Basal ganglia
Several nuclei or nuclear areas of the endbrain ( telencephalon ) that lie below the cerebral cortex ( cortex cerebri ) are combined as basal ganglia or nuclei basales . These subcortical basal nuclei are of great importance for important functional aspects of motor , cognitive and limbic regulation, for example for spontaneity , affect , initiative, willpower, drive, step-by-step planning, anticipatory thinking , expectations, motor selection .
anatomy
The basal ganglia, sometimes also referred to as master ganglia or, according to more recent nomenclature, as basal nuclei (nuclei basales), are one in the narrower sense (anatomical):
- the caudate nucleus (curly nucleus) and
- the nucleus lentiformis (lenticular nucleus). This consists of:
The caudate nucleus and putamen lie together in the early embryonic development and are then separated by the growth of the internal capsule , the longest projection path of the central nervous system. However, they remain connected by fine strips or bridges of gray matter ( Pontes grisei caudatolenticulares ) and are therefore collectively referred to as the striatum (the striped thing). This summary is not only morphologically but also functionally relevant. Ventrally , the caudate nucleus and putamen are still connected. This point is called the "fundus striati" or nucleus accumbens .
To the basal ganglia in the broader sense (functional) one counts:
- the substantia nigra (black substance), a core area located in the midbrain consisting of
- Pars compacta (SNc)
- Pars reticularis (SNr) and lateralis
- the subthalamic nucleus (STN, also called Corpus Luysi ).
The entry point into the basal ganglia is the striatum. It not only receives projections from the cerebral cortex and the substantia nigra, but also from various core areas of the central nervous system, e.g. B. Raphe nuclei , Formatio reticularis . The starting point is the pallidum internum (GPI), which projects GABAerg (inhibitory) directly onto the thalamus and inhibits it (and thus also the cerebral cortex). Both the pallidum and the subthalamic nucleus are evolutionarily part of the ventral thalamus .
function
About the complex function of the basal ganglia, which has only been partially understood to date, it is currently hypothetically postulated that they are significantly involved in the selection and processing of currently required "motor" and "non-motor" (higher integrative) patterns of action as well as at the same time Suppression or inhibition of activation patterns that are currently not required, that is, undesirable and therefore have to be suppressed. The basal ganglia are, as it were, integrated as a filter process (see gating ) in a complex control loop that starts from the cerebral cortex and runs back to the cerebrum ( frontal lobe ) via the basal ganglia and thalamus . From almost the entire cerebral cortex, more precisely from the nerve cells of layer V, with a few exceptions ( primary visual and auditory cortex ), information reaches the striatum as the entrance to the basal ganglia in the form of cortico-striatal connections (excitatory glutamatergic transmission). Via the exit station of the basal ganglia , the substantia nigra (pars reticulata SNR) and the globus pallidus internus (GPI), the end information processed by the basal ganglia (inhibitory GABA-ergic transmission) reaches the thalamus and from the thalamus (excitatory, glutamatergic) primarily to the frontal one Cerebral cortex back. The basal ganglia represent an elementary functional contribution to the frontal, so-called executive part of the brain, which is still little understood in detail.
Today a direct (excitatory) connection from the striatum to the initial structures (SNR and GPI) is differentiated from an indirect (inhibitory) connection . The striatum and the GPI are both GABAerg (inhibitory). Thus, a direct projection of the striatum on the GPI leads to an inhibition of its inhibition (disinhibition), which now means an excitation of the thalamus or the cerebral cortex. The indirect connection is a little more complicated: the striatum inhibits the globus pallidus externus, GPE , which inhibits the nucleus subthalamicus. The inhibition is then inhibited again, i.e. the subthalamic nucleus is excited. In turn, it has an exciting effect on the GPI, which now inhibits the thalamus and thus indirectly the cerebral cortex. When the GPE is inhibited, any direct inhibition on the GPI also disappears, which further increases the inhibitory effect of the GPI. As a result, the output modulation of the basal ganglia activity lies, so to speak, on two oppositely directed reins, which cause more (plus) or less (minus) movement or action patterns (in the broader sense “behavior”).
The dopaminergic projection to the striatum emanating from the nerve cells of the substantia nigra (pars compacta) represents a particularly well-researched modulation path within the basal ganglia because it has been recognized that its disorder as a result of premature degeneration ("aging") is one of the symptoms of Parkinson's disease leads.
