Localisation of Brain Lesions.
Lesions of the cranial nerves and their superficial and deep centres of origin need not here occupy attention. These may be studied in works on anatomy and physiology. Attention may be drawn rather to the remoter effects of ganglia which affect or control distant action, and to general pressure on the encephalon.
General Pressure on the Encephalon, whether through fracture of the cranium and depression of bone, by acute congestion, by blood extravasation, by inflammatory exudation, or by acute abscess, will cause pain, spasms, nausea, dullness, blindness, stupor and coma. After expulsion of the cerebro-spinal fluid from the cranial cavity, the increasing pressure compresses the blood vessels, reduces or interrupts the circulation and abolishes the functions in the parts deprived of blood. Thus congestion of one portion of the encephalon is usually associated with diminished circulation in another portion. Disorder in the first may occur from hyperæmia and irritation and in another part from a consequent anæmia.
Destructive Lesions of Cortex of One Cerebral Hemisphere may or may not cause permanent symptoms, as shown by the passage of a crowbar through the front of the left hemisphere, yet the man survived for 13 years and showed no loss of intelligence, his disposition and character alone having changed for the worse. The one hemisphere may by itself sufficiently control mental acts, while the other lies dormant or may even have undergone degeneration.
Diagnosis of Encephalic and Spinal Lesions. The following may be taken as guiding principles:
Encephalic: Hemiplegic or bilaterally hemiplegic grouping of symptoms.
Spinal: Paraplegic grouping of symptoms.
Encephalic: Frequent contracture or spasms of paretic muscles.
Spinal: Paralysis more perfect and continuous.
Encephalic: Reflexes in affected muscles increased: Cerebral inhibition absent.