Abstract
In the present study, changes in the parahippocampal white matter (PWM), in the region that includes the perforant path, were investigated, in vivo, in 14 individuals with amnestic mild cognitive impairment (aMCI) compared to 14 elderly controls with no cognitive impairment (NCI). For this purpose, (1) volumetry; (2) diffusion tensor imaging (DTI) derived measures of mean diffusivity (MD) and fractional anisotropy (FA); and (3) tractography were used. In addition, regression models were utilized to examine the association of PWM measurements with memory decline. The results from this study confirm previous findings in our laboratory and others, showing that compared to controls, individuals with aMCI have PWM volume loss. In addition to volume reduction, participants with aMCI demonstrated a significant increase in MD, but no difference in FA, both in the PWM region and in fibers modeled to pass through the PWM region. Further, the DTI metric of MD was associated with declarative memory performance, suggesting it may be a sensitive marker for memory dysfunction. These results indicate that there is general tissue loss and degradation (decreased volume; increased MD) in individuals with aMCI compared to older people with normal cognitive function. However, the microstructural organization of remaining fibers, as determined by measures of anisotropic diffusion, is not significantly different from that of controls.
Highlights
Amnestic mild cognitive impairment refers to elderly individuals who show a predominant decline in declarative memory function but do not meet criteria for Alzheimer’s disease (AD)
The two groups of participants did not differ in age or education, but as expected, there was a difference in Mini Mental State Examination (MMSE) [t(26) = 4.3, p < 0.001] scores and in episodic memory z-scores [t(26) = 6.9, p < 0.001]
The present study characterized, in vivo, white matter changes in the parahippocampal region that includes the perforant path in individuals with Amnestic mild cognitive impairment (aMCI) compared to those of elderly controls with no cognitive impairment using volumetry, diffusion tensor imaging (DTI) and tractography
Summary
Amnestic mild cognitive impairment (aMCI) refers to elderly individuals who show a predominant decline in declarative memory function but do not meet criteria for Alzheimer’s disease (AD). Studies of individuals with aMCI compared to normal controls provide a unique opportunity to learn about neuroanatomical changes associated with AD at early stages of the disease process, provide additional information on risk factors for AD, and perhaps allow for the development of earlier therapeutic interventions [1,33]. E.J. Rogalski et al / Changes in parahippocampal white matter integrity in amnestic mild cognitive impairment the entorhinal cortex (EC), since these mesial temporal lobe structures are known to be critically important for successful declarative memory [46,56]. It has been hypothesized that the memory deficits that characterize individuals with aMCI and AD may partly be a consequence of a degradation in the flow of information from the entorhinal cortex to the hippocampus [23]
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