254 INTRODUCTION TO NEUROLOGY 



ance of deep sensibility and the postural sensations, together 

 with an exaggeration of painful sensibility. The modifications 

 of pain and affective sensibility are regarded by Head and 

 Holmes as the most constant and characteristic features of le- 

 sions of the lateral zone of the thalamus. Acute, persistent, 

 paroxysmal pains are always present, often intolerable and 

 yielding to no analgesic treatment. There is also a tendency to 

 react excessively to unpleasant stimuli. This is not necessarily 

 associated with a lowering of the threshold of stimulation. 

 Deep pressure is especially important here. The pain does not 

 develop gradually out of the general sensation, but appears 

 explosively. This pain has some factor to which the normal half 

 of the body is not particularly susceptible. Thermal, visceral, 

 and other sense qualities are similarly affected. Tickling is very 

 unpleasant on the affected side. The pleasurable aspect of 

 moderate heat is accentuated on the affected side, yet the 

 threshold for heat is never lowered. Not only does the side of 

 the body involved react more vigorously to an affective element 

 of a stimulus, but an overreaction can also be evoked by purely 

 mental states. The manifestations of this increased suscepti- 

 bility to states of pleasure and pain are strictly unilateral. 

 Associated with this overreaction to painful stimuli some loss 

 of general sensation will always be manifest on the affected side 

 of the body. 



Pure cortical lesions cause no change in the threshold to pain, 

 nor is there the exaggerated affective quality characteristic of 

 thalamic lesions. Head and Holmes assume that both the 

 thalamus and the cortex are concerned in conscious activity. 

 They say: 



"The most remarkable feature in that group of thalamic cases with 

 which we have dealt in this work is not the loss of sensation, but an excessive 

 response to affective stimuli. This positive effect, an actual overloading of 

 sensation with feeling tone, was present in all our 24 cases of this class." 

 This effect is interpreted as due to the release of the inhibitory or regulatory 

 influence of the cortex arising from the destruction of the ascending and 

 descending fibers between the thalamus and the cortex, thus isolating the 

 thalamus and allowing it to act to excess. These authors add, since "the 

 affective states can be increased when the thalamus is freed from cortical 

 control, we may conclude that the activity of the essential thalamic center 

 is mainly occupied with the affective side of sensation." "This conclusion is 

 strengthened by the fact that stationary cortical lesions, however extensive, 



