Problems with the learning process

Problems with the learning

In some infants, perceptual processing that depends upon innate recognition may be damaged and perceptual attributes that lead to salience may not be perceived. Perception that depends upon temporal processing may be slowed and crossmodality may be impaired. Meaning may be more easily accessed visually (i.e. what is seen may make more sense than what is heard). Infants learn from the repeated familiar and respond to difference – a learning style used in the ‘habituation to repeat stimulus’ in developmental experiment.

Learning from the familiar needs repeated stimulus and is enhanced if as many features as possible are fixed and what is remembered depends upon the match between context and item. This is a stage of normal development referred to as ‘context bound’ learning, when children recognize their own cups or shoes, for example, but not ‘cupness’ or a sentence said by one person in one place but not another. Some children get stuck in this stage and require a sustained high degree of contextual or environmental sameness to show a skill. This is particularly shown in autism.

Children learn from ‘contingency’ – the event that follows within 3–5 seconds of their action. This may be disrupted by a number of mechanisms, such as:
1. failure of the adult to make the response (depressed/mentally ill caregiver);
2. the child not giving a clear enough signal (as for those who are blind or who have cerebral palsy).

Aspects of maternal or caregiver behavior that promote learning need to be sensitively adjusted to developmental level. Thus at 2 years of age, language input needs to be explicitly directive and adult actions tied to the focus of child interests. By 3 years less parental direction is needed because the child has more language and is learning to manage her own goal-setting and problem-solving skills.

Play complexity is enhanced by caregiver behaviors that maintain a child’s focus of attention rather than redirect it. Children also learn more through the process of learning itself. For example, learning particular names of shapes accelerates shape learning generally, as though attention to the ‘shape concept’ allows noticing of ‘shapeness’. The child’s ability to inhibit and select responses and to try alternatives is crucial to all cognitive learning. This is seen in the progression from the ‘trial and error’ approach, where repeatedly forcing the square into the round hole is a less useful strategy than trying alternative placements with inset puzzles, which shows more flexibility of mental skills.

The progress from sensorimotor play, from mouthing to manipulation at 6–10 months, then to imitation and ‘definition by use’ play by 12 months is followed by increasing creativity in play. Make-believe play with dolls, in which the child is reconstructing events observed, is an important element of this period. It indicates early symbolic representation and concept formation. The child begins to use language to direct or describe the action of his play, and as command of language improves the need to act out the events decreases. Lack of ideas, failure of pretence and inability to play constructively are indications of a developmental problem. The cognitive stage of mental symbolic development allows more complex thinking, including reflection and planning. Symbols (word ) facilitate thinking about, and reference to, situations that are not in the ‘here and now’. Answering simple questions dealing with nonpresent situations presents difficulty before 3 years and even primary and junior school children still tend to be concrete in their way of thinking (i.e. real objects, here and now). Early in school life, judgments are made intuitively on superficial appearances. With increasing experience and language at their disposal, children can imagine complex situations, think out the most appropriate solution and anticipate the outcome.

This requires the ability to think abstractly and imaginatively. Thus, children develop logical thinking from assimilating experience into schemes or general laws that they can apply to a range of situations. The use of symbols also helps to inhibit prepotent responses of behaviors and allows increasing distancing from the ‘here and now’ (rather like the red card in football games). Children are developing skills of representation and object substitution in the second year, but the skill of mentally comparing reality with representation (dual reality) is not clearly seen in research studies until aged 3 years. For example, children shown where an object is hidden in a scale model of a room can find it in the real room at 3 years, but not at 30 months. At 3–6 years, children get increasingly skilled at knowing that others can hold particular views, even false views, and thus have what has been called a ‘theory of mind’. In the classic Wimmer and Perner task, roughly half the 4- to 5-year-old children could correctly show ‘knowing’, whereas over 90% of 6- to 9


Cognitive and Learning Development

Learning Development

Children learn about their world by listening, observing, copying and experimenting. The world of infants is very small and their repertoire of skills limited. They learn about their world through observation, by reaching and grasping objects and by copying sounds and actions. By contrast, toddlers are mobile and their worlds are large. Their motor skills are greater and they begin to attempt constructional tasks, thereby learning about aspects such as size, shape, the properties of objects and space.
The child is an active participant in the learning process. Progress depends upon not only the learning opportunities, but also the child’s learning strategies and processes. Information processing in infants is related to later cognitive abilities in memory and speed of processing, thus in visual recognition tasks, habituation, learning, object permanence and attention, including crossmodality.

In older children, the features of new problem solving that are linked to learning are variability, ability to shift focus, frequency of self-correction and diversity of strategies.


B Cells

B Cells

B-Cell Development

B cells constitute approximately 10% of peripheral blood leukocytes. They develop in the bone marrow from hematopoietic stem cells but achieve maturity in peripheral lymphoid organs. Early progenitors committed to the B-cell lineage (pro–B cells) begin recombination at the immunoglobulin heavy-chain loci. Successful recombination leads to expression of μ–heavy chain, distinguishing them from pre–B cells. With the surrogate light chain and the Ig-α/β signaling machinery, an immunoglobulin-like heterodimer is expressed on the surface (pre–B-cell receptor). The pre–B-cell receptor signals a halt to μ–heavy-chain recombination, and Igκ or Igλ light-chain recombination begins. The surrogate light chain is replaced by a successfully formed κ or λ light chain, and the B-cell receptor is expressed as surface IgM, which distinguishes the immature B cell.

