Prologue: Toward the Concept of a Cortical Control of Voluntary Movements
In 1863 John Hughlings Jackson wrote about unilateral epileptic seizures caused by syphilis: “In very many cases of epilepsy, and especially in syphilitic epilepsy, the convulsions are limited to one side of the body; and, as autopsies of patients who have died after syphilitic epilepsy appear to show, the cause is obvious organic disease on the side of the brain, opposite to the side of the body convulsed, frequently on the surface of the hemisphere” (cited from Finger 1994; Jackson 1863). In the middle of the nineteenth century the concept of a cortical control of voluntary movements that is fully accepted today was hotly debated. It was widely believed that the corpus striatum was the uppermost center of motor control and the origin of the descending motor tracts. Jackson, on the other hand, was intrigued by the spread of seizures over specific body parts, e.g., from the hand to the arm to the face on one side of the body or from the hip to the leg to the foot and toes. Most frequently affected were the muscles of the face, hand, and foot. Only in severe cases did the seizure cross the midline and involve the entire body, usually followed by loss of consciousness. In hemiplegic patients Jackson observed that unilateral seizures were most likely to affect those parts of the body that were also most affected in hemiplegia. It appeared to him as if epilepsy were the “mobile counterpart of hemiplegia”. Based on these observations, Jackson proposed a sector of the cerebral cortex with motor functions and topographically organized representations of muscles. In this motor cortex, those body parts most frequently affected by epileptic seizures (i.e., face, hand, and foot) were assumed to have larger spatial representations than body parts less frequently affected.
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