Summaries: the best scientific articles for behavioral neuroscience and neuroendocrinology summarized

Approximately 75 years ago, the concept of fluid and crystallised intelligence was first introduced to the psychological community by Raymond B Catell. The specification of the structure of intelligence has been considered the greatest achievement in psychology. Indeed, a consensus has emerged regarding the taxonomy of intellectual abilities. Nowadays, the concept of intelligence continues to be a topic of active research and controversy. The present article aims to provide a brief overview of the origin of this concept, the early efforts to define intelligence and uses of intelligence tests to study pressing social issues, and the ongoing controversies with fluid intelligence and the structure of intelligence. 

How has the concept of intelligence developed during the nineteenth century? 

The first scientific study into the nature of intellectual functioning dates back to Francis Galton (1883) in the late nineteenth century. Galton used a quantitative index of relationship called correlation to study the nature of basic human abilities. 

Following the spirit of Galton, James McKeen Catell (1890) proposed a series of ten tests. He claimed that this standardised testing procedure could be used to determine the structure of intelligence, although the term intelligence appears nowhere in his article. 

A few years later, C. G. Spearman (1904) published a paper that described his study of Galton's hypothesis that a general mental ability underlies every kind of mental effort. He studied this uniformity of function (also known as general mental ability) using factor analysis, a statistical procedure that he had invented. He studied the relationship between different types of intelligence and student performance on both physical and mental tests. Spearman found four types of intelligence:

1. Present efficiency: the performance on (school) tests. 
2. Native capacity: derived by determining the difference between each student's rank in school and rank in age.
3. The general impression the student presented upon others; teacher's ranking as to whether the student was bright, average, or dull.
4. Common sense: sharpness and common sense out of school.

Spearman arrived at the following conclusion: "all branches of intellectual activity have in common one fundamental function (called g) whereas the remaining or specific elements (called s) of the activity seem in every case to be wholly different from that in all the others" (Spearman, 1904, p.284). This function g could be one function, or a group of functions. This paper is still of influence today and has been cited 1,327 in 2016 on APA PsychNET Gold. 

During the early twentieth century, the development of intelligence tests developed rapidly. One such test was developed by Binet and Simon (1905); they developed an individual intelligence test to help identify cognitively impaired and abnormal school children in France. Intelligence tests were now used by, among others, the American army to recruit soldiers as well as by the industry to assess the suitability of workers for specific jobs and to study presumed differences in intelligence between the sexes and races. In other words, intelligence testing during this period was driven not only by practical concerns, but also by those seeking guidance on how to address various pressing social issues. However, most of the intelligence tests used to assess both individual and group intelligence were not based on an explicit, well-defined, validated theory of intelligence, even though there was no shortage of such theories. 

What were the major attacks on Spearman's g factor? 

After Spearman's publication, it remained silent for a while. It was not until about the 1930s that major attacks on his work began to emerge.  

The first major attack to Spearman's findings came from Thurnstone (1931) who proposed multiple factor analysis to study the structure on intelligence. Thurnstone found that intelligence was not comprised of one factor, but instead of seven: visual imagery, perceptual speed, memory, word fluency, number facility, induction, and verbal relations.

A second attack on Spearman's general intelligence factor came from one of his students; Guilford (1967). Guilford proposed a three dimensional classification model of intelligence.

Another attack on Spearman's work came from R.B. Catell (1971), who began publishing doubts from the 1930s onwards. After several publications, Catell published a book in 1971 entitled Abilities, their structure, growth, and action. In this book, he summarised his prior papers and spent a considerable amount of time discussing the rationale of gf (fluid intelligence) and gc (crystallised intelligence).

Fluid intelligence (fc)

Fluid intelligence (gf) appears to operate whenever the sheer perception of complex relations is involved. It is an expression of the level of complexity of relationships which an individual can perceive and act upon when he does not have resources to answers to complex issues already stored in memory. Fluid intelligence is largely hereditary. 

In other words, fluid intelligence is considered an innate, neurologically based phenomenon. It is, in essence, a novel problem-solving capacity that demonstrates itself when crystallised intelligence abilities are of little or no use. Fluid intelligence determines the upper limit of the amount of crystallised intelligence one accumulates. Fluid intelligence declines with age as a consequence of the neurological insults that occur from adverse environmental events and normal aging.

