Submited on: 25 Mar 2012 11:14:56 PM GMT
Published on: 26 Mar 2012 12:36:34 PM GMT
I read with great interest your latest paper on the claustrum- fascinating hypothesis and very logical, I would say. I do have a coupe of questions/comments:
 
1- Fiber dissection and HDFT studies in the human brain have shown the connectivity of the claustrum with frontal, central, and parietal areas, but failed to show direct connections with primary visual and auditory cortex - this, of course, may well be related to technical limitations -- do we have strong evidence of these connections in the human brain, or this evidence comes from animal studies?
 
2- What is in your opinion the functional relationship between the cortico-thalamic projection system and the claustro-cortical one? We are investigating the overlapping of their connections at the cortical level, since they may have interrelated roles - could the claustrum serve as a modulator of thalamic function?
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Response to Dr. Fernandez-Miranda’s questions. In response to Dr. Fernandez-Miranda’s cogent questions we would like to provide some additional details. Needless to say, there are many gaps in our knowledge, and the picture is not very clear in either of these fields. (Q1) Connections between the claustrum and the primary visual and auditory cortices. All auditory areas of the cat (including A1) have bilateral communications with the claustrum (Beneyto and Prieto 2001). Neurons in A1 receive projections from the claustrum (Budinger et al. 2006). However, in the primate, Crick and Koch (2005) state: “In particular, no projection from primary visual cortex to the claustrum has been found in the macaque monkey (as discussed by Sherk 1986), while there is little doubt about the existence of axons from the claustrum to V1.” (Q2) The claustrum and the thalamus. The claustrum has few connections with the principle thalamic nuclei. However, it has demonstrated communications with midline thalamic nuclei - to n. reuniens (McKenna and Vertes 2004), from n. paratenial and n. paraventricular (Vertes and Hoover 2008), to the posterior thalamus (Morys et al. 1987), from the lateral geniculate n. (Carey and Neal 1986), and to the lateral mediodorsal thalamus (Erickson et al. 2004). There is one particularly interesting question relating to the comparison of the thalamocortical and claustrocortical circuits, namely, “Is the claustrocortical circuit a feed-forward inhibitory system (FFI) similar to the thalamocortical circuit? “Strong feed-forward inhibition in the thalamocortical circuit renders cortex highly sensitive to the thalamic synchrony evoked by a sensory stimulus...The prevalence of strong feed-forward inhibitory circuits throughout the central nervous system suggests that synchrony codes and timing-sensitive circuits may be widespread, occurring well beyond sensory thalamus and cortex.” (Bruno 2011). The key ingredients of a strong FFI circuit are (1) a group of pre-synaptic neurons which directly excite both excitatory neurons (i.e. spiny, glutamatergic) and inhibitory neurons (i.e. aspiny, GABAergic/glycinergic) of a second post-synaptic group, and (2) this excitation provides greater synaptic input to inhibitory neurons than to excitatory neurons. One must then ask the question: Is the synchrony-detecting circuit, which our hypothesis postulates for the