Using explainable artificial intelligence to identify linguistic biomarkers of amyloid pathology in primary progressive aphasia

Introduction

Recent success has been achieved in Alzheimer's disease (AD) clinical trials targeting amyloid beta (β), demonstrating a reduction in the rate of cognitive decline. However, testing methods for amyloid-β positivity are currently costly or invasive, motivating the development of accessible screening approaches to steer patients toward appropriate diagnostic tests. Here, we employ a pre-trained language model (Distil-RoBERTa) to identify amyloid-β positivity from a short, connected speech sample. We further use explainable AI (XAI) methods to extract interpretable linguistic features that can be employed in clinical practice.

Methods

We obtained language samples from 74 patients with primary progressive aphasia (PPA) across its three variants. Amyloid-β positivity was established through the analysis of cerebrospinal fluid, amyloid PET, or autopsy. 51% of the sample was amyloid-positive. We trained Distil-RoBERTa for 16 epochs with a batch size of 6 and a learning rate of 5e-5, and used the LIME algorithm to train interpretation models to interpret the trained classifier's inference conditions.

Results

Over ten runs of 10-fold cross-validation, the classifier achieved a mean accuracy of 92%, SD = 0.01. Interpretation models were able to capture the classifier's behavior well, achieving an accuracy of 97% against classifier predictions, and uncovering several novel speech patterns that may characterize amyloid-β positivity.

Discussion

Our work improves previous research which indicates connected speech is a useful diagnostic input for prediction of the presence of amyloid-β in patients with PPA. Further, we leverage XAI techniques to reveal novel linguistic features that can be tested in clinical practice in the appropriate subspecialty setting. Computational linguistic analysis of connected speech shows great promise as a novel assessment method in patients with AD and related disorders.

Default mode network tau predicts future clinical decline in atypical early Alzheimer's disease

Identifying individuals with early stage Alzheimer's disease (AD) at greater risk of steeper clinical decline would allow professionals and loved ones to make better-informed medical, support, and life planning decisions. Despite accumulating evidence on the clinical prognostic value of tau PET in typical late-onset amnestic AD, its utility in predicting clinical decline in individuals with atypical forms of AD remains unclear. In this study, we examined the relationship between baseline tau PET signal and the rate of subsequent clinical decline in a sample of 48 A + /T + /N + patients with mild cognitive impairment or mild dementia due to AD with atypical clinical phenotypes (Posterior Cortical Atrophy, logopenic variant Primary Progressive Aphasia, and amnestic syndrome with multi-domain impairment and age of onset < 65 years). All patients underwent structural magnetic resonance imaging (MRI), tau ( 18 F-Flortaucipir) PET, and amyloid (either 18 F-Florbetaben or 11 C-Pittsburgh Compound B) PET scans at baseline. Each patient's longitudinal clinical decline was assessed by calculating the annualized change in the Clinical Dementia Rating Sum-of-Boxes (CDR-SB) scores from baseline to follow-up (mean time interval = 14.55 ± 3.97 months). Our sample of early atypical AD patients showed an increase in CDR-SB by 1.18 ± 1.25 points per year: t (47) = 6.56, p < .001, d = 0.95. These AD patients showed prominent baseline tau burden in posterior cortical regions including the major nodes of the default mode network, including the angular gyrus, posterior cingulate cortex/precuneus, and lateral temporal cortex. Greater baseline tau in the broader default mode network predicted faster clinical decline. Tau in the default mode network was the strongest predictor of clinical decline, outperforming baseline clinical impairment, tau in other functional networks, and the magnitude of cortical atrophy and amyloid burden in the default mode network. Overall, these findings point to the contribution of baseline tau burden within the default mode network of the cerebral cortex to predicting the magnitude of clinical decline in a sample of atypical early AD patients one year later. This simple measure based on a tau PET scan could aid the development of a personalized prognostic, monitoring, and treatment plan tailored to each individual patient, which would help clinicians not only predict the natural evolution of the disease but also estimate the effect of disease-modifying therapies on slowing subsequent clinical decline given the patient's tau burden while still early in the disease course.