Diseases
Among the neurological diseases associated with a dysfunction of the basal ganglia include:
- Parkinson's Syndromes, e.g. B. Parkinson's disease , multiple system atrophy (MSA), Hallervorden-Spatz syndrome (HSS)
- Dystonia syndromes, e.g. B. spasmodic torticollis , athetosis , tardive dystonia
- Choreatic syndromes , e.g. B. Huntington , Hemiballism , tardive dyskinesia , choreoathetosis
- PANS / PANDAS
- ADHD
- Tic disorders, e.g. B. Tourette syndrome
In " Parkinson's disease ", as a result of a chronically progressive degeneration of the dopaminergic transmission emanating from the substantia nigra, pars compacta (SNc), there is a pathological change in the striatal modulation, which in very different degrees leads to muscle tone changes ( rigor ), impoverishment of movement ( hypokinesis ), Shaking ( tremor ), postural instability, decreased sense of smell ( hyposmia ) and other symptoms.
In early childhood, perinatal brain damage (e.g. kernicterus, lack of oxygen), damage to the basal ganglia with changes in muscle tone (e.g. athetosis ) is common. In Wilson's disease , copper deposition and a. complex motor and psychological dysfunction in the basal ganglia.
Gating theory
As described above , the filter function of the basal ganglia or the striatum is called gating . The gating theory itself is relatively well established in neuroanatomical and physiological terms, but is currently only found under this name in neuropsychological publications. This is extremely important for the validity of the gating theory, since gating in itself is nothing new in terms of content, but just another name for an already existing concept.
From the gating theory, a number of other theories can be derived, diseases can be explained and inter- individual differences with regard to the personality of people can be described:
- Tic disorders as a faulty connection of the basal ganglia, in which a recurring movement pattern is carried out in that certain behavior plans are incorrectly processed by the striatum.
- ADHD : Here some researchers suspect similar interconnection patterns as in tic disorders, only that in this case not a certain behavior pattern would be processed incorrectly, but a general inadequate filter function in which redundant or "inappropriate" behavior is aroused (hyperactivity), while new ones Behavioral plans are incorrectly inhibited (attention deficit).
- Obsessive-compulsive disorder: The gating theory of obsessive-compulsive disorder is comparable to that of tic disorders, although scientifically and in the opinion of many experts it is rather “on shaky feet”, since it can explain compulsive actions, but neither obsessive-compulsive thoughts nor the affective component of the Obsessive-compulsive disorder.
Another explanatory approach from the gating theory is that of inter-individual personality differences: Hans Jürgen Eysenck described one of the most established personality factors to this day as extraversion vs. Introversion and explained to him about basic cortical arousal. However, this neurophysiological explanation is now increasingly being questioned. Recent research tries to explain this personality dimension through gating. According to this, introverts have a more efficient gating compared to extraverts, which is why extraverts have to increase their gating (i.e. the ability of the striatum to adequately process behavioral plans) by looking for additional internal or external sensory stimuli. According to the theory, this increases the glutamatergic projection of the cerebral cortex onto the striatum, which means that it can now filter better. This theory explains, for example, why extraverts learn better when, e.g. B. Listening to music while introverts tend to be distracted by it.
Gating theory in the broader sense is very promising, but it is still in its infancy. Many of the sub-theories are scientifically founded, with some of the links (although logical) being poorly or not at all investigated.
swell
- Jonathan W. Mink: The Basal Ganglia Chapter 31 - Fundamental Neuroscience 2003 Academic Press
- Bastian Conrad, Andres Ceballos-Baumann: Movement disorders in neurology - recognizing and treating them correctly . 1st edition. Thieme Verlag, Stuttgart / New York 1996, ISBN 3-13-102391-0 .
- Andres Ceballos-Baumann, Bastian Conrad: movement disorders . 2nd Edition. Thieme Verlag, Stuttgart / New York 2005, ISBN 3-13-102392-9 .
- G. Percheron, G. Fénelon, V. Leroux-Hugon, A. Feve (1994): Histoire du système des ganglions de la base. La lente émergence d'un système cérébral majeur. Revue Neurologique Aug-Sep; 150 (8-9): 543-54.
- Lennart Heimer : The Human Brain and Spinal Cord: Functional Neuroanatomy and Dissection Guide. Springer, New York 1995, ISBN 0-387-94227-0 .
Web links
- Models of Basal Ganglia . In: Scholarpedia . (English, including references)
- Functions and disorders associated with the basal ganglia with links to current studies