claustrum, an FFI circuit? To answer this we need to know whether this circuit provides a greater synaptic input to inhibitory interneurons in the claustrum than to its pyramidal cells. By extension, do the corticoclaustral synapses on any one inhibitory interneuron exceed, in efficacy, the synapses on any one pyramidal neuron? We would be most interested to learn if there is any evidence for this. Claustrocortical v. Thalamocortical Circuitry There is another important aspect to the comparison of thalamocortical and claustrocortical circuitry, that is, to which neurons in the cortex does each connect? Details of the connections of the thalamocortical pathway are to be found in Blasdel and Lind (1983) and Fitzpatrick et al. (1985). However, to our knowledge, no such detailed data is available for the claustrocortical pathway except that the main target is layer IV. Synaptic Architecture There is an additional - and no less interesting - question to be asked. With specific regard to layer IV, do thalamic afferents form axosomatic synapses with cell bodies of layer IV pyramidal neurons and/or with the apical dendrites of layer V and VI neurons? And, if so, do the latter project back to the LGN? Likewise, do claustrocortical afferents form similar synapses, and do they do so with pyramidal neurons in layer VI that project back to the claustrum? The authors would like to take this opportunity to thank Dr. Fernandez-Miranda for his insightful and thought-provoking commentary on our paper, and look forward to progressing the conversation with all fellow neuroscientists who share our interest in the claustrum. References Beneyto M, Prieto JJ. (2001) Connections of the auditory cortex with the claustrum and the endopiriform nucleus in the cat. Brain Res Bull. 54(5):485-498. Blasdel GG, Lund JS. (1983) Termination of afferent axons in macaque striate cortex. J Neurosci. 3(7):1389-1413. Bruno RM. (2011) Synchrony in sensation. Curr Opin Neurobiol. 21(5):701-708. Budinger E, Heil P, Hess A, Scheich H.(2006) Multisensory processing via early cortical stages: Connections of the primary auditory cortical field with other sensory systems. Neuroscience. 143(4):1065-1083. Carey RG, Neal TL. (1986) Reciprocal connections between the claustrum and visual thalamus in the tree shrew (Tupaia glis). Brain Res. 386(1-2):155-168. Crick FC, Koch C. (2005) What is the function of the claustrum? Phil Trans R Soc B. 360:1271-1279. Erickson SL, Melchitsky DS, Lewis DA. Subcortical afferents to the lateral mediodorsal thalamus in cynomolgus monkeys. Neuroscience. 129(3):675-690. Fitzpatrick D, Lund JS, Blasdel GG. (1985) Intrinsic connections of macaque striate cortex: afferent and efferent connections of lamina 4C. J Neurosci. 5(12):329-349. McKenna JT, Vertes RP. (2004) Afferent projections to nucleus reuniens of the thalamus. J Comp Neurol. 480(2):115-142. Morys, J, Sloniewski P, Narkiewicz O. (1987) The posterior part of the thalamus and anterior pretectum have two systems of connections with insula and claustrum in the rat. Folia Morphol (Warsz). 46(1-2):67-76. Vertes RP, Hoover WB. (2008) Projections of the paraventricular and paratenial nuclei of the dorsal midline thalamus in the rat. J Comp Neurol. 508(2):212-237.
Responded by Dr. John Smythies on 10 May 2012 12:19:58 AM
claustrum and consciousness
Posted by Ms. Srinivasan Rajarajeswari on 27 Jul 2012 02:06:36 AM GMT

