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A thalamic reticular networking model of consciousness.

Min BK - Theor Biol Med Model (2010)

Bottom Line: Throughout the latticework structure of the TRN, conscious perception could be accomplished and elaborated through accumulating intercommunicative processing across the first-order input signal and the higher-order signals from its functionally associated cortices.This TRN-modulation hypothesis for conscious awareness provides a comprehensive rationale regarding previously reported psychological phenomena and neurological symptoms such as blindsight, neglect, the priming effect, the threshold/duration problem, and TRN-impairment resembling coma.This hypothesis can be tested by neurosurgical investigations of thalamocortical loops via the TRN, while simultaneously evaluating the degree to which conscious perception depends on the severity of impairment in a TRN-modulated network.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, 75 Francis Street, Boston, MA 02115, USA. minbk@bwh.harvard.edu

ABSTRACT
[BACKGROUND]: It is reasonable to consider the thalamus a primary candidate for the location of consciousness, given that the thalamus has been referred to as the gateway of nearly all sensory inputs to the corresponding cortical areas. Interestingly, in an early stage of brain development, communicative innervations between the dorsal thalamus and telencephalon must pass through the ventral thalamus, the major derivative of which is the thalamic reticular nucleus (TRN). The TRN occupies a striking control position in the brain, sending inhibitory axons back to the thalamus, roughly to the same region where they receive afferents. [HYPOTHESES]: The present study hypothesizes that the TRN plays a pivotal role in dynamic attention by controlling thalamocortical synchronization. The TRN is thus viewed as a functional networking filter to regulate conscious perception, which is possibly embedded in thalamocortical networks. Based on the anatomical structures and connections, modality-specific sectors of the TRN and the thalamus appear to be responsible for modality-specific perceptual representation. Furthermore, the coarsely overlapped topographic maps of the TRN appear to be associated with cross-modal or unitary conscious awareness. Throughout the latticework structure of the TRN, conscious perception could be accomplished and elaborated through accumulating intercommunicative processing across the first-order input signal and the higher-order signals from its functionally associated cortices. As the higher-order relay signals run cumulatively through the relevant thalamocortical loops, conscious awareness becomes more refined and sophisticated. [CONCLUSIONS]: I propose that the thalamocortical integrative communication across first- and higher-order information circuits and repeated feedback looping may account for our conscious awareness. This TRN-modulation hypothesis for conscious awareness provides a comprehensive rationale regarding previously reported psychological phenomena and neurological symptoms such as blindsight, neglect, the priming effect, the threshold/duration problem, and TRN-impairment resembling coma. This hypothesis can be tested by neurosurgical investigations of thalamocortical loops via the TRN, while simultaneously evaluating the degree to which conscious perception depends on the severity of impairment in a TRN-modulated network.

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Schematic drawing of the TRN-modulated thalamocortical looping model of conscious awareness. THL: thalamus, V1: the primary visual cortex. As the color of processing-flow lines gets darker (from yellow to orange, and finally to red), more elaborated information processing is being produced by means of iterating thalamocortical loops through the TRN. Cortical networks tie together neuronal assemblies in widespread cortical regions, and the TRN may play a central role in organizing all of the networks.
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Figure 2: Schematic drawing of the TRN-modulated thalamocortical looping model of conscious awareness. THL: thalamus, V1: the primary visual cortex. As the color of processing-flow lines gets darker (from yellow to orange, and finally to red), more elaborated information processing is being produced by means of iterating thalamocortical loops through the TRN. Cortical networks tie together neuronal assemblies in widespread cortical regions, and the TRN may play a central role in organizing all of the networks.

Mentions: Attention possibly acts by biasing the competition among rival candidates of activated neuronal sets, particularly during their formation [79]. Therefore, an antagonistic target-background configuration of information processing seems to be an efficient means to accomplish selective attention. That is, it is advantageous if there is enhancement of neural activity associated with highlighted information processing, while irrelevant neural activity is simultaneously inhibited. Therefore, an efficient and well-organized inhibitory mechanism is necessary for selective attention. As mentioned earlier, it is noteworthy that the TRN provides a major inhibitory input to thalamic relay nuclei [19]. Hence, the feedback synaptic connections from the TRN imply significant control over the signal transmissions through the thalamocortical network. Anatomically, specified sectors of the TRN involve their corresponding thalamocortical connections, including even the related visceral sensory inputs [80], which are assumed to be modulated by attention or distraction. Here, I suggest that such finely organized TRN cells, wrapping around many of the thalamic relay nuclei, play a pivotal role in selective attention by coordinating all thalamocortical transmissions via the GABAergic network synchrony. The initial point of developing synchronization may stem from a modality-specific sector of the thalamic reticular region (e.g., the first red dot on the TRN in Figure 2A), which may be the origin of the eventual spread of its synchronous activity throughout the entire TRN network. This synchronization would be more promoted after the reception of positive iterating feedback from higher-order cortices. Compared to Crick's previous TRN hypothesis regarding 'attention' [81], my current TRN hypotheses also cover consciousness, and emphasize reiterating thalamocortical information processing in relation to conscious awareness.


A thalamic reticular networking model of consciousness.

