Summary
Agenesis of the corpus callosum (AgCC) is a neurological disorder known as developmental absence, which results from the malformation of the congenital brain. It can occur as a comorbid disease in such genetic and prenatal diseases as toxic syndromes and other chromosomal abnormalities (Siffredi et al., 2013). In addition, it can occur in isolation, with a lack of sufficient evidence for neural defects, although such individuals with isolated AgCC indicate a more favorable prognosis with a particular configuration of psychological disorder, which may inhibit mental development, thus, overall well-being (Siffredi et al., 2013). Therefore, the capacity to temporarily preserve necessary information in the brain in the presence of a disorder or defect, also known as working memory (WM), is vital for underpinning higher cognitive developments.
The contemporary study’s objective is to comprehend whether verbal reminiscence impairments are a distinctive pattern of high functioning persons with AgCC in school-aged children and to develop a better appreciation of the function of CC in verbal memory, retrieval of learned, and retention of information. Physical callosal injury in individuals with multiple sclerosis (MS) is linked to defects in list learning and loss of organizational integrity of the callosal zones connecting the frontal and the temporal zones, which are related to loss of verbal memory in Alzheimer’s disease (Paul et al., 2007; Brown & Paul, 2019). The previous studies are vital in providing insight into the direction of the research under study. As such, previous research on persons with AgCC on assessment of their auditory memory indicated contradictory outcomes. One study showed that persons with AgCC had a comparatively integral presentation on tests of vocal memory and performance (Paul et al., 2007).
However, other studies established that people with insulated AgCC also have minor injuries on oral memory tests (Erickson et al., 2014). In another study with partial AgCC, persons showed reduced uttered memory on the California Verbal Learning Test-Children’s Version (CVLT-C), dissimilar to the complete AgCC designated above, the teenagers with pAgCC executed poor performance on the signaled memory (Paul et al., 2016). To address the inconsistency in the previous studies with CVLT, it was predicted that children with AgCC would show reduced performance on a verbal working memory task at 7 years compared with typically developing controls.
Moreover, it was hypothesized that children with AgCC will show poor performance on verbal working memory tasks at 13 years than typically developing controls established in the research CVLT (Paul et al., 2016). However, it was hypothesized that children with AgCC will show similar performance improvement in verbal working memory task performance from 7 to 13 years of age as indicated in the study with CVLT (Erickson, 2014). This is because it was established that such difference does not exist in percent preservation (a manifestation of the capability to recall and recover what was essentially educated), demonstrating that poor recital is a concern of confines during programming and not repossession of what had been educated.
Method
Research Participants
Children with AgCC were enlisted from the Monash Children’s Hospital in Melbourne, Australia, between January 2009 and 2014. Inclusion criteria were a diagnosis confirmed by MRI, 7 years of age, English speaking, and capacity to participate in neuropsychological testing. Another independent group of typically developing 7-year-olds was recruited through hospital advertisements, and their inclusion criteria were no history of brain lesion, neurological disability, or neurodevelopmental disorders.
Materials
- Magnetic Resonance Imaging (MRI) machines are used for assessing AgCC.
- Questionnaires to gather data about the participants.
- Consent forms signed by children’s parents as active participants.
- Medical records describing the children’s neurological conditions.
- Wechsler Intelligence Scale for Children – Fourth Edition (WISC-IV) with Digit Span Backwards subtest: One repeats longer strings of mentioned numbers in reverse order with the values converted into average totals with M=10 and SD=3.
Procedure
Children were involved in a neuropsychological assessment (by a psychologist appraising academic, rational, and educational functioning) and a brain MRI (by a neurologist to portray AgCC and other anomalies). Caregivers finalized the written and oral questionnaires to assess decision-making, behavioral and academic functioning alongside socio-economic status. Information regarding the comorbid disorders was documented in health registers. The study was ratified by the Monash Children’s Hospital Human Research Ethics Committee. Parents or caregivers delivered informed printed consent to contribute to the study. The assessment was directed at ages 7 and 13 between 2009 and 2014. WM was measured using the DSBS based on WISC-IV with values converted into normal scores with M=10 and SD=3. All studies were piloted using age-corrected scaled scores.
Design
A one-sample T-test for independent samples was used to evaluate the variation between the two means of the AgCC group scores and the typically developing group. Moreover, the mean variances within each functional domain were investigated using a paired-sample T-test. Levene’s Test for Equality of Variances was performed, and a 95% CI of the difference between the paired sample tests was conducted using the Exploratory Software for Confidence Intervals (ESCI) (Cumming, 2012). Evaluations comparing the cAgCC and pAgCC groups were presented in Appendix A. In addition, the demographic data in terms of sex were also shown in Appendix B.
Results
Performance on the Backward Digit Span Standard Score analyzed using the T-test of 2 groups (AgCC vs. TD) based on the mean for recall times is indicated in Table 1. This instrument demonstrated no statistical significance with the AgCC group (M=7.59, SD=3.500) compared to the TD group (M=11.13, SDÂ=2.882), with T (-4.252 <0.05), thus the means score between them are insignificant statistically. The results are 95% Cl (-5.196, -1.869), and the means difference between the groups falls within the t-score values. Table 2 demonstrates no significant differences between the equality in means of the groups AgCC (n=28) and TD (n=32) by the Backward Digit Span Standard Score at 7 years with the Levene’s test with AgCC (n=28) and TD (N=32) at (F=1.187, Sig=0.280 >0.005), the first null hypothesis is accepted and equal variance is assumed.
