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EXECUTIVE DYSFUNCTION AND RELATED COGNITIVE DYSFUNCTIONS IN CHILDREN WITH TBI
EF can be impaired after traumatic brain injury (TBI) 12,69–72 6,69 and influence a series of outcomes including academic achievement42,73,74, social cognition10, vocational outcome 15 and ability to live independently. The level of executive dysfunction is found to be related to the injury severity and younger age at injury 14,71,75–79. Relationship between age at injury and outcome is complex and literature begins to suggest that it is not linear19,80. TBI sustained at an earlier age (when cognitive functions have not yet developed) is prone to generalized delayed adverse outcome, but outcome may be even worse when the function is at a rapidly developing stage77 at the time of injury.
Impaired awareness/metacognition, sometimes also termed “anosognosia”, is a common phenomenon described in children who have sustained a TBI 818283, but few studies have explored it, partly because of a lack of underlying models and lack of adequate assessment tools. In children, self-awareness is particularly difficult to capture and assess, as it results from a combination of organically based unawareness (due to brain injury) and simple developmental immaturity 83 present in typically developing children as well, which makes it harder to characterize. In metamemory, children with TBI have exaggerated overconfidence in their performance and poor estimation of memory span84.
Prospective memory (PM) has been shown to be impaired in children with brain injuries 85,86. PM problems are reported as a major concern by the parents of children with TBI 87. The ability to compensate for PM deficits in adults significantly predicts the ability to live independently88. Parents of children with TBI report serious concerns for their child’s safety and ability to be left unsupervised even briefly because of substantial PM impairments87.
EXECUTIVE DYSFUNCTION AND GOAL NEGLECT
As noted earlier, working memory (WM) involves holding information in mind and mentally working with it (or said differently, working with information no longer perceptually present)30,31.
Cowan’s model of WM89,90 in adults distinguished between (1) information that is accessed at any moment for further processing (the focus of attention), and (2) the information held available in the background for later use (the activated part of long-term memory). Only the focus of attention is assumed to have limited capacity. The activation of representations in long-term memory is not capacity limited, but activation may be reduced through decay or interference. In his model, information can be processed in the focus of attention without being impaired by the demand to hold other information in the activated part of long-term memory. Cowan’s model is supported by simple experiments such as Garavan’s 91: Garavan asked participants to count squares and triangles that appeared sequentially, in random order, on the screen, so that participants had to remember and update two running counts simultaneously. The task was self-paced, so the latency of individual counting operations could be measured. Garavan observed that a switch from one mental counter to the other (e.g., when a triangle followed a square) took 300–500 ms longer than updating the same counter again (e.g., when a square followed a square). This indicates that participants held one counter in the focus of attention while memorizing the other outside the focus. He concluded that the 300-500 extra ms reflected the time it takes to switch the focus of attention from one list (square) item to the other (triangle).
Cowan’s “focus of attention” was then split further into two different regions in Oberauer’s model. In a series of experiments, Oberauer 92 showed that:
-There are items memorized for later recall but not accessed during a concurrent processing task: these items do not affect the speed of the processing task because they are in the activated long-term memory (e.g. holding in memory a number list while updating another number list with arithmetic operations).
-There are other items that are held available for direct access and which affect the processing latencies (updating another number list with arithmetic operations).
-Finally, there is a single item at any moment that is actually selected as the object of a cognitive process (the number currently undergoing the arithmetic operation).
Oberauer conceptualized working memory as a concentric structure of representations with three functionally distinct regions (see Intro.2).
1. The activated part of long-term memory can serve, to memorize information over brief periods for later recall.
2. The region of direct access holds a limited number of chunks available to be used in ongoing cognitive processes.
3. The focus of attention holds at any time the one chunk that is actually selected as the object of the next cognitive operation.
So for Oberauer, working memory is an organized set of representations characterized by their increased state of accessibility for cognitive processes and contents of working memory can be categorized with respect to their access status.
OBERAUER’S MODEL EXPLAINING GOAL NEGLECT PHENOMENON
Oberauer’s model can be very useful in explaining goal neglect in patients with executive dysfunction experience. As the focus of attention can manipulate one item only, only the current sub-goal is held in the focus of attention, while the final goal is held in the activated long-term memory. Following Oberauer’s model, the final goal is therefore not accessible directly but linked to the current sub goal through associative links (see figure Intro.4). The activation of representations of the final goal in long-term memory can, however, become lost through decay or interference. As tasks proceed, the final goal progressively drops towards less activated parts of long-term memory. Following Oberauer’s view that WM is an organized set of representations characterized by their increased state of accessibility for cognitive processes, a goal whose activation levels have dropped within long-term memory is less accessible and more likely to be forgotten/neglected. Figure Intro.4: Oberauer’s model applied to goal maintenance that allows an organized behavior during a task and the retrieval and implementation of an intention in prospective memory.
