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1.  A novel frontal pathway underlies verbal fluency in primary progressive aphasia 
Brain  2013;136(8):2619-2628.
The frontal aslant tract is a direct pathway connecting Broca’s region with the anterior cingulate and pre-supplementary motor area. This tract is left lateralized in right-handed subjects, suggesting a possible role in language. However, there are no previous studies that have reported an involvement of this tract in language disorders. In this study we used diffusion tractography to define the anatomy of the frontal aslant tract in relation to verbal fluency and grammar impairment in primary progressive aphasia. Thirty-five patients with primary progressive aphasia and 29 control subjects were recruited. Tractography was used to obtain indirect indices of microstructural organization of the frontal aslant tract. In addition, tractography analysis of the uncinate fasciculus, a tract associated with semantic processing deficits, was performed. Damage to the frontal aslant tract correlated with performance in verbal fluency as assessed by the Cinderella story test. Conversely, damage to the uncinate fasciculus correlated with deficits in semantic processing as assessed by the Peabody Picture Vocabulary Test. Neither tract correlated with grammatical or repetition deficits. Significant group differences were found in the frontal aslant tract of patients with the non-fluent/agrammatic variant and in the uncinate fasciculus of patients with the semantic variant. These findings indicate that degeneration of the frontal aslant tract underlies verbal fluency deficits in primary progressive aphasia and further confirm the role of the uncinate fasciculus in semantic processing. The lack of correlation between damage to the frontal aslant tract and grammar deficits suggests that verbal fluency and grammar processing rely on distinct anatomical networks.
PMCID: PMC3722349  PMID: 23820597
aphasia; white matter; language; tractography; dementia; freesurfer; frontal aslant tract; tractography
2.  Words and objects at the tip of the left temporal lobe in primary progressive aphasia 
Brain  2013;136(2):601-618.
Eleven of 69 prospectively enrolled primary progressive aphasics were selected for this study because of peak atrophy sites located predominantly or exclusively within the anterior left temporal lobe. Cortical volumes in these areas were reduced to less than half of control values, whereas average volume elsewhere in the left hemisphere deviated from control values by only 8%. Failure to name objects emerged as the most consistent and severe deficit. Naming errors were attributed to pure retrieval failure if the object could not be named even when the denoting word was understood, the object recognized and the two accurately matched. Surprisingly many of the naming errors reflected pure retrieval failures, without discernible semantic or associative component. The remaining set of errors had associative components. These errors reflected the inability to define the word denoting the object more often than the inability to define the nature of the pictured object. In a separate task where the same object had to be linked to verbal or non-verbal associations, performance was abnormal only in the verbal format. Excessive taxonomic interference was observed for picture–word, but not picture–picture, matching tasks. This excessive interference reflected a blurring of intra- rather than inter-category distinctions as if the acuity of word–object associations had been diminished so that correspondences were easier to recognize at generic than specific levels. These dissociations between verbal and non-verbal markers of object knowledge indicate that the reduced neural mass at peak atrophy sites of the left temporal tip, accounting for half or more of the presumed premorbid volume, was unlikely to have contained domain-independent semantic representations of the type that would be expected in a strictly amodal hub. A more likely arrangement entails two highly interactive routes—a strongly left lateralized temporosylvian language network for verbal concepts, and a presumably more bilateral or right-sided inferotemporal/fusiform object recognition network, which remained relatively spared because peak atrophy sites were concentrated on the left. The current results also suggest that the left anterior temporal neocortex should be inserted into the language network where it is likely to play a major role in selecting verbal labels for objects and mediating the progression of word comprehension from generic to specific levels of precision.
PMCID: PMC3572925  PMID: 23361063
dementia; semantic; language; naming; frontotemporal
3.  Clinically concordant variations of Alzheimer pathology in aphasic versus amnestic dementia 
Brain  2012;135(5):1554-1565.
