Thomas R. Coyle

Age-related morphology trends of cortical sulci

The age‐related trends of the width and the depth of major cortical sulci were studied in normal adults. Ninety healthy subjects (47 males, 43 females) age 20–82 years were evaluated. Measurements of average sulcal width and depth in 14 prominent sulcal structures per hemisphere were performed with high‐resolution anatomical MRI. The average sulcal width increased at a rate of about 0.7 mm/decade, while the average sulcal depth decreased at a rate of about 0.4 mm/decade. Sulcal age‐related trends were found to be highly influenced by gender in the superior temporal, collateral, and cingulate sulci (P < 0.05), with males showing more pronounced age‐related change in sulcal width than females. Sulcal structures located in multimodal cortical areas showed more profound age‐related changes than sulcal structures in unimodal cortical areas (P < 0.05). Hum Brain Mapp, 2005.

Processing speed is correlated with cerebral health markers in the frontal lobes as quantified by neuroimaging.

We explored relationships between decline in cognitive processing speed (CPS) and change in frontal lobe MRI/MRS-based indices of cerebral integrity in 38 healthy adults (age 57-90 years). CPS was assessed using a battery of four timed neuropsychological tests: Grooved Pegboard, Coding, Symbol Digit Modalities Test and Category Fluency (Fruits and Furniture). The neuropsychological tests were factor analyzed to extract two components of CPS: psychomotor (PM) and psychophysical (PP). MRI-based indices of cerebral integrity included three cortical measurements per hemisphere (GM thickness, intergyral and sulcal spans) and two subcortical indices (fractional anisotropy (FA), measured using track-based spatial statistics (TBSS), and the volume of hyperintense WM (HWM)). MRS indices included levels of choline-containing compounds (GPC+PC), phosphocreatine plus creatine (PCr+Cr), and N-acetylaspartate (NAA), measured bilaterally in the frontal WM bundles. A substantial fraction of the variance in the PM-CPS (58%) was attributed to atrophic changes in frontal WM, observed as increases in sulcal span, declines in FA values and reductions in concentrations of NAA and choline-containing compounds. A smaller proportion (20%) of variance in the PP-CPS could be explained by bilateral increases in frontal sulcal span and increases in HWM volumes.

Relationship among neuroimaging indices of cerebral health during normal aging

Sensitive measures of brain aging show great promise for gauging factors that affect aging and degenerative processes, such as risk genes or therapy. Here we examined age‐related trends for three indices of cerebral health: gyral gray matter (GM) thickness, dilation of sulcal spaces with CSF, and the volume of T2‐hyperintense white matter (HWM) lesions. The study involved 31 healthy adults age 57–82 years old. Measurements of average GM thickness, average sulcal span and HWM volume were performed using high‐resolution 3D T1‐ and T2‐weighted brain MR images. Age‐related trends for the three cerebral health indices were consistent with previously published work though the analysis of their covariance led to a previously unreported relationship. Simultaneous multiple regression found that dilation of cortical sulci were primarily (t = 2.59, P < 0.01) related to the increases in HWM volume and secondarily related (t = −2.51, P < 0.01) to the reductions of the cortical GM thickness. The are‐corrected correlation between reduction in GM thickness and increases in HWM volume, was not significant (P = 0.34). These findings are of interest in designing quantitative measures of brain aging for monitoring individual patients and in large‐scale clinical trials. Hum Brain Mapp 2008.

A review of the worst performance rule: Evidence, theory, and alternative hypotheses

This paper reviews evidence, theory, and alternative hypotheses for the worst performance rule (WPR), which states that on multitrial cognitive tasks, worst performance trials predict general intelligence (g) better than best performance trials. A review of the relevant evidence indicates that the WPR has been found for a variety of participants, tasks, and measures. A review of relevant theories reveals that the WPR appears to be related to cognitive factors (e.g., lapses in working memory) as well as biological factors (e.g., individual differences in neural oscillations). A review of alternative hypotheses shows that the WPR cannot be attributed to statistical or data artifacts such as outliers, unreliable measurement, or variance compression. The preponderance of evidence supports the hypothesis that the WPR holds for cognitive tasks high in g saturation but not for cognitive tasks low in g saturation. The paper ends with a call for research on the causes of the WPR and for research on the correlates of best performance.

Loss of cerebral white matter structural integrity tracks the gray matter metabolic decline in normal aging

Relationships between structural MRI-based markers of declining cerebral integrity, and regional PET measurements of (18)FDG uptake have not been studied well in normal aging. In this manuscript we relate changes in cerebral morphology to regional cerebral glucose uptake for 14 major cortical areas in 19 healthy older individuals (age 59-92 years). Measurements of cerebral integrity included gray matter (GM) thickness, sulcal and intergyral spans, fractional anisotropy (FA) of water diffusion and volume of hyperintense WM (HWM) lesions. (18)FDG-PET measurements were converted to standard uptake values and corrected for partial volume artifact. Following this, cortical FDG uptake was significantly correlated with several indices of WM integrity that we previously observed to be sensitive to cognitive decline in executive function, including intergyral span and HWM volumes. Our findings suggest that the age-related decline in white matter integrity, observed as increases in HWM lesions, intergyral spans and reduction in FA, correlated with a decline in the global and regional cerebral glucose uptake. Our findings support the emerging consensus that WM integrity indices are sensitive predictors of declining cerebral health in normal aging. Specifically, age-related WM degradation in the thinly myelinated association tracts appears to track the decreases in global and regional rates of glucose uptake.

