16 September 2007

Brain Stem Consciousness: Assessing the Importance of the Neocortex in "Consciousness"

Some of the more promising approaches to AGI are attempting to imitate the modular approach to intelligent neural nets that evolution has taken in mammals. Much of the emphasis (eg numenta) is on the structure of the human neocortex and its connections to midbrain structures. Is it possible that by leaving out the brainstem, that these models are neglecting the essential piece, at least for "conscious" intelligence?
With some notable exceptions (e.g. Scheibel & Scheibel 1977; Panksepp 1982; Thompson 1993; Bogen 1995; Watt 2000; Parvizi & Damasio 2001), brainstem mechanisms have not figured prominently in the upsurge of interest in the nature and organization of consciousness that was ushered in with cognitivism in psychology and neuroscience (Mandler 1975; Miller 1986; Baars 1988). Few cognitivists or neuroscientists would today object to the assertion that “cortex is the organ of consciousness”.1 This is, in a sense, a return to an older view of the supremacy of the cerebral cortex from which a fundamental discovery of the late 1940s had stimulated a partial retreat. In keeping with the sense that the cerebral cortex is the organ of higher functions it had been widely assumed that the regulation of its two primary states – sleep and wakefulness – was a cortical function as well (see, e.g., the critical discussion of this stance in Gamper 1926, pp. 68- 78). Then, in the late 1940s, Moruzzi and Magoun (1949) discovered that local stimulation of circumscribed cell groups in the pons and midbrain of experimental animals exerts a global activating influence on the cerebral cortex as well as on behavioral state, and that experimental lesions in these brainstem sites are capable of rendering animals somnolent and even comatose (Magoun 1954; cf. Parvizi & Damasio 2003). This came as a shock to the corticocentric perspective, and stimulated an avalanche of research on brainstem regulation of sleep and wakefulness and its relationship to the conscious state (summarized in symposium volumes edited by Adrian et al. 1954; Jasper et al. 1958; and Eccles 1966).
Read the entire paper here

Of course, what applies to the study of human consciousness may not apply to the quest for AGI--which may not require consciousness as we understand it. Most of us in medicine or the neurological sciences have run across patients with significant hydrocephalus who are also highly functional, and even highly intelligent in some cases. Their neocortex may be compressed by CSF to very thin dimensions, with minimal if any diminution of consciousness, and/or intelligence.

Still, it is fascinating to mentally rearrange the priority of the various parts of the brain, in terms of importance for "consciousness" or "intelligence." The teenage brain is both conscious and intelligent, while at the same time it is highly plastic and in a state of rapid development. Perhaps it is actually the state of "incompleteness" that makes the teenage brain so potent. I suspect so.

The major criticism of the teenage brain--which is not truly a criticism--is that it lacks independent judgment that comes from experience. The question involved in that particular "criticsim" is: Does the lack of forebrain meylination (pertaining to plasticity) cause the lack of judgment, or is it possible to maintain the plasticity over time while supplying the experience that leads to sound situational judgment?

While many persons are insulted or offended by the idea that the lack of teen judgment may at least in part be accounted for by the plasticity and rapid development of the teen brain, it would be more constructive to look at what can actually be demonstrated by imaging studies and other minimally subjective data.

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