Cognition, Intelligence, and Causes of Cognitive Impairment

Introduction: What Is Cognition?

Ever since Binet and Simon developed the first intelligence test in 1905, the field of psychology has maintained a strong interest in the nature of intelligence. How do we think? Why are some people better problem solvers than others? What is cognition — the ability to think about our environment? Why are some people consistently more able to use their brains to think, remember, and problem-solve than others?

The first IQ tests were devised to determine which children were intellectually disabled. These children were separated from mainstream education. However, the tests proved effective at predicting school success for all students, and their use was subsequently broadened (Sternberg, 1999). Multiple tests were developed to measure cognition, which might be defined as the ability to think abstractly. Markman (2001) described it in this way:

Cognition depends on the ability to imagine or represent objects and events that are not physically present at a given moment. Cognitive functions include attention, perception, thinking, judging, decision-making, problem solving, memory, and linguistic ability. One of the most basic cognitive functions is the ability to conceptualize, or group individual items together as instances of a single concept or category, such as 'apple' or 'chair.'

The ability to reason about things that are not in our immediate vicinity, or that are abstract concepts, allows us to think beyond the concrete limitations of our environment. Markman lists some of these kinds of abstract thinking as "deductive reasoning, induction, mental simulation, and analogy" (Markman, 2001). Much research has been done on the nature of cognition and on why some people are consistently much stronger or much weaker in their ability to think, remember, and reason — often measured as an IQ score.

This paper examines what cognition is and identifies some of the causes of significant cognitive impairment, a condition in which an individual has a markedly diminished ability to learn and to retrieve information compared to most people. However, Sternberg (1999) makes the important point that, since we are only beginning to explore how the brain works, any tests devised so far are necessarily incomplete measures of the wide variety of ways in which people can think.

Complicating the exploration of cognition is the fact that the brain uses multiple functions to process information. For instance, memory is more than one thing. Immediate short-term memory — sometimes called "active working memory" — allows us to hold information in mind while it is present, such as a phone number we need only long enough to dial. We may then forget it immediately, deliberately commit it to long-term memory, or find it stored permanently simply because it has been repeated enough times. The ability to recall information is crucial to our ability to compare new information to old, to categorize, to develop new knowledge, and even to maintain a sense of self.

Measuring Intelligence and Its Limits

Another issue in cognition is that of both quantity and speed. Measures of intelligence often include both the amount of information known — for example, "Who was the first President of the United States?" — and processing speed, or how quickly a person can recall or manipulate information (Wenger, 2000).

Recent attempts have been made to quantify some of these brain functions. Can attention be measured? Can we determine how much information a person can hold in active working memory at one time? Wenger (2000) investigated whether these skills are static or changeable, suggesting that the capacity of the short-term memory buffer may vary according to the type of stimulus. A musician with limited mathematical ability, for example, might remember a melody far better than a number sequence. Wenger (2000) also argues that the ability to use very-short-term memory may involve drawing on multiple other cognitive functions simultaneously. Nothing in how we think appears as simple as IQ tests suggest on the surface. Nevertheless, IQ tests remain our best-quantified tool for identifying individuals with significant cognitive difficulties, and their use has spurred research that has yielded important new information about both the brain and genetics.

Environmental Causes of Cognitive Impairment

What causes one person to have such impaired cognitive abilities that he or she faces marked difficulties not only in school but also in everyday functioning? While researchers do not yet have all the answers, two major groups of causes have been identified: environmental and genetic. Among environmental causes, this paper examines prematurity, prenatal alcohol exposure, and lead poisoning. Among genetic causes, it considers a newly discovered chromosomal rearrangement, Fragile X Syndrome, Rett Syndrome, and Williams Syndrome.

Prematurity

Prematurity has long been considered a risk factor for cognitive difficulties, and it was once assumed that the smaller the baby, the more likely significant neurological damage would follow. However, McGrath (2000) conducted important research that measures risk factors more precisely. She devised a composite Neonatal Risk Index — incorporating both medical and neurological complications — as the best predictor of later outcomes, then tracked the progress of premature children against a full-term control group for eight years (measured from due date).

McGrath found that later cognitive difficulties correlated more strongly with the severity of neurological problems than with birth weight alone. Some very small babies performed markedly better than some larger but still premature infants. She also described a "sleeper effect," whereby difficulties apparent by age eight — including motor skill lags and learning problems — were not always detectable at younger ages. Her research is significant because prior studies had produced conflicting conclusions: some suggested prematurity is a major cause of learning problems, while others indicated that affected children catch up by school age (McGrath, 2000). In her study, children were matched for socioeconomic status and other potential confounding variables, and data were gathered objectively from medical charts.

Neurological assessments were conducted at 18 and 30 months (adjusted for prematurity), with evaluators achieving a 95% agreement rate. Evaluators also documented the presence of cerebral palsy, blindness, deafness, treated hydrocephalus, and uncontrolled seizures. Further evaluations at ages 4 and 8 assessed developmentally appropriate gross and fine motor skills, and the age-8 evaluation included screening for attention deficit hyperactivity disorder (ADHD).

