THE THALAMUS 143 



dominance and subordination of parts is altered, 

 probably by an enduring change in the conductivity 

 of certain associational connections, and to this ex- 

 tent new behavior patterns replace the innate action 

 system. The animal has acquired a habit, or learned 

 something. 



We have here dwelt at length on the established 

 facts of the evolution of thalamic structure and a 

 theoretic formulation of the dynamics of thalamic 

 function because some sort of a working schema of 

 thalamic organization is an essential approach to 

 the problems of the cerebral cortex. Moreover, the 

 history of the differentiation of the cortex is in some 

 respects very similar to that of the thalamus, and it 

 seems highly probable that the fundamental dynam- 

 ics are essentially the same, however differently they 

 may work out in detail. 



If we think of the brain as an office building con- 

 taining several rooms, each of which is crowded with 

 many desks where various sorts of business are trans- 

 acted, the relations of the parts of which we have 

 been speaking can be crudely drawn as a diagram of 

 the ground plan of such a house. In Figure 31 I have 

 attempted to express in a rude way the offices and 

 corridors that must be traversed in the course of the 

 ordinary routine of business in the forebrain of the 

 cerebral types enumerated above. Only the relations 

 between the thalamus and the lateral wall of the 

 hemisphere of one side are considered. The olfactory 



