Page 368 - Clinical Anatomy

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The brain 353

afferent input from the thalamus, but, in addition to this, there are well-
established commissural connections with the corresponding area of the
opposite hemisphere by way of the corpus callosum. Associational intracorti-
cal connections also link neighbouring cortical areas on the same side and, in
some cases, connect distant cortical areas; thus, the frontal, occipital and
temporal lobes are directly connected by long association pathways.

Clinical features

It is convenient to summarize here the clinical effects of lesions affecting the
principal cortical areas.
1◊◊Frontal cortex—impairment of higher mental functions and emotions.
2◊◊Precentral (motor) cortex — weakness of the opposite side of the body;
lesions low down the cortex affecting the face and arm, high lesions
affecting the leg. Midline lesions (meningioma, sagittal sinus thrombosis
or a gunshot wound) may produce paraplegia by involving both leg areas.
3◊◊Sensory cortex — contralateral hemianaesthesia (distributed in the same
pattern as the motor cortex) affecting especially the higher sensory modali-
ties such as stereognosis and two-point position sense.
(For area localizations along the motor and sensory cortex, see pages 355
and 356.)
4◊◊Occipital cortex—contralateral homonymous hemianopia.
5◊◊Lesions adjacent to the lateral sulcus in either the frontal, parietal or
temporal lobes of the dominant hemisphere result in aphasia.

The basal ganglia (Figs 246, 248)
These compact masses of grey matter are situated deep in the substance of
the cerebral hemisphere and comprise the corpus striatum (composed of the
caudate nucleus, the putamen and the globus pallidus) and the claustrum.
Together with the cerebellum, they are involved in co-ordination and
control of movement.

The corpus striatum

The caudate nucleus is a large homogeneous mass of grey matter consisting of
a head, anterior to the interventricular foramen and forming the lateral wall
of the anterior horn of the lateral ventricle; a body, forming the lateral wall of
the body of the ventricle; and an elongated tail, which forms the roof of the
inferior (temporal) horn of the ventricle. It is largely separated from the
putamen by the internal capsule, but the two structures are connected anteri-
orly. The putamenis a roughly ovoid mass closely applied to the lateral aspect
of the globus pallidus; together, they are called the lentiform nucleus. The
corpus striatum receives afferent connections from the cerebral cortex and
sends efferents to the globus pallidus. From thence, fibres project to the thal-
amus and, from thence, back to the premotor cortex. Dopaminergic fibres
project from the substantia nigra to the corpus striatum and efferent fibres