THE PHYSIOLOGY OF THE BRAIN. 631 



parent diminution of motor or sensory faculty. By a sort of 

 process of exclusion, the rest of the cortex being allotted 

 (though on unsatisfactory evidence) to motion and sensation 

 the frontal regions have been supposed to have special con- 

 nection with the higher intellectual faculties. 



Mental Habits. Movements which are commonly exe- 

 cuted together tend to become so associated that it is difficult 

 to perform one alone; many persons, e.g., cannot close one 

 eye and keep the other open. From frequent use, the paths 

 of conduction between the co-ordinating centres for both 

 groups of muscles have become so easy that a volitional im- 

 pulse reaching one centre spreads to the other and excites 

 both. This association of movements, dependent on the 

 modification of brain structure by use, finds an interesting 

 parallel in the psychological phenomenon known as the asso- 

 ciation of ideas; and all education is largely based on the 

 fact that the more often brain regions have acted together 

 the more readily, until finally almost indissolubly, do they so 

 act. If we always train up the child to associate feelings of 

 disgust with wrong actions and of approbation with right, 

 when he is old he will find it very hard to do otherwise: such 

 an organic nexus will have been established that the activity 

 of the one set of centres will lead to an excitation of that 

 which habit has always associated with it. The higher nerve- 

 centres are throughout eminently plastic; it is that which 

 marks them out for a far higher utility and greater adaptation 

 to the varying experiences of individual life than the more 

 fixed and machine-like lower centres: every thought leaves 

 in them its trace for good or ill; and the moral truism that 

 the more often we yield to temptation the more often an 

 evil solicitation, sensory or otherwise, has resulted in a wrong 

 act the harder it is to resist the repetition of it, has its par- 

 allel (and we can hardly doubt its physical antecedent) in the 

 marking out of a path of easier conduction from perceptive 

 to volitional centres in the brain. The knowledge that every 

 weak yielding degrades our brain structure and leaves its trail 

 in that organ through which man is the " paragon of animals/' 

 while every resistance makes less close the bond between the 

 thought and the act for all future time, ought surely to 

 "give us pause :" on the other hand, every right action helps 

 to establish a " path of least resistance," and makes its sub- 

 sequent performance easier. 



