Following on from the developmental psychology tradition, developmental cognitive neuroscience has focused on brain-based explanations of developmental change.One particular current approach is termed neuroconstructivism. Like Piaget's approach, this assumes constant interaction between environment and genetic factors, with a mature cognitive system emerging out of transformation of earlier ones.Unlike Piaget's approach, the predetermined aspect of development is construed in terms of multiple, brain-based constraints, rather than the less well-defined notion of predetermined "stages".
Adapting the methods of cognitive neuroscience for infants and children
Methods such as fMRI and EEG are generally considered suitable for infants and children. One advantage of using these methods in younger people that they do not necessarily require a verbal or motor response to be made.
Functional MRI
If one wants to compare across different ages, then the most significant problem is that the structural properties of the brain change during development. The hemodynamic response function is relatively stable after 7 years of age but differs below this age. The differences in both brain structure and blood flow make it harder to compare activity in the same region across different ages. Younger children also find it harder to keep still in the scanner and this motion can disrupt the reliability of the MR signal.
Functional near-infrared spectroscopy (fNIRS)
Unlike fMRI, it accommodates a good degree of movement and is portable. However it has poorer spatial resolution and does not normally permit whole-head coverage.
ERP/EEG
When working with young participants using ERP/EEG, a limiting factor is the child's willingness to tolerate the electrodes, the task and the time commitment required. Children and adults can show quite different patterns of ERP, even for tasks that both groups find easy. These could either reflect age related cognitive differences (i.e. the same task can be performed in different ways at different ages) or non-cognitive differences (e.g. the effects of skull thickness, cell packing density or myelination)
Brain stimulation: TMS and tES
Single and paired pulse TMS is considered to pose minimal risk in children although repetitive TMS isn't recommended except for compelling therapeutic purposes.
STRUCTURAL DEVELOPMENTAL OF THE BRAIN
The genetic code contains a detailed wiring diagram of the brain. In stead of the blueprint analogy, one could instead imagine the genetic code more like a recipe for making a brain. Gottlieb makes a distinction between two key ideas in development:
- Predetermine development: genes dictate the structure of the brain, which enables particular functions of the brain, which determines the kinds of experiences we have.
- Probabilistic development: brain structure, and even the expression of genes, can be influenced by experiences as well as vice versa.
Probabilistic development represents the dominant view in modern developmental cognitive neuroscience.
Prenatal development
The nervous system derives from a set of cells arranged in a hollow cylinder, the neural tube. By around 5 weeks the neural tube has organized into a set of bulges and convolutions that will go on to form various parts of the brain. Closer to the hollow of the neural tube are several proliferatieve zones in which neurons and glial cells are produces by division of proliferating cells → neuroblasts and glioblasts.
The nervous system derives from a set of cells arranged in a hollow cylinder, the neural tube. By around 5 weeks the neural tube has organized into a set of bulges and convolutions that will go on to form various parts of the brain. Closer to the hollow of the neural tube are several proliferatieve zones in which neurons and glial cells are produces by division of proliferating cells → neuroblasts and glioblasts.
Neuroblasts: stem cells for neurons
The newly formed neurons must then migrate outwards toward the region where they will be employed in the mature brain. This occurs in two ways. Passively, older cells tend to be pushed to the surface of the brain. Structures such as the hippocampus are formed this way. There is also an active mechanism by which newer cells are guided to particular destinations, pushing past the older cells. Rakic identified radial glial cells that act like climbing ropes, ensuring that newly formed neurons are guided to their final destination.
Regional differences in various molecular signals affect the neurons' structure, migration and survival.
Although prenatal neurons have very limited functional inputs from the environment, they can still show spontaneous electrical activity that enables networks to form in the brain on the basis of Hebbian learning (what wires together fires together)
Although prenatal neurons have very limited functional inputs from the environment, they can still show spontaneous electrical activity that enables networks to form in the brain on the basis of Hebbian learning (what wires together fires together)
Postnatal development
The vast majority of neurons are formed prior to birth, so the expansion in brain volume during postnatal development is due to factors such as the growth of synapses, dendrites and axon bundles; the proliferation of glial cells and the myelination of nerve fibers.
Synaptic density: this is a measure of the degree to which neurons are connected to each other and is unrelated to the number of neurons per se or how active the synapses are. In all cortical areas studied to date, there is characteristic rise and then fall in synapse formation (synaptogenesis)
Why does the number of synapses fall during the course of development? It is not necessarily the case that more synapses reflect more efficient functioning. During development a process of fine-tuning the brain to the needs of the environment renders some connections redundant.
