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Read this article to learn about the physical basis of mental life.
Physical Basis of Mental Life # Introduction:
It is an accepted fact that there is a close relation between mind and body. Injury to or disease of part of brain produces mental disorder or loss or consciousness.
Some of the influences of bodily conditions on mental processes are matters of common observation.
For example, the mental stimulation by drinking strong coffee, or the various effects of alcohol at different stages of inebriation, the sedative influence of bromide and other sleeping drugs are common facts. As to the influence of mental processes on bodily conditions—under hypnotic suggestion a strong pinprick may not hurt at all; and that ordinary walking suggestion may banish fatigue.
We also find the advancement of behaviour of animals is connected with development of their nervous system. The evolution of brain, in particular, corresponds to that of intelligence. Emotional life is closely connected with thalamus, sympathetic and parasympathetic system. There are many such instances.
There are different theories regarding the relation between mind and body. There is the theory of psychophysical parallelism, and there is also the theory of interactionism. Actually the solution of the final relation between mind and body is beyond the scope of psychology.
It becomes a metaphysical problem, as it is difficult to understand how mind and body, being two entirely different entities in nature, could act and interact upon one another.
The philosopher Spinoza (1632-1677) gave the theory of parallelism. Mind and body, both being expression of God, the ultimate reality, would move in parallel lines. “Parallelism in its extreme form asserts a strict point- to-point correspondence between mental processes and a certain group of physical processes, but denies interaction between the two series. The doctrine of interaction couples the assertion of causal interaction with the denial of parallelism. It is contended by the interactionist either that certain mental occurrence has no bodily correlative or that certain characteristic features in conscious life have no parallel in the bodily process.”
Each of these doctrines has various forms based on the problem of causation. However, as Stout points out, “Neither parallelism nor interaction in the forms, in which these doctrines have generally been expressed, provides a satisfactory account of the relations between physical and psychical facts. There is a certain parallelism between physical and mental change, but the doctrine of strict point-to-point correspondence is not borne out by the empirical evidence nor does it admit any simple hypothetical formulation. Moreover, it leaves the connection of body and mind wholly mysterious. On the other hand, the doctrine of interaction is not without its difficulties. If interaction occurs, it is of an entirely different kind from the interaction of physical things, and ultimately the connection is as mysterious as it is on the alternative theory. The problem is, in fact, largely extra psychological. Its solution depends in part on metaphysical questions with regard to the nature of causation and the ultimate nature of matter and mind.”
It has been pointed out that in both psychological and physiological investigations, the concepts of psychology and physiology must be kept distinct, and the facts of each science be explained only in terms of that science. But this principle does not exclude psycho-physical investigations, and we have ‘physiological psychology’. Still the independence of psychology and physiology must be preserved. In this respect the offender is psychology.
As Dr. Bernard Hart’ says, “No physiologist would consent to admit ‘ideas’ as active elements in the sequence of changes which lake place in the nervous system. But Prof. Fullerton points out that physiologists are also not free from this error.”
However, the psychologist may depend on Professor Titchener’s words that “for all practical purposes we may continue to speak of our mental grief as the cause of our physical tears, just as the astronomer does not scruple to talk, with the rest of us, about sunrise and sunset. What we have to guard against is not the phrasing of these statements, but their popular interpretation.”
However, mental processes and central nervous systems are closely related. It has been substantiated by findings of physiology, pathology and anatomy. Hence, in psychology we have to understand the function of the nervous system.
Physical Basis of Mental Life # Functions of the Nervous System:
The Neuron:
The individual is an organism, and not a disembodied spirit. When he sees, learns, thinks or desires, he is using his nervous system. Here we take the help of physiology. The nervous system consists of about 100 billion of neurons which are its simplest parts. The neuron is the structural unit of die nervous system.
A neuron is a nerve cell which has two types of branches—one single axon and a number of dendrites. The dendrites are short tree like branches while the axon is smooth and slender and may be over a meter long. The function of the dendron is to receive the nerve impulse and transmit it to the cell, while that of the axon is to conduct the nerve impulse to the muscle or gland.