GOAL NEGLECT AND PROSPECTIVE MEMORY
In the same way that goal neglect theory attempts to explain failure to maintain a task’s final goal in WM (i.e. in a time-limited duration), goal neglect can be applied to prospective memory failures, to explain failure to maintain memory for a goal over a longer duration (hours, days or month). Because the construct is the same, again Oberauer model is useful to explain how an intention can inappropriately drop to general (inactivated) long-term memory and no longer be activated and therefore become inaccessible to the focus of attention. In this case, environmental cues (e.g. seeing a letter box and remembering to post a letter) that normally act as associative links are no longer sufficient (because the goal is too low in activation and accessibility for the focus of attention to use it). When exploring PM in the laboratory, PM tasks tend to use infrequent targets: the higher the frequency of target stimuli, the more the task relies on working memory, because the frequent target acts as a constant reminder of the intention and is therefore maintains its activated state in long-term memory92. On the other hand, if the target is infrequent, as the on-going task proceeds, the intention drops progressively to lower attentional levels. Dysexecutive patients therefore are more likely to experience PM failures, by being impaired in upgrading the activation of their intention.
INTERVENTIONS BASED ON THE MODEL OF GOAL NEGLECT AND IMPAIRMENT IN VIGILANT ATTENTION
Goal Management Training (GMT) approaches to executive dysfunction aim to train adult patients to maintain goal activation, by compensating for vigilant attention impairment through the use of content-free cues that can be either external, exogenous (such as auditory alerts9596, text messages with a “Stop” cue97) or patient-generated (by training patients to regularly pause action and remind themselves of their goal 98,99 ) – In GMT patients are encouraged to stop ongoing behaviour in order to define goal hierarchies39 and monitor performance and regularly update current goals in working memory. Goal Management Training methods target executive dysfunction as well as prospective memory, because the underlying impairment (goal neglect resulting from deficient endogenous reactivation of relevant goals) is considered to be the same. While GMT is widely used in adults98–101, the validity of interventions derived from Duncan’s model has never been explored in children. A number of questions arise: Is it possible to alleviate prospective memory impairment by using goal neglect-based interventions? Will an improvement in PM be accompanied by improvement in complex task management?
Table of contents :
Acknowledgments
Table of Contents
Preliminary Note
List of abbreviations (in bold: most often used abbreviations in this PhD)
Introduction
Childhood Traumatic Brain Injury
EF in children
Other cognitive functions relying on executive functions
Executive dysfunction and related cognitive dysfunctions in children with TBI
Executive dysfunction and goal neglect
Rehabilitation of executive dysfunction in children
PhD overview
PART 1: Characterisation and Assessment of Executive Functions and two related functions: Prospective Memory and Self-awareness
Chapter 1: Executive functions following severe childhood traumatic brain injury – the TGE prospective longitudinal study: age at injury vulnerability periods
Introduction
Methods
Results
Discussion
Chapter 2: Ecological Prospective Memory assessment in children with acquired brain injury using the Children’s Cooking Task
Introduction
Methods
Results and Discussion
Chapter 3: Prospective Memory seven years after severe childhood traumatic brain injury – the TGE 2 prospective longitudinal study
Introduction
Methods
Results
Discussion
Chapter 4: Self-awareness assessment during cognitive rehabilitation in children with acquired brain injury: a feasibility study and proposed model of child anosognosia
Introduction
Methods
Results
Discussion
PART 2: Intervention
Intervention theory
Chapter 5: Rehabilitation of Executive Functions in Children EF in children
Developmental Issues in supporting EF for children
Current practices in EF interventions for children
Promising approaches
Problem-Solving Interventions in children with ABI
Examples of effective interventions for dysexecutive children in developmental
pathology
Interventions that have proven to be effective for children’s EF development outside
brain clinical conditions
Challenges, clinical perspectives and future research
Conclusion
Chapter 6: Goal Management Training for rehabilitation of executive functions: a systematic review of effectivness in patients with acquired brain injury.
Introduction
Methods
Results
Discussion
Experimental data
Chapter 7: Context-sensitive Goal Management Training for everyday executive dysfunction in children after severe TBI.
Introduction
Methods
Results
Discussion
Chapter 8: Metacognitive strategy use in children with severe TBI
Introduction
Methods
Results
Discussion
Chapter 9: General discussion
Summaryof findings
Strength and Challenges of the PhD
Limitations of the PhD
Outcome measures
Factors mediating effectiveness that could apply to new interventions
Final conclusions
References