B Cells

B-Cell Responses

B cells provide humoral immunity against extracellular pathogens through the production of antibodies that neutralize pathogens and toxins, facilitate opsonization, and activate complement. Primary infection or vaccination results in prolonged production of high-affinity specific antibodies, the basis of adaptive humoral immunity. On the other hand, IgM antibodies are produced in the absence of infection, are of lower affinity, play a role in first-line defense against bacterial infection, and assist in clearance of endogenous cellular debris. Naïve follicular B cells reside in the follicles of secondary lymphoid tissues. Antigen arrives in these lymphoid organs through circulation of soluble molecules or immune complexes or via transportation by dendritic cells. The B cells, via the B-cell receptors, process the antigens in the context of MHC class II and then migrate to the T cell–B cell interface, the border between the T-cell zone and B-cell follicle, where they encounter primed TH cells of cognate specificity. This generates signals from T-cell–derived cytokines and triggers binding between CD40 ligand (CD40L, on T cells) and CD40 (on B cells) that sustains B-cell activation and promotes immunoglobulin class switching. Signaling through CD40 and its interaction with CD40 ligand on T cells is essential for the induction of isotype switching.

The effector T-cell cytokines have various functions: IL-1 and IL-2 promote B-cell activation and growth, IL-10 causes switching to IgG1 and IgG3, IL-4 and IL-13 cause switching to IgE, and TGF-β causes switching to IgA. IFN-γ, or some other undefined product of TH1 cells, appears to induce switching to IgG2. Activated B cells either migrate into the follicle and, with continued T-cell help, initiate the germinal center reaction or migrate to the marginal zone and differentiate into short-lived plasma cells. These latter cells secrete antibody for 2 to 3 weeks, which provides a rapid but transient source of effector molecules.

The B cells in the germinal center undergo specificity diversification through somatic hypermutation, and high-affinity variants are selected by survival advantage, a process termed affinity maturation. Thus within the germinal centers, sequential cycles of proliferation, B-cell receptor diversification, and selection amplify high-affinity variants of the original activated B cell. The cells that then exit the germinal center reaction give rise to the memory compartment, which consists of affinity-matured memory B cells and long-lived plasma cells. When memory cells reencounter antigen, they divide rapidly and expand their numbers or differentiate into antibody-secreting plasma cells. These long-lived plasma cells are terminally differentiated B cells incapable of further division that home to the bone marrow and secrete high-affinity class-switched antibody. These B cell responses are orchestrated with the help of T cells and their cytokines and are termed T-cell–dependent B-cell responses.


Sound Perception

Sound Perception

The ear is fully developed at birth and sound perception is possible in utero. Speech perception and recognition of voices of different speakers are present shortly after birth. The capacity for smell and touch as well as the other senses are similarly developed at birth and play an important part in the perceptual learning about the environment.


Atopic Dermatitis

Atopic dermatitis

Although atopic (infantile or flexural) dermatitis may begin at any age, it usually commences from about the sixth week onwards. It is characterized by a chronic, relapsing course. In the infantile phase lesions are present mainly on the head, face, neck, napkin area, and extensor aspects of the limbs. As the patient grows older and enters childhood, the eruption shifts to the flexural aspects of the limbs. Chronic atopic cheilitis may also be evident. Pruritus is intense and constant scratching and rubbing leads to lichenification and frequent bouts of secondary bacterial infection. Atopic eczema is commonly associated with dry skin (xerosis). Vesiculation is uncommon. there is an increased risk of dermatophyte and viral infections. The disease improves during childhood and, in over 50% of cases, clears completely by the early teens. approximately 75% of patients with atopic dermatitis have a family history of atopy and up to 50% have associated asthma or hay fever. The condition typically worsens in the winter months.

Atopic dermatitis

It is associated with an increased incidence of contact dermatitis, particularly affecting the hand. Other features that may be seen include ichthyosis (50%), nipple eczema, conjunctivitis, keratoconus, bilateral anterior cataracts, sweat-associated itching, wool intolerance, perifollicular accentuation, food intolerance and white dermatographism. 5 Infraorbital folds (DennieMorgan folds) are said to be characteristic of atopic dermatitis, particularly when double.


Psoriasis

Psoriasis

Psoriasis is a chronic relapsing and remitting disease of the skin that may affect any site. It is one of the commonest of all skin diseases, with a reported incidence of 1–2% in Caucasians. It is rare among blacks, Japanese, and native North and South american populations. Males and females are affected equally. Although psoriasis may occur at any age, it most frequently presents in the teens and in early adult life (type I psoriasis). A second peak in which the disease is often milder appears around the sixth decade (type II psoriasis).

Psoriasis

The classic cutaneous lesion of psoriasis vulgaris (plaque psoriasis), developing in about 85–90% of patients with psoriasis, is raised, sharply demarcated, with a silvery scaly surface. The underlying skin has a glossy, erythematous appearance. If the parakeratotic scales are removed with the fingernail, small droplets of blood may appear on the surface (auspitz’s sign); this is diagnostic. plaques, when multiple, are often symmetrical and annular lesions due to central clearing are a common finding. the scalp, the extensor surfaces (mainly the knees and elbows), the lower back, and around the umbilicus are particularly affected. the clinical features, however, show regional variation: scalp involvement often shows very marked plaque formation, whereas on the penis scaling is commonly minimal and the features may be mistaken for Bowen’s disease. Linear lesions (linear psoriasis) follow previous trauma (koebnerization).

Source: P. McKee, J. Calonje – McKee’s Pathology of the Skin (Elsevier)