THE CENTRAL NERVOUS SYSTEM 753 



to some extent even after destruction of both inferior frontal con- 

 volutions, if the patient only lived long enough. 



Temporary aphasia may occur without any structural change in 

 the speech-centre for example, during an attack of migraine. In 

 children it may even be caused by some comparatively slight irrita- 

 tion in the digestive tract, such as that due to the presence of a 

 tape-worm. 



Sensory Aphasia. In typical motor aphasia spoken and written 

 words convey to the patient their ordinary meaning. They call up 

 in his mind the usual sequence of ideas, but the chain is broken at 

 the speech-centre, and the outgoing ideas cannot be clothed in 

 words. In another class of cases the patient may be perfectly capable 

 of rational speech ; he may talk to himself or on a set topic with 

 fluency and sen^e, but he may be unable to respond to a question or 

 read a single line of print. Damage to two regions of the left 

 hemisphere of the brain has been found associated with this strange 

 condition, (i) the upper portion of the temporo-sphenoidal lobe, 

 (2) the angular gyrus and the occipital lobe. When the temporal 

 region is alone affected, it is the spoken word that is missed, the 

 written that is understood (word-deafness}. When, as occasionally 

 happens, the lesion is confined to the occipital region, spoken 

 language is perfectly understood, written language not at all (word- 

 blindness). Sensory, like motor aphasia, may exist in any degree of 

 completeness, from absolute word-deafness or word-blindness, in 

 which no spoken or printed word calls up any mental image, to a 

 condition not amounting to much more than a marked absence of 

 mind or unusual obtuseness. Motor and sensory aphasia may be 

 present together. In well-marked word-deafness speech is always 

 interfered with to some extent. 



Cortical Epilepsy. While it was still believed that the cortex was 

 inexcitable, epilepsy was supposed to be exclusively due to morbid 

 conditions, structural or functional, of the medulla oblongata (Kuss- 

 maul and Tenner). Some more recent writers have put forward 

 precisely the opposite opinion, that the disease is always cortical in 

 origin (Unverricht, etc.). What we know for certain is that some 

 cases, but only a minority, are associated with irritative lesions in 

 or near the Rolandic area (cortical or Jacksonian epilepsy). It has 

 even been found possible to localize the position of the lesion from 

 the part of the body in which the fit, or the aura (the sensation or 

 group of sensations peculiar to each case, which precedes and 

 .announces it), begins. For example, if the convulsions commence 

 with a twitching of the right thumb and extend over the arm, or if 

 the aura consists of sensations beginning in the thumb, there is a 

 strong presumption that the seat of the lesion is the part of the arm- 

 .area known as the * thumb-centre ' in the left cerebral hemisphere. 

 It is the seat of the convulsion at its commencement, not the regions 

 40 which it may afterwards spread, that is important in diagnosing the 

 position of the lesion. For just as strong or long-continued electrical 

 stimulation of a given 'centre ' of the motor cortex may give rise to 

 'ontractions of muscles associated with other 'centres,' so the excita- 



