Dorsomedial nucleus

The thalamus of both sides is shown in this diagram, focusing on the medial nuclear mass of the thalamus, the dorsomedial nucleus, one of the most important of the association nuclei of the thalamus (see Figure 11 and Figure 12).

Shown below is the amygdala with one if its pathways, the ventral amygdalofugal fibers, projecting to the dorsomedial nucleus (see Figure 75A and Figure 75B). This pathway brings "emotional" information to the thalamus. The dorsomedial nucleus collects information from a variety of sources, including other thalamic nuclei, as well as from various hypothalamic nuclei (see Figure 63).

The dorsomedial nucleus projects heavily to the frontal lobe, particularly to the cortical area that has been called the prefrontal cortex (see Figure 14A). The projection thus includes the emotional component of the experience. This pathway passes through the anterior limb of the internal capsule, between the head of the caudate nucleus and the lentiform nucleus (see Figure 26). The fibers course in the white matter of the frontal lobes.

Our expanded view of the limbic system now includes its extension to this prefrontal cortex, specifically the orbital and medial portions of the frontal lobe; this has been called the limbic forebrain. Widespread areas of the limbic system and association cortex of the frontal lobe, particularly the medial and orbital portions, are involved with human reactions to pain, particularly to chronic pain, as well as the human experiences of grief and reactions to the tragedies of life.

Clinical Aspect — Psychosurgery

The projection of the dorsomedial nucleus to the prefron-tal cortex has been implicated as the key pathway that is interrupted in a now-banned surgical procedure. Before the era of medication for psychiatric disorders, when up to one-half of state institutions were filled with patients with mental illness, a psychosurgical procedure was attempted to help alleviate the distressing symptoms of these diseases.

The procedure involved the introduction of a blunt instrument into the frontal lobes, passing the instrument (bilaterally) through the orbital bone (which is a very thin plate of bone) above the eye. This interrupts the fibers projecting through the white matter, presumably including the projection from the dorsomedial nucleus. This operation became known as a frontal lobotomy.

Long-term studies of individuals who have had frontal lobotomies have shown profound personality changes in these individuals. These people become emotionally "flat" and lose some hard-to-define human quality in their interpersonal interactions. In addition, such an individual may perform socially inappropriate acts that are not in keeping with the personality of that individual prior to the surgery.

Once the long term effects of this surgery became clear, and since powerful and selective drugs became widely available for various psychiatric conditions, this surgery was abandoned in the 1960s and is not performed nowadays.

This same procedure had also been recommended for the treatment of pain in terminal cancer patients, as part of the palliative care of an individual. After the surgery, the individual is said to still have the pain but no longer "suffers" from it, that is, the psychic aspect of the pain has been removed. There may even be a reduced demand for pain medication such as morphine. Again, other approaches to pain management are now used.

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