The cell body consists of four parts, the cell wall or the tough outer coat, the central liquid part called protoplasm, which looks like the white of an egg called the nucleus, and smaller particles floating on the nucleus called the nucleoli.
From the point of view of function, neurons are of two kinds:
Sensory or afferent and motor or efferent. The cell body of an afferent neuron is situated in some or other sense organ, while that of an efferent neuron is situated in some motor centre of the brain or the spinal cord. There is a third kind of neuron from the point of view of its function. It connects afferent and efferent neurons, so it may be called connective neuron, these are central, as these are situated in the centre of the central nervous system.
Stimulation:
When a neuron is stimulated, a nervous impulse of electrical character is produced. A nerve impulse is an energy change in the neuron. A stimulus is a “change in the environment of nervous tissue which is sufficient to excite it”.
Stimulation does not mean the transmission of energy into the reacting nerve cell. The energy change is contained within the neuron. It is simply released by the dendrites. It is then transmitted by way of the axon. End organs have their adequate stimulus to which they most easily react. For example, the eye reacts to light, and the skin to temperature changes.
It is said that the nature of the nervous impulse is partly electrical, partly chemical and partly thermal. A nervous section is called a nerve current or nervous impulse, because electrochemical waves are produced in the process of nervous action.
Nervous impulses are governed by a number of laws. There is the law of:
(1) Excitability or irritability. This is a fundamental character of nerves. Each neuron is excited by its adequate stimulus. For example, photon waves stimulate optic nerve.
(2) Secondly, the neuron conducts the nerve impulse, after excitation to the cell-body or to the central nervous system. This is the law of conductivity.
(3) In conducting the nerve impulse, the neuron gets fatigued so that no further stimulus may excite it. This is known as refractory period. Some regard this fatigue as due to synaptic resistance.
(4) Another is the law of forward conduction. The course of a nervous impulse is from the axon to the Dendron of a neuron, or from a sense organ to some centre of the nervous system and from that centre to some muscle or gland. It is not conducted in the opposite direction, i.e. from a muscle or gland to the centre, or from the centre to a sense organ, or from a Dendron to an axon.
A nervous impulse courses from the neuron of an afferent or a sensory nerve to that of an efferent or motor nerve. The neuron path conducted frequently becoming a path of least resistance. If two or more nerve impulses produce the same reaction simultaneously, they combine together to make the reaction stronger. This is the law of summation.
(5) If, on the other hand, two or more nerve impulses move simultaneously towards opposite direction, then one inhibits the other. This is the law of inhibition. Thus, both facilitation and inhibition are the characteristics of the nervous impulse.
(6) Lastly, the All and none law constitutes another important characteristic of the nervous impulse. A neuron is either excited or not. If excited, it works with all energy, if not, it does not respond at all.
The Synapse:
Neurons begin life as separate, and remain separate cells. The form of connexion, by contact only, is called a synapse. The synapse is not a physical object like the neuron. It is the point of junction between the axon of neuron and the Dendron of the next or two neurons in the conduction path of a nerve impulse. The function of a synapse is to resist the nervous impulse, as it is conducted from one neuron to a Dendron of another. The degree of resistance depends on the frequency of the movement of the nerve impulse.
All habit and learning becomes difficult at the beginning because of synaptic resistance. Repeated practice reduces the resistance.
The Reflex Arc of the Stimulus Response Mechanism:
A reflex action is an unlearned, unconscious, immediate and uniform response to a stimulus exciting the peripheral extremity of a sense organ. The total chain constitutes the reflex arc. “The neural link in this circuit embraces at least two neurons, the afferent neuron which conducts the impulse from the receptor, and the efferent neuron, conducting it outward to the effector. The two are united only by a synaptic point of junction.” The course takes the form of a circuit or arc. The nervous path so traversed by the reflex is called the Reflex Arc.
