What is the influence of early brain insult on cognitive and social development? - Chapter 3

The development of motor and perceptual skills through early childhood is characterised by dramatic progression across cognitive and social domains. The emergence of most functional abilities (such as swallowing, grasping objects, sitting independently, walking independently, running, biking, and (un)dressing independently) cannot be determined accurately as there is considerable variation in the timing of skill acquisition across the normal population. When the developmental process in interrupted by early brain insult, this variability increases even more, so that developmental predictions become even less reliable. 

What is the difference between the domain-specific models and the domain-general framework?

In the literature, there is an ongoing debate regarding the mechanisms underlying the maturation of cognitive abilities. Two frameworks are contrasted: domain-specific and domain-general. The domain-specific approach is based on a 'modular' or 'localisationist approach in which individual cognitive skills are considered as developing according to a unique time-table and set of rules. This approach is often applied to language development. In contrast, the domain-general approach is based on the idea that the emergence of cognitive skills follows a more general path, where the development of specific skills is dependent on a series of cognitive processes. This is more in line with the emergence of functional neural networks. Critical to all aspects of cognitive development, according to this framework, are: information processing skills, including attention, processing speed, and memory. 

A key model within the domain-general framework has been developed by Cowan (1999). It is an integrative systemic model, which is primarily structural, and incorporates components of attention, memory, processing speed, and central executive (directing the focus of attention and formulating strategies for efficient performance). According to this model, the individual must first attend to information, register and encode it, and then store it in memory. All these aspects of processing have limited speed and capacity. Across each of these steps are connections. Consequently, limitations in development of any of these components will reduce the efficiency of the system as a whole. 

Which attentional components are commonly reported in the literature? 

Attentional skills are critical for the development of neurocognitive systems, which subsequently influence adaptive, social, and academic functioning of children. Impairment of attentional skills may yield that children are less able to learn and acquire skills from their environment in order to function independently in daily life and make use of both formal instruction and incidental environmental learning. It is therefore important to accurately map the attentional profile of children, as this may enable the implementation of appropriate and accurately targeted interventions. 

Attention is represented an integrative neural system, which involves contributions from various structures including the brain stem, reticular activating system, and posterior and anterior cerebral regions. The development of attention is characterised by a systematic increase in the ability of the child to override innate response tendencies and replacing these with more appropriate ones in situations where is it beneficial to do so.

Some of the earliest proposed models are the model by Alexander Luria (1973), who proposed two attentional systems operating within the brain, and Posner (1978) who proposed a dual-system model of attention, also suggesting two components to attentional processing; one in the posterior cerebral cortex and a second, higher-order system, in the anterior brain regions. 

Based on this seminal early work, current models of attention describe an integrated system consisting of a number of separate but increasing components. Each component is subsumed by a particular cerebral region underpinned by an attentional brain network. Disruptions to this system will result in deficits in one or more aspects of attention. Although there is not universal agreement of these components, the following attentional components are commonly reported in the literature:

• Vigilance (arousal): sustained attention or the ability to keep attention over time.
• Selective attention: the ability to target attentional resources to a specific task, thereby filtering out distracting stimuli, or to detect relevant stimuli and create motor responses in the context of background distraction.
• Attentional control: comprising inhibition (the ability to intentionally suppress a dominant, automatic, or prepotent response), self-regulation and monitoring (the ability to manage one's own thoughts, feelings, and actions in adaptive and flexible ways across a variety of different contexts). Attentional control mainly refers to shifting attention (the ability to shift attentional focus) and dividing attention (the ability to simultaneously attend to two tasks or stimuli), as these require flexibility and higher-order skills that are consistent with more executive attention processes. 

Disruptions of attentional development can be seen in a range of neurodevelopmental disorders, such as attention deficit hyperactivity disorder (ADHD), autism spectrum disorder ASD) and Tourette's syndrome. There are large differences in the nature of attention deficits across these groups, perhaps due to different underlying cerebral pathology or possibly due to different timing of onset of the condition. 

What are the effects of impaired memory development? 

