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Brain, The and Reality (2020 Edition)



Purposes of Having Brain
Evolution of Brains
Human Brain Structure
The Malleable Brain
Senses
Memory
Reality

Purposes of Having Brain

Heterotrophs There are two types of living organisms in this world. The autotrophs (self-nourishment) live on inorganic materials, while the heterotrophs (different-nourishment) must make use of resource that comes from other organisms in the form of fats, carbohydrates and proteins (Figure 01).

Brains exist because the distribution of resources necessary for survival and the hazards that threaten life vary in space and time. There would be little need for a nervous system in an immobile organism or an organism that lived in regular and predictable environment. Brains are informed by the senses about the presence of resources and hazards; they evaluate and store this input and generate adaptive responses executed by some mechanisms.

Figure 01 Heterotrophs

Chemical Gradient Some of the most basic features of brains can be found in bacteria because even the simplest motile organisms must solve the problem of locating resources and avoiding toxins. They sense their environment through a large number of receptors, which are protein molecules embedded in the cell wall. Action is taken in response to the inputs such as the gradient of the chemicals (see Figure 02). Thus memory is required to compare the inputs from different locations. The strength of the signal is modulated by immediate past experience. This in turn regulates the strength of the response sent by chemical messengers from the receptor to the flagellar motors. Thus even at the unicellular level, the bacteria have already possessed the ability to integrate numerous analog inputs and generate a binary (digital) output of stop or go.

Figure 02 E. coli's Response to Chemical Gradient [view large image]

Therefore even at such primitive level, the brain would modify the signals from the environment and generates a response, i.e., its survival does not directly depend on perceiving the real thing. It doesn't care about reality so cherished by philosophers.

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Evolution of Brain

Neurons and Nerve In multicellur organism, cells specialized for receptor function are located on the surface. Other cells specialized for the transmission and analysis of information are located in the protected interior and are linked to effector cells, usually muscles, which produce adaptive responses (Figure 03). As do unicellular organisms, neurons integrate the diverse array of incoming information from the receptors, the resultant my induce the firing of an action potential (when the summation is above a threshold level) to initiate a response. Once the threshold for generating an action potential is reached, the signal is always the same, both in amplitude and shape (a nerve consists of many neurons, it does not obey the all-or-none law, see "Neurons and Nerves").

Figure 03 Neurons and Nerve
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Action potentials and voltage-gated sodium channels are present in jellyfish, which are the simplest organisms to possess nervous systems. The development of this basic neuronal mechanism set the stage for the proliferation of animal life that occurred during the Cambrian period. Among these Cambrian animals were the early chordates, which possessed very simple brains. Some of these early fish developed a unique way to insulate their axons by wrapping them with a fatty material called myelin, which greatly facilitated axonal transmission and evolution of larger brains. Some of their descendants, which also were small predators, crawled up on the muddy shores and eventually took up permanent residence on dry land. Challenged by the severe temperature changes in the terrestrial environment, some experimented with becoming warm-blooded, and the most successful became the ancestors of birds and mammals. Changes in the brain and parental care were a crucial part of the set of mechanisms that enabled these animals to maintain a constant body temperature.

Table 02 below shows the Evolution of Invertebrate Brain from Sponge to Arthropods.

Phyla Brain Structure
Sponges None. But have nervous components such as synapses and neuro-transmitters. See "Origin of Nervous System".
Cnidarians They have nervous network connecting outer and inner layers of cells; also possess light-sensitive cells.
Flatworms There is a small brain and two lateral nerve cords joined by cross branches.
Roundworms The brain is in the form of ganglia. There are nerve cords along the body connected by commissures.
Cephalopods They have the most complex brains of any invertebrates, very good eyesight.
Annelids There is a ventral nerve cord and lateral nerves. The brain is just a ganglion.
Arthropods The nervous system includes a dorsal brain and nerve cords, ... - similar to the Annelids' but more advanced.