So there are five elements in the reflex are:
(1) Receptive nerve-endings, which are situated at the periphery of a sense organ,
(2) The afferent or sensory nerve which carries the impulse to the nerve centre in the spinal cord or the brain,
(3) The central nervous system which consists of the spinal cord and the brain,
(4) The efferent or motor nerve which carries the motor nerve impulse to a muscle or a gland,
(5) The effector organ consisting of muscles or glands, which produces movement of secretion.
There are different levels of reflex arc. Simple reflexes consist of few reflex arcs, while higher or complex reflexes have a larger number of reflex arcs. Simple reflexes like winking, knee-jerk, etc. are simple spinal reflexes, while, sucking is a cortical reflex centered in the brain. There are three levels or hierarchy of reflex arcs—primary or spinal level, the secondary or intermediate level, and cortical reflex arcs. Association areas of organisms are the centre of cortical arcs. These are compared to very distant telephone calls.
Reflexes which mean sensorimotor arcs are the simplest functional units of the nervous system, just as the neuron is the simplest structural unit of the nervous system. The reflexes may be organised in another way—in chains of greater or less complexity. One reflex may follow another in virtue of the fact that the response to one stimulus inevitably brings about the situation which evokes a second, the response to which provokes a third and so on, until a specific cycle is completed. Stout gives an example of such a chain of reflexes in the case of ‘dart reflex’ of a frog.
The presence of a fly before the eyes reflexly evokes the act of protruding the tongue. If the fly is caught, the mouth is closed in a similar reflex way. This, in turn, automatically leads to swallowing, and swallowing itself involves series of reflex actions organised in a chain. The central nervous system consists of the brain, the spinal cord and the peripheral system. There is the autonomous nervous system as well, though the autonomous nervous system is not directly connected with the central system.
Physical Basis of Mental Life # Structure and Function of the Spinal Cord:
The spinal cord lies with the spinal column or backbone, at its upper end it passed into the head where it branches out into what is known as the medulla oblongata or ‘bulb’. The spinal axis as a whole consists of five parts, viz. the cervical, the thoracic, the lumber, the sacral and the coccyx.
These are all made of bones or vertebrae, altogether there are thirty-three or thirty-four bones. The main function of the spinal cord is that it is the centre of controlling reflex actions and some other acquired or learned actions which by repeated practice become habitual.
Physical Basis of Mental Life # The Parts and Structure of the Brain:
The brain stem and spinal cord taken together are the axis of the whole nervous system.
There are three parts of the brain:
1. The hind brain,
2. The midbrain and
3. The fore-brain.
(1) The hind brain consists of three parts. The medulla oblongata, the pons and the cerebellum. The spinal cord broadens out and looks like the stem of a flower as it enters the brain. This stem-shaped lowest part of the brain is called the medulla oblongata or the brainstem or brain bulb. On both sides and bottom of the medulla is situated one principal part of the hind- brain, called cerebellum.
The cerebellum is divided into two lobes, the major function of cerebellum is to coordinate and control activities involving muscles, like walking, speaking, swimming, cycling, etc. Its main task is to maintain the balance and equilibrium of the body. Too much drinking of alcohol affects the cerebellum. In front of the medulla is situated a bundle of nerves crosswise called the pons. The sensory and motor nerve impulses pass up and down through this centre.
(2) The midbrain connects the medulla oblongata with the forebrain. So, sometimes it is called the brainstem. In case of lower animals the mid-brain works, and their sensations and muscular activities, being undifferentiated, depend on this mid-brain. So it is also called old-brain. Pituitary gland, thalamus and hypothalamus are connected with it.
(3) The cerebrum is the principal forepart of the brain. The cerebrum is divided into two hemispheres.
The functions and structure of the brain have superbly been described by Roger Penrose, Professor of Mathematics at the University of Oxford, in relation to a discussion as to the seat of consciousness in brain or elsewhere. A summary of the same is given below.