Crystallised intelligence (gc)

Crystallised intelligence (gc) is the set of judgemental skills from investigating gf in those cultural activities which need high gf. The form of crystallized intelligence is never the same in two cultures. Crystallised intelligence arises not only from better educational opportunity, but also from a history of persistence and good motivation in applying fluid intelligence to approved areas of learning. In contrast to fluid intelligence, crystallised intelligence results from learning and is more influenced by the amount of education and learning experiences to which an individual is exposed. It may take the form of implicit or explicit semantic knowledge, and skills. 

Nowadays, research is preceding with ongoing research about G and GF-GC, offering refinements of these theories. Overall, it can be stated that the gf-gc theory has been accepted into the mainstream. Evidence therefor comes from test publishers like NCS Pearson, who have explicitly incorporated the gf-gc theory in their test development. 

In summary, it appears that although the concepts of g, gf, and gc have strong empirical support, there is an ongoing debate in regard to whether g is comprised of one, two, or more factors. 

What is currently known about the neuropsychology and neurology of GF?

The final section of this paper briefly addresses some of the putative neuropsychological components of gf and the neurological substrates underlying this domain. As noted earlier, fluid intelligence is defined as a general, relation-perceiving span, or the capacity to perceive relations. In order to perceive such relations between two or more objects, one has to be able to hold those two objects in mind and access one's semantic memory system with regard to what is known about each in order to ascertain their similarities and differences. To do so, working memory is essential. In fact, Kyllonen and Christal (1990) have suggested that working memory capacity might be the neuropsychological mechanism that is responsible for gf. If working memory and fluid intelligence are strongly related, it makes sense that if one could improve the working memory of an individual through training, it should yield a positive effect on the fluid intelligence of that individual. This was, however, not found to be the case in multiple studies. For example, Gignac and Watkins (2015) found that the association between working memory capacity and gf was insignificant after controlling for the general effects of general intelligence. Hence, it appears that the precise relationship between working memory, attention, and fluid intelligence, has yet to be determined. For now, the precise neuropsychological and neurological components of gf remain unclear. It is clear, however, that fluid intelligence involves components which include (among others), short-term memory, working memory, long term memory, and various attention and executive functions. 

In summary, the present paper briefly discussed the nature, origin, and evolution of Catell's (194) gc-gf theory. In doing is, it discussed the seminal work of Spearman (1904) with his discovery of a general function of intelligence, called g, as well as the challenges to his finding. The paper ended with some of the possible neurological substrates of gf. 

What is neurobiology of human attachments?

Neurobiology of human attachments is a new scientific field that integrates insights from other mammals with new tools available for human research to test the biological basis of human attachments.

Which are the four bonds observed across mammalian species?

The four bonds are parent-infant, romantic attachment, peers, and conspecifics (other humans). Attachment bonds in mammals are underpinned by functioning of two ancient systems, namely oxytocin and dopamine, which maintained basic organization across vertebrate evolution and supported group living in harsh ecologies and motivational goal-directed action throughout animal evolution. The integration of oxytocin and dopamine in striatum leads to mammalian bonding. In humans, attachment bonds are marked by selective and enduring features.

How does time sensitivity and pulsatility of the oxytocin and dopamine systems enable plasticity of neural networks to incorporate new attachments?

Oxytocin and dopamine are characterized by pulsatile release that supports time-keeping mechanisms implicated in patterned action and seasonal rhythmicity. The pulsatility and time sensitivity of oxytocin and dopamine enabled their involvement in neural plasticity. This neural plasticity is required for selective recognition and long-term memory, which are two key characteristics of human attachments.

• Pulsatility is a defining feature of oxytocin functionality across evolution. Oxytocin signals cause dendrite release without increasing electrical activity. It can become self-sustaining by creating auto-regulated release primed by salient experiences. Once it is activated, release is repeated in time-sensitive bursts. Special primed signals can trigger dendrite release, cause oxytocin to be relocated in vesicles from reserve to releasable stores. Future release is then shaped by the primed cue.
• Dopamine striatal neurons process the timing of reward and encode reward anticipation, building the internal sense of time in the brain. Dopamine neurons are sensitive to rewards that come from social interactions and can link rewards to attachment experiences, grounding rewards in cycles of caregiving actions. They can integrate social components into their temporal predictions. This permits social signals to act upon a pre-established synaptic tract and associate it with specific reward outcomes, and enables an increase in dopamine activity to become subjective and social.

What is bio-behavioral synchrony?

Bio-behavioral synchrony is the coordination of biological and behavioral processes between attachment partners during social contact and a key feature of human attachments. Temporal sensitivity of dopamine neurons enables humans to draw rewards from the experience of bio-behavioral synchrony, which is built on familiarity with the partner´s repeated social patterns. It evolved from the coordinated group activity of lower species where joint motor action (involving dopamine) is locked with coupled physiology to achieve survival-related collaborative goals (involving oxytocin).