 

Claustrum and Consciousness: I wish to record  my comments on the function of the Claustrum with reference to its containing the neural correlate  to consciousness. I propose  to explain  my understanding, using some concepts  occurring in Advaita  Vedanta  of India (non dualism as expounded by Shri Adhi Shankara )adding my comments/conjectures on the issue. At the outset I believe that, whatever is stated in the Advaita Vedanta is ultimately  valid ,in which case certain concepts cannot, but have a neural representation  in the human brain and I am trying to figure out what that could be and  what neural centres it might involve. For example, let us take the famous Rope -Snake erroneous perception i.e the perceiver's mistaken notion of the snake in the place of the rope . The rope is received by the eyes but interpreted as snake by the brain which creates anxiety. The perceived anxiety causes further anxiety   and certain  autonomic and motor reactions result. It is likely that intra cortical synchronizations  and  intra-clausral  synchronizations may be getting  activated . There are certain  justifications for the rope to be perceived as snake which possibly  get  integrated in the claustral synchronizations: 1. The obscure image of the rope (due to surrounding darkness etc,)as received by the eyes 2. The chances for a real  snake to be present in the external environment and expectation thereof and diffused anxiety due to the same.. 3 The fear of facing a snake as the snake is perceived as a danger to life. The processes of precaution verification and subsequent reasoning  should also be integrated to get into and subsequently come out of the illusion of snake. Perception of non existing snake in the place of rope is called adhyaaropa  (adhyAsa@)or superimposition of false on what is true) This is a function of  Maya(or Avidhya at the individual level which is normally translated as ignorance) .A non-existent snake(superimposition) can cause as much anxiety as an existent snake. The fear due to erroneously perceived  non- existent snake will vanish when the error in perception is understood,  even though the underlying  fear of snakes may not. . I may like to say that claustrum may be containing the neural correlates of mAyA rather than correlates of Consciousness. In a way, both mean the same thing  from an empirical view point. Conscious awareness of any thing(i.e with a subject -object distinction) is  possible  only with a combination of consciousness with avldya or maya sakthi. {(The sanskrit word ma means to measure and mAyA means what can be measured(limited).( The word mAyA can also mean what appears to be ,but truly  is not)} The mAyA is said to be possessing two types of powers, the power of projection and power of concealment or covering (Vikshepa Sakthi and Aavarana Sakthi). The Avarana sakthi is called avidya or ignorance at the individual level and is said to produce dvaita bhava (an impression of duality i.e., the impression that individual consciousness (jiva) is different from the ultimate reality) (ignorance creates an impression of pluraillity of consciousness) The impression of duality is also regarded as the basis for individual doership or agency. MAyA creates an impression of there being a consciousness separate from others in each apparently sentient body. The word claustrm means-a means of closing or shutting in and the sanskrit word aavarana is translated as concealment. My explanation/conjecture  in this regard is ---the individual personality we think we are, is an impression of an idea of self, created out of stored memory images of the experiences after the birth of the body (including perhaps experiences in the womb and  experience of taking birth) and impressions passed through the genes and technically the empirical self is an idea. Due to the associated reactions of autonomic nervous system and the memory images registered of the experiences of bodily reactions, the identification of an idea (or programme), as continuing singular self  takes effect. There may be a mirror like reflection of cognition which reflects consciousness, when this idea arises .The function of claustrum in this regard   may be to interpret the sensory data and other data generated by the brain  internally ,  and  to cast an impression of doer-ship on the idea of continuing self  which may be called ego  This modified ego may be the general context for all perceptions reactions and  understanding as an individual. When the ego programme of doer-ship precedes or co-exists  with action in synchronization  the behaviour appears ,to the individual ,to be voluntary. It may be because of the synchrony created by the claustrum, the ego gets an impression of having a continuing independent existence. As Consciousness (through  cognition) lights up the idea of self or ego, the ego with the help of reflected consciousness, professes to have an existence separate from the body and starts identifying with the body(sometimes being the possessor of the body and sometimes being anchored in the body).And that may be the conscious awareness from the medical angle. Whenever the idea of ego does not show up, its identification with the body does not show up. Nevertheless, when the idea re-occurs the impression of continuity also occurs. Claustrum may be covering its synchronized orchestrations with the veil of the idea of singular continuing self or ego. Claustrum’s synchronizations perhaps interpret the inputs  received  from the cortex to continue the story line of life as that of an individual in tune with what is there in the memory already  and what is desired or to be expected in future(perhaps that is also in the memory) and  thus the history of the Universe gets written by some unseen hand, with many claustrums doing their synchronizations, and many  (apparently) resultant  activities, which may be resulting in further cortical inputs. Claustrum ,that way, is the correlate  (in the brain )of the creator, preserver and destroyer of the Universe and its processes.       @ ADHYASA- Shri Sankaracharya defines adhyAsa  as  atasmin tat buddhi    which   means  understanding one thing as another thing.In the case of awareness of snake in  the place of  a rope  adhyAsa  arises. It  is also defined as   smritirUpa paratra pUrvadrstAvabhasah(as in memory something  prevously perceived appears to be present here and now, when it is absent,so also some thing previously perceived is imposed on something present here and now  (ref:A Dictionary of Advaita Vedanta compiled by Nirod Baran Chakraborrty   Published by The RamakrishnaMission Institute of Culture Kolkata 700029 INDIA  in  2003)

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