Language uncovers visuospatial dysfunction in posterior cortical atrophy: a natural language processing approach

Introduction

Posterior Cortical Atrophy (PCA) is a syndrome characterized by a progressive decline in higher-order visuospatial processing, leading to symptoms such as space perception deficit, simultanagnosia, and object perception impairment. While PCA is primarily known for its impact on visuospatial abilities, recent studies have documented language abnormalities in PCA patients. This study aims to delineate the nature and origin of language impairments in PCA, hypothesizing that language deficits reflect the visuospatial processing impairments of the disease.

Methods

We compared the language samples of 25 patients with PCA with age-matched cognitively normal (CN) individuals across two distinct tasks: a visually-dependent picture description and a visually-independent job description task. We extracted word frequency, word utterance latency, and spatial relational words for this comparison. We then conducted an in-depth analysis of the language used in the picture description task to identify specific linguistic indicators that reflect the visuospatial processing deficits of PCA.

Results

Patients with PCA showed significant language deficits in the visually-dependent task, characterized by higher word frequency, prolonged utterance latency, and fewer spatial relational words, but not in the visually-independent task. An in-depth analysis of the picture description task further showed that PCA patients struggled to identify certain visual elements as well as the overall theme of the picture. A predictive model based on these language features distinguished PCA patients from CN individuals with high classification accuracy.

Discussion

The findings indicate that language is a sensitive behavioral construct to detect visuospatial processing abnormalities of PCA. These insights offer theoretical and clinical avenues for understanding and managing PCA, underscoring language as a crucial marker for the visuospatial deficits of this atypical variant of Alzheimer's disease.

Using Generative Artificial Intelligence to Classify Primary Progressive Aphasia from Connected Speech

Neurodegenerative dementia syndromes, such as Primary Progressive Aphasias (PPA), have traditionally been diagnosed based in part on verbal and nonverbal cognitive profiles. Debate continues about whether PPA is best subdivided into three variants and also regarding the most distinctive linguistic features for classifying PPA variants. In this study, we harnessed the capabilities of artificial intelligence (AI) and natural language processing (NLP) to first perform unsupervised classification of concise, connected speech samples from 78 PPA patients. Large Language Models discerned three distinct PPA clusters, with 88.5% agreement with independent clinical diagnoses. Patterns of cortical atrophy of three data-driven clusters corresponded to the localization in the clinical diagnostic criteria. We then used NLP to identify linguistic features that best dissociate the three PPA variants. Seventeen features emerged as most valuable for this purpose, including the observation that separating verbs into high and low-frequency types significantly improves classification accuracy. Using these linguistic features derived from the analysis of brief connected speech samples, we developed a classifier that achieved 97.9% accuracy in predicting PPA subtypes and healthy controls. Our findings provide pivotal insights for refining early-stage dementia diagnosis, deepening our understanding of the characteristics of these neurodegenerative phenotypes and the neurobiology of language processing, and enhancing diagnostic evaluation accuracy.

Language Uncovers Visuospatial Dysfunction in Posterior Cortical Atrophy: A Natural Language Processing Approach

Introduction

Posterior Cortical Atrophy (PCA) is a syndrome characterized by a progressive decline in higher-order visuospatial processing, leading to symptoms such as space perception deficit, simultanagnosia, and object perception impairment. While PCA is primarily known for its impact on visuospatial abilities, recent studies have documented language abnormalities in PCA patients. This study aims to delineate the nature and origin of language impairments in PCA, hypothesizing that language deficits reflect the visuospatial processing impairments of the disease.

