The Brain and What It Does 129 



useful. It follows from this that besides the regions in the brain which 

 are able to register sensations, there must be those which are capable 

 of finding significant patterns in the sensations as they are received, 

 which are concerned with the meaning and interpretation of the 

 sense pictures of the moment. It is quite likely that at this stage 

 much of the detail is lost. Also the actual size and orientation of the 

 object becomes of less importance. We recognize an object as the 

 same at different distances, although the area it occupies on the retina 

 may be quite different. We recognize a particular shape such as a 

 square whatever its size. This means that the recognition occurs at a 

 level where the actual size is unimportant, only the pattern is sig- 

 nificant. We have very little idea how this is effected in the brain. 



It might be natural to expect that this process of finding meanings 

 takes place in the cerebral cortex. It is surprising, however, how 

 much damage can be done to the brain without apparently impairing 

 its functions. A hundred years ago a quarryman in Vermont, Phineas 

 Gage, had a crowbar driven through his skull, causing an ugly wound 

 in both of the frontal lobes of the brain. By good luck the wound 

 healed and the man was able to return to work. His intelligence and 

 abihty were not seriously impaired and his memory was good; 

 however, he was said to be less balanced and more easily excited to 

 anger. 



An operation known as prefrontal lobotomy or leucotomy, in 

 which many of the nerve connections between the frontal lobes are 

 severed, has been performed on a considerable number of people 

 with mental derangements. It appears to have a genuine effect on the 

 tendency of the patient to worry, but it does not radically affect his 

 memory. 



From this it would seem that a considerable number of nerve 

 connections in the brain can be broken without seriously affecting 

 the memory or the general ability of the person, although it may be 

 that some of the more general abilities, which we call judgment and 

 character, may be lost. 



A possible reason for this is that the total number of possible 

 paths between the nerve cells is so enormous that only a small 

 proportion of them is actually used. When some paths are broken, 

 alternative ones are available. Another conceivable explanation is 

 that the number of nerve cells is very much greater than is actually 

 required, or at least greater than the number made use of. There is 

 little doubt that in some people there is a great deal more mental 

 activity than in others. Is it possible that many people only use a 

 small part of the brain they have? 