Primary progressive aphasia is a neurodegenerative syndrome characterized by gradual dissolution of language but relative sparing of other cognitive domains, especially memory. It is associated with asymmetric atrophy in the language-dominant hemisphere (usually left), and differs from typical Alzheimer-type dementia where amnesia is the primary deficit. Various pathologies have been reported, including the tangles and plaques of Alzheimer’s disease. Identification of Alzheimer pathology in these aphasic patients is puzzling since tangles and related neuronal loss in Alzheimer’s disease typically emerge in memory-related structures such as entorhinal cortex and spread to language-related neocortex later in the disease. Furthermore, Alzheimer pathology is typically symmetric. How can a predominantly limbic and symmetric pathology cause the primary progressive aphasia phenotype, characterized by relative preservation of memory and asymmetric predilection for the language-dominant hemisphere? Initial investigations into the possibility that Alzheimer pathology displays an atypical distribution in primary progressive aphasia yielded inconclusive results. The current study was based on larger groups of patients with either primary progressive aphasia or a typical amnestic dementia. Alzheimer pathology was the principal diagnosis in all cases. The goal was to determine whether Alzheimer pathology had clinically-concordant, and hence different distributions in these two phenotypes. Stereological counts of tangles and plaques revealed greater leftward asymmetry for tangles in primary progressive aphasia but not in the amnestic Alzheimer-type dementia (P < 0.05). Five of seven aphasics had more leftward tangle asymmetry in all four neocortical regions analysed, whereas this pattern was not seen in any of the predominantly amnestic cases. One aphasic case displayed higher right-hemisphere tangle density despite greater left-hemisphere hypoperfusion and atrophy during life. Although there were more tangles in the memory-related entorhinal cortex than in language-related neocortical areas in both phenotypes (P < 0.0001), the ratio of neocortical-to-entorhinal tangles was significantly higher in the aphasic cases (P = 0.034). Additionally, overall numbers of tangles and plaques were greater in the aphasic than amnestic cases (P < 0.05), especially in neocortical areas. No significant hemispheric asymmetry was found in plaque distribution, reinforcing the conclusion that tangles have greater clinical concordance than plaques in the spectrum of Alzheimer pathologies. The presence of left-sided tangle predominance and higher neocortical-to-entorhinal tangle ratio in primary progressive aphasia establishes clinical concordance of Alzheimer pathology with the aphasic phenotype. The one case with reversed asymmetry, however, suggests that these concordant clinicopathological relationships are not universal and that individual primary progressive aphasia cases with Alzheimer pathology exist where distributions of plaques and tangles do not account for the observed phenotype.
PMCID: PMC3338929  PMID: 22522938
neurodegenerative disorders; primary progressive aphasia; AD pathology; hemispheric differences; stereology
4.  Quantitative classification of primary progressive aphasia at early and mild impairment stages 
Brain  2012;135(5):1537-1553.
The characteristics of early and mild disease in primary progressive aphasia are poorly understood. This report is based on 25 patients with aphasia quotients >85%, 13 of whom were within 2 years of symptom onset. Word-finding and spelling deficits were the most frequent initial signs. Diagnostic imaging was frequently negative and initial consultations seldom reached a correct diagnosis. Functionality was preserved, so that the patients fit current criteria for single-domain mild cognitive impairment. One goal was to determine whether recently published classification guidelines could be implemented at these early and mild disease stages. The quantitative testing of the recommended core and ancillary criteria led to the classification of ∼80% of the sample into agrammatic, logopenic and semantic variants. Biological validity of the resultant classification at these mild impairment stages was demonstrated by clinically concordant cortical atrophy patterns. A two-dimensional template based on orthogonal mapping of word comprehension and grammaticality provided comparable accuracy and led to a flexible road map that can guide the classification process quantitatively or qualitatively. Longitudinal evaluations of initially unclassifiable patients showed that the semantic variant can be preceded by a prodromal stage of focal left anterior temporal atrophy during which prominent anomia exists without word comprehension or object recognition impairments. Patterns of quantitative tests justified the distinction of grammar from speech abnormalities and the desirability of using the ‘agrammatic’ designation exclusively for loss of grammaticality, regardless of fluency or speech status. Two patients with simultaneous impairments of grammatical sentence production and word comprehension displayed focal atrophy of the inferior frontal gyrus and the anterior temporal lobe. These patients represent a fourth variant of ‘mixed’ primary progressive aphasia. Quantitative criteria were least effective in the distinction of the agrammatic from the logopenic variant and left considerable latitude to clinical judgement. The widely followed recommendation to wait for 2 years of relatively isolated and progressive language impairment before making a definitive diagnosis of primary progressive aphasia has promoted diagnostic specificity, but has also diverted attention away from early and mild disease. This study shows that this recommendation is unnecessarily restrictive and that quantitative guidelines can be implemented for the valid root diagnosis and subtyping of mildly impaired patients within 2 years of symptom onset. An emphasis on early diagnosis will promote a better characterization of the disease stages where therapeutic interventions are the most likely to succeed.