Methods

We compared the language samples of 25 patients with PCA with age-matched cognitively normal (CN) individuals across two distinct tasks: a visually-dependent picture description and a visually-independent job description task. We extracted word frequency, word utterance latency, and spatial relational words for this comparison. We then conducted an in-depth analysis of the language used in the picture description task to identify specific linguistic indicators that reflect the visuospatial processing deficits of PCA.

Results

Patients with PCA showed significant language deficits in the visually-dependent task, characterized by higher word frequency, prolonged utterance latency, and fewer spatial relational words, but not in the visually-independent task. An in-depth analysis of the picture description task further showed that PCA patients struggled to identify certain visual elements as well as the overall theme of the picture. A predictive model based on these language features distinguished PCA patients from CN individuals with high classification accuracy.

Discussion

The findings indicate that language is a sensitive behavioral construct to detect visuospatial processing abnormalities of PCA. These insights offer theoretical and clinical avenues for understanding and managing PCA, underscoring language as a crucial marker for the visuospatial deficits of this atypical variant of Alzheimer's disease.

Measuring Sentence Information via Surprisal: Theoretical and Clinical Implications in Nonfluent Aphasia

OBJECTIVE

Nonfluent aphasia is characterized by simplified sentence structures and word-level abnormalities, including reduced use of verbs and function words. The predominant belief about the disease mechanism is that a core deficit in syntax processing causes both structural and word-level abnormalities. Here, we propose an alternative view based on information theory to explain the symptoms of nonfluent aphasia. We hypothesize that the word-level features of nonfluency constitute a distinct compensatory process to augment the information content of sentences to the level of healthy speakers. We refer to this process as lexical condensation.

METHODS

We use a computational approach based on language models to measure sentence information through surprisal, a metric calculated by the average probability of occurrence of words in a sentence, given their preceding context. We apply this method to the language of patients with nonfluent primary progressive aphasia (nfvPPA; n = 36) and healthy controls (n = 133) as they describe a picture.

RESULTS

We found that nfvPPA patients produced sentences with the same sentence surprisal as healthy controls by using richer words in their structurally impoverished sentences. Furthermore, higher surprisal in nfvPPA sentences correlated with the canonical features of agrammatism: a lower function-to-all-word ratio, a lower verb-to-noun ratio, a higher heavy-to-all-verb ratio, and a higher ratio of verbs in -ing forms.

INTERPRETATION

Using surprisal enables testing an alternative account of nonfluent aphasia that regards its word-level features as adaptive, rather than defective, symptoms, a finding that would call for revisions in the therapeutic approach to nonfluent language production. ANN NEUROL 2023;94:647-657.

Automated analysis of written language in the three variants of primary progressive aphasia

Despite the important role of written language in everyday life, abnormalities in functional written communication have been sparsely investigated in primary progressive aphasia. Prior studies have analysed written language separately in each of the three variants of primary progressive aphasia-but have rarely compared them to each other or to spoken language. Manual analysis of written language can be a time-consuming process. We therefore developed a program that quantifies content units and total units in written or transcribed language samples. We analysed written and spoken descriptions of the Western Aphasia Battery picnic scene, based on a predefined content unit corpus. We calculated the ratio of content units to units as a measure of content density. Our cohort included 115 participants (20 controls for written, 20 controls for spoken, 28 participants with nonfluent variant primary progressive aphasia, 30 for logopenic variant and 17 for semantic variant). Our program identified content units with a validity of 99.7% (95%CI 99.5-99.8). All patients wrote fewer units than controls (P < 0.001). Patients with the logopenic variant (P = 0.013) and the semantic variant (0.004) wrote fewer content units than controls. The content unit-to-unit ratio was higher in the nonfluent and semantic variants than controls (P = 0.019), but no difference in the logopenic variant (P = 0.962). Participants with the logopenic (P < 0.001) and semantic (P = 0.04) variants produced fewer content units in written compared to spoken descriptions. All variants produced fewer units in written samples compared to spoken (P < 0.001). However, due to a relatively smaller decrease in written content units, we observed a larger content unit-to-unit ratio in writing over speech (P < 0.001). Written and spoken content units (r = 0.5, P = 0.009) and total units (r = 0.64, P < 0.001) were significantly correlated in patients with nonfluent variant, but this was not the case for logopenic or semantic. Considering all patients with primary progressive aphasia, fewer content units were produced in those with greater aphasia severity (Progressive Aphasia Severity Scale Sum of Boxes, r = -0.24, P = 0.04) and dementia severity (Clinical Dementia Rating scale Sum of Boxes, r = -0.34, P = 0.004). In conclusion, we observed reduced written content in patients with primary progressive aphasia compared to controls, with a preference for content over non-content units in patients with the nonfluent and semantic variants. We observed a similar 'telegraphic' style in both language modalities in patients with the nonfluent variant. Lastly, we show how our program provides a time-efficient tool, which could enable feedback and tracking of writing as an important feature of language and cognition.

