A thalamic reticular networking model of consciousness

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.

General Anesthesia and Human Brain Connectivity

“…One could assume that the connectivity of the various thalamic nuclei may not change in a homogeneous manner under anesthesia. An important distinction between the roles of first-order and second-order relay nuclei (Guillery and Sherman, 2002), the reticular nucleus (Min, 2010), and the nonspecific intralaminar nuclei (Bogen, 1995;John, 2002) has been made with reference to consciousness. For example, the nonspecific thalamic system is involved in the regulation of cortical arousal and the higher integration of information ( Jasper, 1998a, b), and it is thought to enable consciousness.…”

Grey matter alterations in patients with depersonalization disorder: a voxel-based morphometry study

“…Previous studies have indicated that during discrete, consciously perceived events the thalamic γ activity matches the cortical γ activity, 47 and it has been suggested that the thalamus drives this coherence and thus enables cross-modal consciousness. 48 Rather than exerting unidirectional governance, the thalamus is thought to be a central node in complex cortico-thalamo-cortical loops. 46 The central recipient of cortical feedback is the caudate, which in turn back-projects to the thalamus.…”

Electrical modulation of neuronal networks in brain-injured patients with disorders of consciousness: A systematic review

“…Schiff [41] captured this key role of the thalamus in arousal and consciousness disorders by proposing the notion of central thalamus for the anterior and posterior intralaminar nuclei plus paralaminar portions of related thalamic-associative dorsomedial, ventral anterior, ventral lateral and inferior pulvinar nuclei. The reticular thalamus, stratum and nucleus wrapping the thalamus should be involved in attention, the prerequisite to consciousness, filtering stimuli like a gateway to the cortex [42][43][44]. The case report by Sturm et al [16] supports this hypothesis.…”