5. Anterior cerebral.
(c) Twig disorders.
1. Medullary.
2. Cortical.
Some reference should be made, perhaps, to the focal symptoms resulting from more or less sharply circumscribed lesions which are productive of certain fairly well known complexes, whether due to arteriosclerotic softenings, hemorrhages, or growths. These have been concisely summarized by Barker[165] somewhat as follows:—
Frontal Lobes—Lesions of the left inferior frontal in righthanded persons cause motor aphasia. Subcortical involvements cause word dumbness. Disturbances in the anterior part of the frontal region are sometimes associated with the Witzelsucht of the German writers—a tendency towards joking and witticisms.
Central and Paracentral Lobules—Contralateral sensory, motor symptoms or a combination of the two. Monoplegias, anesthesias and Jacksonian epilepsies are characteristic. Contralateral tactile agnosia and apraxia occur, especially in lesions of the left hemisphere. An involvement of the left side may also cause a homolateral apraxia, dyspraxia or a tactile agnosia.
Parietal Lobes—Lesions in the anterior part cause contralateral somesthetic disturbances, tactile agnosia or apraxia. Involvement of the left angular gyrus may cause optic aphasia or alexia; if deep enough, hemianopsia results. The voluntary movement of the eye may be interfered with.
Temporal Lobe—Lesions in the posterior half of the first temporal may cause Wernicke's sensory aphasia and a subcortical involvement, word deafness. Bilateral destruction of the first and transverse temporals causes cortical deafness. Extensive bilateral lesions in the lower part of these lobes result in mind deafness. Irritative lesions in the uncinate gyrus lead to hallucinations of taste and smell, with smacking of the lips and tongue movements.
Island of Reil—Lesions of the anterior part cause symptoms resembling Broca's motor aphasia. Lesions of the posterior part result in symptoms suggesting Wernicke's sensory aphasia. Transcortical motor and sensory aphasia may result.