The brain is a magnificent structure that controls our actions and evokes our awareness of the world around. It has a very intricate structure and sophisticated organisation. The large convoluted (and most porridge like) portion on the top is referred to as the cerebrum. It is divided clearly down the middle into left and right cerebral hemispheres, and considerably less clearly front and back into the frontal lobe and three other lobes; the parietal, temporal and occipital.
Further down, and at the back lies a rather smaller, somewhat spherical portion of the brain perhaps resembling two balls of wool—the cerebellum. Deep inside, and somewhat hidden under the cerebrum lie a number of curious and complicated looking different structures – the pons and medulla (including the reticular formation) which constitute the brainstem, the thalamus, hypothalamus, hippocampus, corpus callosum, and many other stranger and oddly named constructions.
The cerebrum is the largest part of the human brain, it is also larger, in its proportion to the brain as a whole, in man than in other animals. The cerebellum is also larger in man than in other animals. The cerebrum and the cerebellum have comparatively these outer surface layers of grey matter and larger inner regions of white matter.
These regions of grey matter are referred to as, respectively, the cerebral cortex, and the cerebellar cortex. The grey matter is where various kinds of computational task appear to be performed while the white matter consists of long nerve fibres carrying signals from one part of the brain to another.
Functions:
Various parts of the cerebral cortex are associated with very specific functions. The visual cortex is a region within the occipital lobe, right at the back of the brain, and is concerned with the reception and interpretation of the vision (while eyes are situated right at front of the head).
The right cerebral hemisphere is concerned exclusively with the left hand side of the body, while the left cerebral hemisphere- is concerned with the right hand side of the body so that virtually all nerves must cross over from one side to the other as they enter or leave the cerebrum. In case of visual cortex, it is not that the right side is associated with the left eye, but with the left hand field of vision of both eyes.
Similarly, the left visual cortex is associated with the right hand field of vision of both eyes. This means that the nerves from the right hand side of the retina of each eye must go to the left visual cortex. Signals from the ear also tend to cross over to the opposite side of the brain in this curious way.
The right auditory cortex (part of the right temporal lobe) deals mainly with sound received on the left and the left auditory cortex, on the whole, with sounds from the right. Smell seems to be an exception to the general rule. The right olfactory cortex, situated at the front of the cerebrum (in the frontal lobe which is itself exceptional, for a sensory area) deals largely with right nostril and the left with left nostril.
The sensations of touch have to do with region of the parietal lobe referred to as the somatosensory cortex. This region occurs just behind the division between the frontal and parietal lobes. There is a very specific correspondence between the various parts of the surface of the body and regions of the somatosensory cortex. This correspondence is sometimes graphically illustrated in terms of what is referred to as the ‘somatosensory homunculus’ which is a distorted human figure pictured as lying along the somatosensory cortex.
The right somatosensory cortex deals with sensations from the left hand side of the body, and the left, with the right hand. There is a corresponding region of the frontal lobe, lying just in front of the division between the frontal and parietal lobes, known as the motor cortex. This is concerned with activating the movement of different parts of the body, and, again, there is a very specific correspondence between the various muscles of the body and the regions of motor cortex. We now have a ‘motor homunculus’ to depict this correspondence. The right motor cortex controls the left hand side of the body, and the left motor cortex, the right hand side.
The regions of the cerebral cortex just referred to (the visual, auditory, olfactory, somatosensory, and motor) are called primary, since they are the most directly concerned with the input and output of the brain. Near to these primary regions are the secondary regions of the cerebral cortex which are concerned with a more subtle and complex level of abstraction.
The sensory information received by the visual, auditory, and somatosensory cortexes is processed at the associated secondary regions, and the secondary motor region is concerned with the conceived plans of motion which get translated into more specific directions for actual muscle movement by the primary motor cortex (except olfactory). The remaining regions of the cerebral cortex, are referred to as tertiary (or the association cortex).