Less is more in language production: an information-theoretic analysis of agrammatism in primary progressive aphasia

Agrammatism is a disorder of language production characterized by short, simplified sentences, the omission of function words, an increased use of nouns over verbs and a higher use of heavy verbs. Despite observing these phenomena for decades, the accounts of agrammatism have not converged. Here, we propose and test the hypothesis that the lexical profile of agrammatism results from a process that opts for words with a lower frequency of occurrence to increase lexical information. Furthermore, we hypothesize that this process is a compensatory response to patients' core deficit in producing long, complex sentences. In this cross-sectional study, we analysed speech samples of patients with primary progressive aphasia (n = 100) and healthy speakers (n = 65) as they described a picture. The patient cohort included 34 individuals with the non-fluent variant, 41 with the logopenic variant and 25 with the semantic variant of primary progressive aphasia. We first analysed a large corpus of spoken language and found that the word types preferred by patients with agrammatism tend to have lower frequencies of occurrence than less preferred words. We then conducted a computational simulation to examine the impact of word frequency on lexical information as measured by entropy. We found that strings of words that exclude highly frequent words have a more uniform word distribution, thereby increasing lexical entropy. To test whether the lexical profile of agrammatism results from their inability to produce long sentences, we asked healthy speakers to produce short sentences during the picture description task. We found that, under this constrained condition, a similar lexical profile of agrammatism emerged in the short sentences of healthy individuals, including fewer function words, more nouns than verbs and more heavy verbs than light verbs. This lexical profile of short sentences resulted in their lower average word frequency than unconstrained sentences. We extended this finding by showing that, in general, shorter sentences get packaged with lower-frequency words as a basic property of efficient language production, evident in the language of healthy speakers and all primary progressive aphasia variants.

Association of Regional Cortical Network Atrophy With Progression to Dementia in Patients With Primary Progressive Aphasia

BACKGROUND AND OBJECTIVES

Patients with primary progressive aphasia (PPA) have gradually progressive language deficits during the initial phase of the illness. As the underlying neurodegenerative disease progresses, patients with PPA start losing independent functioning due to the development of nonlanguage cognitive or behavioral symptoms. The timeline of this progression from the mild cognitive impairment stage to the dementia stage of PPA is variable across patients. In this study, in a sample of patients with PPA, we measured the magnitude of cortical atrophy within functional networks believed to subserve diverse cognitive and affective functions. The objective of the study was to evaluate the utility of this measure as a predictor of time to subsequent progression to dementia in PPA.

METHODS

Patients with PPA with largely independent daily function were recruited through the Massachusetts General Hospital Frontotemporal Disorders Unit. All patients underwent an MRI scan at baseline. Cortical atrophy was then estimated relative to a group of amyloid-negative cognitively normal control participants. For each patient, we measured the time between the baseline visit and the subsequent visit at which dementia progression was documented or last observation. Simple and multivariable Cox regression models were used to examine the relationship between cortical atrophy and the likelihood of progression to dementia.