Myelination refers to the increase in the fatty sheath that surrounds axons and increases the speed of information transmission. Again the prefrontal cortex is one of the last areas to achieve adult levels of myelination and this together with the late fine-tuning and elimination of synapses in this region maybe contribute to the development of mature social behaviour during adolescence and the control of behavior in general.
Plasticity refers to experience dependent changes in neural functioning.
One cant take gray matter density/thickness as a simple proxy of cognitive ability as it depends on the underlying mechanisms: developmental pruning of synapses (thinner is better) or experience-dependent changes (thicker is better)
Plasticity refers to experience dependent changes in neural functioning.
One cant take gray matter density/thickness as a simple proxy of cognitive ability as it depends on the underlying mechanisms: developmental pruning of synapses (thinner is better) or experience-dependent changes (thicker is better)
FUNCTIONAL DEVELOPMENT OF THE BRAIN
Recovery of function after early brain damage
Plasticity and recovery is greatest earlier in life, often referred to as the Kennard Principle: The idea that the earlier brain damage is sustained, the better the functional outcome. While early plasticity can aid recovery, this may not be completely without a cost.
Critical and sensitive periods in development
Filial imprinting: The process by which a young animal comes to recognize the parent.
A critical period has two defining features:
A critical period has two defining features:
- Learning can only take place within a limited time window
- Learning is hard to reverse in the face of later experience
Subsequent evidence suggests that the window of opportunity can be extended by lack of suitable early experience and that learning can be reversed in certain circumstances. Many researchers prefer the moderate terminology of sensitive period.
Sensitive period: a time window in which appropriate environmental input is particularly important (but not necessarily essential) for learning to take place.
Language sensitive period: as late as 17.4 years beyond which syntax learning ability declines steadily.
What general properties of the nervous system give rise to sensitive periods in development?
- One possibility is that there is a strict maturational timetable in which a set of neurons are readied for learning (e.g. by synaptogenesis) and are later fossilized (e.g. reducing plasticity, removing weaker connections) according to strict timetable.
- Second possibility is that a set of neurons are readied for learning that the process is self terminating to some extent i.e. the sensitive period will "wait" for suitable exposure.
Innate knowledge
Innate knowledge division has a long historical and philosophical tradition between so called empiricists (who believed that the mind is a blank slate) and nativists (who believed that at least some forms of knowledge are innate)
Instinct: a behavior that is a product of natural selection.
Instinct: a behavior that is a product of natural selection.
In the sense of instinct, "innate" there is a readiness for certain knowledge to be acquired, but the knowledge itself is not strictly innate.
Second way in which the word "innate" is applied: knowledge or behavior can be said to be innate if it comes about in the absence of appropriate experience.
Second way in which the word "innate" is applied: knowledge or behavior can be said to be innate if it comes about in the absence of appropriate experience.
Prepared learning: the theory that common phobias are biologically determined from an evolutionary pressures.
Some preferences could, arguably, be said to be innate in the sense that they do not appear to depend on experience. newborn infants prefer sweet tastes over neutral and sour one and they prefer some visual patterns over others.
Some preferences could, arguably, be said to be innate in the sense that they do not appear to depend on experience. newborn infants prefer sweet tastes over neutral and sour one and they prefer some visual patterns over others.
Studies suggest that certain dispositions, preferences and abilities can be in said to be innate. However the issue of whether the specific content of knowledge is innate is much harder to substantiate.
NATURE AND NURTURE OF INDIVIDUAL DIFFERENCES
Behavioral genetics: a field concerned with studying the inheritance of behavior and cognition.
The origins of genetic differences
The human genetic code is organized onto 23 pairs of chromosomes, making a total of 46 chromosomes. Genes may exist in difference forms termed alleles. The different alleles represent changes (or mutations) in the sequence of the gene that is propagated over many generations, unless natural selection intervenes. Most behavioral traits will be an outcome of the concerted action of many genes. Disorders such as autism, dyslexia and schizophrenia also appear to be polygenic in nature.
The human genetic code is organized onto 23 pairs of chromosomes, making a total of 46 chromosomes. Genes may exist in difference forms termed alleles. The different alleles represent changes (or mutations) in the sequence of the gene that is propagated over many generations, unless natural selection intervenes. Most behavioral traits will be an outcome of the concerted action of many genes. Disorders such as autism, dyslexia and schizophrenia also appear to be polygenic in nature.