It is largely in these tertiary regions that the most abstract and sophisticated activity of the brain is carried out. It is here in conjunction, to some extent, with the periphery—that the information from various different sensory regions is inter-wined and analyzed in a very complex way, memories are laid down, pictures of the outer world are constructed, general plans are conceived and evaluated, and speech is understood or formulated.
Speech is particularly interesting because it is normally thought of as something very specific to human intelligence. It is curious that (at least in the vast majority of right-handed people and in most left-handed people) the speech centres are mainly just on the left-hand side of the brain.
The essential areas are Broca’s area, a region in the lower rear part of the frontal lobe, another called Wernicke’s area, in and around the upper rear part of the temporal lobe. Broca’s area is concerned with the formulation of sentences, and Wernicke’s area with the comprehension of language.
Damage to Broca’s area impairs speech but leaves comprehension intact, whereas damage to Wernicke’s area, speech is fluent but with little content. A nerve bundle called the actuate fasciculus connects the two areas. When this is damaged, comprehension is not impaired and speech remains fluent, but comprehension cannot be vocalized.
So far, it is a brief account of the cerebrum’s functions. The brain’s input comes from visual, auditory, tactile, and other signals which first register in the cerebrum at the primary portions of (mainly) the rear lobes (parietal, temporal and occipital). The brain’s output in the form of activating movements of the body is mainly acted by primary portions of the frontal lobes of the cerebrum.
Here we have a picture of superb computing device. However, besides cerebrum, there is cerebellum, whose function is precise coordination and control of the body—its timing, balance, and delicacy of movement. During the first acquiring of a skill, the cerebrum is in charge, but when the skill is mastered, and has become a ‘second nature’, it is the cerebellum that takes over.
There are other parts of the brain. The hippocampus plays a vital role in laying down long-term (permanent) memories, the actual memories being stored somewhere in the cerebral cortex—probably in many places at once. The brain can also hold images for sometimes. But to recall such images, after they have left one’s attention, it is necessary that they are laid permanently somewhere. For this hippocampus is necessary.
The corpus callosum is the region via which the right and left cerebral hemispheres communicate with one another. The hypothalamus is the seat of emotion- pleasure, rage, fear, despair, hunger, and it mediates between both the physical and mental manifestations of emotion.
There is a continuous flow of signals between the hypothalamus and different parts of the cerebrum. The thalamus acts as an important processing centre and relay station, and it conveys many of the nerve inputs from the external world to the cerebral cortex. The reticular formation is responsible for the general state of awareness involved in the brain as a whole, or in different parts of the brain. There are numerous pathways of nerves connecting these and many other vitally important areas.
In short, to sum up the brain’s organisation as a whole, the different parts of the brain are classified into three regions which taken in order, moving away from the spinal column, are called the hind brain (or rhombenecephalon), the mid-brain (or mesencephalon), and the forebrain (or pros-encephalon). In the developing early embryo, one finds these three regions in this order as three swellings at the end of the spinal column.
The one at the very end—the developing forebrain—sprouts two bulbous swellings, one on either side, which becomes the cerebral hemispheres. The fully developed forebrain includes many important parts of the brain—not just the cerebrum, but the corpus callosum, thalamus, hypothalamus, hippocampus, and many other parts as well.
The cerebellum is part of the hind brain. The reticular formation has one part in the mid-brain and another part in the hind brain. The forebrain is the ‘newest’ in the sense of evolutionary development, and the hindbrain is the most ‘ancient’.
Where is the Seat of Consciousness ?
There are different views and controversies with regard to the relation of the state of brain to the phenomenon of consciousness. There is remarkably little consensus of opinion for a phenomenon of such obvious importance. It is clear that all parts of the brain are not equally involved in producing awareness.
Cerebellar control is concerned more with automatic activities. Same may be said about unconscious reflex actions which are controlled not by the brain but by the upper part of the spinal column. So there is the tendency to infer that the phenomenon of consciousness is likely to have more to do with the action of the cerebrum than with the cerebellum or the spinal column.