What is trophallaxis?

Trophallaxis refers to the exchange of sensory signals among members of a social group. The term was extended to include social stimuli and to denote the reciprocal multisensory stimulation of low intensity that elicits approach response. Parenting is a form of trophallaxis. Three aspects of trophallaxis have been integrated into mammalian bonds:

• The low intensity and arousal-modulatory nature of attachments.
• The social reciprocity and online construction embedded in them.
• The trophallaxic process as charting a line from parent-child bond to life within social groups.

What is myoactivity?

Myoactivity refers to the stimulation of rhythmic tissue contraction. It is the most conserved function of the oxytocin system. Due to pulsatility there exists a dendritic release that supports oxytocin´s role in bonding. This leads to autoregulated, feed-forward release that is triggered by primed attachment experiences which, once activated, release repeated rhythmic bursts. These time-sensitive mechanisms make it possible for early attachment experiences to shape the organization of oxytocin in specific places in an infant´s brain.

What are the two key features of attachment bonds and how are they expressed in the four different bonds?

Two key features characterize attachment bonds, namely that they are selective (specific to attachment target) and long-lasting.

• The parent-child bond is selective and enduring.
• Romantic bonds are selective and enduring, but more precarious. Romantic attachments can terminate under normative conditions.
• Close friendships are selective and enduring, but in a weaker form. Humans can have numerous friendships at the same time and enduring friendships may dwindle without a clear breakup.
• Humans´ relationships to conspecifics is not selective nor enduring. However, humans have the unique ability to activate the behavioral and neurobiological systems of affiliation towards other humans.

What is unique about behavioral synchrony in humans?

During or following social contact, human synchrony is evident in four systems: behavior, autonomic, hormones, brain. Behavioral synchrony takes place in different ways in the human attachment bonds. Unlike other mammals, humans display behavioral synchrony toward strangers. They may coordinate gaze, use vocal turn-taking during conversations, display heart-rate coupling, or show brain-to-brain synchrony of alpha rhythms.

Which tools are used to measure human attachments?

• Autonomic response: measures of heart period and respiratory sinus arrhythmia, skin conductance.
• Peripheral measures of hormones, such as cortisol, oxytocin, testosterone, estradiol, progesterone, etc.
• Micro/macroanalysis of social behavior and behavioral synchrony: observations, global rating scales, and micro- and macro-level analysis.
• Peptide administration.
• Brain imaging, such as fMRI.
• Brain oscillations, such as EEG and MEG.
• Genetics and epigenetics.

Which main interconnected neural systems integrate to establish, maintain, and enhance our affiliative bonds with others?

• The reward-motivation system includes the striatum, amygdala, ventral tegmental area, orbitofrontal cortex, ventromedial prefrontal cortex, and anterior cingulate cortex. This system supports multiple attachment-related motivational behaviors, such as social seeking, social orienting, and maintaining contact across extended periods. The system is based on the fact that attachments have intrinsic motivational value that combine immediate hedonic response with approach motivation, goal-directed behavior, and learning.
• The embodied simulation/empathy network includes the insula, anterior cingulate cortex, inferior frontal gyrus, inferior parietal lobule, and supplementary motor area. This mechanism recreates other´s state in one´s brain via automatic interoception and internal representations. It relies on neural pathways that involve the experience of internal body formats and the perception of similar states in others via perceptual-motor coupling.
• The mentalizing system includes frontotemporal-parietal structures, particularly the superior temporal sulcus, posterior cingulate cortex, temporoparietal junction, temporal pole, and medial prefrontal cortex. Mentalizing processes involve complex top-down inferences of others´ mental states by attributing beliefs, thoughts, and intentions to others to create a full sense of ´togetherness´. They underlie the forming of attachments by building on one´s ability to appreciate multiple perspectives, understand the others´ goals and motives, and keep in mind the others´ values and concerns.

What correlations have been found that link socioeconomic inequality with brain structure?

• Socioeconomic status has been linked to cortical surface area, cortical thickness, and gray matter volume, especially in frontal and temporal regions which support the development of language, executive function, attention, memory, and emotion regulation.
• Family socioeconomic characteristics (parental education and family income) have been linked to children´s hippocampal volume, which is a structure that is important for learning and memory.
• Socioeconomic disadvantage has been linked with slower longitudinal growth of the hippocampus.
• Socioeconomic differences have been found in white matter microstructure, especially in areas that support executive functions, reading, and language.

