Biological development begins with conception. Psychological development is closely linked to biological development and has thus been universally recognized by psychological theories of development..
In the last decades there has been a remarkable increase in neurobiological knowledge linked to the invention and design of new neuroimaging methods and techniques that allow studying the molecular and cellular activity of the nervous system, as well as checking the functioning of the brain of babies, children and adolescents, during the very process of carrying out cognitive tasks.
NEUROIMAGING TECHNIQUES: evoked potentials, magnetic resonance imaging, positron emission tomography.
The cognitive neuroscience of development is the union of several disciplines dedicated to the studies of cognitive development, the evidences obtained in the works on brain development and those that come from ethology. Among his study methods we can highlight functional brain imaging techniques and the study of brain injuries and their effects on behavior and cognition..
Prenatal development begins with conception giving rise to a new simple cell called a zygote. Through cell division (meiosis) the zygote receives 23 chromosomes from the mother and 23 chromosomes from the father.
The maturation process of the zygote until its full development lasts 38 weeks and is divided into three stages: germinal period, embryonic period and fetal period..
a) The germinal period. From conception to the first two weeks.
Conception takes place when a sperm fertilizes an egg and the ZYGOTE is formed, initiating the process of cell division. In three days it goes from being in the fallopian tubes to the uterus and after four or five more days it settles in the uterus. After the first two weeks the cells will have multiplied and will begin to differentiate. The embryo has an outer membrane (chorion) and an inner membrane (amnion) that surrounds and protects it. You can also see the placenta, which provides nutrients and oxygen to the new being.
Cell differentiation occurs thanks to a substance called activin.
-Cells with higher amounts of activin = endoderm = digestive and respiratory system.
-Cells with medium concentration of activin = mesoderm = bones, muscles, blood, kidneys and heart.
-Cells with a lower concentration of activin = ectoderm = sit. Nervous, skin, hair and sensory organs.
b) The embryonic period
It covers from the third week to the eighth. In this period it is called EMBRYO. The organs and the nervous, respiratory and digestive systems develop. It is a very critical period where the embryo is very vulnerable to environmental influences. Congenital alterations such as deafness, blindness or cleft palate can occur.
There are two principles that guide the development of the embryo and that continue until adolescence:
The proximodistal principle: indicates that the development takes place from the part closest to the central axis of the body to the farthest part.
The cephalocaudal principle: indicates that development progresses from head to toe. At the end of the embryonic period the organism measures 2.5 cm. The head is clearly distinguished from the body, the face and the heart beats strongly. The kidney and stomach and the system begin to function. Endocrine begins to produce hormones. The sexual organs are also formed. All organs are formed but in a very primitive way.
c) The fetal period
It covers from the ninth week to birth (38 weeks + -). In this phase the FETUS increases in size and volume drastically, producing external and internal changes. The organs begin to acquire more precise structure and establish functions and the first bone cells appear.
At 16 weeks the FETUS measures 15-17 cm and weighs 100g. Most of the basic systems are developed, but the FETUS is not prepared to survive outside the uterus because it has no connection between the different neurons in the cerebral cortex. The FETUS must produce a liquid called surfactant that will allow it to transmit oxygen from the air to the blood..
From the 29th week, the FETUS can survive on its own. The heart rate is very fast, the activity of all your organs accelerates, and a layer of fat forms around the entire body. A child born on time weighs about 3k and measures about 50cm.
Physical development is the product of the interaction between the child and his environment. The growth of infants and children continues in the cephalocaudal and proximal distal patterns. In this way we can say that growth is fundamentally characterized by progressing from head to toe (see figure 2.1). The dimensions of the head of a newborn are closer to that of an adult than the rest of the body. In addition, babies learn to use their upper extremities earlier than their lower ones. The proximal distal principle causes the trunk to develop before the extremities and the arms and legs before the hands and fingers.
In the first three months of life growth is much faster than in the rest of the life cycle. The weight increases, the size and the head begins to be more proportionate in relation to the body.
In early childhood (3-6 years) they lose weight, their body, arms and legs grow. Bones are strengthened which makes it easier for them to develop many motor skills.
In middle childhood (7-12 years) they continue to grow and gain weight. Girls retain slightly more fat tissue than boys.
In adolescence there are important changes in the physical appearance that we will mention below:
-Sudden growth. Sudden growth in height and weight that girls begin to have earlier than boys. Lasts two years and is a symptom of sexual maturity.
-Primary sexual characteristics. They are the organs involved in reproduction. In girls, the ovaries, uterus and vagina mature and Menarche (menstruation) is reached. In boys, the penis, testes, prostate, and seminal vesicles enlarge and mature.
