Medial Nuclear Group
The
medial nuclear group (medial complex) (B5)
consists of a medial magnocellular nucleus, a lateral parvocellular nucleus,
and a caudal nucleus. All nuclei project to the frontal lobe, namely, to thepremotor
cortex,the polar cortex, and the orbital cortex (B6). Afferent fiber bundles run via the inferior thalamic radiation
from the globus pallidusn(B7) and from the basal nucleus of
Meynert(substantia innominata) to the medial nuclear group. The
medial magno-cellular nucleus has fiber connections to the hypothalamus (B8) (preoptic area and tuber cinereum)
and to the amygdaloid body (amygdala). The lateral parvocellular nu-cleus
receives fibers from the adjacent ven-tral nuclei of the thalamus.
The
medial nuclear complex is thought to receive visceral and somatic impulses via
pathways from the hypothalamus and ven-tral nuclei; the impulses are integrated
here and then transmitted via the anterior thalamic radiation to the frontal
cortex. The basic affective mood,
which is essentially de-termined by unconscious stimuli from the visceral and
somatic spheres, is thought to enter consciousness in this way.
Clinical Note: It has been observed in
patientswith severe agitation that incision of the thalamocortical tracts
(prefrontal lobotomy) had a calming effect but was also associated with
in-difference and a regression of personality. The stereotactic destruction of
the medial nuclear complex has similar effects.
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