There are analyzed the design and technological problems, including the functional illnesses of the brains. The theory treats also the paranormal phenomenon and suggest some methods to develop such activities. The Application section (ETAs) contains also many items as a history of the evolution of the brain, the evaluation of the problems of psychological tests and performance tests for a brain, some problems associated with the present and future levels of evolution of the brain, some long range problems associated with the development of the human society (including the terrorism) and many others. The basic elements of MDT occurs in 1993 and the first written form (on WEB) in 1997. In 2003 a printed edition of the theory was published (in Romanian language) by the Romanian Publishing House "Editura Albastra" and in 2004, in the frame of Gutenberg Project, a new edition also in Romanian. The process of developing is continuing. Dorin T. MOISA moisa@zappmobile.ro THE BASIC FUNCTIONS OF THE BRAIN ABSTRACT This theory, called by me as MDT (Modeling Devices Theory) considers that the basic hardware function of any brain (human or animal) is to make and operate image models (or analogic models) which are associated with the external reality. In this frame, for the human brain only, there is an additional hardware facility: to make and operate symbolic models. FUNDAMENTAL TERMS (KEYWORDS) Image model (or analogic model), symbolic model, simulation on model, information, truth, reality, input reality (IR), external reality, image, harmony, logic, general communications language (GCL), logical and mathematical language. DEFINITIONS ASSOCIATED WITH THE BASIC TERMS This theory is a symbolic model. Any symbolic model has a limited number of fundamental terms. For these terms and only for them, there are accepted descriptive definitions. A descriptive definition is, usually, not precise enough for a scientific approach. This lack of precision is due to the fact that it uses terms which must be defined before. The terms used in the definition must also be defined using already defined words. This process seems to be endless. In any positive science, the descriptive definitions are accepted only for a very limited number of terms. These are called "fundamental terms". For instance, in the symbolic model of Newton's Mechanics, the fundamental terms are mass, space and time. None of these terms have a normal definition (i.e. generated by the model). They have only descriptive definitions. Once the fundamental terms are introduced by description, all the other terms have normal definitions, which are generated by the symbolic model, by logical and mathematical operations. Let's see the definitions of the terms used by the MDT theory. Model: this is a term used on large scale in science and technology. The MDT theory accepts the definition used there.