CogniFit - The Human Brain

What is the brain?

The brain is a complex organ located inside the skull and it manages activity for our nervous system. It is part of the Central Nervous System (CNS). It is located in the anterior and superior region of the cranial cavity, and it's present in all vertebrae. It floats in the cranium in a transparent liquid, called cerebrospinal fluid, which protects it both physically and immunologically.

Is the brain a muscle? Although it is commonly said that it should be trained and exercised like a muscle to prevent atrophy, we must actually be clear that the brain is not a muscle. It is not made up of myocytes, like our muscles, but rather millions of neurons that are interconnected by axons and dendrites. They regulate each and every one of our brain and body functions. From breathing, eating or running, to the ability to reason, to fall in love, or to argue, etc.

What does our brain do? Brain Functions

As a fundamental part of the CNS, the brain could be defined as the "manager" that controls and regulates the majority of brain and body functions. From vital brain functions like breathing to other functions like hunger, or thirst, and finally to superior functions like reasoning, attention, and memory (Corbetta & Shulman, 2002). It is responsible for making sure all of these conscious and subconscious functions are being carried out.

Everything that happens in our lives, when we're awake or asleep, whether it be breathing, swallowing, seeing, hearing, touching, reading or writing, singing or dancing, thinking silently or talking out loud, loving or hating, planning or acting spontaneously, etc is thanks to our brain. To put it in a list, some of the functions are:

• Controlling vital functions: Like controlling body temperature, blood pressure, heart rate, breathing, sleeping, eating, etc.
• Receiving, processing, integrating, and interpreting all of the information that we receive through our senses: Sight, hearing, taste, touch, smell.
• Controlling movements and our posture: Walking, running, talking, standing.
• It is responsible for our emotions and behavior.
• It allows us to think, reason, feel, be, etc.
• Controlling superior cognitive skills: Memory, learning, perception, executive functions, etc.(Miller, 2000; Miller & Cohen, 2001)

"Men ought to know that from nothing else but the brain come joys, delights, laughter and sports, and sorrows, griefs, despondency, and lamentations. And by this, in an especial manner, we acquire wisdom and knowledge, and see and hear, and know what are foul and what are fair, what are bad and what are good, what are sweet, and what unsavory... And by the same organ we become mad and delirious, and fears and terrors assail us... All these things we endure from the brain, when it is not healthy...I am of the opinion that the brain exercises the greatest power in the man" Hippocrates(IV BC) On the Sacred Disease.

Hippocrates knew it then, the human brain is one of the most complex, enigmatic, and at the same time, perfect creations in the universe. Thanks to technological advancements in neuroimaging, medicine, biology, psychology, and neuroscience, we have been able to uncover grand mysteries about anatomy and how we function. However, there are still many questions left unanswered.

Parts of the brain

All vertebrates (animals with bones) have a brain, although their size, shape, and certain characteristics may vary greatly from one species to another. Below is a human brain which is composed of the following parts:

• The Brain, made up of the cerebral cortex (hemispheres and cerebral lobes).The cerebral cortex is divided into different areas: the frontal lobe (A), the parietal lobe (B), the cingulate cortex (C), the occipital lobe (D), the temporal lobe and the insular cortex (these two are hidden in the image). In addition, these lobes are divided in half into two hemispheres: the right and the left. Subcortical structures refer to those under the cerebral cortex, such as the callous body (1) that joins the two hemispheres, the thalamus (2), the basal ganglia, amygdala, hippocampus and mammillary body (6). It is in charge of integrating all of the information collected by our sensory organs and organizing a response. It controls motor, emotional and all higher cognitive functions: reasoning, emotional expression, memory (Squire, 1992), learning, etc.
• Cerebellum(10): It is the second largest organ in the encephalon, and it is mainly involved in controlling posture and movement.
• Hypothalamus(4), pituitary gland(5) and pineal gland (11) responsible for visceral functions like regulating body temperature and basic behaviors, like eating, sexual response, pleasure, aggression, etc. The pineal gland has an important role in synchronizing the release of the melatonin hormone, involved in the regulation of sleep/wakefulness cycles, which is coordinated with the optic chiasma (3).
• The Brainstem: made up of the spinal cord (9), the pons (8), and the midbrain (7). The brainstem controls automatic functions, like blood pressure and heartbeat, limbic movements and visceral functions, like digestion or urination.

Characteristics of the human brain

How much does the human brain weigh? How big is it? How many neurons do we have?

• The cerebral cortex in humans is one of the most evolved and complex among all animal species. It's not only bigger, but it's also rolled and folded back over itself, forming grooves and folds which give it that characteristic wrinkled appearance.
• The human encephalon weighs about 1.4-1.5 kilos (3.3 lbs), and has a volume of about 1130 cc (69 ci) in women and 1260 cc (77 ci) in men.
• It is covered by membranes, called meninges, that protect the skull when it is hit.
• For even more protection, the brain "floats" in cerebrospinal fluid.
• It is estimated that it is made up of more than 100 billion nerve cells, mostly glial cells and neurons.