PMCID: PMC3577099  PMID: 22525158
aphasia; logopenic; semantic; agrammatic; anomic
5.  Sensitivity of revised diagnostic criteria for the behavioural variant of frontotemporal dementia 
Brain  2011;134(9):2456-2477.
Based on the recent literature and collective experience, an international consortium developed revised guidelines for the diagnosis of behavioural variant frontotemporal dementia. The validation process retrospectively reviewed clinical records and compared the sensitivity of proposed and earlier criteria in a multi-site sample of patients with pathologically verified frontotemporal lobar degeneration. According to the revised criteria, ‘possible’ behavioural variant frontotemporal dementia requires three of six clinically discriminating features (disinhibition, apathy/inertia, loss of sympathy/empathy, perseverative/compulsive behaviours, hyperorality and dysexecutive neuropsychological profile). ‘Probable’ behavioural variant frontotemporal dementia adds functional disability and characteristic neuroimaging, while behavioural variant frontotemporal dementia ‘with definite frontotemporal lobar degeneration’ requires histopathological confirmation or a pathogenic mutation. Sixteen brain banks contributed cases meeting histopathological criteria for frontotemporal lobar degeneration and a clinical diagnosis of behavioural variant frontotemporal dementia, Alzheimer’s disease, dementia with Lewy bodies or vascular dementia at presentation. Cases with predominant primary progressive aphasia or extra-pyramidal syndromes were excluded. In these autopsy-confirmed cases, an experienced neurologist or psychiatrist ascertained clinical features necessary for making a diagnosis according to previous and proposed criteria at presentation. Of 137 cases where features were available for both proposed and previously established criteria, 118 (86%) met ‘possible’ criteria, and 104 (76%) met criteria for ‘probable’ behavioural variant frontotemporal dementia. In contrast, 72 cases (53%) met previously established criteria for the syndrome (P < 0.001 for comparison with ‘possible’ and ‘probable’ criteria). Patients who failed to meet revised criteria were significantly older and most had atypical presentations with marked memory impairment. In conclusion, the revised criteria for behavioural variant frontotemporal dementia improve diagnostic accuracy compared with previously established criteria in a sample with known frontotemporal lobar degeneration. Greater sensitivity of the proposed criteria may reflect the optimized diagnostic features, less restrictive exclusion features and a flexible structure that accommodates different initial clinical presentations. Future studies will be needed to establish the reliability and specificity of these revised diagnostic guidelines.
PMCID: PMC3170532  PMID: 21810890
behavioural variant frontotemporal dementia; diagnostic criteria; frontotemporal lobar degeneration; FTD; pathology
6.  With or without FUS, it is the anatomy that dictates the dementia phenotype 
Brain  2009;132(11):2906-2908.
PMCID: PMC2915502  PMID: 19861505
7.  Neurology of anomia in the semantic variant of primary progressive aphasia 
Brain  2009;132(9):2553-2565.
The semantic variant of primary progressive aphasia (PPA) is characterized by the combination of word comprehension deficits, fluent aphasia and a particularly severe anomia. In this study, two novel tasks were used to explore the factors contributing to the anomia. The single most common factor was a blurring of distinctions among members of a semantic category, leading to errors of overgeneralization in word–object matching tasks as well as in word definitions and object descriptions. This factor was more pronounced for natural kinds than artifacts. In patients with the more severe anomias, conceptual maps were more extensively disrupted so that inter-category distinctions were as impaired as intra-category distinctions. Many objects that could not be named aloud could be matched to the correct word in patients with mild but not severe anomia, reflecting a gradual intensification of the semantic factor as the naming disorder becomes more severe. Accurate object descriptions were more frequent than accurate word definitions and all patients experienced prominent word comprehension deficits that interfered with everyday activities but no consequential impairment of object usage or face recognition. Magnetic resonance imaging revealed three characteristics: greater atrophy of the left hemisphere; atrophy of anterior components of the perisylvian language network in the superior and middle temporal gyri; and atrophy of anterior components of the face and object recognition network in the inferior and medial temporal lobes. The left sided asymmetry and perisylvian extension of the atrophy explains the more profound impairment of word than object usage and provides the anatomical basis for distinguishing the semantic variant of primary progressive aphasia from the partially overlapping group of patients that fulfil the widely accepted diagnostic criteria for semantic dementia.
PMCID: PMC2766179  PMID: 19506067
aphasia; frontotemporal lobar degeneration; language processing; progressive aphasia; semantic categorization

Results 1-7 (7)