WASHINGTON -- Psychologists may have found the "missing link" between the aging brain and declining cognitive abilities, via studies that show where younger and older people part ways in "context processing." The gradual loss of the ability to gather and use contextual clues could explain why older people decline cognitively across a range of functions. By developing a comprehensive, brain-based model of normal aging, psychologists may ultimately be able to slow or stop these vexing cognitive declines. The research appears in the December issue of the Journal of Experimental Psychology: General, published by the American Psychological Association (APA).

In the model, context processing is a kind of mental "operating system" that sits between the brain's prefrontal cortex and cognition. Psychologists believe that given adequate levels of the chemical messenger dopamine, the prefrontal cortex reliably enables us to process context for a thought, memory or behavior. Thus, context processing can have broad impact, spanning cognitive operations once thought to be independent -- from attention and inhibition to episodic and working memory. In everyday life, context processing -- and the ability to override a default behavior to do something in a contextually appropriate way -- helps us decide everything from which way to turn to go to the grocery store, to what to say based on who is listening or what an ambiguous word would mean in a particular sentence.

The creators of this model of cognition, Todd S. Braver, Ph.D., and Deanna M. Barch, Ph.D., both of Washington University, and their colleagues, believe that in normal aging, erratic or declining dopamine levels would start shutting the gate to contextual information, thereby weakening all of the cognitive functions that depend on it -- an effect supported by their study.

In the study, Braver et al. compared the performance of 175 young adults (ages 18-29) and 81 older adults (age 65-85) on an "AX-Continuous Performance Test." Researchers measured how quickly and accurately participants hit a button when they saw "X" on a computer screen. Braver et al. told them to hit the button only if "X" followed "A" but not another letter. This test reveals how well someone depends on context to act, in this case responding to the cue (A or not A, with any other letter referred to as B). "AY" trials, in which participants responded to non-X ("Y") probes after they followed A cues, would be additional "false alarm" evidence of sensitivity to context.

By comparing results from various AX, BX and AY trials, the researchers learned that context processing correlated with the different kinds of cognitive functions tapped by the different trials. For example, participants who were primed to respond to "X" and couldn't hold back, or inhibit, when they saw it after a "B" instead of an "A," also performed worse on AX trials -- the basic measure of context processing.

The researchers also compared the performance of young and the old participants. The results supported their model in several ways. First, older adults performed worse on AX and BX trials, which meant impaired context processing. Second, on AY trials, the old actually did better than the young -- had fewer "false alarms" -- because their impaired context processing made them less predisposed to hit the button after they saw "A." Third, interference during the test (which increases demands on context processing) accentuated age-related differences, whereas increased difficulty (which does not affect context processing) did not affect them.

Taken together, the results support the notion of a single, fundamental deficit in the ability to "properly represent, maintain and update task-relevant context" as the underpinning for a range of age-related cognitive declines.

The authors call for additional testing to determine how changes in the dopamine system (which has also been implicated in brain-based diseases such as schizophrenia, Alzheimer's and Parkinson's, as well as in alcohol and drug addiction) might affect cognition, including context processing. And, although there may be biological and pharmaceutical obstacles to overcome, Braver says that, "more work examining the cognitive enhancing effects of dopaminergic drugs is a promising direction."

Article: "Context Processing in Older Adults: Evidence for a Theory Relating Cognitive Control to Neurobiology in Healthy Aging," Todd S. Braver, Ph.D., Deanna M. Barch, Ph.D., and Beth A. Keys, Ph.D., Washington University; Cameron S. Carter, Ph.D., University of Pittsburgh; Jonathan D. Cohen, Ph.D., University of Pittsburgh and Princeton University; Jeffrey A. Kaye, Ph.D., and Jeri S. Janowsky, Ph.D., Oregon Health Sciences University; Stephan F. Taylor, Ph.D., University of Michigan; Jerome A. Yesavage, Ph.D., and Martin S. Mumenthaler, Ph.D., Stanford University; and William J. Jagust, Ph.D. and Bruce R. Reed, Ph.D., University of California, Davis; Journal of Experimental Psychology --General, Vol. 130, No. 4.

Full text of the article is available at http://www.apa.org/journals/xge/press_releases/december_2001/xge1304746.html
 

---American Psychological Association

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