RESULTS

Forty-nine patients with PPA (mean age = 66.39 ± 8.36 years, 59.2% females) and 25 controls (mean age = 67.43 ± 4.84 years, 48% females) were included in the data analysis. Greater baseline atrophy in not only the left language network (hazard ratio = 1.47, 95% CI = 1.17-1.84) but also in the frontoparietal control (1.75, 1.25-2.44), salience (1.63, 1.25-2.13), default mode (1.55, 1.19-2.01), and ventral frontotemporal (1.41, 1.16-1.71) networks was associated with a higher risk of progression to dementia. A multivariable model identified contributions of the left frontoparietal control (1.94, 1.09-3.48) and ventral frontotemporal (1.61, 1.09-2.39) networks in predicting dementia progression, with no additional variance explained by the language network (0.75, 0.43-1.31).

DISCUSSION

These results suggest that baseline atrophy in cortical networks subserving nonlanguage cognitive and affective functions is an important predictor of progression to dementia in PPA. This measure should be included in precision medicine models of prognosis in PPA.

Feasibility of multidisciplinary telehealth evaluations in atypical dementia

INTRODUCTION

While cognitive assessment by videoconference has become possible over the past decade, the COVID-19 pandemic underscores the critical need for expansion and examination of these methods, their appropriateness for various patient populations, and their benefits and limitations. Validity and reliability studies of tele-neuropsychological testing have been conducted in MCI or mild AD dementia patients (e.g., MMSE=25+); few studies have assessed the feasibility of neurologic examination by video, and none in atypical dementias, assuming that patients with some types (e.g., language, comportment) or greater severity of cognitive-behavioral impairment would be unable to participate. Here we report the feasibility of telehealth services for a multi-disciplinary dementia subspecialty clinic that include cognitive-behavioral and neurologic assessment with patients with atypical neurodegenerative syndromes.

METHODS

104 patient-carepartner (P-C) dyads met with providers in the MGH FTD Unit by videoconference (March-December, 2020) for routine clinical care. P-Cs completed validated questionnaires assessing cognition-mood/behavior/function on REDCap prior to video clinical interview and cognitive assessment, including the MoCA and Boston Cognitive Exam (BCE2.0), a newly revised brief cognitive assessment battery adapted for telehealth. P-Cs met with a neurologist for a basic neurologic examination (including eye-movement examination), review of assessment results, and discussion of care plan. P-Cs completed a satisfaction survey.

RESULTS

The 104 P-Cs included a range of atypical neurodegenerative disorders (bvFTD, PCA, PPA, CBS, PSP, eoAD, Multidomain syndrome) mild-to-severe impairment (CDR range: 0-3). 76% completed the MoCA (25% had CDR=2). 36% also completed the BCEv2. Comparison of remote assessment data to previous in-person testing is ongoing. Of P-Cs who completed a satisfaction survey, all reported being "very satisfied" with the appointment, with 93% open to participating in a remote visit again. 87% found the telehealth visit comparable to an in-person visit. 66% preferred a future combination of remote and in-person visits.

CONCLUSIONS

Multi-disciplinary telehealth visits appear to be feasible with patients with atypical cognitive-behavioral syndromes of across the severity spectrum. P-Cs report a high degree of satisfaction with the telehealth visit and an openness to ongoing telehealth visits. Results have implications for increasing accessibility of multidisciplinary medical services for patients and families living with complex forms of dementia.