Processing Speed Mediates the Development of General Intelligence (g) in Adolescence

In the research reported here, we examined whether processing speed mediates the development of general intelligence (g) in adolescence. Using the Armed Services Vocational Aptitude Battery, a battery of 12 diverse cognitive tests, we assessed processing speed and g in a large sample of 13- to 17-year-olds obtained from the National Longitudinal Survey of Youth (N = 6,969). The direct effect of age on g was small compared with the total effect of age on g, which was almost fully mediated through speed. The results suggest that increases in g in adolescence can be attributed to increases in mental speed.

Can structural MRI indices of cerebral integrity track cognitive trends in executive control function during normal maturation and adulthood

We explored the relationship between structural neuroimaging‐based indices of cerebral integrity and executive control function (ECF) in two groups of healthy subjects: A maturing group (33 subjects; 19–29 years) and a senescing group (38 adults; 30–90 years). ECF was assessed using the Executive Interview (EXIT) battery. Cortical indices of cerebral integrity included GM thickness, intergyral span, and sulcal span, each measured for five cortical regions per hemisphere. Subcortical indices included fractional anisotropy (FA), measured using track‐based‐spatial‐statistics (TBSS), and the volume of T2‐hyperintense WM (HWM). In the maturing group, no significant relationships between neuroanatomical changes and ECF were found; however, there were hints that late‐term maturation of cerebral WM influenced variability in ECF. In the senescing group, the decline in ECF corresponded to atrophic changes in cerebral WM (sulcal and intergyral span) primarily in the superior frontal and anterior cingulate regions. A large fraction of the variability in ECF (62%) can be explained by variability in the structural indices from these two regions. Hum Brain Mapp 2009.

IQ, the worst performance rule, and Spearman's law: a reanalysis and extension

This paper focused on two hypotheses: the worst performance rule, which states that worst performance on a cognitive task predicts g-loaded measures such as IQ better than best performance, and Spearmans law, which states that the g-loading of IQ decreases with aptitude and with age during childhood. Combining these two hypotheses, the present study tested a new hypothesis: the worst performance rule should hold for younger and lower-IQ children, whose IQs should be highly g-loaded, but perhaps not for older and higher-IQ children, whose IQs should be less g-loaded. The new hypothesis was tested by reanalyzing archival data and extending Coyles [Intelligence 29 (2001) 117] worst performance analysis. Nongifted (n=81, mean IQ=108.94) and gifted (n=85, mean IQ=140.19) children in second through fourth grade received five study-recall trials of words. IQ was correlated with worst performance (fewest words recalled across trials), best performance (most words recalled across trials), and strategy use. As predicted, only the younger nongifted children showed evidence of the worst performance rule (i.e., worst performance was the best predictor of IQ). However, gifted–nongifted difference tests of the IQ-worst performance correlation were not significant at any grade level, although the magnitude of the differences varied in the predicted direction (i.e., gifted–nongifted differences were most pronounced at the lower grades and declined with age). The results were interpreted in the context of the differentiation hypothesis, which states that mental ability becomes more differentiated and less g-loaded with increases in age and IQ.

IQ is related to the worst performance rule in a memory task involving children

Abstract Larson and Alderton [Intelligence 14 (1990) 309.] observed that on elementary cognitive tasks (ECTs), worst performance (i.e., slowest reaction time (RT)) was a better predictor of IQ than best performance (i.e., fastest RT). This suggested to them a Worst Performance rule, which states that “The worst RT trials reveal more about intelligence than do other portions of the RT distribution” (p. 310). The present study examined whether the Worst Performance rule could be applied to a strategic memory task in which children were asked to remember different lists of categorizable words (e.g., boat, bus, car, banana, apple, peach). The results revealed strong support for the Worst Performance rule, with worst performance (i.e., fewest words recalled) predicting more unique variance in IQ than any other variable (e.g., most words recalled; fewest strategies used). These results demonstrate that the Worst Performance rule can be used to predict IQ using performance measures other than RT and in tasks other than ECTs.

The common genetic influence over processing speed and white matter microstructure: Evidence from the Old Order Amish and Human Connectome Projects.

Speed with which brain performs information processing influences overall cognition and is dependent on the white matter fibers. To understand genetic influences on processing speed and white matter FA, we assessed processing speed and diffusion imaging fractional anisotropy (FA) in related individuals from two populations. Discovery analyses were performed in 146 individuals from large Old Order Amish (OOA) families and findings were replicated in 485 twins and siblings of the Human Connectome Project (HCP). The heritability of processing speed was h(2)=43% and 49% (both p<0.005), while the heritability of whole brain FA was h(2)=87% and 88% (both p<0.001), in the OOA and HCP, respectively. Whole brain FA was significantly correlated with processing speed in the two cohorts. Quantitative genetic analysis demonstrated a significant degree to which common genes influenced joint variation in FA and brain processing speed. These estimates suggested common sets of genes influencing variation in both phenotypes, consistent with the idea that common genetic variations contributing to white matter may also support their associated cognitive behavior.