A broad range of evidence regarding the functional organization of the vertebrate brain - spanning from comparative neurology to experimental psychology and neurophysiology to clinical data - is reviewed for its bearing on conceptions of the neural organization of consciousness. A novel principle relating target selection, action selection, and motivation to one another, as a means to optimize integration for action in real time, is introduced. With its help, the principal macrosystems of the vertebrate brain can be seen to form a centralized functional design in which an upper brain stem system organized for conscious function performs a penultimate step in action control. This upper brain stem system retained a key role throughout the evolutionary process by which an expanding forebrain - culminating in the cerebral cortex of mammals - came to serve as a medium for the elaboration of conscious contents. This highly conserved upper brainstem system, which extends from the roof of the midbrain to the basal diencephalon, integrates the massively parallel and distributed information capacity of the cerebral hemispheres into the limited-capacity, sequential mode of operation required for coherent behavior. It maintains special connective relations with cortical territories implicated in attentional and conscious functions, but is not rendered nonfunctional in the absence of cortical input. This helps explain the purposive, goal-directed behavior exhibited by mammals after experimental decortication, as well as the evidence that children born without a cortex are conscious. Taken together these circumstances suggest that brainstem mechanisms are integral to the constitution of the conscious state, and that an adequate account of neural mechanisms of conscious function cannot be confined to the thalamocortical complex alone.
The surprising fit between the basic pattern of hominid sociality (inferred from shared features of human and chimpanzee sociality) and one of the models developed to explain the evolution of synchronous chorusing in insects suggests that synchronous chorusing played a role in the late Miocene separation of the hominid ancestors of humans from our common ancestor with the chimpanzee. A detailed evolutionary scenario for this process is presented which implies that the roots of human music extend some five million years into the past. This perspective sheds new light not only on the origins of rhythmic song and dance — and thus of music — but on the relationship between music and language in human evolution and on the cross-cultural ubiquity of rhythmic music and dance in present-day human cultures. It also carries implications for our interpretation of the lack of agreement concerning the very term “music” in different human languages.
The 20 billion neurons of the neocortex have a mere hundred thousand motor neurons by which to express cortical contents in overt behavior. Implemented through a staggered cortical “efference cascade” originating in the descending axons of layer five pyramidal cells throughout the neocortical expanse, this steep convergence accomplishes final integration for action of cortical information through a system of interconnected subcortical way stations. Coherent and effective action control requires the inclusion of a continually updated joint “global best estimate” of current sensory, motivational, and motor circumstances in this process. I have previously proposed that this running best estimate is extracted from cortical probabilistic preliminaries by a subcortical neural “reality model” implementing our conscious sensory phenomenology. As such it must exhibit first person perspectival organization, suggested to derive from formating requirements of the brain's subsystem for gaze control, with the superior colliculus at its base. Gaze movements provide the leading edge of behavior by capturing targets of engagement prior to contact. The rotation-based geometry of directional gaze movements places their implicit origin inside the head, a location recoverable by cortical probabilistic source reconstruction from the rampant primary sensory variance generated by the incessant play of collicularly triggered gaze movements. At the interface between cortex and colliculus lies the dorsal pulvinar. Its unique long-range inhibitory circuitry may precipitate the brain's global best estimate of its momentary circumstances through multiple constraint satisfaction across its afferents from numerous cortical areas and colliculus. As phenomenal content of our sensory awareness, such a global best estimate would exhibit perspectival organization centered on a purely implicit first person origin, inherently incapable of appearing as a phenomenal content of the sensory space it serves.
One contribution of 12 to a theme issue 'Biology, cognition and origins of musicality'. The diverse forms and functions of human music place obstacles in the way of an evolutionary reconstruction of its origins. In the absence of any obvious homologues of human music among our closest primate relatives, theorizing about its origins, in order to make progress, needs constraints from the nature of music, the capacities it engages, and the contexts in which it occurs. Here we propose and examine five fundamental constraints that bear on theories of how music and some of its features may have originated. First, cultural transmission, bringing the formal powers of cultural as contrasted with Darwinian evolution to bear on its contents. Second, generativity, i.e. the fact that music generates infinite pattern diversity by finite means. Third, vocal production learning, without which there can be no human singing. Fourth, entrainment with perfect synchrony, without which there is neither rhythmic ensemble music nor rhythmic dancing to music. And fifth, the universal propensity of humans to gather occasionally to sing and dance together in a group, which suggests a motivational basis endemic to our biology. We end by considering the evolutionary context within which these constraints had to be met in the genesis of human musicality.
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