Table 01 Evolution of Brain (click small icon to view large image of the nervous system)

Figure 04 below shows the Evolution of Vertebrate Brain from Fish to Mammals.



Animals with large brains are rare -- there are tremendous costs associated with large brains (the active human brain consumes about 20 watts). The brain must compete with other organs in the body for the limited amount of energy available, which is a powerful constraint on the evolution of large brains. Large brains also require a long time to mature, which greatly reduces the rate at which their possessors can reproduce. Because large-brained infants are slow to develop and are dependent on their parents for such a long time, the parents
Maternal Care must invest a great deal of effort in raising their infants. Young reptiles function as miniature versions of adults, but baby mammals and birds are dependent because of their poor capacity to thermo-regulate, the consequence of their need to devote most their energy to growth. Most mammals solve the problem with maternal care (Figure 05), shelter, warmth, and milk. In most birds, both parents cooperate to provide food and shelter to their young. The expanded forebrain and parental care provide mechanisms for the extra-genetic transmission of information from one generation to the next. This transmission results from the close contact with parents during infancy, which provides the young with opportunity to observe and learn from their behavior; the expanded forebrain provides an enhanced capacity to store these memories. The expanded forebrain and the observation of parents are probably necessary for the establishment of

Figure 05 Maternal Care
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successful care giving behavior itself, as the young mature into adults that will in their turn have to serve dependent young. During the period of infant dependency, baby mammals and birds play, behavior that may be essential for the development of the forebrain. The baby's playful
interaction with its environment may serve to provide the initial training of the forebrain networks that ultimately will enable the animal to localize, identify, and capture resources in its environment.

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Human Brain Structure

Brain 1 Brain 2 The human brain can be divided into three parts: the hindbrain, which has been inherited from the reptiles; the limbic system, which was first emerged in mammals; and the forebrain, which has its full development in human. Different views of the human brain are shown in Figures 06, 07, and 08. Table 02 lists the functions of the different parts of the human brain. The brain is separated into two hemispheres. Apart from a single little organ -- the pineal gland in the centre base of the brain -- every brain module is duplicated in each hemisphere. The left brain is calculating, communicative and capable of conceiving and executing complicated plans -- the reductionistic brain; while the right one is considered as gentle, emotional and more at one with the natural world -- the holistic brain.

Figure 06 Human Brain 1

Figure 07 Human Brain 2
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Brain 3 The cerebral cortex is covered in a thin skin of deeply wrinkled grey tissue called the grey matter (densely packed neurons for information processing). Each infold on the surface is known as a sulcus, and each bulge is know as a gyrus. While the white tissue inside are axons -- tentacles which reach out to other cells (to relay information). The cortex can be broken down into many functional regions, each containing thousands of cortical columns (oriented perpendicular to the cortical surface). Columns are typically about half a millimeter in diameter and contain about one hundred thousand neurons. They are the units of cognition (the mental process of acquiring knowledge by the use of reasoning, intuition or perception).

Figure 08 Human Brain 3
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Table 02 below lists the location and functions of the major components in the human brain.


Structure Location Functions
Hindbrain
(Reptilian Brain)
   
Medulla at the top of the spinal cord controls breathing, heart rate, and blood pressure.
Pons above the medulla regulates sensory information and facial expressions.
Cerebellum at the lower rear controls movement, coordination, balance, muscle tone, and learning motor skills.
Reticular Formation a network of nerves extends from the medulla to the cerebrum monitors the general level of activity in the hindbrain and maintains a state of arousal; essential for the regulation of sleep and wakefulness.
Midbrain (superior & inferior colliculus) above the pons between the hindbrain and forebrain relays sensory information from the spinal cord to the forebrain.
Pineal Gland on top of the midbrain behind the thalamus (the third eye¤ for fishes, amphibians, reptiles, and some birds) involves in circadian and circannual rhythms; possibly involves in maturation of sex organs.
Limbic System
(Mammalian Brain)
   
