Comparator system
The comparator system according to Gray and Rawlins is a thesis developed in 1986, according to which sensory impressions ( bottom-up ) with conceptual understanding ( top-down ) are measured, compared and analyzed. They postulated hippocampal structures as the possible seat of this comparison system . It is assumed that in psychotic episodes the adaptability of the internal correction of perception is faulty.
Current understanding of the hippocampal comparison system
According to studies from 2001, the comparator system represents a global control mechanism in the brain that essentially brings about and regulates selective attention on the one hand and selective information filtering and storage organization for explicit, episodic, declarative and perceptual memory on the other .
Orientation in everyday life
Incoming, actual sensory impressions are compared and evaluated with previous experiences and the imprinted consequences of these experiences (sometimes also referred to as an internal worldview ). But dynamic behavior also plays an important role in many daily situations. Assuming you have to make your way through a crowd on foot, the interactive process is simulated , probably largely unconsciously, by the nervous system in order to compare the expected movements of passers-by with the effective movement patterns through analyzes. Deviations are constantly incorporated into the internal model. One can assume permanent fine-tuning ( readjustment ) of the local and current world conception through the recurring sensory impressions. If changes are registered, the hippocampal comparison system is involved. The perception of new things, changes and known things between imagined expectation and effective development enable the organism to orientate itself in the world.
Animal experiments and clinical findings
In animal experiments by hippocampectomy, the animals showed a pronounced disorientation, which was noticeable through persistent orientation reflexes, incessant curiosity and insatiable tracking behavior. Hippocampal dysfunctions caused a severe impairment of selective attention, where those affected inadvertently became receptive to superimpositions of unimportant stimuli and also had problems switching from one object to another. Associated with this, the lack of transfer from short-term memory to long-term memory (anterograde amnesia) is characteristic.
Neurophysiology
The comparator theory could be confirmed experimentally on a neurophysiological level, according to which neurons in the CA3 region of the hippocampus function as a comparator. They transmit the two afferents from the reticular formation and the neocortex , depending on their synchronous or asynchronous activity, to the CA1 region of the hippocampus or intermediately to the median raphe nucleus. An informational and a regulatory cycle are effective. The following results were obtained from animal experiments on rabbits.
When the stimuli are presented for the first time
the CA3 region receives a weak signal from the neocortex. The reticular formation sends a strong theta modulation to the CA3 region, which is understood as the perception of the novelty of a stimulus and an important step in the creation of selective attention. The theta modulation, so one could conclude from the test results, isolates a stimulus on which the attention is directed from being influenced and additionally prolongs the stimulus response. CA3 neurons send predominantly tonic impulses to the CA1 region via Schaffer collaterals. The second efference from the CA3 region to the medial raphe nucleus is not activated because of the weak activity of the CA3 input from the neocortex. The CA1 nerve cells, which have an afferent intermediate connection with the neocortex, no longer receive any impulses from the cerebral cortex because of the input from CA3. The CA1 neurons fire signals to the subiculum which, in contrast to the CA3 neuron activity, contain stimulus-specific information. Activation of the CA1 output to the subiculum creates a chain of memory integration whereby fleeting, irrelevant and improbable perceptions are neither registered nor stored.
With repeated presentations of the stimuli
the CA3 region receives strong signals from the neocortex and the efferent signal transmission from the reticular formation ebbs due to the increased CA3 activity to the raphe nucleus, which blocks the theta modulation. The strength of the cortex signal is understood as the perception of the level of awareness (recognition) of a stimulus. What makes you get used to the stimuli or, in other words, causes a decrease in selective attention to them. The output stream from CA3 to CA1 is interrupted, so that the connection from the neocortex to the CA1 region is again permeable for information. After several repetitions of the stimuli presentations, the new stimuli had been learned well by the test animals, a. from their behavior of habituation and decreasing interest could be deduced. If the stimuli were partially modified, the neurological processes of the initial presentation were repeated, whereby the repetition rate of the stimulus adaptation decreased.
Perception smoothing
For three-dimensional (rotating) objects that are modeled in such a way that they have a front side and an interior, e.g. B. a hollow mask are sometimes perceived as a front view of the object in the inverse position. This phenomenon, known as "binocular depth inversion" (BDI), was observed in studies more frequently in temporal lobe - epilepsy and reduced in schizophrenia . Spatial clues (bottom-up) of the inverse and thus unfamiliar view of objects and faces are overridden by the abstract idea of what is known (top-down) and understood as a perception that matches the usual normality. The comparator system seems to occupy a key position in the interpretation of perception. Situation- related sensory impressions usually agree plausibly with prior conceptual knowledge and experience, and the internal correction of a slight sensory deviation from the interpretation that is known and likely is perceived as continuous and stable. An attempt to explain the lack of convex illusion in some of the schizophrenia test subjects is to take into account the decrease in emotional relationship and familiarity with the environment and society that usually occurs in the course of this disease, so that the associated emotions are weaker and the Top-down signals have less or no corrective effect on the sensory data.
Similar effects are to be observed when administering cannabinoids .
Drug influencing the comparator system
If there is a large deviation from the model and (processed) sensory impressions, fears are triggered. The high density of GABA / benzodiazepine - receptors in the hippocampus is an indication that the anxiolytic effect of benzodiazepines on the regulation of the comparator system is based.
Individual evidence
- ↑ Torsten Passie et al .: Effects of different subanaesthetic doses of (S) -ketamine on psychopathology and binocular depth inversion in man . In: Journal of Psychopharmacology 17 (1) (2003) pp. 51–56, here p. 54
- ^ OS Vinogradova: Hippocampus as comparator: role of the two input and two output systems of the hippocampus in selection and registration of information. ( Memento of the original from September 4, 2011 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF; 696 kB) In: Hippocampus. Volume 11, Number 5, 2001, pp. 578-598, ISSN 1050-9631 . doi : 10.1002 / hipo.1073 . PMID 11732710 . (Review).
- ↑ J. Zanker, University of London: Example of a rotating hollow mask
- ↑ FM Leweke, C. Helmstaedter et al: Lesion Specific Differences of Binocular Depth Inversion in Patients with Temporal Lobe Epilepsy. ( Memento from October 7, 2013 in the Internet Archive )
- ↑ Wilfried Belschner: Consciousness transformation as an individual and social goal: Approaches in meditation, psychotherapy and empirical research , LIT Verlag, 2005, ISBN 978-3-8258-8522-9 . P. 90
