Page 367 - Clinical Anatomy

ECA6 7/18/06 6:54 PM Page 352

352 The central nervous system

system. This is an important substrate for emotions, behaviour and memory.
The circuit is completed by projections of the hypothalamus to the thala-
mus, from the thalamus to the cingulate gyrus and from thence back to the
hippocampus. Bilateral hippocampal damage results in inability to form
new long-term memories.

The amygdaloid nuclear complex
The amygdaloid nuclear complex is also a prominent temporal lobe struc-
ture, situated immediately rostral to the hippocampus. It is conveniently
divided into three groups of nuclei: corticomedial, central and basolateral,
which receive largely olfactory, gustatory, and association cortical afferents
respectively. These divisions also have more or less separable projections to
the hypothalamus and septum, brainstem autonomic centres and ventral
striatum. The amygdala is involved in the control of emotional behaviour
and conditioned reflexes. Its neuroanatomical connections are clearly
appropriate for such a role, since it is in a position to affect emotional
responses in endocrine, autonomic and motor domains. Destruction of the
amygdala is particularly associated with reduced aggressive behaviour,
whilst the very high density of benzodiazepine receptors here has sug-
gested amygdaloid involvement in anxiety and stress and their treatments.

Occipital lobe

The occipital lobe lies behind the parietal and temporal lobes. On its medial
aspect it presents the Y-shaped calcarine and postcalcarine sulci (Fig. 247).
The following cortical areas are noteworthy:
1◊◊The visual cortex surrounds the calcarine and postcalcarine sulci and
receives its afferent fibres from the lateral geniculate body of the thalamus
of the same side; it is concerned with vision of the opposite half field of
sight (see Fig. 248).
2◊◊The occipital association cortex lies anteriorly to the visual cortex. This
area is particularly concerned with the recognition and integration of visual
stimuli.

The insula (Fig. 246)
If the lips of the lateral sulcus are separated, it is seen that there is a consid-
erable area of cortex buried in the floor of this sulcus. This area is known as
the insula of Reil. It is divided into a number of small gyri and is crossed by
the middle cerebral artery. Apart from its upper part, which abuts on the
sensory cortex and probably represents the taste area of the cerebral cortex,
the function of the insula is unknown. Its stimulation excites visceral effects
such as belching, increased salivation, gastric movements and vomiting.

The connections of the cerebral cortex

As has been indicated, most areas of the cerebral cortex receive their main