A system of practical medicine. By American authors. Vol. 5

by Unknown

(b) A lesion involving the caudal part of the thalamus and of the internal capsule. With such a lesion the motor symptoms consist in transient paralysis, with usually persistent post-paralytic chorea or ataxia. The sensory symptoms are more marked, and resemble those produced by lesion (a). It may be determined with some degree of accuracy whether the lesion be in the thalamus border, or in the internal capsule near to the nucleus lentiformis by the absence in the latter case of lateral hemianopsia.

The topography of such lesions is illustrated by Fig. 7.

FIG. 7.

Horizontal Section through the Centre of the Right Cerebral Hemisphere: M, median line; Nc, nucleus caudatus; Nucleus lent., nucleus lentiformis with its three segments; To, thalamus opticus; c. i., internal capsule with its frontal division, its bend or knee, and its caudal division. 1, mass of fibres destined for pons and others forming a part of the corona radiata, non-pyramidal fibres; 2, knee of the internal capsule, containing fasciculus from cortical centre for the face to the nucleus of facial nerve (non-pyramidal fibres); 3, fasciculus for the tongue and throat to nucleus of hypoglossus, etc. (non-pyramidal fibres); 4, fasciculi from the pre- and postcentral gyri and the paracentral lobule to the pyramid of the oblongata (the true pyramidal fasciculus, continued in the cord as fasciculi, 10 and 11 of Figs. [5] and [6]); 5, the caudal third of the internal capsule, containing fasciculi destined to the sensory cortical centres.

(c) Lesions of cortical areas connected with fasciculi of the sensory part of the internal capsule (c. i. 5).

(α) Lesion of the cortical area or centre for smell cannot at present be diagnosticated. From the results of experiments upon higher mammals we would expect such a centre to be in the cortex of the mesal gyri of the temporal lobe.

(β) Lesions of the cortical centre for taste are equally unknown; it is probably situated in the meso-basal aspect of the temporal lobe.

(γ) Lesions of the acoustic centre are somewhat better known, at least as far as the function of hearing language-sounds (psychic hearing) is concerned. A number of recently-published cases⁹ have quite positively shown that the existence of word-deafness indicates a destructive lesion of the dorsal gyri (more particularly the first and second) of the temporal lobe (the left always?). The lesion may also be in the inferior parietal lobule and gyrus supramarginalis, penetrating deeply enough to injure the acoustic fasciculus on its way from the internal capsule to the centre.