Different models have been developed to explain the process by which information is registered, encoded, stored, and retrieved. Although these models vary greatly, there is some consistency with respect to the major components described in these models:

• Sensory store: where information enters the system via the sensory organs and is briefly held.
• Short-term memory, long-term memory, and working memory: although models incorporating these structures are less consistent, they generally incorporate notions of encoding and analysis, which involve active processes such as rehearsal and chunking.
• Central executive: taking a managerial role in directing voluntary attention and enabling voluntary retrieval and activation of stored information. 

The development of memory skills begins already at birth. Research has shown that newborns already exhibit habituation to familiar stimuli; memory for the familiar stimulus. Advances in memory function are clearly documented throughout childhood, although -not surprisingly- there is variation among individuals in the developmental trajectories. Generally, recognition skills are first acquired, followed by immediate memory capacity (measured by the number of digits or letters a child can remember at a time), recall and repetition. 

The development of memory is particularly vulnerable to interference following early cerebral insult. The earlier such insult occurs, the higher the degree and generalisation of the problem. Memory impairment occurring during childhood interferes with the efficient acquisition and consolidation of most or sometimes all knowledge and skills, limiting the potential development of the child. These problems are commonly manifested by poor educational progress and difficulties in learning social rules. 

How does impaired processing speed affect cognitive and social development?

Processing speed is the rate at which information is transmitted throughout the information processing system. Processing speed is a reflection of the efficiency of the overall system. Generally, processing speed increases as children become older. Impaired processing speed may have wide-ranging implications for children. They will be unable to keep up with peers in various circumstances. For example, if speech input or output speed is slowed, the child may appear dysfluent and experience difficulties in (general) conversations. A slowed motor output may restrict the child within the classroom, failing to complete tasks within the set time limit. Slowed responses may limit the capacity of the child to participate in sporting and other leisure activities.

How does impaired executive function affect cognitive and social development?

Although there is a vast body of literature on executive function (EF), there is little agreement on its exact definition. Executive function can possibly best be seen as a referring to a neurobehavioural managerial role, directing attention, monitoring activity, and coordinating and integrating information and activity. A model proposed by Anderson (2002) considers the following distinct, yet integrated domains underpinning the cognitive and behavioural aspects of executive function: 

• Cognitive flexibility (divided attention, working memory, conceptual transfer, feedback utilisation).
• Goal setting (initiative, conceptual reasoning, planning, strategic organisation).
• Information processing (efficiency, fluency, speed of processing). 
• Attentional control (selective attention, self-regulation, self-monitoring, inhibition).

Development of executive skills emerges in infancy and continues throughout early adulthood. Different components of executive function develop at different rates. These different developmental trajectories are largely determined by the maturation of particular brain structures that underpinning the particular process and the improved interconnectivity of brain regions that form the executive neural system. 

Impairment in the development of executive function, also known as executive dysfunction, has been consistently reported in children with developmental and acquired conditions, such as traumatic brain injury, low birth weight, congenital brain disorders, and phenylketonuria. Although the identification and documentation of executive (dis)function is possible, it is more difficult to determine the neural causes. As executive function is reliant on lower-order skills, it is important to first identify any deficits in these abilities before attributing the cause of impaired test performance to pure executive impairment.

How do impaired social skills influence social and cognitive development? 

Social skills, or social competence, is a term that is used to refer to a range of components:

• Social competence: the ability to achieve personal goals in social interaction while simultaneously maintaining positive relationships with others over time and across different situations.
• Social interaction: the ability to modify social actions and reactions between individuals and groups to the interaction partner(s).
• Social adjustment: the capacity to adapt to the demands of the social environment.

The development of social skills emerges gradually throughout childhood and adolescence as the result of a dynamic interplay between the individual and the environment. New-borns already are sensitive to facial stimuli, for instance direct gaze, upright faces, and straight heads. Around two to three months, infants demonstrate social initiatives and preferences in processing and recognition of visual and auditory stimuli.

Social functioning requires the efficient working of an intricate neural system. Impaired social skills (mainly observed by damage to the prefrontal cortex and the orbitofrontal cortex) can cause psychological distress, social isolation, and reduced self-esteem. Each of these can have major implications for the quality of life.