1st symptom of female sexual maturity menstruation .
1st symptom of male sexual maturity presence of sperm in urine.
-Secondary sexual characteristics. In girls the growth of the breast and the appearance of hair on the pubis and armpits. In children changes in the voice, hair on the pubis, armpits and face. And in both the skin becomes rougher and more oily.
Factors that affect human growth and maturity:
Genetic inheritance: tall parents = tall children
Nutrition: essential for the correct development of the child. Poor nutrition is accompanied by poor intellectual development, slower growth, and delayed puberty.
Eating disorders also affect the development of the person.
Anorexia nervosa produces serious health risks, loss of menstruation in girls, muscle weakness, dry skin, dehydration.
Bulimia damages teeth, irritates gums, and cracks lips.
Obesity causes girls to reach puberty earlier and boys “stretch” earlier. To this must be added that obese children have school problems and social difficulties.
Exercise is very beneficial if done in moderation. High training produces less growth and irregular menstruation in women.
Social class is a factor that influences growth. Poverty is often associated with growth and development retardation, especially if it occurs between 3 and 36 months of age.
Physical deficiencies. Both the pituitary and the thyroid glands are crucial for normal growth. A malfunctioning thyroid can lead to dwarfism or gigantism. Also metabolic alterations, infections, liver diseases ...
Trauma and psychological abuse can cause growth retardation. In homes where aggressiveness, alcohol intake or sexual abuse of minors can be found children with short stature and weight.
Psychomotor development is of vital importance since it is the basis for cognitive, language, social and emotional development. It is the external manifestation of the Central Nervous System. This development can be divided into two general categories: locomotion and postural development and pressure, that is, the ability to use the hands..
a) Locomotion and postural development
It's gross motor skills. During the first two months of life it can be observed that his legs increase in volume but not in muscles. This causes in the baby a series of stereotyped movements that gradually disappear. From the fifth month on, he gains stability and his body proportions begin to change: his legs are stretched and his shoulders are widened. By eight or nine months the baby can crawl. By the time they control their posture, they are able to walk. Walking encourages social interaction and autonomy. This whole process is governed by the cephalocaudal principle.
b) The ability to use the hands
They are fine motor skills. The correct use of the hands can be considered as a type of manual intelligence.
Initially the movement of the baby's hands occurs as a reflex action. By 2 months they try to pick up objects with their fists instead of with their open hands. At two months the cortical system is still not coordinated with the system that controls the grosser motor movements. At around 4-5 months, he picks up objects with open hands (very harmonized operation of the sensorimotor system). At 9 months, he shows an agile, fast and precise gesture when reaching an object. Finally, at 12 months they explore everything around them with their hands. This whole process is governed by the proximal distal principle.
From the second year on, motor development as a whole begins to be observed: fine and gross motor skills. At 2 years of age they begin to overcome their battle with gravity and balance. They can also throw and catch different objects with precision.
Psychomotor development is the privileged link between physical and intellectual development.
Differences in human brain development with that of other primates consist in the marked increase in the cerebral cortex and the existence of a much longer period of postnatal development. From this fact arise the specific cognitive capacities of the human being.
The neurons that the baby possesses at birth have been generated in the first months of pregnancy (especially 3-4 months). These neurons have to migrate and make connections with other neurons to form brain tissue. By month 4.5 of gestation, neuronal migration has created three differentiated strata and from the seventh month it reaches six strata. Prenatal brain development includes the process of growth and development of axons and dendrites and the establishment of axon-dendrite synaptic connections (5th month of gestation).
In order to relate brain development with cognitive development, it is important to see some characteristics of postnatal development that we are going to list:
1- Postnatal growth of the human brain: Brain mass quadruples between birth and adulthood due to increased number and complexity of dendrites, increased density of synaptic connections in the cerebral cortex and increased myelination.
2- Loss or "pruning" of synaptic connections: Process of loss of synaptic density that appears at different ages depending on the cortical zone. The initial overproduction of synaptic connections and their subsequent pruning seems to be related to the PLASTICITY of the infant brain..
3- Brain plasticity: Fundamental property of the development of the cortex. The process of differentiation and specialization of the different areas of the cortex is highly influenced by neuronal activity and by intrinsic factors related to automatic "on".
The frontal cortex is in charge of executive functions that involve the ability to plan behavior, control attention during complex tasks, inhibit erroneous behaviors or activate knowledge stored in long-term memory. Only after the age of 25 is synaptic pruning completed, that is, the establishment of specific connections that allow complex cognitive tasks (solving mathematical problems), which require the action of EXECUTIVE control processes, are under development during adolescence and are get full into adulthood.