Performance on the Backward Digit Span Standard Score at 13 years analyzed by T-test of 2 groups (AgCC vs. TD) by the mean for recall times is indicated in Table 2. The t-test showed no statistical significance with the AgCC group (M=7.93, SD= 3.222) compared to the TD group (M=9.88, SDÂ=3.508), t =0.883 >0.005, hence the second null hypothesis is accepted and equal variance assumed at (F=1.170, sig=0.284>0.005).
As per Table 3, the improvements between children in AgCC at 7 and 13 years indicated statistical significance, thus accepting the third hypothesis that children with AgCC show similar changes in performance on verbal working memory tasks (Backward Digit Span Standard Score at 7 years and Backward Digit Span Standard Score at 13 years. (n=28, correlation, 0.434, sig. 0.024>0.005). The mean-variance is also in acceptable ranges with an AgCC Vs. TD at (M=-.333, SD=3.584, t (-4.83<0.005), df =27 at a 95% Cl (-1.751, 1.085). Regarding the t-test sig of (0.633>0.005), the third hypothesis is equally accepted.
Table 4 demonstrates that the TD group’s performance at 7 and 13 years by the Backward Digit Standard Score is statistically significant. It supports the third hypothesis at (M=1.25,SD=3.455, df=31 at 95% Cl (0.004, 2.496), at t (31)=2.047, sig=0.049=0.005). The equal t-test significance indicates that the hypothesis is accepted without variations in the mean difference.
Discussion
The study investigated verbal memory in AgCC (n=28) and TD (n=32) students by using the Backward Digit Span Standard Score WISC-IV. The knowledge and memory presentation of the AgCC group was different from the TD group in subsets. The former showed worse performance on the recall than the latter (7 years) after learning and no TD variation on long-term memory (13 years). The groups were similar in retention in both 7 and 13 years. Moreover, the hypothesis regarding AgCC teenagers demonstrating equal progress on verbal WM tasks was confirmed. In verbal learning tasks, they had poorer instantaneous performance than the TD, even though both groups improved. Erickson et al. (2014) also established equivalent outcomes in AgCC and TD persons and no evidence of group variance. Therefore, the study provides more support reflecting verbal retention, retrieval of new information and lower efficiency of AgCC students compared to TD individuals in encoding information for later reminiscence. It could be attributed to other diseases, affecting both recalls in 7 and 13 years.
Similarly, Erickson et al. (2014) reported damages to spoken learning and retention in AgCC. The same results between 7 and 13 years are also accredited to deferred reminiscence on the CVLT-II and are imperfect by the extent of initial data. Hence, future studies on the memory’s effect in AgCC should aim to implement such tasks on isolated participants with callosal agenesis as a primary disorder. Comparing cAgCC and pAgCC participants in Appendix D did not link augmented recall with callosal network disruptions. Consequently, it is recommended to consider this aspect in the pAgCC patients when conducting future studies. This interrelation emphasizes the mechanism of action of the corpus callosum in redirecting huge neural systems to synthesize data. Thus, AgCC would explain the lowered presence of cortical networks in processing information.
References
Brown, W. S., & Paul, L. K. (2019). The neuropsychological syndrome of agenesis of the corpus callosum.Journal of the International Neuropsychological Society, 25(3), 324-330. Web.
Cumming, G. (2012). Understanding the new statistics: Effect sizes, confidence intervals, and meta-analysis. New York: Routledge.
Erickson, R. L., Paul, L. K., & Brown, W. S. (2014). Verbal learning and memory in agenesis of the corpus callosum.Neuropsychologia, 60(1), 121-130. Web.
Paul, L.K., Brown, W.S., Adolphs, R., Tyszka, J.M., Richards, L.J., Mukherjee, P., and Sherr, E.H. (2007). Agenesis of the corpus callosum: genetic, developmental, and functional aspects of connectivity. Nature Reviews Neuroscience, 8(4), 287-299. Web.
Paul, L. K., Erickson, R. L., Hartman, J. A., & Brown, W. S. (2016). Learning and memory in individuals with agenesis of the corpus callosum.Neuropsychologia, 86, 183-192. Web.
Siffredi, V., Anderson, V., Leventer, R. and Spencer-Smith, M. (2013). Neuropsychological profile of agenesis of the corpus callosum: A systematic review. Developmental Neuropsychology, 38(1), 35-57. Web.
Appendix A
Table 6: Frequency Table Indicating the Demographic Profile of the Children in Terms of Sex.
Appendix B
From Table 5 Below, both the cAgCC and pAgCC did not differ significantly on age, each indicating a valid percept of 50%. However, in other abnormalities, there was a significant difference between seizure and genetic disorders, indicating an absent score of 85.7% and 78.6%, respectively. Regarding School, mainstream showed high frequency with 75% followed by special development with 21.4% and least in 3.6%.
Table 5: Frequency Table on AgCC Type.