42 K. S. LASHLEY 



we cannot say that the cerebral cortex is necessary for their 

 performance. Nevertheless, attempts to set up such habits in 

 decerebrate birds and mammals have not as yet been suc- 

 cessful. In these forms the cortex seems to have usurped 

 these functions or to have acquired some dynamic relation 

 to the thalamus which prevents the latter from functioning 

 in the absence of cortical facilitation. 



The evidence at hand is inadequate to decide whether the 

 activity in question involves facilitation within the cortical 

 area or merely conduction over isolated paths through the 

 cortex. If the former, then there must be facilitation without 

 determinate association paths ; if the latter, the cortex is left 

 without any significant integrating function. Neither con- 

 clusion conforms with our notions of cerebral activity, yet 

 there seems no third alternative. We can only deal in proba- 

 bilities here; yet in view of the fact that the direction taken 

 by further investigation, both experimental and clinical, will 

 in some measure be determined by our preconceptions of 

 cerebral function in such cases as this, it seems worth while 

 to balance the probabilities and to formulate the problem 

 more definitely. 



Although we have abandoned the doctrine that single 

 memories are stored in single brain cells, we still cling to a 

 somewhat similar belief in the theory that the capacity for 

 each particular response is maintained by a condition of low 

 synaptic resistance between certain definite neurons arranged 

 in a more or less intricate pattern. This has proved to be a 

 useful conception, but that it fully describes all neural organi- 

 zation is open to question. Data on equipotentiality of cere- 

 bral areas suggest that to some extent the habit mechanism 

 is independent of particular neurons. The possibility of 

 facilitation between cerebral areas in spite of the section 

 of any particular group of association fibers may indicate 

 a still further lack of dependence upon determinate neuron 

 connections. Once we grant this as a possibility, a host of 

 facts suggest themselves which seem explicable in no other 

 way than by a mass action of nervous tissue independent of 



