The paper begins with a general introduction to the nature of human consciousness and outlines several different philosophical approaches. A critique of traditional reductionist and dualist positions is offered and it is suggested that consciousness should be viewed as an emergent property of physical systems. However, although consciousness has its origin in distributed brain processes it has macroscopic properties - most notably the `unitary sense of self', non-deterministic free will, and non-algorithmic `intuitive' processing - which can best be described by (...) quantum-mechanical principles. (shrink)

Conscious experience is one of the most difficult and thorny problems in psychological science. Its study has been neglected for many years, either because it was thought to be too difficult, or because the relevant evidence was thought to be poor. Bernard Baars suggests a way to specify empirical constraints on a theory of consciousness by contrasting well-established conscious phenomena - such as stimulus representations known to be attended, perceptual, and informative - with closely comparable unconscious ones - such as (...) stimulus representations known to be preperceptual, unattended, or habituated. Adducing data to show that consciousness is associated with a kind of global workplace in the nervous system, and that several brain structures are known to behave in accordance with his theory, Baars helps to clarify many difficult problems. (shrink)

A hypothesis on the physiological conditions for the occurrence of phenomenal states is presented. It is suggested that the presence of phenomenal states depends on the rate at which neural assemblies are formed. Unconsciousness and various disturbances of phenomenal consciousness occur if the assembly formation rate is below a certain threshold level; if this level is surpassed, phenomenal states necessarily result. A critical production rate of neural assemblies is the necessary and sufficient condition for the occurrence of phenomenal states.

Little, Brown, 1992 Review by Glenn Branch on Jul 5th 1999 Volume: 3, Number: 27.

A hypothesis on the physiological conditions of consciousness is presented. It is assumed that the occurrence of states of consciousness causally depends on the formation of complex representational structures. Cortical neural networks that exhibit a high representational activity develop higher-order, self-referential representations as a result of self-organizing processes. The occurrence of such states is identical with the appearance of states of consciousness. The underlying physiological processes can be identified. It is assumed that neural assemblies instantiate mental representations; hence consciousness depends (...) on the rate at which large active assemblies are generated. The formation of assemblies involves the activation of the N-methyl-D-aspartate receptor channel complex which controls different forms of synaptic plasticity including rapid changes of the connection strengths. The various causes of unconsciousness (e.g., anaesthetics or brain stem lesions) have a common denominator: they directly or indirectly inhibit the formation of assemblies. (shrink)

How certain neural mechanisms momentarily endow with the subjective awareness percepts and affects represented elsewhere is more likely to be clarified when structures essential to Mc are identified. The loss of C with bilateral thalmic lesions involving the intralaminar nuclei contrasts with retention of C after large cortical ablations depriving C of specific contents. A role of ILN in the perception of primitive sensations is suggested by their afference of directly ascending pathways. A role for ILN in awareness of cortical (...) activity is suggested by their widespread afference from cortex, a property shared with striatum. A role for ILN in volition is suggested by their heavy projection to striatum. Unlike striatum, ILN also project widely to almost all neocortex, enabling an effect on ideation; this last property is in common with other structures but none of them has the same direct cortical afference. And passage through the reticular nucleus of ILN efferents to cortex could impact the attention-selective action of nRt. It is suggested that the quickest route to a better understanding of C involves more intensive study of ILN. No other structure seems, in the light of our current knowledge, a more likely site for Mc. (shrink)

The extent to which observed behavior in the complete commissurotomy patients is supported by only one hemisphere would depend on individual differences interacting with a variety of factors such as genetics, intelligence, and so on. The lesson imparted here is that there is sufficient functional redundancy in the neocortex so that the capacity to maintain a wide range of abilities is within the control of one hemisphere. And, yet, as seen in what is missing in the patients' behavior, one hemisphere (...) is not quite enough. Nature seems to have intended that the two hemispheres complement each other, that the full range of human behavior be best accomplished through interaction between the left and right hemispheres. (shrink)

We argue that the current known anatomy of connections between the intralaminar nuclei of the thalmus and visual cortical areas makes it unlikely that neuronal activity in the ILN mediates visual awareness.