Vertebrate brain theory

1.4  The substructures of the diencephalon of vertebrates

 

A large part of the facts presented here are non-wordly quotations from the work "Wie einzigartig ist der Mensch" by Gerhard Roth, [48], pages 180 to 185. They would not gain substance by a reformulation.

According to Roth, the diencephalon in vertebrates contains important switching stations of ascending sensory and descending motor information between the brain stem and the diencephalon. It is formed by the brain walls surrounding the third brain ventricle and is divided into

• the epithalamus
• the thalamus
• the subthalamus
• the hypothalamus.

The diencephalon, like the endbrain, has been constantly expanded during the evolution of vertebrates, with differences in structure, signaling pathways and even cytoarchitectonics emerging between reptiles, birds and mammals.

The epitalamus consists of

• the paired habenula, consisting of the two nuclei habenularum, a switching centre that transmits, among other things, olfactory information to the salivatory and motor nuclei of the masticatory and swallowing muscles and is connected to the septum nuclei, the amygdala and the preoptic region.
• the Commissura habenularum
• of the Stria medullaris
• the pineal gland, a light-sensitive organ in the lower vertebrates for the recognition of the day and night change. In higher vertebrates with thicker skullcap, this information is provided by the nucleus suprachiasmaticus, which is synchronized by retinal fibres.
• of the Commissura epithalamica (posterior)
• the parietal organ
• the pineal organ.

The thalamus is the largest and most prominent structure in the diencephalon. Located between the midbrain and the endbrain, it serves to exchange signals between these two systems, although it certainly also has regulatory functions. The thalamus is regarded as the gateway to consciousness, whose representation is imagined in the cortex.

With the increase of sensory species and their development, numerous nuclei differentiated in the thalamus. These partly process their own modalities, but there are also multimodal nuclei.

Much of the output of the thalamus reaches the endbrain. However, the latter projects reciprocally back to the thalamus.