What correlations have been found that link socioeconomic inequality with brain function?

• At six months of age, higher socioeconomic status was linked to greater high-frequency EEG power (which is associated with language development).
• At six months of age, family income and maternal education were associated with functional connectivity in the default mode network and the sensorimotor network.
• Lower family income has been linked to reduced connectivity between the hippocampus and amygdala and other cortical regions (for children).
• Connectivity partially explained the relationship between lower family income and negative mood and depression (for children).
• Functional brain development may be influenced by family level socioeconomic disadvantage as well as neighborhood socioeconomic disadvantage. Young people living in more advantaged neighborhood had a stronger positive association between age and functional connectivity than young people from more disadvantaged neighborhoods, in a pattern suggestive of faster functional brain development.

How do socioeconomic factors relate to the neural bases of language, emotion processing, and executive function?

• Inferior frontal gyrus lateralization of five-year-olds has been associated with maternal education.
• Socioeconomic differences have been linked to the neural response to learning new words.
• Neighborhood poverty has been associated with inferior frontal gyrus activation, supporting the idea that neighborhood disadvantage may account for extra variation in experience that is not caused by socioeconomic status of the family.
• Lower family income and lower socioeconomic status have been associated with increased neural activation to angry facial expressions in the fusiform gyrus, and increased amygdala responses to negative infant faces.

How can differences in experience be at least partially responsible for socioeconomic differences in brain and behavior?

Two mechanism are identified to help answer the questions whether socioeconomic status related differences in experiences and exposures lead to differences in outcomes, or whether outcome differences are the product of social selection, in which genetic underpinnings of academic achievement lead to differences in socioeconomic status:

• Cognitive/linguistic stimulation in the home may contribute to the emergence of socioeconomic disparities in the development of brain regions that contribute to higher-order language and cognitive skills.
• Exposure to chronic stress has serious effects on multiple brain and body systems, and is considered a mechanism linking socioeconomic disadvantage to neurodevelopmental differences.

What is the role of the prefrontal cortex in executive function?

The prefrontal cortex (PFC) is involved in multiple forms of higher-order cognition, such as working memory, inhibitory control, conflict monitoring, and shifting between rule sets. These cognitive processes are referred to as executive functions. They allow the formation and execution of future-oriented plans as well as the inhibition of behaviors that do not serve those plans. It provides the foundation for decision-making and self-regulation.

How do environmental influences affect executive function and PFC development?

Environmental experiences shape developmental processes through:

• Experience-expectant processes. The neural circuits that process sensory information are sculpted by specific environmental inputs during sensitive periods in early development. Think of the sensory system development and the processing of light and sound.
• Experience-dependent processes. These reflect emergent connections between neuronal populations in a way that reflects each person´s unique environmental experiences. Think of long-term memory and home stimulus exposure.

Recent research indicates that there is unlikely to be one set of specific environmental experiences for optimal PFC development, but instead, that PFC development reflect adaptation to the child´s changing environment.

How is socioeconomic status thought to influence executive function development?

A variety of mechanisms operating at multiple levels of influence have been suggested. Children in poverty lack rules, structure, and routines, and their environments are more chaotic, unstable, and disorganized. This is thought to produce poor executive function. Also, exposure to high levels of stress has adverse effects on PFC function and executive function development. However, these explanations are limited in their ability to explain the types of environmental influences that are required for healthy PFC and executive function development.

How can cognitive stimulation be a mechanism linking socioeconomic status and executive function?

Cognitive stimulation is characterized by access to a complex environment with developmentally appropriate learning materials, a complex linguistic environment, a rich variety of experiences, and the presence of a caregiver who interacts with the child consistently and uses strategies that promote learning. This cognitive stimulation supports development of the feed-forward and feedback loops between sensory processing regions and the PFC, laying the groundwork for executive function development.

How do caregiver interactions and linguistic experience shape early PFC development?

Two pathways have been identified:

• Attention Regulation Pathway. In environments with limited caregiver interactions, children receive less guidance to attention regulation and have less experience involving competition between sensory inputs for attention that needs to be resolved. Combined with reduced access to sensory complexity this may result in limited organized feed-forward information from the ventral visual stream to the PFC.
• Linguistic Pathway. As children learn language, which facilitates object recognition and semantic knowledge, the PFC is continually engaged in conflict resolution and performing computations that are necessary for engagement in more complex forms of competition resolution that are considered in the domain of executive function.

