Misplaced Pages

This is an old revision of this page, as edited by Bird (talk | contribs) at 16:10, 27 February 2004 (incorporate homonculus discussion in text w/ explanation). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.

In the anatomy of animals, the human brain is the most complex computational structure among all species on Earth. Humans' unique capacity for intelligent behavior results both from a larger brain size typical of a larger animal, and from encephalization, which is an increase of brain size in relation to body size.

Encephalization of the human brain is especially pronounced in the neocortex. The human brain not only is larger in proportion to the human body than brains of other animals of the same size; much more of the human brain is neocortex than in other animals. Profound capacities for language, planning, extended memory, empathy and fabrication all can be related to structural features of enlarged frontal lobes that form about a third of the neocortex. In humans, the medulla, metencephalon and diencephalon make up a smaller proportion of the brain than those of older species.

Humans enjoy unique neural capacities, but much of the human neuroarchitecture is shared with ancient species. Basic systems that alert the nervous system to stimulus, that sense events in the environment and that monitor the condition of the body are similar in some ways to those of the most basic vertebrates. Human consciousness involves both the extended capacity of the modern neocortex in particular as well as profoundly developed protypical structures of the paleopallium.

The 19th Century discovery of a primary motor control area mapped to correspond with regions of the body led to popular belief that the brain was organized around a homunculus. A distorted figure drawn to represent the body's motor map in the pre-frontal cortex was popularly recognized as the brain's homonculus, but function of the human brain is far more complex.

The human brain appears to have no localized center of conscious control. Like the brains of other vertebrates, it derives consciousness from interaction among numerous systems within the brain. Executive decision-making functions rely on cerebral activities, especially those of the frontal lobes, but redundant and complementary processes within the brain result in a diffuse assignment of executive control that can be difficult to attribute to any single locale.

A definite description of the biological basis for consciousness so far eludes the best efforts of the current generation of researchers. But reasonable assumptions based on observable behaviors and on related internal responses have provided the basis for general classification of elements of consciousness and of likely neural regions associated with those elements. Researchers know people loose consciousness and regain it, they have identified partial losses of consciousness associated with particular neuropathologies and they know that certain conscious activities are impossible without particular neural structures.

Correlation of particular conscious activities in relation to neural structures suggest three levels of consciousness in humans. A protoself represents the most basic level of consciousness shared with animals as primitive as amoeba. A core consciousness similar to that of other vertebrates lets humans see and hear their environment. An extended consciousness allows us to develop profound narratives describing our own lives and environment.

Related topics

• Regions in the human brain
• cephalic disorders
• homunculus - the distorted human figure drawn to reflect the relative sensory space our body parts represent on the cerebral cortex.