‘THE OTHER SIDE OF THE BRAIN’

‘THE OTHER SIDE OF THE BRAIN’ THIS striking title suggests terra incognita, as though it were the other side of the moon: in fact, Dr BOG EN'-^ uses it to draw attention to the particular functions of the right cerebral hemisphere, the side of the brain which he knows at least as well as the left and a great deal better than most of us do. The title is that of a trilogy of papers which could indeed stand as a monograph in its own right, in which BOGEN contrasts the functions of the right hemisphere with those of the left and proposes a theoretical model of the interaction of the two halves of the cerebrum. The clinical basis of this study arises from the examination of 8 patients in whom the corpus callosum was surgically divided (for intractable epilepsy) at ages ranging from 13 to 48 years. The point of interest which BOGEN takes up is that in all these patients, for at least a few weeks after the operation and in some cases for at least four years, the right hand was able to write normally but was unable to copy a geometrical f igure4.g. a cube in perspective, or a Greek cross-whereas the left hand was able to copy geometrical figures but was quite unable to write. This contrast is a succinct statement of the differences in function between the two hemispheres and, in fact, confirms the evidence from an impressive review of the literature (the bibliography has nearly 400 items) emphasising the special functions of the right half of the brain. Although these functions were first suggested by HUGHLINGS JACKSON in 1864, they were overlooked, except in one or two papers by perceptive neurologists, for nearly a century; until ZANGWILL and his co-workers in a series of papers4 drew attention to the specific syndrome of disability in construction, drawing, spatial perception and topographical memory associated with posterior lesions of the right hemisphere. BOGEN reviews these and other studies in a discussion of constructional apraxia, a disability which, when associated with a left hemisphere lesion, appears to be primarily one of organization of movement; with right hemisphere lesions, it arises from a disorganization of spatial perception.6 The analysis of this disability has been pursued further, by WARRINGTON and othersH, than BOGEN recognizes. It is also evident from propri~ceptive~ and vestibular8 disorders associated with lesions in the same region, that this particular part of the brain is largely concerned in integrating data from our senses not only to orient us in space but also to enable us to integrate our external perceptions. (It is worth emphasizing the external nature of this perception, in contrast to disorders of body scheme such as finger agnosia and right-left disorientation which are associated with left hemisphere lesions and evidently depend on a different mechanism.) BOGEN mentions also the special part played by the right hemisphere in musical ability, drawing particularly on accounts of aphasics (among the most distinguished of whom was the composer Ravel) whose melodic and rhythmic senses were unimpaired in spite of gross speech and reading disabilities. This distinction has recently been carried further by KIMURA, who has not only found greater impairment of recognition of melody in patients with right hemisphere lesionse~ but also that melodies are more easily recognized in the intact subject by the left ear than by the rightlo (the opposite being the case for verbal material). A large part of BOGEN’S discussion is devoted more to a philosophical than to a clinical exposition. He suggests the term ‘appositional’ (as opposed to propositional) as describing the function of the right hemisphere. A similar hypothesis-extended to include personality differences-has already been advanced by MACFARLANE SMITH”. From the developmental point of view, the most interesting observation is that in the