168 SECTIONAL ADDRESSES 
the disturbances they produce ; consequently he welcomes the slightest 
evidence of localisation of function in the cortex, and finds the anatomical 
model valuable for correlating his observations. Undoubtedly there are 
well-defined nervous pathways, clear differences in cell structure and 
localised activity in different parts of the brain. As a modern addition 
to the evidence we have Foerster’s recent work on the electrical stimulation 
of the human cortex, and his finding that stimulation of the temporal 
lobe may cause sounds and words to arise in consciousness whilst stimu- 
lation of the occipital lobe gives lights or images. Bard has given another 
remarkable example of strict cortical localisation by his observations on 
certain postural reactions in the cat. These depend on a small area in 
the frontal region, are not affected by damage to other parts of the brain, 
and are permanently lost if the frontal area is destroyed. The danger 
nowadays is that we may pay too little attention to such facts ; but it is 
true, nevertheless, that the localisation is a matter of areas rather than 
of single neurones. This is shown by examination of habit formation, 
and by the remarkable way in which the nervous system adapts itself to 
injury. 3 
It has often been pointed out that we learn to recognise shapes—the 
letters of the alphabet, for instance—however they are presented to us. 
The pattern of black and white made on our retina by the letter A need 
not fall on a particular set of retinal endings connected with particular 
cortical neurones. We have learnt to recognise a relation of lines and 
angles, a pattern of activity in the cortex rather than an activity of specific 
points. ‘This kind of reaction is not due to our superior intelligence. 
Lashley finds it in the rat, and psychologists of the Gestalt school have 
pointed out examples from all manner of animals. There is the same 
neglect of specific neurones in the formation of motor habits, for if we 
have once learnt to write the letter A with our right hand, we can make 
a fair attempt to write it with any group of muscles which can control a 
pencil. 
The adaptations to injury present a different aspect of the same story. 
An insect which has lost a leg will at once change its style of walking to 
make up for the loss. This may involve a complete alteration of the 
normal method, limbs which were advanced alternately being now 
advanced simultaneously ; the activities of the nervous system are 
directed to a definite end, the forward movement of the animal—it uses 
whatever means are at its disposal and is not limited to particular pathways. 
When the central nervous system is injured there is more evidence of 
localised function, but the localisation is no hard-and-fast affair. A rat 
uses its occipital cortex in the formation of certain visual habits. When 
this part of the cortex is destroyed the habit is lost, but it can be re-learnt 
just as rapidly as before with what remains of the brain. A monkey’s 
arm is paralysed if the corresponding motor area of the cortex is destroyed, 
but the paralysis soon passes away although there is no regeneration 
of the motor cortex. What is more remarkable is that the recovered 
functions are not associated with the development of a new visual region 
or motor region in the brain. Though they were originally localised 
there is no longer any one part of the cortex which is essential. 
