Introduction
The thalamus is the largest structure of the diencephalon and is located once in each hemisphere. It is a bean-shaped structure connected to each other by a kind of bridge. In addition to the thalamus, other anatomical structures belong to the diencephalon such as the hypothalamus with pituitary gland, the epithalamus with the epiphysis and the subthalamus. The thalamus is closely connected to the cerebrum via certain pathways. Information that the body receives via the ears, eyes, skin or even the position of one’s own body in space first flows to the thalamus.
Anatomy and Function
The various stimuli that are to penetrate to consciousness are switched in the thalamus nuclei and then passed on. A distinction is made between specific and non-specific thalamus nuclei, and both take up certain information and pass it on to different areas of the cerebrum. The specific thalamus nuclei are further divided into anterior, middle and posterior groups.
The anterior lateral core group (nucleus ventralis anterolateralis) processes mainly motor information, i.e. signals for the movement of the body. This is followed by the anterior posterior nucleus (nucleus vertralis posterior). These take up signals of depth sensitivity and the sense of touch.
Depth sensitivity describes information from the muscles, tendons and joints. It is used to constantly record and adjust the position of the joints in space. A process that is necessary for our brain to plan and execute movements.
As a kind of first filter station, this information is pre-processed and sorted out. Information that is important, i.e. that should be consciously perceived by the human being, is passed on from the thalamus to the corresponding regions in the cerebrum. Because of this information processing, the thalamus is often referred to in medicine as the “gateway to consciousness”.
Through this kind of switch-over point, unimportant information is filtered out, so that the person in a situation only perceives what is important and essential. At the same time, the brain is also protected from a flood of stimuli. The anterior thalamus nuclei (Nuclei anteriores thalami) receive important signals for functions such as learning, memory, feelings, food intake and digestion.
These services are summarized as the limbic system, which includes various structures distributed throughout the cerebrum. The middle thalamic nuclei (Nuclei mediales thalami) transmit information that affects cognitive abilities such as thinking and are particularly well connected to the frontal cerebral areas. In addition, two special areas called lateral and medial knee bumps (Corpus geniculatum laterale and mediale) belong to the specific nuclei.
The lateral part belongs to the visual path. This receives the stimuli from the visual field, more precisely from the retina of the eyes. They are processed and passed on to the visual cortex in the cerebrum, which is located at the back of the head, and processed into an image.
The medial knee bumps are part of the auditory pathway and therefore transmit the stimuli that we perceive with our ears to the corresponding areas in the cerebrum. Finally, the pillow-shaped pulvinar, or ‘cushion’, belongs to the specific nuclei. This is responsible for the further processing of perception, memory and language.
The unspecific thalamus nuclei are not given proper names. They include an intermediate group (Nuclei intralaminares), which is said to be important for the control of consciousness. The middle nuclei are also connected to the limbic system like some specific nuclei. They also contain a part of the olfactory tract, although the olfactory tract is the only exception and does not reach the cerebrum via the thalamic nuclei.
