Hippocampus

“ The corpus callosum now first appears as a bridge between the neopallia, and its development leads to the stretching of the hippocampal formation, so that in the higher mammals the hippocampus is only found in the lower and back part of the ventricle, while the rudiments of the dorsal part remain as the striae longitudinals on the corpus callosum. The dorsal part of the original anterior commissure becomes the fornix, and the paraterminal area is modified to form the septum lucidum. ”

“ A hippocampus minor is present in all apes and monkeys, and in some Cebidae is larger relatively than in man, and absolutely larger than the hippocampus major. Of all apes and monkeys the orang-utan has a brain most like that of man; indeed it may be said to be like man's in all respects save that it is much inferior in size and weight, and that the hemispheres are more symmetrically convoluted and less complicated by minor foldings. ”

“ Hippocampus can move its eyes independently of each other, thus looking backward and forward at the same time. It would be rather difficult for a predaceous organism to take it by surprise, but on the other hand it would have little ability to fight back or flee if attacked. ”

“ The hippocampus of our public aquariums, a bony pipefish some six or eight inches in length, swimming upright, his favourite position in the water, with the general resemblance of his head to that of a horse, is very striking; anchored to the seaweed stems by their tails they dart on their prey with great quickness.
[Pg 232] Hippocampus (ἵππος, hippos, a horse; κάμπη, campe, a bending) , the steed of Neptune, had only the two forelegs of a horse, the hinder quarter being that of a dolphin. The word means “coiling horse.” ”

“ When the gravest errors respecting points so easily settled as this question respecting the posterior lobes can be authoritatively propounded, it is no wonder that matters of observation, of no very complex character, but still requiring a certain amount of care, should have fared worse. Any one who cannot see the posterior lobe in an ape's brain is not likely to give a very valuable opinion respecting the posterior cornu or the hippocampus minor. ”

“ Given that Neto1 is expressed in the CA1 region of the hippocampus (Figure 1C) , we studied synaptic transmission and plasticity at Schaffer collateral-CA1 synapses, which are widely used to investigate glutamatergic synaptic physiology [31] . We recorded field excitatory postsynaptic potentials (fEPSPs) in acute hippocampal slices from adult animals and used theta-burst pattern stimulation to induce long-term potentiation (tbLTP) , a robust form of NMDAR-dependent synaptic plasticity [32] . ”

“ Owen declared that the human brain was distinguished from that of all other animals by the backward projection of the cerebral hemispheres, so as to cover the cerebellum, and by the backward prolongation of the cavity of each cerebral hemisphere into a 'posterior horn,' with an associated 'hippocampus minor.' It is difficult to understand how an anatomist of Owen's experience can have made these statements ”

“ Every lemur which has yet been examined has its cerebellum partially visible from above, and its posterior lobe, with the contained posterior cornu and hippocampus minor, more or less rudimentary. Every marmoset, American monkey, Old World monkey, baboon, or man-like ape, on the contrary, has its cerebellum entirely hidden, and possesses a large posterior cornu, with a well-developed hippocampus minor. ”

“ However, we were not able to find evidence for the relationship in our third analysis, which focused on a smaller group of exclusively male subjects at a later date. This region may be especially deserving of attention in future investigations of the neural correlates of dominance. Although neonatal lesions of the hippocampus do not appear to affect social status in macaques [38] , the region is smaller in human individuals that have suffered stressful events particularly when they occurred in childhood [39] . ”

“ Marshall's paper above referred to. a, posterior lobe; b, lateral ventricle; c, posterior cornu; x, the hippocampus minor. systematic value, for the simple reason that, as may be concluded from what has been already said respecting cranial capacity, the difference in weight of brain between the highest and the lowest men is far greater, both relatively and absolutely, than that between the lowest man and the highest ape. ”

