Introduction
Agenesis of the corpus callosum (AgCC) is a neurological disorder also referred to as developmental absence, which results from the malformation of the congenital brain. It can occur as a co-morbid disease in such genetic and prenatal diseases as toxic syndromes and other chromosomal abnormalities (Siffredi et al., 2013). 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 tests of oral memory (Erickson et al., 2014; Paul et al., 2007; Brown & Paul, 2019). In another study with partial AgCC, persons showed reduced uttered memory on the California Verbal Learning Test-Children’s Version (CVLT-C), indicating that dissimilar the complete AgCC designated above, the teenagers with pAgCC executed poor performance on the signalled memory (Paul et al., 2016). The objective of the contemporary study is to comprehend whether verbal reminiscence impairments are a distinguishing 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.
To address the inconsistency in the previous studies with CVLT it was predicted that children with AgCC will 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 compared with typically developing controls as established in the research CVLT (Paul et al., 2016). However, it was hypothesized that children with AgCC will show similar improvement in performance on 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 identified with AgCC were enlisted from hospitals in the years (2009-2014) 2014 from the Monash Children’s Hospital, located in the Melbourne city, Australia. Inclusion criteria comprised: a diagnosis which was established by MRI, children who are aged 7, native English speakers, and capacity to contribute in neuro-psychological analysis. Another independent group of consisting of a TD who are aged 7 years were enrolled through announcements made at the facility with inclusion criteria based on: no past brain lesion, or any other neurological defect.
Materials
- Magnetic Resonance Imaging (MRI) machines are used to assess AgCC.
- Questionnaires containing information regarding more information about the child.
- Consent forms to be signed by the parents as the active participants were till children participated in consent signing.
- Medical records describing the underlying neurological conditions of the children under the study.
- Wechsler Intelligence Scale for Children – Fourth Edition (WISC-IV) with Digit Span Backwards subtest: Where a child repeats longer strings of mentioned numbers in reverse order and the values converted into average totals with M=10 and SD=3.
Procedure
Children who were listed for the program as indicated above were involved in a neuropsychological assessment (steered by a teaching child psychologist to appraise overall academic, rational, and educational functioning) and a brain MRI (revised by a child neurologist to portray AgCC and other neurological anomalies). Caregivers finalized the written and oral questionnaires to assess child decision-making, behavioral and academic functioning as well as socio-economic status. Information regarding the co-morbid stores such as seizure disorder, genetic disorder) was documented from health registers. The study was ratified by the Monash Children’s Hospital Human Research Ethics Committee. Parents or caregivers delivered informed printed consent for their offspring to contribute to the study. Being a working memory study, the assessment was directed at ages 7 and 13 between 2009 and 2014. WM was measured using the DSBS based on WISC-IV, where values were converted into normal scores with M=10 and SD=3. All studies were piloted using age-corrected scaled scores.
Design
To evaluate the variation between the two means of the AgCC group mean scores and the typically developing group, a one-sample T-test for independent samples were used. Moreover, the mean variances in the test scores within each functional domain were investigated using the 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 were conducted using the Exploratory Software for Confidence Intervals (ESCI) (Cumming, 2012). Evaluations comparing the cAgCC and pAgCC groups were presented in Supplementary Materials Table 6. In addition, the demographic data in terms of sex were also recorded and presented in Table 5.
Table 6: Frequency Table Indicating the Demographic Profile of the Children in Terms of Sex.
From Table 5 Below, the both the cAgCC and pAgCC did not differ significantly in age, each indicating valid percept of 50%. However, in other abnormalities, there was significant difference with seizure and Genetic disorder indicating an absent score of 85.7% and 78.6% respectively. With regards to Schools, mainstream indicated high frequency with 75% followed by special development with 21.4% and least in 3.6%.
Table 5: Frequency Table on AgCC Type.
Results
Table 1 below demonstrates that there are no significant differences between the equality of difference in means of the two groups AgCC (n=28) and TD (n=32) based on the scores of 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 it is equal variance assumed.
Performances on the Backward Digit Span Standard Score at 13 years analyzed using the T-test of 2 groups (AgCC vs. TD) based on the mean for recall times is indicated in Table 2. Based on the table, the t-test indicated no statistical significance with the AgCC group (M=7.93, SD= 3.222) compared to the TD group (M=9.88, SD=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 illustrated in Table 3, the performance improvements between children in AgCC at 7 and 13 years indicated statistical significance, thus accepting the third hypothesis that children with AgCC will show similar improvement in performance on verbal working memory task performance from 7 to 13 years of age (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). With regards to the t-test sig of (0.633>0.005), the third hypothesis is equally accepted.
Table 4 below demonstrates that the performance of the children with TD group at 7 and 13 years based on the Backward Digit Standard Score is statistically significant. Thus, supporting 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 and no variation in the mean difference.
Discussion
The current study investigated verbal memory in AgCC (n=28) and TD (n=32) using the Backward Digit Span Standard Score WISC-IV. Comparative to the TD group, the knowledge and memory presentation of the AgCC group was different through the subsets. As predicted, the two groups did not vary on the recall retention indicated by the performance of both 7 and 13 years. Moreover, the hypothesis with regards to teenagers with AgCC showing similar development in performance on verbal WM task recital from 7 to 13 years was right. Cumulatively across the verbal learning tasks, the AgCC groups had poorer instantaneous performance than the TD, even though both groups represented comparable performance improvements. Erickson et al. (2014) also established equivalent performances in persons with AgCC and TD on Donders’ Attention Span Factor and no evidence of significant group variance in the performance improvements. Similarly, Erickson et al. (2014) reported damages to spoken learning and retention in AgCC, specifically for word lists. The similar performance improvements between the 7 and 13 years could also be accredited to deferred reminiscence scores on the CVLT-II and could principally be imperfect by the extent of data initially programmed during the first knowledge acquisition.
In this regard, future studies on the effect of memory in AgCC should aim to implement such learning and memory tasks on isolated participants whose callosal agenesis is the primary neurological disorder. However, group-wise comparison between the participants with cAgCC and pAgCC did not attempt to support the configuration of augmented knowledge and recall in individuals with some callosal networks (partial AgCC) related to those with no such influences (complete AgCC). As such, it might be instructive in prospective studies to associate cognitive recital with the zone and grade of enduring callosal network in the pAgCC patients as evaluated with MRI procedures.
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., 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.
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.
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.