La integración regional como política estatal

“Traditionally cognition has been viewed as a higher-level cortical function that can be divided into separate sub skills such as attention, memory, organisation, reasoning,

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and problem solving” (Pedretti, 1981 and Trexler, 1982 cited in Toglia 1998, p.5). In this section, studies focussing on the impact of preterm birth on cognitive skills will be presented. Studies on language and speech, although part of the assessment of the verbal performance of intelligence in several batteries, are presented later in this chapter.

In the meta-analysis by Bhutta et al (2002), the cognitive outcome of children that were born preterm was explored. Fifteen case-control studies, comprising 1556 cases and 1720 controls, were reviewed. The studies included had a case-control design, performed assessment after the fifth year of age of their participants, had an attrition rate of less than 30% and, were published in 1980 or later. Gestational age was the main criterion of prematurity (GA<37 weeks), with studies using solely LBW being excluded due to the possibility of finding SGA participants in their samples. The meta-analysis demonstrated an association between preterm birth and low cognitive outcomes with the weighed mean difference significantly favouring the controls (p<.001). Moreover, GA significantly correlated with mean cognitive scores (p<.001).

These findings highlight possible cognitive difficulties that preterm children might present, with the authors stressing careful interpretation of findings given the assumptions they made about all the assessment instruments, employed in the studies, having a comparable sensitivity and specificity, something that could mean

“overlooking” any subtle but clinically significant differences between those. Yet, the meta-analysis offers a useful insight into the studies focusing on cognition, since it used a strict study selection set of criteria and attempted to devise a “quality assessment tool” for the objective selection of the studies.

In a similar fashion, Sjernqvist and Sverringsen (1999), when comparing 61 extremely preterm children (GA<29 weeks) with their full-term peers at the age of 10 years, in Sweden, found that the overall IQ was within normal range (mean IQ=90, SD=15) but significantly lower than that of the full-term group (p<0.05). Although the authors do not provide more information on the subtests or possible underlying neurodevelopmental deficits, they offered information on how this was reflected on the educational outcome of the preterm children, with 30% of those receiving extra

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support, a frequency significantly lower (p<0.001) of that of their peers who were born full-term (1.6%).

Other studies have used BW or GA and BW, as reference criteria. In the cohort study of Anderson and Doyle (2003), the effect of short GA (<28 weeks) or ELBW (<1000g) on the cognitive outcomes of 298 children at the age of 8 years, were investigated.

Cognitive ability was assessed with the use of WISC-III examining cognitive areas such as verbal reasoning, attention and working memory and information processing, among others. Although the mean IQ of the preterm group was found to be within the average range, it was significantly lower (p<.001) than that of the full-term group even when the children with neurosensory deficits were excluded, similarly to the studies of Bhutta et al (2002) and Sjernqvist and Sverringsen (1999). Performance was lower in cognitive domains such as perceptual organisation (p<.001) and freedom from distractability (p<.001), associated with visual perception and attention/working memory respectively. The weighed mean difference in IQ between the groups was similar to the one in the meta-analysis of Bhutta et al (2002). Although the full-scale IQ was within normal range, this cohort presented with a plethora of difficulties within school tasks, and had experienced grade failure or required educational assistance.

This fact highlights once more the discrepancy between significant score deviances and functional outcome.

However, not all cognitive skills are explained by discrepancies in intelligence scoring. In the study of Boehm, Smedler and Forrsberg (2004) the executive functions (EF) of a cohort of 182 preterm children were compared to 125, matched for age and place of birth, controls with the use of the standardised comprehensive neuropsychological battery (Nepsy). The children were included in a prospective neonatal project examining their cognitive and motor development and, although BW was once again the focus, information was provided on GA (mean GA< 37 weeks) as well as for the BW ratio (ratio between actual and expected weight at birth), that could provide information on AGA and SGA infants. Executive functions were defined by the authors as “a complex system of functions including or dependent on interference control, non-verbal and verbal working memory, planning and reconstitution that

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enable the person to achieve certain (social) goals” (p. 1363). It becomes, therefore, apparent that the actual term encompasses a plethora of developmental skills, of which cognitive and attentional skills are of central importance. The study revealed significant differences between the groups. The effect of IQ was controlled after it was found that it correlated strongly to EF scores. There were however persistent differences found in some measures that related to impulse control, working memory and mental speed, indicating the insufficiency of traditional intelligence assessment and IQ scoring to explain deficits in cognitive and/or executive functioning skills.

Findings on the behavioural outcomes of the study are discussed in the relevant section.

An area that has attracted research interest was the one that could investigate a possible association between intelligence and structural “irregularities” of the brain of preterm children. In the UK study of Abernethy, Cooke and Foulder-Hughes (2004), cognitive skills, here defined by the IQ quotient, and motor skills were studied in order to explore whether such a relationship exists. One hundred and five, 7-year-old children, born before 32 weeks of gestation to mothers who resided in a geographically defined area, and were attending mainstream school were assessed.