Min BK - Theor Biol Med Model (2010)

Schematic drawing of the TRN-modulated thalamocortical looping model of conscious awareness. THL: thalamus, V1: the primary visual cortex. As the color of processing-flow lines gets darker (from yellow to orange, and finally to red), more elaborated information processing is being produced by means of iterating thalamocortical loops through the TRN. Cortical networks tie together neuronal assemblies in widespread cortical regions, and the TRN may play a central role in organizing all of the networks.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2857829&req=5

Figure 2: Schematic drawing of the TRN-modulated thalamocortical looping model of conscious awareness. THL: thalamus, V1: the primary visual cortex. As the color of processing-flow lines gets darker (from yellow to orange, and finally to red), more elaborated information processing is being produced by means of iterating thalamocortical loops through the TRN. Cortical networks tie together neuronal assemblies in widespread cortical regions, and the TRN may play a central role in organizing all of the networks.
Mentions: Attention possibly acts by biasing the competition among rival candidates of activated neuronal sets, particularly during their formation [79]. Therefore, an antagonistic target-background configuration of information processing seems to be an efficient means to accomplish selective attention. That is, it is advantageous if there is enhancement of neural activity associated with highlighted information processing, while irrelevant neural activity is simultaneously inhibited. Therefore, an efficient and well-organized inhibitory mechanism is necessary for selective attention. As mentioned earlier, it is noteworthy that the TRN provides a major inhibitory input to thalamic relay nuclei [19]. Hence, the feedback synaptic connections from the TRN imply significant control over the signal transmissions through the thalamocortical network. Anatomically, specified sectors of the TRN involve their corresponding thalamocortical connections, including even the related visceral sensory inputs [80], which are assumed to be modulated by attention or distraction. Here, I suggest that such finely organized TRN cells, wrapping around many of the thalamic relay nuclei, play a pivotal role in selective attention by coordinating all thalamocortical transmissions via the GABAergic network synchrony. The initial point of developing synchronization may stem from a modality-specific sector of the thalamic reticular region (e.g., the first red dot on the TRN in Figure 2A), which may be the origin of the eventual spread of its synchronous activity throughout the entire TRN network. This synchronization would be more promoted after the reception of positive iterating feedback from higher-order cortices. Compared to Crick's previous TRN hypothesis regarding 'attention' [81], my current TRN hypotheses also cover consciousness, and emphasize reiterating thalamocortical information processing in relation to conscious awareness.

Bottom Line: Throughout the latticework structure of the TRN, conscious perception could be accomplished and elaborated through accumulating intercommunicative processing across the first-order input signal and the higher-order signals from its functionally associated cortices.This TRN-modulation hypothesis for conscious awareness provides a comprehensive rationale regarding previously reported psychological phenomena and neurological symptoms such as blindsight, neglect, the priming effect, the threshold/duration problem, and TRN-impairment resembling coma.This hypothesis can be tested by neurosurgical investigations of thalamocortical loops via the TRN, while simultaneously evaluating the degree to which conscious perception depends on the severity of impairment in a TRN-modulated network.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Radiology, Brigham and Women's Hospital, Harvard Medical School, 75 Francis Street, Boston, MA 02115, USA. minbk@bwh.harvard.edu

ABSTRACT
[BACKGROUND]: It is reasonable to consider the thalamus a primary candidate for the location of consciousness, given that the thalamus has been referred to as the gateway of nearly all sensory inputs to the corresponding cortical areas. Interestingly, in an early stage of brain development, communicative innervations between the dorsal thalamus and telencephalon must pass through the ventral thalamus, the major derivative of which is the thalamic reticular nucleus (TRN). The TRN occupies a striking control position in the brain, sending inhibitory axons back to the thalamus, roughly to the same region where they receive afferents. [HYPOTHESES]: The present study hypothesizes that the TRN plays a pivotal role in dynamic attention by controlling thalamocortical synchronization. The TRN is thus viewed as a functional networking filter to regulate conscious perception, which is possibly embedded in thalamocortical networks. Based on the anatomical structures and connections, modality-specific sectors of the TRN and the thalamus appear to be responsible for modality-specific perceptual representation. Furthermore, the coarsely overlapped topographic maps of the TRN appear to be associated with cross-modal or unitary conscious awareness. Throughout the latticework structure of the TRN, conscious perception could be accomplished and elaborated through accumulating intercommunicative processing across the first-order input signal and the higher-order signals from its functionally associated cortices. As the higher-order relay signals run cumulatively through the relevant thalamocortical loops, conscious awareness becomes more refined and sophisticated. [CONCLUSIONS]: I propose that the thalamocortical integrative communication across first- and higher-order information circuits and repeated feedback looping may account for our conscious awareness. This TRN-modulation hypothesis for conscious awareness provides a comprehensive rationale regarding previously reported psychological phenomena and neurological symptoms such as blindsight, neglect, the priming effect, the threshold/duration problem, and TRN-impairment resembling coma. This hypothesis can be tested by neurosurgical investigations of thalamocortical loops via the TRN, while simultaneously evaluating the degree to which conscious perception depends on the severity of impairment in a TRN-modulated network.

Show MeSH
Related in: MedlinePlus