The full-term children had significantly higher IQ scores as a group, with an average IQ of 104, compared to the more severely neurologically impaired premature children, whose scores typically fell in the 70s and 80s. All groups included children requiring special services, but those with neurological impairments from premature birth required significantly higher levels of intervention. Importantly, this study confirms that there is no simple cause-and-effect relationship between premature birth and subsequent cognitive impairment; events following birth that increased difficulty for the newborn were the controlling variables.

Fetal Alcohol Syndrome

Fetal alcohol effects were first identified in animal research, but clinicians soon recognized that maternal alcohol consumption during pregnancy could harm the developing fetus. These effects include growth and behavioral problems as well as cognitive difficulties (AAP, 2000). The difficulties occur along a continuum and may not all be apparent at birth, although some children display facial anomalies that make the diagnosis immediately visible. The disabilities these children experience typically persist throughout their lives.

The American Academy of Pediatrics cited research describing the cognitive and behavioral consequences of maternal alcohol exposure as "profound, pervasive, and persistent." Specific cognitive problems included "specific mathematical deficiency, difficulty with abstraction (e.g., time and space, cause-and-effect), and problems with generalizing from one situation to another… poor attention and concentration skills, memory deficits, and impaired judgment, comprehension, and abstract reasoning" (AAP, 2000). Behavioral difficulties ranged from ADHD-type symptoms — hyperactivity and impulsivity — to oppositional behavior and, in more serious cases, lying and stealing. These behavioral presentations differ from those typically seen in other forms of intellectual disability, where behavior more closely mirrors the individual's mental age (AAP, 2000).

Lead Poisoning

Lead poisoning is another common and entirely preventable cause of diminished cognitive function in children. Soong (1999) reported cases in which reducing or eliminating lead exposure lessened its negative effects, though other research has not replicated this finding. The children in Soong's study were of kindergarten age; Soong acknowledges that lead exposure in younger children — especially those two years old and under — causes more severe and lasting disabilities.

It was once believed that blood lead levels as high as 25 µg/dL were safe, but Soong found that exposure at that threshold could cause measurable and irreversible neurological damage. Some researchers argue that levels as low as 10 µg/dL may be cause for concern. Because lead poisoning is preventable through vigilant monitoring of children's blood lead levels, it represents a critical public health priority.

Conclusion: The Future of Cognitive Research

In summary, a wide range of causes for cognitive impairment has been identified, but researchers continue to contemplate the very nature of what we call cognition. While we know that some people have marked cognitive strengths and others have marked cognitive weaknesses — with the great majority falling somewhere in the middle — experts universally agree that current measures, however refined, are limited by a fundamental lack of understanding about what intelligence truly is.

It is reasonable to expect that as our understanding of how humans learn and process information deepens, the field of testing and measurement will expand accordingly. The definition of "intelligence" may broaden to reflect a more nuanced understanding of brain function, and the uses of IQ tests may be refined as well. Gruneau (2000), for instance, has delineated the limitations of the Stanford-Binet Intelligence Scale for very young children: although the test is normed for children as young as three, it proved a poor predictor of later cognitive strengths and weaknesses. This raises reasonable questions about whether testing the IQ of three-year-olds is genuinely necessary. Developing the field of neuropsychology for very young children might prove more productive. Designing assessments that reveal how the brain takes in and processes different types of information — for example, identifying that a child perceives visual information accurately but struggles to manipulate it — could lead to more targeted and effective interventions.

Genetic research holds additional promise. Early IQ tests led investigators astray in some respects — evaluating infants based on gross motor skills caused some clinicians to classify children with cerebral palsy as cognitively impaired regardless of their actual intellectual ability, and for many years it was incorrectly assumed that early intervention would make no difference for children with Down Syndrome.

Cognition is an area of psychology that will require continued intensive research for years to come. Brain processes currently grouped together are likely to be further subdivided, and much work remains to be done examining how different brain functions interact. Advances in neuroimaging — particularly MRI technology with its capacity to visualize brain activity — may reveal connections within the brain of which we are currently entirely unaware.

References

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Baker, O. (1999, October). Faulty control gene underlies retardation (Rett Syndrome). Science News.

Bower, B. (1999, November 20). DNA furnishes tips to mental retardation. Science News.

Eliez, S. (2000, February). Genetics of childhood disorders: XI. Fragile X Syndrome. Journal of the American Academy of Child and Adolescent Psychiatry.

Grunau, R. E. (2000, December). Predicting IQ of biologically "at risk" children from age 3 to school entry: Sensitivity and specificity of the Stanford-Binet Intelligence Scale IV. Journal of Developmental & Behavioral Pediatrics.

Markman, A. B. (2001). Thinking. Annual Review of Psychology.

McGrath, M. M. (2000, December). Longitudinal neurologic follow-up in neonatal intensive care unit survivors with various neonatal morbidities. Pediatrics.

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Posthuma, D., Neale, M. C., Boomsma, D. I., & de Geus, E. J. (2001, November). Are smarter brains running faster? Heritability of alpha peak frequency, IQ, and their interrelation. Behavior Genetics, 6, 567–579.

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Wenger, M. J. (2000, January). Basic response time tools for studying general processing capacity in attention, perception, and cognition. Journal of General Psychology.