensory (S1) and motor(M1) cortical areas”. However, a collicular man such as myself can’t help but note that there are several channels through which wisker-related information from the rostro-lateral enlargement of the intermediate layers of the superior colliculus could access the striatum via relays in the intralaminar thalamus ( see Krout KE, Loewy AD, Westby GWM, Redgrave P. 2001. Superior colliculus projections to midline and intralaminar thalamic nuclei of the rat. J Comp Neurol 431:198-216.). Either you might want to expand the article to consider likely subcortical contributions to the vibrissal basal ganglia, or just simply re-title it making it clear that it is restricted to the cortical loops.
2) You give the impression that input from SI goes into the basal ganglia and returns via the thalamus to “frontal cortical areas where motor decisions are made”. I thought the whole point about the ‘closed’ loop component of basal ganglia architecture is that the return connections from the basal ganglia channels return to the regions from which the channels originate (Alexander GE, DeLong MR, Strick PL. 1986. Parallel organization of functionally segregated circuits linking basal ganglia and cortex. Ann Rev Neurosci 9:357-381 + others). How sure are you that layer 1 of the barrel field doesn’t receive return input from the ventromedial thalamic nucleus ?
3) Maybe I’m being a bit functionally picky here but I’m not sure what the differences are between ‘motor decisions’ taken in the frontal cortex and ‘selecting and executing coordinated behavioural movements…’ performed by the vibrissal circuits through the basal ganglia.
Vibrissal basal ganglia connections
1) You present the traditional, but now somewhat dated ‘direct’/’indirect’ idea of basal ganglia internal connectivity in this section. However, this view has been undermined somewhat by reports of: (i) ‘direct pathway’ collaterals to globus pallidus (Wu Y, Richard S, Parent A. 2000. The organization of the striatal output system: a single-cell juxtacellular labeling study in the rat. Neurosci Res 38:49-62.); (ii) direct projections from the globus pallidus to the output nuclei and back to the striatum; and (iii) that the subthalamic nucleus is now widely viewed as a principal input nucleus to the basal ganglia, rather than exclusively as the relay between globus pallidus and the output nuclei – see Fig 2 in my Scholarpedia article + associated references (http://www.scholarpedia.org/article/Basal_ganglia). I don’t know how important this is for your article….but the way you have it, just doesn’t seem quite right any more….
Vibrissal coreticostriatal projections
1) This point is just me wondering – are your sections on ‘divergence’ and ‘convergence’ another way of describing an anatomy that would support ‘broad tuning’ of responses to single whisker stimulation ? Manuel Castro-Alamancos recently described something very similar for the superior colliculus.
1) Again the traditional view is that medium spiny neurone membrane potentials exist in bimodal ‘up’ and ‘down’ states. However, this was shown to be a property of sleep and anaesthesia and not to be the case when the animal is awake (Mahon S, et al. 2006. Distinct patterns of striatal medium spiny neuron activity during the natural sleep-wake cycle. J Neurosci 26(48):12587-12595.) That said, nothing that you go on to say is wrong – i.e. MSNs need to be in an ‘up’ state to fire action potentials and to achieve this they need a large synchronised inputs.
Neostriatal vibrissal responses
1) The last sentence…. Absence of any response to whisker stimulation under anaesthesia is difficult to interpret in any way other than the anaesthetic wrecks transmission in afferent sensory pathways. We have been able to show that local injections of bicuculline into the deep layers of the superior colliculus reinstates visual sensitivity to all basal ganglia input nuclei in anaesthetised animals….(the striatum Schulz JM, et al. 2009. Short-Latency Activation of Striatal Spiny Neurons via Subcortical Visual Pathways. Journal Of Neuroscience 29(19):6336-6347; the subthalmus, Coizet V, et al 2009. Short-Latency Visual Input to the Subthalamic Nucleus Is Provided by the Midbrain Superior Colliculus. Journal Of Neuroscience 29(17):5701-5709; and substantia nigra pars compacta Dommett E, et al. 2005. How visual stimuli activate dopaminergic neurons at short latency. Science 307(5714):1476-1479). I wouldn’t be surprised is something similar was true for the whiskers too….
Minor point: the Figures need numbering and legends…..
As you can see these points are mainly general basal ganglia ones rather than specific comments on the meat of your paper which is really good. My suggestion would therefore be to make only minor modifications rather than any major restructuring.
If you have any questions or queries concerning these comments please get back to me.
Best wishes, Pete Redgrave