New findings by Bar-Ilan University researchers and collaborators pave the way for targeted interventions and educational programs to improve quality of life as life expectancy continues to increase
A new study by researchers from Bar-Ilan University, Ariel University, and Levinsky College of Education has revealed encouraging findings on cognitive growth and development in adults with non-specific intellectual disability (NSID), especially those with Down syndrome (DS), and challenges previous assumptions about the cognitive potential of individuals with Down syndrome.
The cross-sectional study examined 340 individuals from adolescent (16-21 years) and adult (22-45 years) age groups, comparing crystallized intelligence (involving acquired knowledge, language, and facts) and fluid intelligence (involving reasoning and problem-solving ability). The results, recently published in the journal Scientific Reports, provide a comprehensive picture of patterns of cognitive development in these populations and new hope for continued cognitive development well into adulthood.
Among the key findings:
- Adults with intellectual disabilities demonstrated higher cognitive performance compared to adolescents on three key intelligence tests (vocabulary, similarities, and block design of the Wechsler Adult Intelligence Test), supporting the age-compensation theory (Lifshitz, 2020), which suggests that learning and development potential continues into the mid-40s.
- Differences in fluid intelligence: Participants with Down syndrome performed better on tasks measuring fluid intelligence, including the Raven's Matrix and Block Design tests, which involve visuospatial reasoning and problem-solving skills compared to those with no defined intellectual disability.
- Differences in crystallized intelligence: Individuals with undefined intellectual disability scored higher on the vocabulary test, a measure of crystallized intelligence, compared to those with Down syndrome.
- There were no differences in verbal reasoning: On the Similarities Test, a measure of verbal reasoning, no differences were found between the two groups, suggesting that verbal skills in individuals with Down syndrome may be less impaired than previously thought.
- Distinct cognitive profiles: Graph analysis revealed distinct cognitive networks between the groups. Surprisingly, participants with Down syndrome showed more integrated connections between crystallized and fluid intelligence, especially in adulthood, while adults with noninvasive intelligence disorder showed more fragmented cognitive connections.
The relative strength of verbal ability and the more consistent connections between the two types of intelligence in participants with Down syndrome indicate a more cognitively and neurologically coherent profile in the etiology of Down syndrome, especially in adulthood.
In a typical population, the scientists examined the association between fluid and crystallized intelligence across the lifespan. The higher correlations between the two suggested that participants who show higher scores in one type of intelligence also show higher scores in the other.
Surprisingly, in the current study, the interconnections between the two types of intelligence are consistent with correlations between the two types of intelligence found in the typical population in the same age period (22-45), but only in adults with Down syndrome and not in those with noninvasive intelligence disorder.
“Our findings indicate a relative strength and compensation of cognitive abilities in visuospatial areas, and even in verbal and language abilities in a clear diagnostic etiology such as Down syndrome, especially in adulthood, compared to unclear genetic etiologies such as noninvasive developmental disorder,” said Professor Hefziba Lifshitz of the Faculty of Education at Bar-Ilan University, senior author of the study. “We now have evidence that cognitive development continues well into adulthood in these populations. These findings have significant implications for educational and support services,” added Lifshitz, who collaborated with Dr. Roi Yozevitch of the Department of Informatics at Ariel University and Dr. Shlomit Shnitzer-Meirovich of the Levinsky Faculty of Education.
Research confirms that educational and developmental programs should extend beyond adolescence, as adults with Down syndrome and non-invasive developmental disorder demonstrate capacity for continued cognitive growth. This is particularly relevant as life expectancy for people with intellectual disabilities continues to increase, with many now living into their 80s.
In July 2024, six students enrolled in the Empowerment Project at Bar-Ilan University’s Faculty of Education became the first cohort of adults with intellectual disabilities (ID) in Israel to receive their bachelor’s degree. Two of them have DS. The Empowerment Project, a pioneering program of its kind established by Prof. Lifshitz, is based on her compensation age theory, which postulates that chronological age, as opposed to mental age, plays a major role in determining the cognitive ability of adults with intellectual disabilities. The current study confirmed this postulation most strongly in adults with DS.
The findings of this study open new avenues for research and development of targeted interventions and educational programs designed specifically for adults with intellectual disabilities, potentially improving the long-term outcomes and quality of life of these individuals.