These deficiencies are described here mainly for the human brain, but some can be met also in the animal brain. The design deficiencies as MDT can detect them, are: XD1: The tendency to associate an image-model to any situation met by a person. This deficiency is explained due to the "image nature" of the brain. This deficiency explains why so many persons "stay" on level 3, when level 5 is accessible since 100 years ago. This deficiency can be corrected by education. XD2: There is no hardware protection to prevent the uncontrolled jump from a model to another, in interaction with a complex external reality. The stability in a model is a quality parameter of a brain. Long-range models can stabilize a person. The XD2 deficiency is not related to them. XD2 is related to the capacity to stay in a model, when faced with a complex external reality. This deficiency can be corrected by software (education, for instance). The lack of stability in a model can induce the illness called schizophrenia because this lack of stability has the tendency to favor short-range models. Indeed, when there is no stability in a model, the brain will make a specialized model for any particular situation met in the external reality. Such models are not able to see that some different facts can be correlated. Only a long-range model can detect such correlation. So, the stability in a model is a parameter of quality for a brain and the lack of stability indicates a low quality brain. This deficiency can be met in the animal world too. For example, a dog has to watch a perimeter. That dog can jump from watch-model to food-model, if it gets food from strangers. Such a dog is a low quality dog, due to the lack of stability in the model. The dolphins have a good stability in a model, and so, we consider them as advanced animals. For human beings, the lack of stability in a model is a major drawback. Such persons are not good for any complex activity. XD3: This is a basic deficiency. Let's start with its description, based on examples. So, the brain interacts with an external reality and makes a harmonic model with 3 elements. If, that external reality has, in fact, 4 elements, the missing element cannot be discovered based on the 3-element model. As a 3- element model has a number of wrong predictions, it is not easy to see what is the problem from the analysis of the mistakes. The reason is that, once the 3- element model is activated, the reality is just that one which is generated by this model. There is no other reality! We cannot be outside of our active model. In such a case, the brain tries to correct the model. Usually, it will try to correct the model by changing the importance of some elements or relations. Sometimes this procedure works, and the brain will continue to use the 3-element model.