682 THE BRAIN. 



but we should be going beyond the evidence if \ve concluded that they were 

 identical with the ordinary efferent impulses of motor nerves. And above 

 all it must not be left unnoticed that the cortical area has close, if not direct, 

 connections of a sensory nature with the part in whose movements it is con- 

 cerned. This is shown by the following remarkable results which may make 

 their appearance when stimulation of the cortex is carried on while the animal 

 (dog) is in a particular stage of the influence of morphine. If a submini- 

 mal stimulus be found, that is, a current of such intensity that applied to a 

 motor area it will produce no movement, but if increased ever so slightly 

 will give a feeble constriction of the appropriate muscle, it may be observed 

 that a slight stimulus, such as gently stroking the skin over the muscles in 

 question, will render the previous subminimal stimulus effective, and so call 

 forth a movement. Thus, if the area experimented on be that connected 

 with the lifting of the forepaw, and the subminimal stimulus be applied to 

 the area at intervals, after several applications followed by no movements, a 

 gentle stroke or two over the skin of the paw w r ill lead to the paw being* 

 lifted the next time the stimulus is applied to the area. A similar result, 

 but less sure and striking, may follow upon the stimulation of parts of the 

 body other than the part corresponding to the area stimulated. Then, again, 

 it has been observed that in certain other stages of the influence of morphine, 

 the cortex and the rest of the nervous system are in such a condition that 

 the application of even a momentary stimulus to an area leads not to a sim- 

 ple movement, but to a long-continued tonic contraction of the appropriate 

 muscles. Under these circumstances a gentle stimulus, such as stroking the 

 skin or blowing on the face, applied immediately after the application of the 

 electric stimulus to the area, suddenly cuts short the contraction, and brings 

 the muscles at once to rest and normal flaccidity. 



These experiments show that the development of the processes in the 

 cortex leading to the issue of what we have agreed to call efferent impulses 

 along the pyramidal fibres is markedly affected by sensory impulses, and 

 especially by sensory impulses started in the skin overlying and corresponding 

 to the muscles put into movement. How these sensory impulses reach the 

 cortex we do not exactly know ; but we have no evidence to show that 

 afferent, centripetal impulses can travel backward, so to speak, along the 

 pyramidal fibres ; and it is more reasonable to suppose that the sensory im- 

 pulses in question reach the cortex by the ordinary paths of sensory impulses, 

 which we shall presently discuss. We may therefore take the results of the 

 experiments as showing how close is the connection of the motor area with 

 the sensory mechanisms of the spinal cord and lower parts of the brain, and 

 as illustrating the complexity of the chain of events by which the motor 

 area brings about voluntary movements. 



575. We have above used the general phrase " movements of the limb," 

 since in the dog it is not easy to pick out certain movements as being particu- 

 larly skilled movements. In the monkey such a distinction is easier. In 

 this animal, as we have said, recovery of voluntary movement also takes 

 place after removal of a cortical area, or at least has done so in many cases ; 

 and while the phenomena immediately following removal on the whole re- 

 semble those witnessed in the dog, a certain order of recovery may be ob- 

 served ; the more skilled movements are the last to return. When, for 

 instance, the arm area is removed, the delicate movements of the hand, of 

 the thumb and finger, are the last to be reestablished ; and a condition of 

 things may be met with in which the animal after removal, say of the arm 

 area in the left hemisphere, uses by preference the left hand at a time when, 

 if prevented from using that hand, he is able to use the right ; that is to say, 

 the recovery in the right limb after the removal of the area on the left side 



