Zona Incerta - Connections

Connections

The zona incerta has connections to the cerebral cortex, diencephalon, basal ganglia, brainstem and spinal cord.

Cerebral cortex

Projections to the zona incerta arise across the cortical mantel from the frontal to the occipital lobes. The heaviest projections are from cingulate cortex, frontal and parietal areas. The head area of the body seems from these areas to have the largest representation in the zona incerta. These projections preferentially go to cortical layer I neurons. There are projections from the zona incerta back to the cerebral cortex.

Diencephalon

Projections with the diencephalon are reciprocal and mainly to the thalamus such as the intralaminar nucleus (parafascicular nucleus and central lateral nucleus) and higher-order nuclei such as the lateral posterior nucleus. The zona incerta avoids the thalamus nuclei of the primary sensory areas such as the ventral posterior nucleus of the somatosensory system and the lateral geniculate of the visual system.

Hypothalamus

Projections to the hypothalamus go mainly to the paraventricular nucleus areas in the anterior hypothalamus, lateral hypothalamus, lateral preoptic area, horizontal diagonal band of Broca, and the parvocellular region of the paraventricular nucleus.

Basal ganglia

Zona incerta is connected in the basal ganglia to the substantia nigra (both pars compacta and pars reticulata) and pedunculopontine tegmental nucleus (but only its pars dissipata area). It also has less important connections to the entopeduncular nucleus and globus pallidus. These projections are glutamatergic and excitatory rather than GABAergic and inhibitory. The zona incerta also receives input from these areas.

Brainstem

Zona incerta receives input from many parts of the brainstem nuclei including the periaqueductal gray, raphe nuclei, thalamic reticular nucleus, and the deep layers of the superior colliculus. It is regulated by inputs from brainstem cholinergic nuclei such as the Laterodorsal tegmental nucleus and pedunculopontine nucleus upon its neuron’s muscarinic receptors.

Spinal cord

Zona incerta afferents terminate within the spinal cord gray matter, particularly the anterior horn, while spinal projections back to the zona incerta arise from cells located across the posterior horn and intermediate gray.

Other

Zona incerta also has connections to the amygdala, basal forebrain, the osmoreceptors in the subfornical organ, olfactory bulb, posterior pituitary and habenula.

Some of these projections appear in register; the representation of the same body part in cortex and spinal cord connect to the same areas in the zona incerta. This is possibly so with the superior colliculus.