At the same time it is not clear at all that the activity of the cerebrum must itself always impinge upon consciousness:
1. Views of US-Canadian neurosurgeon, Wilder Penfield (who, in the 1940s and 1950s, was responsible for much of the detailed mapping of the motor and sensory regions of the human brain) have argued that one’s awareness is not associated with the cerebral activity. He suggested, on the basis of his numerous brain operations, that some regions of the upper brain stem, consisting largely of the thalamus and the mid-brain (the reticular formation) may be regarded as the seat of consciousness.
His view was that consciousness is a manifestation of activity of the upper brainstem, but since in addition there needs to be something to be conscious of, it is not just the brain stem that is involved but also some region in the cerebral cortex which is at that moment in communication with the upper brainstem, and whose activity represents the subject (sense impression or memory) or object (willed action) of that consciousness..
2. Another viewpoint (O’Keefe, 1985) is that it is the action of the hippocampus that has more to do with the conscious state. It was mentioned earlier that the hippocampus is the seat of long-term memories.
3. Others would hold that it is the cerebral cortex itself which is responsible for awareness, since the cerebrum is man’s pride (though dolphin’s cerebrum is as big), and since the intellectual activities are more closely associated with the cerebrum it is here that the soul of man resides.
This is also the conclusion of the point of view of strong A2, for example, if awareness is merely a feature of the complexity of an algorithm—or perhaps with its ‘depth’ or some kind of ‘level of subtlety’—then according to the strong A1 view, the complicated algorithms being carried out by the cerebral cortex would give the region the strongest claim to be that capable of manifesting consciousness.
Many split-brain operations also indicate that there may not be a unique ‘seat of consciousness’, but it is evident that some parts of the cerebral cortex are more associated with consciousness than others.
Physical Basis of Mental Life # Brain and Computer:
Brain research has contributed to, as well as benefited from, advances in computers. The brain and the nervous system are marvelously effective in processing sensory information, relying on complex connections between neurons that give the brain the crucial ability to recognise patterns and learn them. Japan is trying to develop computers to mimic the human brain.
Their project will seek to develop computers that are able to perform some of the tasks that people do intuitively to survive the “real world” like recognising objects and scenery and making decisions even when all facts are not known.
So far we have discussed mainly about the central nervous system and the working of the brain. There is the autonomic nervous system as well. The functions of the autonomic nervous system: it regulates the automatic vital processes of digestion, respiration, circulation and reproduction.
The autonomic nervous system can be divided into three parts:
Upper, middle and lower
(1) The upper or cranial autonomic helps digestion by stimulating the ductile glands of the stomach which pours out the gastric juice, and its muscles help in churning the food and it also slows the heart, and thereby tends to lower the muscular action of the limbs.
(2) The middle autonomic or the sympathetic has diametrically opposite functions. It checks digestion by stopping the gastric secretions and the churning of the muscles, and it hastens the heart, thereby increasing the blood secretion. It also causes the secretion from the endocrine or ductless glands, called the adrenal glands, lying near the kidneys. This secretion produces energy, and very much active in strong emotions, like fear and anger.
(3) The lower or sacral autonomic stimulates the sex or reproductive glands. It is the brain which coordinates the sympathetic and the parasympathetic systems.
Physical Basis of Mental Life # Glands:
Glands are the internal effectors inside the body producing liquids and chemicals. There are two classes of glands: the ductless or endocrine glands, which secrete chemicals called hormones directly into the blood vessels. These are the pituitary, thyroid, parathyroid and adrenal glands.
In short, the nervous system with its effectors and receptors is the mechanism through which the organism reacts with the world. The behaviourists tried to reduce all the reactions to the formula S-R. But it is too simple. Woodworth gives the formula W-S-OW-R-W, in which W stands for world of objects, S for stimulus, OW for organism as he knows the world, R for response and W for world.