Thalamus in the middle of the limbic system relays incoming information (except smell) to the appropriate part of the brain for further processing.
Hypothalamus, Pituitary Gland beneath thalamus regulates basic biological drives, hormonal levels, sexual behavior, and controls autonomic functions such as hunger, thirst, and body temperature.
Optic Chiasm in front of the pituitary gland left-right optic nerves cross-over point.
Septum adjacent to hypothalamus stimulates sexual pleasure
Hippocampus within the temporal lobe mediates learning and memory formation.
Amygdala in front of the hippocampus responsible for anxiety, emotion, and fear
Mammillary Body, Fornix linked to the hippocampus have a role in emotional behavior, learning, and motivation.
Basal Ganglia (Striatum): Caudate Nucleus, Putamen, Globus Pallidus outside the thalamus involves in movement, emotions, planning and in integrating sensory information
Ventricles and Central Canal from tiny central canal within the spinal cord to the enlarged hollows within the skull called ventricles fills with cerebrospinal fluid for mechanical protection.
Cingulate Gyrus above corpus callosum concentrates attention on adverse internal stimuli such as pain, contains the feeling of self.
Corpus Callosum under the cingulate gyrus is a bundle of nerve fibers linking the cerebral hemispheres, involve in language learning.
Forebrain
(Human Brain)
   
Frontal Lobe
(Conscious Brain)
in front of the head controls voluntary movement, thinking, and feeling.
Prefrontal Cortex in front of the frontal lobe inhibits inappropriate actions, forms plans and concepts, helps focus attention, and bestows meaning to perceptions.
Parietal Lobe in top rear of the head contains the primary somatosensory area that manages skin sensation.
Occipital Lobe in the back of the head contains the visual cortex to manage vision.
Temporal Lobe on each side of the head above the temples contains the auditory cortex to manage hearing and speech.

Table 02 Human Brain

See "Connectome" -- a modern project for studying the wiring of the neurons inside the brain.

It turns out that the brain is rather malleable. Living examples include a girl born with only half brain. She lives a normal life only with higher neuron density in the available half (see "Teenager Excels with Half a Brain"). Then there are people performing tasks with feet when both hands are missing, additional brain region for navigation in London taxi drivers, blind people use the visual cortex for language processing, ...

¤The parietal eye is not an eye in the traditional sense in that it does not see images, but rather is a photosensitive organ which only reacts to light and dark. The parietal eye is connected to the pineal body and is used to trigger hormone production and thermoregulation. It often shows up as either a dark spot or an opalescent spot. Opsin proteins sensitive to blue and green light has been identified in the cell.

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The Malleable Brain

Throughout its lifetime, the human brain undergoes more changes than any other part of the body. They can be broadly divided into five stages. Table 03 summarizes the significant events within each stage, the "DO" and "DON'T" to keep a healthy mind.