As well as differences in alleles, individuals differ in the spacing genes on the chromosomes (most of the genome contains nongene segments). While it is unclear whether this contributes to observable individual differences, an analysis of spacing of various genomic markers is central techniques such a genetic finger-printing.
Heritability estimates of brain and behaviour
Heritability: the proportion of variance in a trait, in a given population, that can be accounted for by genetic differences among individuals. The degree to which an MZ correlation is less than the perfect 1.0 is assumed to reflect unshared environment, the remaining portion of variance is attributed to shared environment.
Unshared environment: the portion of variance in a trait, in a given population, that can be accounted for by events that happen to one twin but not the other, or events that affect them in different ways. Shared environment: the proportion of variance in a trait, in a given population, that can be accounted for by events that happen to both twin, affecting them in the same way.
Unshared environment: the portion of variance in a trait, in a given population, that can be accounted for by events that happen to one twin but not the other, or events that affect them in different ways. Shared environment: the proportion of variance in a trait, in a given population, that can be accounted for by events that happen to both twin, affecting them in the same way.
The concept of heritability, although useful, is easily misunderstood. It measures how much variability is due to genetics within a given population, not the contribution it makes in a given individual. If the heritability of height is about 0.69 it doesn't mean that 69% of a persons height has to come from their genes and 31% from their environment. It means that 69% of the differences in height between different people, within that population are due to their genes.
The more our society is based upon equal opportunities, the more that genetic differences will matter.
Linking genetic differences to brain and behavior
Heritability is a statistical measure that doesn't say anything directly about particular genes of their function.
The two approaches that one could adopt for analysis of genetic differences are called:
- Genotype-first: an analysis approach in which different genotypes are used to explore for phenotypic variation.
- Genotype-first: an analysis approach in which different genotypes are used to explore for phenotypic variation.
- Phenotype-first: an analysis approach in which different phenotypes are used to explore genetic differences.
Genome-wide association study (GWAS): a phenotype-first approach in which the presence/absence, or continuous variation,in a trait is linked to variations at many different sites in the genetic code.
Orofacial dyspraxia: an impaired ability to perform the coordinated movements that are required for speech. Linked to a mutation in a single gene called FOXP2.
There is a reduced volume in the basal ganglia (caudate nucleus) that correlates with the level of orofacial dyspraxia. The basal ganglia have a key role in the control of voluntary movement.
What do studies of the normal version of the FOXP2 gene reveal about its possible function? The product of the FOXP2 gene is what is called a transcription factor i.e. its molecular function is to affect the expression of other genes.
There is a reduced volume in the basal ganglia (caudate nucleus) that correlates with the level of orofacial dyspraxia. The basal ganglia have a key role in the control of voluntary movement.
What do studies of the normal version of the FOXP2 gene reveal about its possible function? The product of the FOXP2 gene is what is called a transcription factor i.e. its molecular function is to affect the expression of other genes.
Epigenetics
Although the structure of the genetic code for each person is fixed at conception, the functioning (or "expression") of the genetic code is highly dynamic. The expression of the genetic code is also influenced by the environment - a phenomenon termed epigenetics. In epigenetic markings the genes are not changed but get tagged with a chemical marker that dampes (e.g. a methyl group) or accentuates (e.g. an acetyl group)
Although the structure of the genetic code for each person is fixed at conception, the functioning (or "expression") of the genetic code is highly dynamic. The expression of the genetic code is also influenced by the environment - a phenomenon termed epigenetics. In epigenetic markings the genes are not changed but get tagged with a chemical marker that dampes (e.g. a methyl group) or accentuates (e.g. an acetyl group)
Gene-environment correlation (rGE)
Gene-environment correlations: genetic influences in people exposure to different environments. For example, people will seek out different environments depending on their genotype.
Gene-environment interactions
Gene-environment interactions: susceptibility to a trait depends on a particular combination of a gene and environment.
Gene-environment interactions: susceptibility to a trait depends on a particular combination of a gene and environment.
Monoamine oxidase A: the genes codes for an enzyme involved in the metabolism of dopamine, norepinephrine and serotonin. Mutation: antisocial behaviour.
MOA-A, 5-HTT, COMT all 3 are essentially normal genes that given a particular environment leads to an increased vulnerability of psychiatric problem but without a need for simple reductionism (e.g. a gene for depression) or determinism (i.e. that an outcome is guaranteed).