From Big Medical Encyclopedia

ARCH OF THE BRAIN [fornix (PNA, JNA, VNA)] — the morfofunktsionalny formation of a brain of mammals representing the conduction collector of limbic system connecting structures of final, intermediate and average departments of a brain. Being the major element limbic system (see), the arch of a brain plays a noticeable role in formation of purposeful behavioural acts, selectively modulating and korrigiruya the level of emotional activity and motivational vozbuzhdeniye of an organism (see. Motivations ).

the Diagrammatic representation of a part of a hemicerebrum with the otpreparirovanny arch a vegetable pulp and a hippocampus: 1 — a leg of the arch; 2 — a body of the arch; 3 — columns of the arch; 4 — mastoidal (mamillary) bodies; 5 — front commissure; 6 — a temporal pole; 7 — an average temporal crinkle; 8 — a hippocampus; 9 — an occipital pole; 10 — a small fringe of a hippocampus; 11 — a corpus collosum.

Page of m it is formed (fig.) two arc-shaped white tyazha, to-rye in a middle part are connected among themselves, forming a body of the arch (corpus fornicis), and in front and behind disperse, forming ahead columns of the arch (columnae fornicis), and behind — legs of the arch (crura fornicis). Legs of the arch, falling to the lower horns of side ventricles (see. Ventricles of a golovky brain ), pass into fimbrias of a hippocampus (fimbriae hippocampi). The front ends of columns of the arch pass through gray matter hypothalamus (see), terminating in mastoidal bodies (see. Mamillary bodies ). Both legs of the arch at the beginning of the discrepancy and before immersion in the lower horns connect the lamina of the triangular shape consisting of cross fibers and the called commissure of the fornix (commissura fornicis). It represents as if the cross arch (fornix transversus), bunches to-rogo connect right and left hippocampus (see).

The detailed description of system of the fibers coming to S. of m from a hippocampus is given to S. R Amon-i-K akha-ly (1903, 1911) and Johnston (J. Century of Johnston, 1913). Long enough S. m considered as purely efferent way of a hippocampus, however in 20 — the 40th 20 century found that it contains also afferent fibers. Improvement of methods of identification of the degenerating axons allowed to specify extensive system of the ways connecting S. by m with ancient, old, interstitial, new bark and subcrustal formations of a brain.

All system of the fibers forming S. of m is subdivided into two big groups: pre-and postkomissu-ralny fibers.

Several conduction systems enter into prekomissuralny group. Fornikalny limbiko-gi-petalamicheskiye ways are formed by yarns, to-rye from front department of limbic area go down and cross a corpus collosum, further through septal area go to a leg of the arch, with fibers reach a cut outside mamillary, supraoptic and a periventrikulyarny hypothalamus of kernels. Temporal and septal ways consist of few group of the fibers going from temporoparietal area of bark of big hemispheres (see. Cerebral cortex ) through prekomissuralny department of S. of m to septal area. Gippokamposep-talny ways are formed by extensive system of the fibers going from a gip-pokakhmp and representing axons of its pyramidal cells, to-rye penetrate S. of m throughout and come to the septal area. Forniko-tegmentalnye ways represent group of fibers C. of the m reaching a perednemozgovy bunch and going in its structure to the central gray matter mesencephalon (see).

The Postkomissuralny group of fibers is formed in the main two ways: gippokampomamillyarny and gippokampotalamichesky. The most powerful of them gippokampomamillyarny way. It begins in a small fringe of a hippocampus and comes to an end in ipsilateralny medial kernels of mamillary ph. the Gippokampotalamichesky group of fibers also begins in a small fringe of a hippocampus and reaches a limit in nuclear formations of front thalamus (see).

Elektrofiziol. researches (see. Electrophysiology ) allowed to specify distribution of fibers C. of m. According to Green and Adee (J. D. Green, W. R. Adey, 1956), it is possible to observe the reactions caused by S.'s stimulation in m in a hippocampus, entorinalny bark, septal area, a medial dorsal kernel of a thalamus, a lateral hypothalamus and ventral department of a tire of a mesencephalon. S.'s irritation of m causes development of brake postsynaptic potentials in the majority of cells of a hippocampus.

