Susan Greenfield:
THE HUMAN MIND EXPLAINED (Henry Holt & Co, 1996)

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(Copyright © 1999 Piero Scaruffi | Legal restrictions - Termini d'uso )

The British neuroscientist Susan Greenfield has derived a definition of consciousness from her studies of mental infermities: consciousness is the process of propagating a stimulus through a network of connected neurons, the same way one perceives the widening ripples created by an object falling in a pond.

Her investigation starts with the postulate that, while there is no "Cartesian theater" in the brain, nonetheless some type of "temporary" localization must exist. There is no site of consciousness, but consciousness originates from processes happening locally somewhere sometime. She believes that different groups of neurons take over at different times, a picture that resembles theories by Michael Gazzaniga, Derek Parfit and Daniel Dennett. Therefore, consciousnessness is multiple in space but unitary in time.

These groups of neurons she calls "gestalts": highly dynamical and transient, they are created by some kind of "arousal" and they are localized around an "epicenter".

She calls them "gestalts" because the dynamic properties of the brain "emerge" in a gestalt fashion from the connectivity of such neuronal assemblies. An arousal can be an external (sensory) phenomenon or an internal (cognitive) phenomenon. The arousal causes the formation of a "gestalt" around an epicenter. The gestalt causes the "emergence" of a conscious event. Each instance of consciousness arises from such a gestalt, caused by an arousal and localized around an epicenter. Overall consciousness develops from epicenters spread around the brain.

The passage from one conscious event to another conscious event, from one gestalt to another gestalt, which is typical of our inner life, is due to a ripple effect: the ripples of one gestalt's concentric action may act as an arousal and trigger another gestalt.

The size of a gestalt depends, in primis, on the strength of the arousal. But it also depends on the power of the epicenter to recruit neurons, a power which in turn depends on rival gestalts that all compete for neurons. The size of the gestalt has a direct meaning for us, because it corresponds to the depth of consciousness, to the intensity of the feeling.

During growth epicenters tend to shift from "outside" to "inside", from external stimuli to internal associations.

Mental life is a dual process of searching for information and adaptation to information, the former leading to more conscious access, the latter reducing conscious access (things become habitual and automatic). Consciousness "grows" as the brain does (from foetus to neonate to child to adult).

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