How does socioeconomic status influence cognitive stimulation in a child’s household?

Environmental complexity varies as a function of socioeconomic status. Children growing up in low socioeconomic status households tend to experience lower levels of cognitive stimulation, including language exposure, environmental complexity, and caregiver interactions. Children growing up in higher socioeconomic status household tend to experience more cognitively stimulation environments, through enriching experiences (such as daytrips, museums), educational information (e.g. books), greater visual complexity of the home, and greater parental involvement in learning.

How can cognitive stimulation support executive function development?

Research shows that cognitive stimulation is associated with individual differences in working memory, cognitive flexibility, and inhibitory control. Caregiver involvement plays an important role in this relationship. Parental scaffolding and a rich linguistic environment support a child´s language ability and brain systems. Finally, cognitive stimulation has been linked to the structure and function of the ventral visual stream and the PFC. Specifically, a lack of cognitive stimulation appears to influence the cortical structure and function of the ventral visual stream regions, as well as the connectivity between those regions. 

How does socioeconomic status affect the ventral and dorsal visual streams?

Variation in environmental experience is associated with development of the ventral visual stream and associated functions. Socioeconomic status appears to influence ventral visual stream-dependent processes, but not dorsal visual stream dependent processes. Several research results support this idea:

• Socioeconomic status is positively associated with feature-based attention for color and object-based attention (ventral visual stream processes).
• Socioeconomic status is not associated with attention to motion (dorsal visual stream processes).
• Cognitive stimulation in early development predicts differences in cortical thickness in the PFC and ventral visual stream, but not the dorsal stream.

Does development of the ventral visual stream scaffold PFC development and executive function?

There is no direct evidence to support this relationship, but there are research results that are consistent with this hypothesis:

• Functional changes in the ventral visual stream across development play an important role in the development of higher order cognitive function among children.
• Structural maturation of the PFC is protracted and occipital, temporal, and parietal cortex maturation precede that of the PFC.

Earlier development of more posterior regions, including the ventral and dorsal visual streams, may help support the development of the PFC by feeding the PFC information about the environment.

What is the aim of the present study? 

Stress can be defined as any condition that perturbs physiological and psychological homeostasis and is reflected in behaviors varying from mild memory impairment to dissociation and flashbacks. Much research has been conducted on stress, with many studies suggesting that stress has a negative impact on neurological structures involved in learning and memory. In addition, stress has been found to be a factor that may accelerate age-related cognitive decline. Yet, although there is a lot of research suggesting the negative impact stress has on neurological structures and cognition, much less psychometric investigation has been conducted on stress encountered in daily life and its effects on the memory tests currently used to discern mild cognitive impairment. To fill this gap, the current study aimed to investigate the impact of everyday stress on the episodic memory test performances of young, mid-life, and older adults. Everyday stress is defined as the appraisal of hassles and irritations of daily life, and as an accumulation of challenging events. Episodic memory is the memory of every day events (for example: times, location, associated emotions and other contextual information) that can be explicitly stated or conjured. It is the collection of past personal experiences that occurred at a particular time and place. 

How is the study conducted?

The sample consisted of 98 adults that were recruited via media advertisements. Individuals with neurological diseases (for example Parkinson's disease), psychiatric disorders (for example alcohol abuse or major depression), and use of medications producing sedative effects, were excluded. The sample was predominantly white with 96 Caucasian adults. The female to male ratio was 69:29. Participants ranged in age from 19 to 89 years with a mean of 42.10 years. 

All measures were individually administered. The study included measures that were well known for their ease of administration and clinical efficacy in discerning cognitive function. In total, each study session took approximately 45 minutes. A brief battery of memory tests was used, including the: (a) Logical Memory Scale (LM) and Verbal Paired Associates of the Wechsler Memory Scale; (b) the Digit Symbol Substitution of the Wechsler Adult Intelligence Scale; and (c) the cued-recall Digit Symbol Incidental Learning test. After administration of these memory tests, participants were asked to complete a self-report questionnaire that contained two measures of stress: (a) the Perceived Stress Scale (PSS), and; (b) the Elders Life Stress Inventory (ELSI). 

The Logical Memory Scale (LM) assesses episodic memory for orally presented information. It involves immediate (LM-I) and delayed (LM-II) recall of two prose passages that are read to the person. A total score of both the immediate and delayed conditions are obtained by averaging the recall for both prose passages at each respective time of recall. 

Data analysis was conducted in SPSS. Correlational and hierarchical multiple regression correlational techniques were used to study the association between variables and the unique influence of everyday stress on episodic memory performance. 

