Elsevier

Cortex

Volume 71, October 2015, Pages 58-67
Cortex

Note
Anatomical substrates and neurocognitive predictors of daily numerical abilities in mild cognitive impairment

https://doi.org/10.1016/j.cortex.2015.05.031Get rights and content

Abstract

Patients with mild cognitive impairment experience difficulties in mathematics that affect their functioning in the activities of everyday life. What are the associated anatomical brain changes and the cognitive correlates underlying such deficits? In the present study, 33 patients with Mild Cognitive Impairments (MCI) and 29 cognitively normal controls underwent volumetric MRI, and completed the standardized battery of Numerical Activities of Daily Living (NADL) along with a comprehensive clinical neuropsychological assessment. Group differences were examined on the numerical tasks and volumetric brain measures. The gray (GM) and white matter (WM) volume correlates were also evaluated. The results showed that relative to controls, the MCI group had impairments in number comprehension, transcoding, written operations, and in daily activities involving time estimation and money usage. In the volumetric measures, group differences emerged for the transcoding subtask in the left insula and left superior temporal gyrus. Among MCI patients, number comprehension and formal numerical performance were correlated with volumetric variability in the right middle occipital areas and right frontal gyrus. Money-usage scores showed significant correlations with left mesial frontal cortex, right superior frontal and right superior temporal cortex. Regression models revealed that neuropsychological measures of long-term memory, language, visuo-spatial abilities, and abstract reasoning were predictive of the patients' decline in daily activities. The present findings suggest that early neuropathology in distributed cortical regions of the brain including frontal, temporal and occipital areas leads to a breakdown of cognitive abilities in MCI that impacts on numerical daily functioning. The findings have implications for diagnosis, clinical and domestic care of patients with MCI.

Introduction

Deficits in mathematical abilities contribute to the difficulties experienced by patients with mild cognitive impairment (MCI) in everyday life activities (Nygård, 2003, Winblad et al., 2004). For instance, MCI patients have been recently shown to experience problems in understanding numerical information concerning health care (Delazer et al., 2013, Pertl et al., 2014). Moreover, impairments in tasks tapping financial capacities such as financial conceptual knowledge, bank statement management and bill payment have been also reported in these patients (Griffith et al., 2003, Griffith et al., 2010, Marson et al., 2009, Okonkwo et al., 2006, Sherod et al., 2009).

The numerical deficits in MCI may be primary or secondary to other cognitive difficulties. Griffith et al. (2003), in particular, related financial impairments to deficits in executive functions. Similarly, Zamarian, Semenza, Domahs, Benke, and Delazer (2007) and Zamarian, Stadelmann, et al. (2007) found that executive dysfunctions affect the patients' performance even on basic mathematical tasks. In particular, the studies of Zamarian and colleagues found that MCI patients who score within the normal range on basic arithmetic assessments show difficulties on arithmetic applied to daily-life by having to recruit additional, non-numerical resources. Accordingly, further studies have emphasized the relevance of age-associated attentional and executive decline in accounting for numerical difficulties in the elderly (Cappelletti et al., 2014, Duverne and Lemaire, 2005, Lemaire and Arnaud, 2008). These studies have conjectured that such decline plays a role in those everyday numerical problems that show the typical features of a multistep problem, i.e., requiring focused attention, planning, reasoning and monitoring of the solution procedure.

One interesting question is whether the mathematical difficulties experienced by MCIs are the result of specific regional anatomical changes. The hypothesis of the present study is that, if previously learned mathematical concepts and facts are deteriorating in MCI, then age-related compensatory mechanisms and functional reorganization might increasingly be more salient. Thus, for instance, a shift from parietal to frontal functioning, for which there is existing evidence in aging (Lövdén, Bäckman, Lindenberger, Schaefer & Schmiedek, 2010) is expected, independently of whether these changes lead to effective compensation. Such functional reorganization is likely to reflect increasing load on frontal executive functions. Parallel deterioration of linguistic and visuospatial abilities might also modulate this process. In order to investigate these neural changes, the present study will explore the pattern of association between numerical abilities assessed with neuropsychological instruments, and volumetric properties of the brain, both in patients diagnosed with MCI and in healthy controls.

Between-group qualitative differences in these maps would provide a rationale for the presence of both subjective and objective impairment of numerical processing in the MCI population.

Section snippets

Participants

Sixty-two elderly adults were invited to undertake a comprehensive clinical, neuropsychiatric, and neuropsychological examination at the IRCCS San Camillo Hospital (Lido-Venice, Italy). After completing a full neurological and neuropsychological assessment, participants were divided in two groups according to the Petersen et al., criteria for diagnosing MCI (Petersen et al., 2001). Thirty-three participants were diagnosed as having MCI (20 males), and twenty-nine (11 males) were enrolled in the

Behavioral results

A summary of the performance of the two groups on the NADL sub-sections and their corresponding domains is presented in Table 1. The first set of analyses comparing the scores of the two groups in the three NADL sub-sections (total scores) showed no significant differences between the groups in the Interview (Z = 2.02, p = .043), but there were significant differences in the Informal (Z = 3.55, p = .0003) and Formal assessments (Z = 3.50, p = .0004). The subsequent set of analysis carried out

Discussion

Basic numerical abilities and their use in everyday life were found to be significantly poorer in MCI patients than in healthy controls. In contrast, no significant group difference was found in the score assessing awareness of numerical difficulties in everyday life. This is an important finding insofar as it shows that MCI patients, typically complaining about memory and naming difficulties (e.g., Joubert et al., 2010), do not express concerns about progressively deteriorating numerical

Acknowledgments

The present study was supported by the Italian Ministry of Health (F-2009-1530973) and by “Progetto strategico NEURAT” from the University of Padua to Carlo Semenza.

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