NEURONS: Are the cells that are specialized in receiving, processing, and transmitting information on intercellular and intracellular levels. This is done through electrochemical signals (nerve pulses) called action potential. Structurally, neurons have the same cytoplasmic elements and the same genetic information as the rest of the cells in the organism. Neurons are made up of three parts:

• Cell body or soma: is the main part of the cell that contains the nucleus (with DNA), the endoplasmic reticulum and ribosomes (produce proteins), and mitochondria (generate energy). The soma is where the majority of the cell's metabolic functions take place. If the soma dies, the cell dies.
• Axons: are an extension that comes off of the cellular soma. It is a type of "cable" that has terminal buttons (varicosities) at the end, which are the synaptic contact points, through which nerve pulses are transmitted (pre-synaptic element). The length of the axons can vary from neuron to neuron: there are some very short ones (less than 1 mm), and others that are very long (more than a yard, which are usually peripheral nerves like motorneurons). Some axons (especially motor and sensory neurons) are covered by a layer of myelin which speeds it up and makes it easier to transmit information. The more myelin an axon has, the stronger it will arrive to the impulse nerve. The neurons that have the most myelin are the periphery neurons (sensory and motor), which is where the information has to travel the furthest.
• Dendrites: are some nerve endings that come off of the cellular soma which branch off into the shape of a tree. Dendrites make up the main component for information reception (post-synaptic element), and they are what make it possible to communicate between two neurons.

GLIAL CELLS: Are the most abundant type of cell in the CNS. They have the ability to divide in the adult brain (neurogenesis), and their presence is necessary for the brain to function properly. These cells make up the structural support for neurons, the cover axons with myelin for a better synaptic transmission (Schwann cells), they play a roll in the cell's nutrition, they participate in regeneration mechanisms and nerve reparation, in the immunization mechanisms, maintaining the blood barrier, etc. There are various types of glial cells, among which are astrocytes, oligodendrocytes, and microglia. In the peripheral nervous system Schwann cells, satellite cells, and macrophages.

How does the brain work?

It works by transmitting information between neurons (or other receptor or effector cells) through electrochemical pulses. This transmission of information is produced during synapsis. During synapsis, neurons and cells connect and through chemical charges and electric pulses and neurotransmitters are exchanged, which are in charge of activating or inhibiting the action of the other cell. The axon's terminal buttons are the pre-synaptic elements of neural communication, through which the neuron establishes communication with the dendrites, the soma, or even another axon.

All of this transmission of information by neurons happens in just milliseconds. Hundreds of connections that allow us to perceive, understand, and react appropriately are coordinated. We receive thousands of inputs, and we generated thousands of outputs in a matter of seconds, and everything works with the precision of a Swiss watch.

How does the human brain develop?

The development of the human brain starts in the embryonic stage and ends at youth. After only 4 weeks after conception, it starts forming a neural tube which is key in the development of the nervous system. The vertiginous process starts after, where the proliferation, migration, and cell differentiation processes start, where the formation and development of the brain will take place. Neurons are produced in the neural tube and later migrate to form the important parts of it. Lastly, they are differentiated and specialized in the function they'll have.

It has been calculated that in the pre-natal stage up to 250,000 cells could be produced a minute. In fact, a baby's encephalon at birth already has all of the nerve cells that it will need, but they are yet to be connected. During the first two years, these connections begin to form mediated by a genetic component, but mainly by interaction with the environment and the stimuli that they received. The mylenization processes (process where the neural fibers are covered with an isolating layer of fat that transfers information) makes it easier to do this faster, and they are responsible for increasing the size of the encephalon.

From 0-12 months: Babies haven't developed a spinal cord, which is why they only respond to reflex stimuli and basic survival functions like sleeping, eating, or crying. As they relate to their environment, new connections will be created, and they'll quickly learn things like how to direct their eyes, repeat sounds, understand language, etc.

At 3 years: it already is already almost 80% of its adult size, and the limbic system and the cerebral cortex are quite developed. This allows children to express themselves and recognize emotions, play, and start counting and talking. This is why it is considered that at this age, it has its maximum plasticity, or neuroplasticity, where even if an area is damaged it will regain functions (because it isn't completely specialized yet).

It doesn't stop developing until after youth: The area that takes longest to mature are the frontal lobes, which specialize in behavior, reasoning, problem solving, etc.

However, even when its maturation ends in youth, it continues with its neurogenesis processes (creation of new neurons), and they can create new connections through training and reinforcement. This is the basis of neuroplasticity.

Is it possible to train and improve the brain? How CogniFit helps

Thanks to neuroplasticity and to our brain's ability to create new connections and strengthen old ones, we can improve our cognitive capacity.

References

Corbetta, M. y Shulman, G. L. (2002). Control of goal-directed and stimulus-driven attention in the brain. Nat Rev Neurosci, 3 (3), 201-215.

Miller, E. K. (2000). The prefrontal cortex and cognitive control. Nat Rev Neurosci, 1 (1), 59-65.

Miller, E. K. y Cohen, J. D. (2001). An integrative theory of prefrontal cortex function. Annu Rev Neurosci, 24, 167-202.

Squire, L.R. (1992) Memory, and the hippocampus: a synthesis from findings with rats, monkeys and humans. Psychol Rev, 99, pp.195-231.