Synopsis and Introduction

Abstract

The human brain is probably the most complex system we know. From a global point of view it is organized in localizable functional units such as the visual cortex, the speech center, etc. Its individual components, the neurons, can be made visible by stains. According to present days estimates there are 10¹⁰ – 10¹¹ neurons in the brain. An individual neuron may have several hundred or more dendrites as input lines transmitting signals from other neurons. Depending on the specific classification scheme used, there are a dozen to several dozens of different types of neurons. There is increasing evidence that in the visual cortex and possibly other parts of the brain neurons are organized within functional subunits in the form of columns whose boundaries are to some extent flexible. These few remarks make it clear how complex the structure of the brain may be.