Stage Age Event(s) DO DON'T
1 0 - 10 months
Gestation
* Growing neurons and connections
* Making sure each section of the brain grows properly and in the right place
Mother should:
* be stress-free, eats well
* take folic acid and vitamin B12
* stimulate the young brain with sounds and sensations
* Mother should stay away from cigarettes, alcohol and other toxins
2 Birth - 6
Childhood
* A sense of self develops as the parietal and frontal lobe circuits become more integrated.
* Development of voluntary movement, reasoning, and perception
* Frontal lobes become active leading to the development of emotions, attachments, planning, working memory and attention
* Life experiences shape the emotional well-being in adulthood
* At age 6, the brain is 95% of its adult weight and at its peak of energy consumption
* Parents should provide a nurturing environment and one-on-one interaction
* Parents should beware of the emotional consequence of neglect or harsh parenting
3 7 - 22
Adolescence
* Wiring of the brain is still in progress
* Grey matter (neural connections) pruning
* White matter (fatty tissue surrounding neurons) increase helps to speed up electrical impulses and stabilize connections
* The prefrontal cortex (involving control of impulses, judgment and decision-making) is the last to mature
* Teenagers should learn to control reckless, irrational and irritable behaviors
* Do learn a skill to support life in the future
* Teenagers should avoid alcohol abuse, smoking, drug and unprotected sex.
4 23 - 65
Adulthood
* The brain reaches the peak power at around age 22 and lasts for about 5 years; thereafter it's downhill all the way
* The last to mature and first to go brain functions are those involve executive control in the prefrontal and temporal cortices
* Episodic memory for recalling events also declines rapidly
* Processing speed slows down
* Working memory is able to store less information
* Stay active mentally and physically
* Eat healthy diet
* Avoid cigarettes, booze, and mind-altering drugs.
5 > 65
Old Age
* Losing brain cells in critical areas such as the hippocampus where memories are processed
* Exercise to improve abstract reasoning and concentration
* Learn new skill such as guitar playing to attain the same effect
* Practice meditation can promote neutral emotions
* Avoid grumpiness by eating certain foods, such as yogurt, chocolate, and almonds to get a good dose of dopamine (for promoting positive emotions)
* Don't stressed out as it is related to higher risk of developing dementia.

Table 03 The Five Stages of Human Brain

Figure 09 below depicts pictorially the four stages of human brain after birth tracing the up and down of physiology, aptitudes, and emotions as we grow old.

Four Stages of Human Brain

Figure 09 The Four Stages of Human Brain [view large image]

It is known that many mental processes in sense, language, and higher cognition etc. go through a sensitive or critical period after
Learning Curve which the window of opportunity slams shut, and learning anything new in that realm becomes difficult, if not possible (Figure 10). For years, it is assumed that the brain's plasticity, or the ability to learn within the critical periods, was the work of excitatory neurons, which encourage neighboring neurons to fire. Recent study using inhibitory neurotransmitter (such as GABA) indicates that inhibition actually causes the onset of the critical period. It is found that termination of the mental process can be separated into two categories - structural and functional. The former involves physical structures such as neural network and is not easy to change; while the latter is just chemical compounds not difficult to administer. It may be very useful to reopen the critical period later in life. However, no one should

Figure 10 Learning Curves [view large image]

tamper the brain's critical periods casually. There is always the possibility of an adverse response, as we break the rule of nature.

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Senses

Sight, Hearing, Smell, Taste, Sensations, Balance


Sense organs receive external stimuli; therefore, they are called receptors. Each type of receptor is sensitive to only one type of stimulus
Senses Cerebrum Mapping as listed Table 04, while Figure 10a shows many types of receptors. When a receptor is stimulated, it generated nerve impulses that are transmitted to the spinal cord and/or the brain, but we are conscious of a sensation only if the impulses reach the cerebrum.

It is immediately clear that reality of the external world is transformed to nervous impulses via various kinds of receptors. The brain then interprets the inputs as colors, sound, pain, ... These kinds of sensations

Figure 10a Senses
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Figure 10b Cerebrum
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are one level away from the real things such as electromagnetic waves, sound waves, molecules in various states of motion, ... In other words, the brain just offers a very subjective experience.

The general receptors distribute all over the skin. They are usually grouped together as sensation. The special receptors locate only at certain part of the body in the head. Altogether, they are referred to as the five senses. The followings present a further break down into components, and functions.

Receptor Type Sense Stimulus / Limits
General      
Ruffini's endings, Krause end bulbs Radioreceptor Hot-cold Heat flow
Merkel's and Meissner's endings Mechanoreceptor Touch Mechanical displacement of tissue
Pacinian corpuscles Mechanoreceptor Pressure Mechanical displacement of tissue
Free nerve endings Chemoreceptor Pain Tissue damage
Proprioceptors Mechanoreceptor Limb placement Mechanical displacement
Special      
Eye Radioreceptor Sight Light / wave of (370 - 730) nm, dimmest star at 10-14 watt/cm2 ~ 104 photons/sec-cm2, and resolution of ~ 1' (arc minute)
Ear Mechanoreceptor Hearing Sound / frequency range of (20 - 20K) Hz
Olfactory cells Chemoreceptor Smell Chemicals / 400 types of receptors, 109 different odours
Taste buds Chemoreceptor Taste Chemicals / 104 taste buds

Table 04 Receptors

  • Papillae - The papillae are those small elevations visible to the naked eyes. There are three types of papillae located from the back of the tongue toward the tip. Filiform papillae are generally conical or pointed; fungiform papillae are flat-toped; vallate papillae are larger with an outer groove (see Figure 20). Many taste buds lie along the walls of the papillae. Isolated ones also are present on the palate, the pharynx, and the epiglottis.
  • Sense of Taste
  • Taste buds - The tasting, or gustatory, cells in the buds have hairy tips which detect chemicals in solution (secreted by the gland at the bottom of papilla). When stimulated by flavor molecules, these cells generate nerve signals, which they send to the taste center on the brain's cortex, and also to the hypothalamus, which is concerned with appetite and the salivating reflex.
  • Taste nerve pathway - The nerve signals are carried by three nerves in each side of the tongue (cranial nerves) to a small part of the medulla (brain stem). The signals then travel to parts of the brain, such as the hypothalamus, the thalamus, and the gustatory part of the sensory cortex - the "taste center", where the signals are interpreted (Figure 21). The thalamus acts like a relay station, shunting the data onto appropriate cortical areas for processing. The sense of taste tells us what is good to eat. It evolved to pick out sweet, ripe fruits and energy-packed sugars and starches. Likewise, taste is is extremely sensitive to bitter flavors, because many poisonous berries, fruits and fungi are bitter-tasting.
  • Figure 21 Sense of Taste
    [view large image]

    Balance

      Balance is an ongoing process that keeps our two-legged posture stable. Four main sets of sensory input are involved:

    1. Information from the skin is important, especially from the touch and pressure sensors on different parts of the feet, which tell the brain if you are leaning. This sense is not available in a free falling environment such as in a spacecraft.
    2. Eyesight is used to judge verticals and horizontals to which your body should be parallel and at right angle respectively.
    3. The body's proprioceptive sense of stretch in muscles, tendons, and joints tell the brain about the positions and angles of the arms, legs, torso, and neck.
    4. The sensory parts dedicated to balance is located deep inside each inner ear, next to the cochlea (see Figure 10a). These parts are known collectively as the vestibular apparatus and are part of the same network of fluid-filled chambers as the cochlea. They consist of the utricle, the saccule, and the semicircular canals (Figure 23a). In certain parts of their linings are tinny hairs, whose roots are embedded in lumpy crystals or gels. The crystals or gels are attracted downward by gravity, and they are also pushed to and fro by the fluid in the chambers, which swirls as the head changes its position.
    Balance
      The functions of the these organs are shown in Figure 23a:
    • (a) The ampullae of the semicircular canals contain hair cells with cilia embedded in a gelationous material.
    • (b) When the head rotates, the material is displaced and the bending of the cilia initiates nerve impulses in sensory nerve fibers for maintaining dynamic equilibrium.
    • (c) The utricle and saccule are sacs that contain hair cell with cilia embedded in the gelationous material.
    • (d) When the head bends, otoliths are displaced, causing the gelationous material to sag and the cilia to bend. This initiates nerve impulses in sensory nerve fibers for maintaining static equilibrium.

    Figure 23a Balance
    [view large image]

    The vestibular nerve feeds its information chiefly to the cerebellum and to four structures in the medulla known as vestibular bodies. Using these data, as well as input from the other three sensory sources, the brain works out what to do, usually subconsciously.

    Neuromast It turns out that such structure of hair within gel to detect disturbance has been around hundred of million years in the shark and fish (Figure 23b). This is the neuromasts embedded in the skin of fish. They give the fish information about the flow of water. Amphibians and reptiles have a simple uncoiled inner ear. Jawless fish has only one semicircular canal instead of three in mammals (for detecting three dimensional movement). Ultimately, it is the Pax 2 gene that give rise to these structures. It is also known that the Pax 6 gene is responsible for the development of eye. The connection to ancient creatures goes even deeper when it is found that the box jellyfish carries a gene which is the combination of Pax 2 and Pax 6.

    Figure 23b Neuromast
    [view large image]

    The box jellyfish is an amazing animal with more than 20 eye pits and many eyes very similar to ours. They seem to double for ears as well.

    Threshold of the Senses Now we known that it is the senses and the brain to keep us informed about the external environment through many special setups. In addition, the process consumes a lot of energy and requires intricate wiring (of neurons), it has to impose limits beyond which survival is not at stake (Figure 23c). For examples : the sight is limited to the visible range of the electromagnetic spectrum, the senses ignore those frequent inputs bearing no threat to life, and it processes inputs in discrete intervals (there are blanks in between that we are not aware of, see "Saccades"). Therefore, the brain not only distorts

    Figure 23c Threshold of the Senses

    the reality to suit the requirement of survival, it also neglects lot of details in order to expedite the task. It is definitely that we are not perceiving the reality, which is always modified by the brain.

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    Memory

    Types of Memory As shown in Figure 02, the ability to modify our behaviour in response to life's experiences is shared by all animals including the bacteria E. coli. Such feat requires the brain's willingness to learn. Learning results in the formation of memories and in humans this process reaches its most sophisticated form, allowing us creatively to associate different reflections on the past, to generate new ideas, and most importantly to acquire language as a medium of expression and communication. Memory requires the brain to be physically altered by experience and it is this remarkable property that makes thought, consciousness, and language possible. The basic mechanism of memory formation is highly conservative over billion years of biological evolution. The difference in humans is that we have a lot more of the stuffs. There are about 100 trillion synaptic connections in our brain.

    Figure 24a Memory Classification
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    Memory There are many ways to classify the memory. The concept of explicit and implicit memory refers to whether or not the recollection is produced consciously and intentionally. While the scheme of declarative and nondeclarative memory depend on the retrieval that can be declared verbally or not. Associative memory is triggered by clues; nonassociative memory can be habitual or sensitive. There are also short term and long term memory. One of the classification schemes is shown in Figure 24a. Table 07 is an attempt to put them all together. In the table, the declarative, and the procedural memory are explicit with the rest of nondeclarative memories being implicit. Only the working memory belongs to the category of short term memory fading away in hours, while the others are long term, and available for retrieval in years. Figure 24b shows the components, locations, and pathways for many types of memory.

    Figure 24b Types of Memory
    [view large image]



    Type Location(s) Function Example(s)
    Working Memory
    Phonological Loop Left hemisphere Rehearsing verbal information to keep it in the short-term memory String of numerals and alphabets such as telephone numbers
    Visual-spatial Scratch Pad Visual Cortex Controlling visual imagery Scanning text
    Central Executive Frontal lobe Controlling awareness of the information in working memory Constructing sentence, comprehending speech
    Non-declarative Memory
    Procedural Memory Cerebellum, temporal lobes Managing "how to" Riding a bicycle, kungfu exercise
    Classical Conditioning Cerebellum Forming habitual behaviour Coffee break, afternoon tea
    Fear Memory Amygdala Emotional conditioning Phobias, flashbacks
    Nonassociative Memory Spinal cord Habituation and Sensitization Decreased or increased responsiveness to stimulus
    Remote Memory (Priming) Scattered around the cortex Foundation for new memories Childhood memory
    Declarative Memory
    Episodic Memory Cortex Remembering past experience Some enchanted evening
    Semantic Memory Frontal lobe, temporal lobe Registering facts Meanings of words and symbols

    Table 07 Types of Memory