Hippocampal Formation of Brain as Detector-Coder of Temporal Patterns of Information

Publisher Website
Google Scholar
Abstract
HIPPOCAMPAL FORMATION OF BRAIN AS DETECTORCODER OF TEMPORAL PATTERNS OF INFORMATION TURNER McLARDY, M.B.E., B.Sc, M.D., D.P.M.* I. Thesis The allocortical hippocampal formation, the isocortical cingulate gyrus, the amygdaloid nuclear complex, and the brain-stem ramifications ofthe fornix together form the main substance ofthe "limbic lobe" ofthe mammalian cerebral hemisphere. In recent years this complex has lost its claim to be called the "rhinencephalon," wholly concerned with the functions ofsmell, and has instead been variously deduced to be, in whole or in part, "a harmonious mechanism which may elaborate the functions ofcentral emotion"; "a modulator ofcomplex somatic, autonomic, and behavioral mechanisms integrated in subcortical structures"; "the visceral brain, concerned largely with mechanisms essential to preservation of the self and the species"; and "part of a broad positive motivational system." These descriptive conclusions affirm the common-sense expectation that, because it possesses the phylogenetically most invariant parts of the mammalian cortex, the limbic lobe probably contains the anatomical structures most proximately concerned with the innate and the learning mechanisms that operate the basic behavioral requirements of the mammal—-namely, species preservation through mating and rearing ofyoung and self-preservation through nutriton and countering ofthreats. The following preliminary, condensed presentation attempts to break through such laudable, but relatively superficial, structure-function identification to a deeper level of "causal explanation" in terms of specific microstructural "whats" and organizational "hows" (within a framework ofnon-teleological, ethological "whys"). It is the first sample airing ofa comprehensive new interpretation ofall the constant morphological char- * Research Laboratory, St. Andrew's Hospital, Northampton, England. 443 t. % f® ©® ®® H Fig. i.—Diagrammatic para-transverse section of the hippocampal formation in one cerebral hemisphere ofa mammal, showing proposed basic circuitry for the detection and coding of intensity gradients and of complex temporal patterns of information. Only those representative neuronal somata and processes discussed in the present text are illustrated. Full lines represent dendritic processes ; interrupted lines, axonal processes; G. granular cell offascia dentata; X, mossy system synapse; ooo, functional group ofCA3 pyramids; 9 , CAi pyramid; © , subiculum cell; f, presubiculum cell; ®, medial entorhinal cortex; O, mid- and lateral entorhinal cortex; A, amygdala; F, fornix and hippocampal commissures; S, basal striatum; T, temporal isocortex. acteristics ofthe mammalian brain, arrived at after some eight years ofsuccessive digestion and elimination of the conceptual approaches to brain mechanics proposed especially by Warren McCulloch, by Grey Walter, by Ross Ashby, and by Sholl and Uttley and finally developed largely within the conceptual principles being evolved and used by certain British electronic engineers concerned with control mechanisms which "learn to behave" probabilistically from goal-directed experience. It is fairly well established that the ipsilaterally derived inputs to the granular cells of the fascia dentata are the axons (i, Fig. i) of neurons whose somara lie within the ipsilateral medial entorhinal cortex; these axons constitute those thinly myelinated elements of the "temporo-ammonic perforant path" that cross the hippocampal fissure to course circumferentially , in an outer zone, within the molecular layer ofthe fascia dentata, where they synapse with the dendrites of the granular cells (whether in successive synapses-de-passage fashion or in single point-topoint fashion has apparently not been determined). Contralaterally derived inputs to the inner zone ofthe granular-cell dendrites have been less confidently deduced (i) to course—by way ofthe left and right posterior pillars ofthe fornix and the ventral hippocampal commissure, and then through the hilum of the fascia dentata and the granular-cell layer—from the subiculum ofthe opposite hemisphere {za and 2b, Fig. 1). Neither the input to these medial entorhinal cells nor the input to the subiculum is at all established. I postulate, on the basis ofmicroscopic observations and other evidence which will be described elsewhere, that the main input to both, in each hemisphere, is derived from bifid collaterals (5, Fig. 1)—which bypassthe thalamus—fromallipsilateralchannelsofallmodalities ofsensation and that topos-related intra-modal channels and the different modalities are projected systematically, predominantly axiaily, along the molecular layer ofthe fascia dentata. It is well established that axons of granular cells of the fascia dentata course out ofthe hilum ofthe fascia dentata into the "regio inferior," CA3, ofgiant pyramids ofthe hippocampus to make a succession...

This publication has 0 references indexed in Scilit: