Vertebrate brain theory

6.2   The time sensitive difference mapping in the nucleus centromedianus

The nucleus centromedianus is a thalamic nucleus whose input comes from the spinocerebellum, where it is supplied by the nucleus emboliformis cerebelli.

However, the nucleus emboliformis projects as a cerebellar nucleus also into the frontal lobe. Its output is maximum coded.

We assume that the frontal lobe, as well as the primary cortex areas of the other lobes of the brain, projects into the basal ganglion system. The class 3 neurons of the frontal lobe therefore project via the substantia nigra into the matrix system, from where the signals reach the globus pallidus. The output of the globus pallidus contains (among other things) the time-delayed signal of the class 3 neurons of the frontal cortex. It was double inverted as described in chapter 3. This output is inhibitory.

It was found that the output of the globus pallidus reaches the nucleus centromedianus again. Thus, two types of signals converge in the nucleus centromedianus: 

-        The excitatory output of the spinocerebellum.

-        The inhibitory output of the globus pallidus obtained from the same signal, but inhibited and delayed.

The additive overlay in a point-to-point mapping provides a time-sensitive difference mapping. This is obtained from the output of the spinocerebellum. Thus, movements and temporal signal changes can be detected from the cerebellar signals. The output of this difference image is available in the nucleus centromedianus, which in turn projects back into the frontal cortex. There, association areas exist which serve the recognition of motor movements, because the spinocerebellum predominantly evaluates motor signals from muscle spindles or muscle tension receptors as well as tendon organs. The time-sensitive differential formation is limited to signals from one and the same half of the body, i.e. it is monolateral.

Theorem of the input of the nucleus centromedianus

The nucleus centromedianus of one hemisphere of the primordial brain receives the signals of the contralateral spinocerebellum in the form of excitatory signals in a point-to-point image.

At the same time, he received from the globus pallidus the double inverted, time-delayed and GABA-switched cortex output of the ipsilateral frontal cortex in the form of inhibitory signals, also originating in the contralateral spinocerebellum. Thus, the nucleus centromedianus receives the excitatory and the time-delayed and inhibitory signals from the same source and forms a time-sensitive differential signal by additive superposition. This enables the detection of movements and signal changes in the cerebellum output, which are transmitted to the frontal cortex and are available there in a separate association area for further use.

When vertebrates were still quite small and the sizes of their brains were still in the millimeter range, the time difference between the striatal and cerebellar signals in the nucleus centromedianus was negligible. With increasing size, however, this time difference grew to relevant values of about 10 milliseconds or more. This enabled the basal ganglion system in interaction with the cerebellum to analyze temporal changes and use them for motor responses. This also enabled the recognition of movements and an appropriate motor response. A suitable example would be the registration of moving objects that were detected via the lateral line system. Their signals also reached the spinocerebellum.