The Draw Back of Hebb's Rule: Though being simple, the classical Hebb’s rule has some disadvantages. Depending the application area of neural network, some drawbacks are tolerable but some need improvement. Generally speaking, for the purpose of data processing and statistical analysis, the speed and power of computation are valued more than the resemblance between the model and the physiological realism. On the other hand, for unraveling the memory formation mechanism and harvesting the emerging properties of biological network, the models need to be built upon a certain degree of biophysical basis.