Likewise, the myelination process occurs in different waves from the prenatal period, reaching adulthood in specific areas. The most important changes in myelination occur in adolescence (decrease in gray matter and increase in white matter).
Specific changes occur in the hippocampus during adulthood.
Genetically regulated developmental processes. The formation and development of neurons, the proliferation and overproduction of synapses.
Development processes regulated by the environment. Synaptic pruning processes and the establishment of new synaptic circuits and networks.
The typical rise-fall pattern of synaptic connections and neuronal activity appears to be related to cortical plasticity during childhood, as well as to the existence of sensitive periods in development..
Sensitive periods: Periods or phases of development of special susceptibility to environmental influences that allow or facilitate the achievement of certain cognitive abilities. A prototypical example is the acquisition of language during childhood.
The notion of critical period emphasizes the importance that biological maturation has in development by highlighting the need for certain experiences to occur at a certain point in time. Let's take several examples:
Imprinting or stamping: the young of certain birds show a behavior of following the first object that they see immediately after hatching. Generally, the mother is the first thing they see for this, the imprinting behavior offers obvious benefits for the survival of the offspring. The imprinting period is quite short as the brain matures very quickly and in several days the ducklings avoid unknown objects.
Early development of the visual system in cats: Hubel and Wiesel found that if a newborn kitten had one eye covered for a certain time, when the visual cortex is undergoing changes, the animal will be blind in that eye. Although later research maintains that part of the functions can be partially recovered by experience.
In no case can one speak of critical periods in human development, although certain learning can be carried out more easily in sensitive periods. These periods are related to the rise-fall pattern in the development of the different areas of the cerebral cortex. For example, language acquisition (phonemes and grammar). Children are able to quickly learn other languages and it is from puberty that they begin to have difficulties in doing so.
In this section we will analyze the relationships between brain development and cognitive development, focusing on a cognitive process: memory systems. Neuroscientific evidence confirms that we can speak of two basic memory systems: explicit or declarative memory, and implicit, non-declarative or procedural memory..
The distinction between explicit and implicit cognitive processes affects memory, learning, thinking and reasoning.
Explicit processes are usually conscious, intentional, controlled and consume cognitive resources.
The development of explicit memory in infants begins in the second half of the first year of life. Eg: sticking out the baby's tongue when an adult has stuck it out before. This explicit memory depends on specific neo-cortical areas, as well as other areas of the cortex that surround the hippocampus and the hippocampus itself..
There is a pre-explicit memory characterized by its early appearance (newborns) and by depending on the hippocampus.
The gradual development of explicit memory during childhood is linked to the development of the hippocampus, the cortical areas that surround it, and other areas of the prefrontal cortex, as well as the establishment of connections between these areas.
The brain bases of implicit memory are different from those of explicit memory. A first type of implicit memory is conditioned behaviors. Soon after birth, babies are able to acquire and remember conditioned responses. Babies are able to learn and remember a response from the eyelid reflex. Burst of air plus sound, presented repeatedly is equal to the baby's blinking when presenting the sound alone. It seems clear that the neural basis for learning and conditional memory of this type is in the cerebellum..
The acquisition of operant conditioned behaviors, such as achieving a pleasant sound from a rattle, appears after three months and depends on the basal ganglia of the cerebellum. The acquisition of these non-semantic, procedural behaviors, which includes riding a bike or typing, continues throughout childhood and depends on the basal ganglia and the frontal and motor cortices..
There is a clear dissociation between the two types of memory: explicit (remembering facts) implicit (remembering skills).
People with amnesia have lesions in the hippocampus and are unable to acquire new memories, but they can perform motor sequences.
People with Parkinson's, with affected basal ganglia, show problems in motor skills but have good memories of the past.
Human beings are biological organisms that after conception go through a long period of prenatal development. Biological changes continue throughout life but are most noticeable in childhood, adolescence, and old age.
Studies on the brain bases of psychological development have in common the search for parallelism between the psychological level of behavior and the biological level of brain activity. Both developments are parallel, although psychological development cannot be reduced to brain development.
Various authors have argued that the establishment of a specific and precise map of active brain regions for a certain cognitive process such as executive functions or inhibitory control is probably not possible. We can affirm that these cognitive processes have a main neurological basis in the prefrontal cortex, but the computational components that underlie different cognitive processes seem to reside in this brain region.
The relationship between behavior and brain, between psychological and biological knowledge, works in both directions. (bidirectional)
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