[Brain and consciousness].

Abstract

The philosophical and biological concepts of consciousness are briefly reviewed, from Aristoteles to Descartes to the modern neurobiologist of the last 15 years. The CRICK's corticothalamic integration view, the Edelman's primary and higher order consciousness concept as well as the Edelman and Tononi's dynamic core concept were discussed. Then the corticothalamic resonance theory by Llinás was reported. Central to Llinás's theory is the existence of electrical intrinsic properties of neurones in the central nervous system that allows them to oscillate at different frequencies and if the membrane properties are suitable also to resonate at specific frequencies. From this oscillation and the neuronal connectivity result the corticothalamic dynamic loops specific and non specific. The dynamic corticothalamic loop of the specific thalamic nuclei connect directly as well as through the inhibitory interneurones in layer 4, with the pyramids in layer 5 and 6. The pyramids's rhythmic discharge excite the thalamic specific neurones and indirectly through the reticular neurones a rebound burst is also generated in the specific relay neurones. The oscillatory properties of cortical inhibitory interneurones initiates the action of the recurrent circuit whose function is to inform the cerebral cortex of the content of the sensory pathways. On the other side, the thalamocortical resonant loops of the non especific nuclei, particularly the intralaminar, connect with theapical dendrites of layer 1 pyramids whose discharge go to the thalamic relay neurones directly and through the reticular nucleus. The clinical and MEG data are consistent with the suggestion that the intralaminar nucleus works as providing the binding signal to the sensory specif le information conveyed by the specific pathways. In this way the non specific corticothalamic loop would act as the conjunction mechanism along the dendritic apical shaft with the specific sensory information. The specific loop will give the content and the non specific loop the context. Conciousness would be the final result of the summation of specific and non specific 40 Hz activity conveyed by the resonant corticothalamic loops.