Ebook Psychology Psyc2020 Psyc2021 Custom Edition by Schutte E Ed Et A PDF Full Chapter PDF
Ebook Psychology Psyc2020 Psyc2021 Custom Edition by Schutte E Ed Et A PDF Full Chapter PDF
Ebook Psychology Psyc2020 Psyc2021 Custom Edition by Schutte E Ed Et A PDF Full Chapter PDF
(a) A lesion of the internal capsule, just above the crus cerebri,
involving its bend or knee and caudal segment, with or without injury
to the nucleus lentiformis and thalamus, will give rise to the following
symptoms: Complete typical hemiplegia and total hemianæsthesia
on the opposite side of the body; the anæsthesia involves the special
senses as well as the body. Vision is, however, unaffected, unless
the lesion extend far enough back to involve the pulvinar and
fasciculus opticus, when lateral hemianopsia occurs (dark half-fields
on the side opposite the lesion). When this lesion is in the left
hemisphere, sensory aphasia also occurs.
(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.
(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.
(δ) The centre for visual impressions is now the best known of any of
the sensory cortical areas. The experimental studies and
pathological results of the last few years have indicated that the
occipital lobe was probably the seat of higher, organized vision (for
form and color). More recent autopsies and re-examination10 of the
subject point to the cuneus and adjacent gray matter as the visual
centre. The anatomical arrangement is, however, peculiar and
complex, in that each cortical visual area receives impressions from
one lateral half of both retinæ, through the fasciculus opticus.
10 E. C. Seguin, “A Contribution to the Pathology of Hemianopsia of Central Origin
(Cortex-hemianopsia),” Journal of Nervous and Mental Diseases, 1886, No. 1.
FIG. 8.
Diagram of Visual Paths, designed to illustrate specially Left Lateral
Hemianopsia from any lesion. L. T. F., left temporal half-field; R. N. F.,
right nasal half-field; O. S., oculus sin.; O. D., oculus dexter; N. T., nasal
and temporal halves of retinæ; N. O. S., nervus opticus sin.; N. O. D.,
nervus opticus dext.; F. C. S., fasciculus cruciatus sin.; F. L. D., fasciculus
lateralis dext.; C., chiasma, or decussation of fasciculi cruciati; T. O. D.,
tractus opticus dext.; C. G. L., corpus geniculatum laterale; L. O., lobi
optici (corpus quad.); P. O. C., primary optic centres, including lobus
opticus, corp. genic. lat., and pulvinar of one side; F. O., fasciculus
opticus (Gratiolet) in the internal capsule; C. P., cornu posterior; G. A.,
region of gyrus angularis; L. O. S., lobus occip. sin.; L. O. D., lobus occip.
dext.; Cu., cuneus and subjacent gyri, constituting the cortical visual
centre in man. The heavy or shaded lines represent parts connected with
the right halves of both retinæ. The reader may place the lesion as he
pleases.
From this level the fibres of the internal capsule again diverge, as
fasciculi whose physiological independence has been well
determined, going dorsad and frontad to certain gyri of the cerebral
cortex where their fibres join ganglion-cells. Three large fasciculi and
corresponding cortical areas are recognized as constituting the
pyramidal tract, strictly speaking: (1) A fasciculus which extends
frontad to the base of the second frontal gyrus where it coalesces
with the precentral, the centre and fasciculus for movements of the
facial muscles of the opposite side; (2) a fasciculus which extends to
the precentral and postcentral gyri, more especially in their middle
part, constituting the centre and fasciculus for movements of the arm
and hand; (3) another fasciculus which goes dorso-mesad, almost
vertically in the brain, to join the ends of the pre- and postcentral gyri
at the top of the hemisphere, and their continuation upon its mesal
aspect known as the paracentral lobule, centre and fasciculus for
movements of the opposite foot and leg. Besides these three great
cortical areas and their connected fasciculi of nerve-fibres, which go
to make up the pyramidal tract, we recognize (4) a cortical centre for
speech movement of the tongue and lips in the base of the left third
frontal gyrus over the fissure of Sylvius (Broca's speech-centre), with
a connected white fasciculus which passes into the elbow of the
internal capsule, and can be traced (by means of secondary
degeneration) into the inner part of the base of the crus and into the
pons, but not to the pyramid. Another probable centre (5), for coarse
lingual movements and for the various movements of deglutition, is
in the folds of the insula, its fasciculus not joining the pyramid.
FIG. 9.