What are the results of the study? 

First and foremost, as expected, differential associations of everyday stress indexes (PSS and ELSI) with memory tests were observed. That is, PSS and ELSI were fund to be significantly correlated with the recall of the prose passages (LM-I and LM-II), but not with other memory tasks.

Second, age and education were found to be significantly correlation with memory measures. A poorer performance on all memory tests was found with advanced age. A enhanced performance on recall of prose passages was found for participants with higher educational levels.

In sum, the results of this study suggest that everyday hassles and irritations as well as the accumulation of challenging life events may exacerbate age-related decline on episodic memory tests that require greater executive resources and more integrated and elaborative processing. 

Lastly, a note for future research: To allow for more sensitive interpretation of episodic memory tests that are commonly used to discern mild cognitive impairment, the authors suggest to consider individual differences in everyday stress. 

How does one ensure ecological validity?

Assessment in neuropsychology can help to rule out or to confirm diagnoses or to decide which treatment a patient should be offered. It is also useful to predict in which way the brain injury will affect the daily life of a patient. An example of a question of this goal is: will the patient be able to resume his or her previous work and will he or she be able to resume other daily-life activities? To get the answer on these questions, tests can be used. The problem in neuropsychological assessment is that many of the tests that are available, are not valid enough to make recommendations. This is especially true for when a patient is brain-injured and there are issues with executive functions (EF). EF is about problem solving, planning, goal formation and goal management. Especially the maintenance of goals and subgoals and things such as self-initiative, self-monitoring and self-regulation are considered important when talking about EF. Ecological validity, meaning that the methods, materials and setting of the study must resemble a real-life situation as much as possible is very important in the neuropsychological context, because one of the goals is to predict the everyday functioning of patients with brain injuries. The exact definition of ecological validity for neuropsychology according to Sbordone (1996) is: “the functional and predictive relationship between the patient’s performance on a set of neuropsychological tests and the patient’s behaviour in a variety of real-world settings”.

To ensure ecological validity, one way could be to use tests that have certain items or tasks that resemble everyday life situations. This does not guarantee that the test is useful in predicting behaviour, because this has to be empirically tested. There are now several tests for testing the EF of patients, such as the Trail Making Test, the Stroop test, Wisconsin Card Sorting test, Tower of London test, and the Behavioral Assessment of Dysexecutive Syndrome.  The last one has the highest ecological validity, but is still limited in predicting everyday behaviour in patients with brain injury.

It is a fact that most tests of EF are not very good at predicting everyday behaviour. One reason for this could be that most of these tests were invented with the goal of determining whether there is or there is not a cognitive impairment. The Executive Secretarial Task (EST) aims to predict everyday executive functioning. This test is different than others, because it is based on functioning instead of on theoretical constructs. Because of this, the test ensures that the way the assessment is done (the test) is more representative for daily life. The EST is also different than other tests in that it extends over a longer period of time, that organization and prioritization of multiple tasks is tested and that participants have to deal with delayed intentions, interruptions and deadlines.

What was this study about?

In the first phase of the study it was expected that the EST would be able to discriminate between healthy people and brain-injured patients (that were already diagnosed). Another part of this study was to examine if the EST was able to determine which components of EF were most damaged. If these two expectations are met, then the EST would be very helpful to be used in neuropsychological assessment to predict a patient's’ performance in specific daily-life situations. And eventually this will lead to useful recommendations for how to overcome problems or for a certain treatment for the patient.

What conclusion could be drawn?

The EST seems to provide valuable information on the EF of brain-injured patients. It met the two expectations that it would be able to discriminate between healthy people and brain-injured patients. The EST also seemed to provide good indications of which parts of the EF were most damaged in the brain-injured patients. So, when testing the EST in a clinical population (being the brain-injured patients) the conclusion is that it is useful for neuropsychological assessment. This is true for in the diagnostic phase as for in the treatment phase, when it needs to be decided which goals the treatment has. This study has therefore demonstrated that scores on the EST are associated with executive functioning in daily life situations. There are also some negative aspects of the EST. An example is that some questions remain, such as: is it helpful in the process of selecting which job or other daily-life activities a brain-injured patient can resume? This is about the predictive validity of the EST. When this has been established, it is well recommended to use the EST in clinical practice. Other things are that it is a long test and that it is not suitable for retesting a patient: it seems to only give reliable results the first time a patient is tested. So, there are recommendations to develop an ecologically valid parallel test for EST.