Working memory capacity links cognitive reserve with long-term memory in moderate to severe TBI: a translational approach

Abstract

Traumatic brain injury (TBI) can have devastating negative consequences on an individuals' ability to remember information; however, there is variability among memory impairment resulting from TBI. Some individuals exhibit long-term memory (LTM) impairment while others do not. This variability has been explained, at least in part, by the theory of cognitive reserve (CR). The theory suggests that individuals who have spent significant time engaged in intellectually enriching activities (higher CR) are better able to withstand LTM impairment despite neurological injury. The cognitive mechanisms that underlie this relationship are not well-specified. Recent evidence suggests that working memory (WM) capacity may be one mediating variable that can help explain how/why cognitive reserve (CR) protects against LTM impairment. The present research tested this hypothesis in a sample of fifty moderate to severe TBI patients. Specific neuropsychological tests were administered to estimate CR, LTM and WM. The results were congruent with a recent theoretical model that implicates WM capacity as a mediating variable in the relationship between CR and LTM (Sobel's Z = 2.62, p = 0.009). These data corroborate recent findings in an alternate neurological population and suggest that WM is an underlying mechanism of CR. Additional research is necessary to establish whether (1) WM is an important individual difference variable to include in memory rehabilitation trials and (2) to determine whether rehabilitation and treatment strategies that specifically target WM may also lead to complimentary improvements on diagnostic tests of delayed LTM in TBI and other memory impaired populations.

Effects of Cognitive Reserve on Cognitive Performance in a Follow-Up Study in Older Adults With Subjective Cognitive Complaints. The Role of Working Memory

“… Sandry and Sumowski (2014) suggested WM capacity as a possible means whereby intellectual enrichment, as a proxy for CR, helps to preserve long-term memory in participants with multiple sclerosis. In a later study, Sandry et al (2015) also found that WM capacity mediated the relationship between CR and long-term memory in participants with traumatic brain injury. In the same way, Constantinidou et al (2014) reported that the effect of age on verbal episodic memory was mediated by WM capacity and observed that years of education influenced the rate of age-related decline in immediate verbal episodic memory.…”

“… Verhaeghen (2011) also reported a series of meta-analyses on aging and executive control, concluding that WM is one of cognitive functions that best explain age-related differences in the performance of many cognitive tasks. Evidence for the mediating role of WM in the relationship of CR on other cognitive constructs or functions has been obtained in studies involving different types of neurological damage/disorders such as traumatic brain injury ( Sandry et al, 2015 ), multiple sclerosis ( Sandry and Sumowski, 2014 ) and MCI ( Constantinidou et al, 2014 ). Sandry and Sumowski (2014) suggested WM capacity as a possible means whereby intellectual enrichment, as a proxy for CR, helps to preserve long-term memory in participants with multiple sclerosis.…”

Balanced bifrontal transcranial direct current stimulation enhances working memory in adults with high-functioning autism: a sham-controlled crossover study

“…One reason that composite z -scores were used in the primary analysis was because the number of participants was suboptimal with regard to power, and the participants were anticipated to vary widely in IQ and education. Composite z -scores are an effective tool to evaluate performance on a battery of tests that recruit resources from a common cognitive domain [ 74 – 76 ] because they increase statistical power by attenuating floor and ceiling effects, they reduce random variability, and they lower the number of correlated data in analyses [ 77 ]. Participants’ raw scores were transformed to z -scores using all 36 data points (12 participants × 3 sessions) obtained for each test.…”

Predicting long-term outcome following traumatic brain injury (TBI)

“…For example, Sandry, DeLuca, and Chiaravalloti (2014) have recently reported that working memory capacity mediated the relationship between CR and long-term memory impairment in adults with moderate-to-severe TBI. Similarly, Karver et al (2014) found that CR moderated the responsiveness to a problem-solving intervention in adolescents with mild-to-severe TBI.…”