7 May 2008. For people who struggle with cognitive problems related to schizophrenia or who simply want to hone their ability to think on the fly, a new study may provide a glimmer of hope. In yesterday’s PNAS early edition, available online, Susanne M. Jaeggi of the University of Michigan at Ann Arbor and her colleagues report that the ability to adapt to new situations, to reason, and to solve problems may not be set in stone after all. The researchers contend that this kind of ability, known as fluid intelligence or Gf, can improve through training on a working memory task. Although the study examined healthy subjects, its findings may someday inform the design of cognitive remediation programs to help people with schizophrenia function better at work and school.
Interest in cognitive training reflects, in part, disappointment in the power of existing drugs to normalize cognition in schizophrenia (see SRF forum discussion). Despite clinical trials showing that atypical antipsychotics may produce modest cognitive improvement, repeated test-taking alone can enhance subjects’ performance on tests of mental functioning (Szöke et al., 2008), and controlling for practice effects may wipe out many of the supposed cognitive benefits of these medications (see SRF related news story). Other trials suggest that cognitive rehabilitation improves the test performance of people with schizophrenia and their real-world functioning as reflected, for instance, in work outcomes (McGurk et al., 2007; Lindenmayer et al., 2008). Yet practice can confound these trials, too.
A problem to solve
Turning specifically to fluid intelligence, Jaeggi and collaborators Martin Buschkuehl, John Jonides, and Walter J. Perrig note that practice can improve scores on Gf tests; “however, it has been demonstrated that practice on these tests decreases their novelty and with that the underlying Gf-processes ([te Nijenhuis et al., 2007 Intelligence 35:283–300]) so that the predictive value of the tests for other tasks disappears.” In other words, the so-called gains may not transfer to other situations. To determine whether cognitive training would improve fluid intelligence, the researchers sought “a task that shares many of the features and processes of Gf tasks, but that is still different enough from the Gf tasks themselves to avoid mere practice effects.”
The notable correlations between working memory and fluid intelligence have prompted sparring over the extent and meaning of the overlap between them (see, for example, Ackerman et al., 2005; Oberauer et al., 2005; Kane et al., 2005). According to Jaeggi and associates, both rely on the ability to direct attention; they also share capacity limits, as shown by the number of items held in working memory or the number of connections made in a reasoning task. In addition, they apparently involve similar neural pathways in the prefrontal and parietal cortices (see SRF related news story). Given these similarities, the researchers thought that the benefits of training to enhance working memory might transfer to fluid intelligence.
To test this notion, the researchers recruited 70 healthy, young adults, half of whom received working memory training in four different scenarios that varied according to whether training occurred on eight, 12, 17, or 19 days. The remaining subjects comprised the matched control groups. Subjects in the training groups received alternate forms of the same Gf test before and after the training; the control groups underwent testing at the same intervals. Gf measures consisted of either the short form of the Bochumer Matrizen-Test or, for the eight-session trial, Raven’s Advanced Progressive Matrices.
The memory task required subjects to monitor two series of simultaneously presented stimuli—specifically, single consonants played over headphones and marks appearing at various spots on a computer screen. As in other n-back tasks, subjects then had to indicate whether the stimulus matched one that was presented a certain number, or n, of trials ago. In this paradigm, n increased by one if they performed well or decreased by one if they did poorly. The authors write that changing the n and using two different kinds of stimuli “discouraged the development of task-specific strategies and the engagement of automatic processes.”
High-performing transfer students
Along with the expected memory gains, the researchers report “the striking result of a training-related gain in Gf,” with subjects who received the intervention showing “dramatic improvement.” The control groups made significant gains, too, presumably from repeated test taking, but the trained groups improved more. In fact, those who trained more gained more, as shown by a dose-response relationship between the amount of training received and the benefits gained.
To explain how the working memory task might foster fluid intelligence, Jaeggi and colleagues suggest that it engages many of the same processes. For instance, they write, “One reason for having obtained transfer between working memory and measures of Gf is that our training procedure may have facilitated the ability to control attention,” a skill that aids adaptive thinking. In addition, both working memory and Gf involve executive functions, such as those involved in multi-tasking, and the ability to relate one item to another.
On the other hand, the similarities do not tell the whole story. According to the researchers, “These data indicate that the transfer effect on Gf scores goes beyond an increase in working memory capacity alone.” They based that conclusion on analyses that controlled for working memory, as measured by subjects’ performance on digit-span and reading-span tasks.
Despite the lack of a direct link to schizophrenia, these findings may lead to some adaptive thinking about the cognitive problems that comprise some of its most disruptive symptoms. As Jaeggi and her coauthors write, “Instead of regarding Gf as an immutable trait, our data provide evidence that, with appropriate training, there is potential to improve Gf.” Whether their study and those to come will spur a rethinking about how fluid this kind of intelligence might be in schizophrenia, and how to design rehabilitation programs that address deficits, remains to be seen.—Victoria L. Wilcox.
Jaeggi SM, Buschkuehl M, Jonides J, Perrig WJ. Improving fluid intelligence with training on working memory. PNAS early edition. 2008 April 28. Abstract