UNTIL QUITE RECENTLY, THE FUNCTION and organization of the human cerebral cortex—the region of the brain concerned with perceptual, motor, and cognitive functions—has eluded both clinicians and neuroscientists. In the past, the analysis of brain function relied largely on observations of loss of brain functions resulting from brain damage and cell loss caused by strokes or trauma. These natural experiments provided much of the early evidence that distinct brain regions serve specific functions, or as the famous American neurologist C. Miller Fisher said, “We learn about the brain ‘stroke by stroke.’” Observation of patients with seizures and epilepsy has been equally important in the study of brain function because the behavioral consequences of these disorders of neural hyperactivity inform clinicians how activation affects the brain regions from which they originate.
Temporary disruptions of brain function resulting from abnormal, excessive neuronal activity are called seizures, whereas the chronic condition of repeated seizures is called epilepsy. For centuries, understanding the neurological origins of seizures was confounded by the dramatic, and sometimes bizarre, behaviors associated with seizures. The chronic condition of epilepsy was widely associated with possession by evil spirits, yet seizures also were thought to be a sign of oracular, prescient, or special creative powers.
The Greeks in the time of Hippocrates (circa 400 BC) were aware that head injuries to one side of the brain could cause seizure activity on the opposite side of the body. In those earlier times, the diagnosis of epilepsy was probably much broader than the contemporary definition. Other causes of episodic unconsciousness, such as syncope as well as mass hysteria and psychogenic seizures, were almost certainly attributed to epilepsy. Moreover, historical writings typically describe generalized convulsive seizures involving both cerebral hemispheres; thus, it is likely that seizures involving a very limited area of the brain were misdiagnosed or never diagnosed at all. Even today, it can be difficult for physicians to distinguish between episodic loss of consciousness and the various types of seizures. Nevertheless, as our ability to treat and even cure epilepsy continues to improve, these diagnostic distinctions take on increasing significance.
The early neurobiological analysis of epilepsy began with John Hughlings Jackson’s work in London in the 1860s. Jackson realized that seizures need not involve loss of consciousness but could be associated with localized symptoms such as the jerking of an arm. His observation was the first formal recognition of what we now call partial (or focal) seizures. Jackson also observed patients whose seizures began with focal neurological symptoms, then progressed to convulsions with loss of consciousness by steadily involving adjacent regions in an orderly fashion (the so-called Jacksonian march). His observations gave rise to the concept of the motor homunculus (the anatomical map representing the body organization or “wiring diagram” over the cortical surface) long before functional organization was established using electrophysiological techniques (Chapter 4).
Another pioneering development that ...