This is an exciting time for brain science. Recent progress has been such that it now seems realistic to look toward an explanation of mind in terms of the brain's anatomy and physiology. Models based on artificially symmetrical arrays of idealized neurons are now being superseded by ones which properly take into account the brain's actual circuitry. This book presents a comprehensive overview of the current state of brain modeling, containing contributions from many leading researchers in this field. It will (...) be of interest not only to researchers in the fields of brain science and neurobiology, but also to psychologists and those involved in the study of artificial intelligence. (shrink)

It is suggested that consciousness is primarily associated not with stimuli and perception, as commonly supposed, but with movement and responses. Consciousness of stimuli arises in situations in which possible movements are planned, or in which information must be actively acquired rather than passively registered, and may or may not require overt movements to be performed. By emphasizing response, this formulation provides a simple explanation for the perceived unity of consciousness: though stimuli can be diverse, with independent components, movements must (...) necessarily be coordinated. Therefore, if we are to look for a `site' for consciousness, it is likely to be in a region such as the anterior cingulate that is neurally close to the higher motor hierarchical levels, and also accessible both to real sensory feedback and also to virtual feedback derived through mechanisms of efference copy from actual or proposed motor commands. It is suggested that synchrony of arrival of such information may be an important prerequisite of this unity, and that on this basis such a `master node' might be expected to be temporally `equidistant' from each of these sources; this may well be true of the anterior cingulate, but no doubt also of other structures. (shrink)

The first brief description is given of a project aimed at searching for the neural correlates of consciousness through computer simulation. The underlying model is based on the known circuitry of the mammalian nervous system, the neuronal groups of which are approximated as binary composite units. The simulated nervous system includes just two senses - hearing and touch - and it drives a set of muscles that serve vocalisation, feeding and bladder control. These functions were chosen because of their relevance (...) to the earliest stages of human life, and the simulation has been given the name CyberChild. The system's pain receptors respond to a sufficiently low milk level in the stomach, if there is simultaneously a low level of blood sugar, and also to a full bladder and an unchanged diaper. It is believed that it may be possible to infer the presence of consciousness in the simulation through observations of CyberChild's behaviour, and from the monitoring of its ability to ontogenetically acquire novel reflexes. The author has suggested that this ability is the crucial evolutionary advantage of possessing consciousness. The project is still in its very early stages, and although no suggestion of consciousness has yet emerged, there appears to be no fundamental reason why consciousness could not ultimately develop and be observed. (shrink)

The master-module theory of consciousness is considered in the light of experimental evidence that has emerged since the model was first published. It is found that these new results tend to strengthen the original hypothesis. It is also argued that the master module is involved in generation of the schemata previously postulated to be associated with consciousness . The recent discovery of attention-related activity in the thalamic intralaminar nuclei is taken to indicate that these structures constitute an important part of (...) the feedback loop which the theory conjectured to mediate thought. The theory is shown to lead to a remarkably simple rationalization of the cerebral cortex, and it offers explanations of attention, binocular rivalry and qualia. It also makes the surprising prediction that Broca's area might not exclusively serve speech. (shrink)

It is suggested that the evolutionary advantage of consciousness lies in its mediating the acquisition of novel context-specific reflexes, particularly when the context has temporally varying components. Such acquisition is conjectured to require evaluation of feedback stimuli evoked by the animal's self-paced probing of its environment, or by memories of the outcome of previous such probings, and the evaluation is postulated to be predicated on attention. It is argued that such an approach automatically incorporates sensation into the phenomenon, sensation arising (...) from an interplay between the nervous system and the skeletal musculature, and not from the nervous system alone. This theory avoids the increasingly untenable view that consciousness is part of the normal chain of events linking unprovoked stimuli in the outside world with immediate voluntary reactions to them. The theory should prove attractive to those who might otherwise feel compelled by neurophysiology to embrace epiphenomenalism. It also provides a means of bridging the explanatory gap, and of resolving the celebrated hard problem of consciousness. (shrink)

Recent conjectures regarding the nature and mechanism of consciousness are extended to include the contribution of the cerebellum. The role of this brain structure appears to be a rather sophisticated form of prediction, as exemplified by certain dynamical capabilities of the visual system, and by the difficulty of self-administered tickling. The pars intermedia of the cerebellum is perceived as a direct feedback device, functioning in parallel to the primary neuronal circuit involved in consciousness; this leads to the suggestion that it (...) serves as a tutor for the putative master node, the latter governing the collective movements of all the body's muscles. The cerebellar hemispheres are believed to act as an internal feedback device, and to be more directly coupled to the master node; they are seen as serving plenisentient unconsciousness. The possible importance of muscular spindles for the generation of qualia is discussed, as are the significance of the frontal lobes, the basal ganglia and the limbic system for the content of consciousness. Finally, the stages through which infant consciousness gradually acquires its sophistication are tentatively identified. (shrink)

It is suggested that the anatomical structures whichmediate consciousness evolved as decisiveembellishments to a (non-conscious) design strategypresent even in the simplest monocellular organisms.Consciousness is thus not the pinnacle of ahierarchy whose base is the primitive reflex, becausereflexes require a nervous system, which the monocelldoes not possess. By postulating that consciousness isintimately connected to self-paced probing of theenvironment, also prominent in prokaryotic behavior,one can make mammalian neuroanatomy amenable todramatically simple rationalization.

This book delivers much more than its title appears to promise; it is not merely a description of current methods for remotely monitoring brain activity. It primarily concentrates on just one such method: positron emission tomography, but it demonstrates beautifully how far that technique can now take us in the quest to discover the mechanisms underlying thought.

An easily-accessible introduction is provided for theauthor''s book Enchanted Looms , which is reviewedelsewhere in this volume by Jesse Prinz and by MarcelKinsbourne, and also for the article Didconsciousness evolve from self-paced probing of theenvironment, and not from reflexes? , which alsoappears in this volume and which summarises theauthor''s more recent thoughts on consciousness.