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Convolutions and asymmetries of the brain
  1. J M S PEARCE
  1. 304 Beverley Road, Anlaby, Hull, East Yorkshire HU10 7BG, UK

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    The “coils” of the brain are considered to have been first noted by Praxagoras of Cos c300 BC, and by Erasistratus c260 BC, who noted a resemblance to the coils of the intestines. Vesalius likened them to clouds and noted their presence and their rough similarity in the ass, horse, and ox.1 Thomas Willis attempted to correlate the organisation of the convolutions with intelligence, and believed that: “movement is initiated in the cerebrum, convolutions and gyrations provide a more commodious area for (expansion of the animal spirits) in the use of memory and phantasy.”2 He also stressed that the brain’s workings were mediated by the brain parenchyma and not, as previously held, by the ventricles. This was a fundamentally new idea, escaping the vague notions of the brain as affected by the humours and functioning by means of defined animal forces or spiritus animalis. Francois Leuret, 1797–1851, born in Nancy, France, was an impecunious “scrawny” boy who enlisted in the army to pursue his studies; he then trained with Esquirol at Salpêtrière and published a remarkable text3 on the comparative cerebral anatomy with his pupil and friend Pierre Gratiolet ( who named the central fissure as the fissure of Rolando). Leuret thought that intelligence related to the number of convolutions with their increasing complexity in primates. In England, Gall realised that convolutions “were an expansion of fibre bundles”; he put forward the idea that:

    “different phenomena suppose different apparatus; consequently, the various functions of the brain likewise suppose different organs” (local areas).

    However, he went too far in extending this to surface contours of the skull, a concept that led to the bogus “art” of phrenology.

    In 1889, Henry Maudsley, father of the Bethlem and Maudsley Hospitals, asked:

    “Is the brain which is notably double in structure, a double organ, seeming parted, but yet a union in partition?”

    This provocative enquiry reflected longstanding arguments about the greater asymmetry of the human brain convolutions than that seen in lower mammals. Vicq d’Azyr, a physician and a considerable artist, had described the convolutions in 1786 noting the differences in morphology in other animals. Magendie similarly had written:

    “The number, the volume, the disposition of the circumconvolutions are variable; in some brains they are very large; in others they are less and more numerous. They are differently disposed in every individual; those of the right side are not disposed like those of the left. It would be an interesting research to endeavour to discover if there exists any relation between the number of circumconvolutions and the perfection, or imperfection, of the intellectual faculties—between the modifications of the mind and the individual disposition of the cerebral circumconvolutions”.4

    In England, in 1839, Henry Holland, physician to the Royal household, had considered the same problems:

    “… these deviations [are] more frequent in man than in many other mammalia most nearly approaching him in structure . . .in the brain and spinal marrow, the external parts on the two sides are less frequently symmetrical than those within; …”5

    In 1854 Gratiolet6 deduced that the two sides of the brain controlled movement of the opposite side of the body. He claimed that the frontal convolutions on the left side were in advance of those on the right in their development in the foetus. Jackson extended the notion saying that “if this be so, the left side of the brain is sooner ready for learning. It is the elder brother.”7Paul Broca8 showed that expressive speech was “localised” to the third left frontal convolution. However, it was preceded by Marc Dax’s unpublished thesis submitted to Montpelier University in 1836 who had observed that the left hemisphere was damaged in aphasiacs (the source of the Broca-Dax controversy). The idea gradually evolved, partly owing to Broca, that the various areas of the brain were informed or “educated” by the functions they performed; it took many decades for it to be challenged.

    Handedness was another example of lateralised hemispheric function which attracted Broca and other French physicians in the 1860s. DJ Cunningham9 had noticed that the Sylvian fissure was higher on the right side than the left. Much later, Norman Geschwind and colleagues observed in right handers that the left planum temporale is much larger than the right, but the right frontal lobe is wider and may extend further forward than the left.10

    Anatomical variants of the ventricular size, the degree of crossing of the pyramidal tracts, and later asymmetries in response to visual stimuli and to evoked potentials were to follow. It was understood that the dual brain was marked by one dominant hemisphere which, through the vital corpus callosum, held sway over the lesser non-dominant one, until the importance of non-verbal functions of the right hemisphere was appreciated.

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