They were matched by age, sex and first language to their classroom peers. The Weschsler Intelligence Scales for Children (III), the Movement ABC and, MRI scans were used to assess intelligence, motor skills and, the presence of any cerebral lesions/structural abnormalities, respectively. Lower IQs, as measured by the WISC-III, in the group of preterm children, was found to be significantly related to smaller volumes of both caudate nuclei of the brain (p<0.01). On the contrary, there was no significant correlation between ABC scores, measuring performance of motor skills, and caudate volume. No significant correlation with the hippocampal volume was found. These results could indicate that certain cerebral structures could affect cognitive function in preterm children although, in this study, it was not possible to investigate many other regions of the brain volumetrically and isolate the “caudate nuclei effect”.

Similarly in the study of Isaacs et al (2000) the potential association of cognitive

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problems, specifically everyday memory, and any underlying structural pathophysiology, was studied. The hippocampus, as a structure that is vulnerable to complications during preterm birth (Fuller et al, 1983 cited in Isaacs et al, 2000), was studied. Hippocampal volume and memory function was tested in 11 children (mean age= 13,6 years), who were born before or at 30 weeks and weighed under 1500g at birth, and were compared with 8 full-term children. All children attended mainstream schools. Magnetic resonance techniques were one again used for the investigation of any cerebral abnormalities while neurophychological assessment (WISC-III,Wechsler, 1984; Rivermead Behavioural Memory Test; Wilson, Cockburn and Baddeley, 1991) were used for assessing memory. The latter assessments revealed that the children demonstrated lower performance in the everyday memory assessment, and especially, in immediate rather than delayed recall (Wechsler Memory Scale/Immediate recall; p=0.039 for stories and p=0.038 for designs). There was also a difference between the hippocampal volumes of the two groups. The full-term cohort had a significantly larger hippocampal volume, for both the right and the left structure, than the preterm cohort (p<0.002). The memory deficits found in the preterm group were not significantly correlated to their IQ scores. This could mean that the memory impairment was independent of the overall cognitive ability.

However, although this study included very small (GA≤30 weeks) and, at birth, critically ill children, with a much smaller sample, it has, similarly to the study of Boehm, Smedler and Forrsberg (2004) revealed that IQ scoring does not always offer

“adequate” explanation as to what underlines cognitive difficulties. Both the study of Abernethy, Cooke and Foulder-Hughes (2004) and that of Isaacs et al (2000) sought abnormalities of specific structures of the brain, which could potentially explain the cognitive difficulties that some preterm children might present. They did not, however, acknowledge possible co-existing abnormalities, of other parts of the brain, which could be “accountable” for deficient cognitive performance.

Some differences, to the above findings, was revealed in the study of Briscoe, Gathercole and Marlow (2001), who investigated everyday memory and its association to language ability. The sample consisted of 20, five-year-old preterm children that were compared to 20 full-term children, matched for age and

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socioeconomic disparities. No significant differences were found to exist between the two groups, in relation to memory. The authors did however acknowledge that there is an “increased risk” for these children to present with memory and language problems which might deserve our attention, as they might lead to learning problems in more demanding learning environments such as the classroom. Again, differences in the sample size, presence of risk factors at the time of birth (a fact that the study of Briscoe, Gathercole and Marlow, 2001 did not account for) and, the age of the children at the time of the study, may account for differences between the studies.

The type of memory that is being investigated, e.g. short or long-term memory, episodic or semantic memory, might also affect these findings. Again, caution is suggested in the interpretation of the findings due to the small sample size of the participants cohort, as well as the lack of clarity with regards to the matching of the two groups (preterm and control). With regards to the latter, the authors state that most children of the control group “had been recruited through friend and relatives of the preterm children in order to minimise social and economic disparities between groups” (p.750), although they are not clear as to whether children were matched for those, or any other, characteristics.

Finally, attention deficits were revealed in the study of Dupin et al (2000). Although problems interfering with attention are often associated with Attention Deficit Hyperactivity Disorder (ADHD) and its behavioural manifestations, the study presented here rather investigates the potential influence of attention on self-regulation and concentration (Cherkes-Julkowski, 1998). Twenty 5-year-old children born prematurely (GA between 26-32 weeks) were compared to 20 children born full-term matched for maternal education level, socio-economic status, and the child’s IQ, with regards to their auditory processing and auditory attention. In the two experiments conducted, event-related potentials (ERPs) were used. This technique employs electrodes placed at different scalp sites, and records neural activity associated with specific sensory tasks. Hearing capability and auditory stimulation did not differ, but significant discrepancies were found in the number of correct hits (number of times the children detected certain tones and pressed a keyboard space bar), with the preterm group scoring a significantly lower frequency (p<0.05). This

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was attributed to attention problems, or, according to the authors, difficulties of the preterm group to “put the logical effort, task demanding, focusing attention” (p479).

The authors suggested that preterm and full-term children seem to have the same attention mechanisms with the difference lying in the flexibility of retrieving and utilising those. Putting greater effort and maintaining a level of performance could lead to fatigue and, consequently, underachievement in the school environment when tasks like arithmetic reasoning or reading comprehension become an everyday school demand. This could be of interest when designing educational programmes although the study findings have to be viewed with caution when attempting any generalisation of findings, given the relatively small size (20 participants) of the sample.