“ The earliest cerebral cortex is formed in connexion with the neurone-chains coming into the central nervous organ from the patch of olfactory cells on the surface of the head. The region of cerebrum thus developed is the so-called olfactory lobe and hippocampal formation. The greater part of the cerebral hemisphere is often termed the pallium, because as its development extends it folds cloak-wise over the older structures at the base of the brain. The olfactory lobe, from its position, is sometimes called the pallium basale, and the hippocampal formation the pallium marginale ”

“ In the reptilian cerebrum the hippocampal region, the pallium marginale, coexists in addition. These are both of them olfactory in function. Even so high up in the animal scale as the lowest mammals they still form one half of the entire pallium. But in the higher apes and in man the olfactory portion of the pallium is but a small fraction of the pallium as a whole. It is indeed so relatively dwarfed and obscured as to be invisible when the brain is regarded from the side or above. The olfactory part of the pallium exhibits little variation in form as traced up through the higher animals. ”

“ The brain is that portion of the cerebrospinal axis within the cranium, which may be divided into four parts—the medulla oblongata, the cerebellum, the pons Varolii, and the cerebrum—and it is covered by three membranes, called the meninges. The outer of these membranes, the dura mater, is a thick, white, fibrous membrane which lines the cavity of the cranium, forming the internal periosteum of the bones; it is continuous with the spinal cord to the extremity of the canal. The second, the arachnoid, is a delicate serous membrane, and loosely envelops the brain and spinal cord ”

“ The name cerebrum is also applied to this portion of the brain; frequently, however, the name cerebrum is used as signifying the entire mass of the brain craniad of the rhombencephalon,—therefore including mesencephalon, diencephalon, and telencephalon. The term will here be used as synonymous with telencephalon.
The cerebral hemispheres arise as two lateral outgrowths from the cranial end of the primitive forebrain. They have undergone great increase in size in the course of evolution, so as to form the larger part of the brain ”

“ In other words, there is every reason to believe that numerous "centres," in this restricted sense, exist in the brain that have as yet eluded the investigator. Indeed, the current conception regards the entire cerebral cortex as chiefly composed of centres of ultimate co-ordination of impressions, which in their cruder form are received by more primitive nervous tissues—the basal ganglia, the cerebellum and medulla, and the spinal cord.
This, of course, is equivalent to postulating the cerebral cortex as the exclusive seat of higher intellection. ”

“ From it in turn come a great many connecting nerve cells whose axons pass along the spinal cord and form nerve junctions with the motor nerve cells; and so nervous disturbances coming from the cerebellum can arouse the muscles to activity. We all know that walking or any other locomotor act, after it has once been learned, is carried on successfully without our performing any intellectual work in connection with it. What we do have to do is to start the act, and this is done through a discharge from the cerebrum ”

“ The largest nerve cells of all are found in the motor area, and are called, from their shape, the "giant pyramids". They have large dendrites and very long axons, which latter, {53} running in a thick bundle down from the cortex through the brain stem and cord, constitute the "pyramidal tract", the principal path of communication from the cerebrum to the lower centers. The motor area of the brain has no direct connection with any muscle, but acts through the pyramidal tract on the lower centers, which in turn act on the muscles. ”

“ Carpenter's theory of unconscious cerebration is in accordance with what we may call his regional physiology of the brain. He places the higher psychical functions in the convolutions of the cerebrum, but the cerebral ganglia or the sensorium is the seat of our consciousness of these functions, as it is that of external sensations, but of that class of "truly subjective sensations" which comes to the sensorium, "the result of changes in that cortical layer of the cerebrum which we have reason to regard as the seat of the higher psychical operations." ”

“ The cerebellum thus appears to be the great brain center whence are issued the commands and directions which guide the muscular actions and movements of our lives. Contrariwise, the true functions of the cerebellum are proved by experiments in which this part of the brain has been left intact while the cerebrum or true brain has been removed—an operation absolutely painless, as will presently be more particularly mentioned. A bird or higher animal in such a case will lose all power of volition; it will be deprived of sight, hearing, and other senses; it will die of hunger unless fed ”