THE NERVOUS FUNCTIONS 35 



two factors and the acquired automatisms (p. 32), is responsible 

 for much confusion in the current discussions of instinct. 



In the nomenclature of the correlation centers there is considerable 

 diversity of usage. In describing the adjustments made by these centers 

 neurologists frequently use the words coordination, correlation, and associ- 

 ation in about the same sense; but the adjustments made in those centers 

 which lie closer to the receptors or sense organs are physiologically of dif- 

 ferent type from those made in the centers related more closely to the 

 effector apparatus. In recognition of this fact the following usage has been 

 suggested to me by Dr. F. L. Landacre and will be adopted in this work: 



The term correlation is applied to those combinations of the afferent 

 impulses within the sensory centers which provide for the integration of 

 these impulses into appropriate or adaptive responses; in other words, the 

 correlation centers determine what the reaction to a given combination of 

 stimuli will be. Nervous impulses from different receptors act upon the 

 correlation centers, and the reaction which follows will be the resultant of 

 the interaction of all of the afferent impulses (and physiological traces or 

 vestiges of previous similar responses) involved in the process. When this 

 resultant nervous discharge passes over into the motor centers and path- 

 ways, the final common paths (see p. 62) innervated will lead to a response 

 whose character is determined by the organization of the particular motor 

 centers and paths actuated. 



To the term coordination we shall give a restricted significance, applying 

 it only to those processes employing anatomically fixed arrangements of the 

 motor apparatus which provide for the co-working of particular groups of 

 muscles (or other effectors) for the performance of definite adaptively useful 

 responses. Every reaction even the simplest reflex involves the com- 

 bined action of several different muscles, and these muscles are so inner- 

 vated as to facilitate their concerted action in this particular movement. 

 These are called synergic muscles. Coordination involves those adjust- 

 ments which are made on the effector side of the reflex arc (p. 56). This 

 is the sense in which the term is applied by Sherrington in the following 

 passage (Integrative Action of the Nervous System, p. 84) : 



"Reflex coordination makes separate muscles whose contractions act 

 harmoniously, e. g., on a lever, contract together, although at separate 

 places, so that they assist toward the same end. In other words, it excites 

 synergic muscles. But it in many cases docs more than that. Where two 

 muscles would antagonize each other's action the reflex arc, instead of 

 activating merely one of the two, causes when it activates the one depression 

 of the activity (tonic or rhythmic contraction) of the other. The latter is 

 an inhibitory effect." 



The motor paths and centers in general are more simply organized than 

 are the sensory paths and centers. The nervous discharges through these 

 motor systems are very direct and rapid. Complex nervous reactions 

 require more time than simple reflexes, and this delay or central pause is 

 chiefly in the correlation centers rather than in the efferent coordination 

 mechanisms (see pp. 98, 181). 



The word association may be reserved for those higher correlations 

 where plasticity and modifiability are the dominant features of the response 

 and whose centers are separated from the peripheral sensory apparatus by 

 the lower correlation centers which are devoted to the stereotyped invari- 

 able reflex responses. Correlation may be mechanically determined by 