Results elektrofiziol. researches confirm gistol. the data obtained S. Ramone-and-Kakhalem and Laurent by R. Lorente de No. They showed that S. the m contains preferential axons of pyramids of a hippocampus; and a part of these axons gives returnable collaterals directly in a hippocampus, a part — within S. to m. There is an assumption of participation of returnable collaterals in mechanisms of checking of cash afferent and trace vozbuzhdeniye, i.e. in mechanisms of formation acceptor of results of action (see). As confirmation to this assumption serve observations that neurons of the field CA3 of a hippocampus and the axons of the arch corresponding to them answer all applied irritants with the same tonic reactions. At repeated stimulation reaction weakens, after several uses of an incentive it completely disappears. Any change of a signal or conditions of its giving immediately leads to recovery of initial reaction. Thus, a significant incentive for neurons of system a hippocampus — the arch of a brain is discrepancy of afferent parameters of a signal to the prepared model of excitement, i.e. level of a mismatch; an elekt-roentsefalografichesky correlate of reaction of a mismatch in system a hippocampus — the arch of a brain serves a theta rythm. It is established that the theta rythm appears at all orientation and search purposeful responses whereas at the automated behavior it is absent. According to a number of researchers, the theta rythm reflects a motivational component in purposeful behavior: the gippokampofornikalny theta rythm amplifies in process of increase of motivation and decreases in process of satisfaction of requirement.

Numerous data on S.'s role of m in formation of emotional and motivational states are saved up. At the same time the most various methodical receptions were used: electric stimulation, cold blockade, S.'s destruction of m, pathoanatomical and wedge, observations. Heterogeneous influence of S. of m on manifestations of emotional reactions was proved. The irritation of a body and S.'s legs of m causes both reactions of rage and attack, and fear reaction and concealment; at dekortitsirovanny animals, at to-rykh S. the m remained safe, the threshold of aggressive reactions considerably raised. On the other hand, N. N. Bragina (1966) described composite pseudo-defensive reactions with the expressed affective coloring at patients with the tumors of a hippocampus anyway breaking S.'s intaktnost of m. Data on S.'s participation were obtained by m in formation of emotional and motivational reactions in experiments on self-stimulation. It is established that points, from to-rykh are caused effects self-stimulations (see), are located on all length of S. of m. Close connection between the frequency of self-stimulation and level of various motivational motives is found (e.g., hunger, thirst). S.'s section of m breaks process of fixing of biologically significant information, complicating course of the main stages of the behavioural act: stages of afferent synthesis, decision-making and formation of the device of an acceptor of result of action. As a key to understanding of a role of S. of m in adaptive behavior serve its close functional linkages with various formations of limbic system.

S.'s role m in physiology and pathologies of the person, methods of a research and use of their results in to clinicodiagnostic practice are a subject of studying of the researchers working in the field of biology and medicine (see. Brain , Conduction paths ).

Bibliography: Anokhin P. K. Biology and neurophysiology of a conditioned reflex, M., 1968; Vinogradova O. S. Hippocampus and memory, M., 1975; To the island and l I. N. and Sarkisov G. T. Motive conditioned reflexes after injury of a hippocampus and the arch at cats, Zhurn. vyssh. nervn. deyateln., t. 33, century 1, page 20, 1983, bibliogr.; Neurophysiological mechanisms of behavior, under the editorship of B. F. Lomov, etc., page 129, M., 1982; Modern problems of electrobiology, the lane with English, under the editorship of L. M. Chaylakhyana, page 241, M., 1964; Fox of Page A. Stria terminalis, longitudinal association bundle and precommissural fornix fibers in cat, J. comp. Neurol., v. 79, p. 277, 1943; G u i 1 - 1 e r y R. W. Degeneration in the post-commissural fornix and t | ie mamillary peduncle of the rat, J. Anat. (Lond.), v. 90, p. 350, 1956; Limbic system symposium, Limbic mechanisms, continuing evolution of limbic system concept, ed. by K. E. Livingston a. O. Hornykiewicz, N. Y., 1978; Lorente de No R. Studies on structure of cerebral cortex, J. Psychol. Neurol. (Lpz.), Bd 46, S. 113, 1934; N an u t a W. J. H. An experimental study of the fornix system in the rat, J. comp. Neurol., v. 104, p. 247, 1956; Woods B. T., Schoene W. Kneisley L. Are hippocampal lesions sufficient to cause lasting amnesia? J. Neurol. Neurosurg. Psychiat., v. 45, p. 243, 1982, bibliogr.

V. O. Albert.