The results of the regression analyses are listed in . The R2 values for the regression models are listed on the far right; with the exception of the individual Episodic Memory test parameters (i.e., Recognition, Delayed Recall, and Total Correct for the Word List), the regression models fits were significant, typically accounting for over 40% of the observed variance. Completion of all instruments by every participant was not possible; the number completing each inventory is listed on the far right. The ratios of test score units changed per 10 cc of absolute total volume lost (i.e., the fitted slopes or β-values) are reported in boldface when significant (p < .05) or in italics when trending toward significance (.05 < p < .10). With the exception of the Social Disorder score, in which a higher score indicates increasing deficit, all other indices score performance positively. Thus, the negative ratios represent the decline of performance on a particular neuropsychological index among participants within a subgroup with increasing disease severity.
Regression of psychosocial indices versus total cortical loss for subgroups by dominant cortical loss
The DOM-dominant subgroup showed declines in performance with disease severity for most indices within our neuropsychological protocol. Of particular note, only this subgroup showed a significant correlation between the total cortical atrophy and the Social Disorder scale (). There are some differences between the right- and the left-dominant patient subgroups, perhaps best demonstrated by the Semantic Category Judgment subscores, “Picture—Vegetables” and “Picture—Tools,” respectively. Additionally, Confrontation Naming (i.e., Boston Naming Test) and all the episode memory test indices (i.e., Word List Recognition, Delayed Recall, and Total Correct) saw declines with increasing total cortical atrophy for the DOM_Left subgroup, but decline in performance was overall much weaker for the DOM_Right subgroup. Thus, the more significant language deficits for DOM_Left as contrasted with the more significant visuospatial deficits for DOM_Right would appear to give some modest support to distinguishing between these two subgroups.
The small AMT_Right-dominant patient subgroup showed no degradation in their neuropsychological performance with increasing severity of total cortical atrophy. By comparison, the larger AMT_Left-dominant subgroup’s language-based performance (i.e., Boston Naming Test, Delayed Recall, Semantic Category Judgment, and “Animal” Fluency) is reliably degraded with increasing total cortical atrophy. Of note, the decline of the AMT_Left group’s Delayed Recall with increasingly severe total cortical atrophy specifically suggests the temporal lobe’s role in memory retrieval, in contrast with the DOM involvement across other Episodic Memory measures.
In general, FPO-dominant patient subgroups display a markedly different neuropsychological profile (). The several single-cluster-dominant patient subgroups do not demonstrate significant correlations of deficit with atrophy for the language components of our neuropsychological protocol virtually across the board. The one exception may be the decline on Figure Copy (Visual Praxis) for the left central sulcus (FP_Left)-dominant subgroup. These results should be interpreted with some care, given the small numbers of participants in these individual subgroups and the more tentative support for the partitioning of the FPO- dominant patients by seriation.
These null results for the FPO single-cluster-dominant subgroups are to be contrasted with the significant correlations found in the “CBS-like” MCL patient subgroups. In particular, MCL_Left is a relatively large subgroup that shows significant performance degradation with increased disease severity for the Boston Naming Test and trending toward significance on some language measures (Delayed Recall and the Total Correct for Word List indices and “Lexical—Vegetables” score from Semantic Category Judgment), while MCL_Right shows significance for visually guided Semantic Category Judgment (i.e., “Picture—Tools” and “Picture—Vegetables” subscores). Both MCL_Right and MCL_Left are likewise associated with Figure Copy (Visual Praxis) performance decline with increasing disease severity.