Longitudinal (sagittal) Section through the Brain, to show the distribution
of the fasciculi of the internal capsule. Fasciculi of motor tract in dotted
lines, to fronto-parietal convolutions. Fasciculi of sensory tract in full lines,
to temporo-parieto-occipital convolutions: N. C., nucleus caudatus; N. L.,
nucleus lentiformis; T. O., thalamus opticus. 1, level of crus cerebri; 2,
level of pons; 3, level of oblongata. (This diagram is to be used in
conjunction with Fig. 7.)
With respect to the anterior part of the frontal lobe, forward of the
oblique line A B across Figs. 10 and 11, the study of human cases of
destructive injury and disease would indicate that it is not associated
either with the kinesodic or with the æsthesodic systems.
The SYMPTOMS of lesions of the kinesodic system, particularly of the
pyramidal tract, are exclusively motor, consisting of spasm and
paralysis. Contracture of the paralyzed parts follows the paralysis
after a few weeks if the lesion be a destructive one.
(b) Lesion of the facial centre (1) and of its associated fasciculus is
characterized by the occurrence of spasm or paralysis, or of both in
rapid succession, in the facial muscles; their electrical reactions
remaining normal.
(c) Lesion of the brachial centre (2) and of its associated fasciculus
is made known by spasm or paralysis, or by both in succession, in
the hand and arm. In many cases (tumor especially) the first
symptom is clonic convulsive movements of two or more fingers,
extending to other parts of the arm. Such brachial monospasm or
monoplegia is usually accompanied or followed by incomplete
hemiplegia.
(d) Lesion of the crural centre (3) in the paracentral lobule and of its
associated fasciculus of white substance is indicated by priority and
predominance of convulsive and paralytic phenomena in the foot and
leg: a crural monospasm or monoplegia exists with or without
incomplete hemiplegia.
(e) Lesion of the insula and adjacent white substance laterad of the
nucleus lenticularis (5) may be suspected from the rapid or sudden
development of symptoms imitating those of acute bulbar paralysis,
but without bilateral paresis of the body and anæsthesia. Aphasia is
very apt to coexist with the bulbar symptoms if the lesions involve
the left insula, whose frontal folds are continuous with the speech-
centre.
(b) Focal lesions of the caudal part of the frontal lobes, of the insula,
the pre- and postcentral gyri, and other parts of the motor zone are
usually easy of diagnosis. The symptoms of such lesions have
already been detailed when speaking of lesions of the kinesodic
system.
(c) Focal lesions of the parietal, temporal, and occipital lobes of the
brain have the characteristic semeiology of lesions of the æsthesodic
system, considered supra.
FIG. 11.
3. FOCAL LESIONS OF THE BASE OF THE BRAIN, either within the nervous
substance or springing from the dura, and acting by irritation and
pressure upon various parts of the basal aspect of the encephalic
mass.
(a) Diffused bilateral lesions of this class situated frontad of the crura
give rise to more or less distinct symptoms, and a diagnosis is
sometimes possible. (1) Lesions in the vicinity of the sella turcica
and optic chiasm produce symptoms in the optic apparatus very
early, and these remain prominent throughout the illness. These
symptoms are, irregular (at least not lateral) hemianopsia, neuro-
retinitis followed by atrophy of the optic nerve, temporary or
permanent paralysis of one or several ocular nerves. If these exist
without symptoms of lesion of other parts of the brain (reasoning by
the process of exclusion), we may strongly suspect the seat of the
lesion to be in the region named. Other symptoms are paroxysmal
headache and occasional vomiting, epileptiform convulsions (never
Jacksonian in distribution), partial hemiplegia, or general muscular
weakness. By such data we were recently led to the correct
localization of a tumor. (2) If the lesion be farther frontad—i.e. strictly
in the orbital areas of the basis cerebri—anosmia, uni- or bilateral,
usually with hallucinations of smell, will be an early symptom, along
with neuro-retinitis and obscure motor and sensory symptoms
(headache and convulsions more especially).
(2) Unilateral focal lesions of the base of the encephalon from the
crura caudad to the pyramidal decussation.
(β) The lesion occupies the latero-ventral part of the crus. This rare
localization would give rise to direct paralysis of the fourth nerve,
indicated by homonymous diplopia in the lower inner field of vision;
to lateral hemianopsia with dark half-fields opposite the lesion, from
injury to the tractus opticus (vide Fig. 8); and to a mixed motor and
sensory disturbance in the opposite side of the face and body,
without anæsthesia of the olfactory and auditory apparatus. A very
large lesion involving almost the entire crus would probably also
cause direct paralysis of N. iii.