A category-selective semantic memory deficit for animate objects in semantic variant primary progressive aphasia

Data are mixed on whether patients with semantic variant primary progressive aphasia exhibit a category-selective semantic deficit for animate objects. Moreover, there is little consensus regarding the neural substrates of this category-selective semantic deficit, though prior literature has suggested that the perirhinal cortex and the lateral posterior fusiform gyrus may support semantic memory functions important for processing animate objects. In this study, we investigated whether patients with semantic variant primary progressive aphasia exhibited a category-selective semantic deficit for animate objects in a word-picture matching task, controlling for psycholinguistic features of the stimuli, including frequency, familiarity, typicality and age of acquisition. We investigated the neural bases of this category selectivity by examining its relationship with cortical atrophy in two primary regions of interest: bilateral perirhinal cortex and lateral posterior fusiform gyri. We analysed data from 20 patients with semantic variant primary progressive aphasia (mean age = 64 years, S.D. = 6.94). For each participant, we calculated an animacy index score to denote the magnitude of the category-selective semantic deficit for animate objects. Multivariate regression analysis revealed a main effect of animacy (β = 0.52, t = 4.03, P < 0.001) even after including all psycholinguistic variables in the model, such that animate objects were less likely to be identified correctly relative to inanimate objects. Inspection of each individual patient's data indicated the presence of a disproportionate impairment in animate objects in most patients. A linear regression analysis revealed a relationship between the right perirhinal cortex thickness and animacy index scores (β = -0.57, t = -2.74, P = 0.015) such that patients who were more disproportionally impaired for animate relative to inanimate objects exhibited thinner right perirhinal cortex. A vertex-wise general linear model analysis restricted to the temporal lobes revealed additional associations between positive animacy index scores (i.e. a disproportionately poorer performance on animate objects) and cortical atrophy in the right perirhinal and entorhinal cortex, superior, middle, and inferior temporal gyri, and the anterior fusiform gyrus, as well as the left anterior fusiform gyrus. Taken together, our results indicate that a category-selective semantic deficit for animate objects is a characteristic feature of semantic variant primary progressive aphasia that is detectable in most individuals. Our imaging findings provide further support for the role of the right perirhinal cortex and other temporal lobe regions in the semantic processing of animate objects.

Neural substrates of verbal repetition deficits in primary progressive aphasia

In this cross-sectional study, we examined the relationship between cortical thickness and performance on several verbal repetition tasks in a cohort of patients with primary progressive aphasia in order to test predictions generated by theoretical accounts of phonological working memory that predict phonological content buffers in left posterior inferior frontal sulcus and supramarginal gyrus. Cortical surfaces were reconstructed from magnetic resonance imaging scans from 42 participants diagnosed with primary progressive aphasia. Cortical thickness was measured in a set of anatomical regions spanning the entire cerebral cortex. Correlation analyses were performed between cortical thickness and average score across three phonological working memory-related tasks: the Repetition sub-test from the Western Aphasia Battery, a forward digit span task, and a backward digit span task. Significant correlations were found between average working memory score across tasks and cortical thickness in left supramarginal gyrus and left posterior inferior frontal sulcus, in support of prior theoretical accounts of phonological working memory. Exploratory whole-brain correlation analyses performed for each of the three behavioural tasks individually revealed a distinct set of positively correlated regions for each task. Comparison of cortical thickness measures from different primary progressive aphasia sub-types to cortical thickness in age-matched controls further revealed unique patterns of atrophy in the different subtypes.

Altered functional connectivity of cortical networks in semantic variant Primary Progressive Aphasia

As their illness progresses, patients with the semantic variant of Primary Progressive Aphasia (svPPA) frequently exhibit peculiar behaviors indicative of altered visual attention or an increased interest in artistic endeavors. In the present study, we examined changes within and between large-scale functional brain networks that may explain this altered visual behavior. We first examined the connectivity of the visual association network, the dorsal attention network, and the default mode network in healthy young adults (n = 89) to understand the typical architecture of these networks in the healthy brain. We then compared the large-scale functional connectivity of these networks in a group of svPPA patients (n = 12) to a group of age-matched cognitively normal controls (n = 30). Our results showed that the between-network connectivity of the dorsal attention and visual association networks was elevated in svPPA patients relative to controls. We further showed that this heightened between-network connectivity was associated with a decrease in the within-network connectivity of the default mode network, possibly due to progressive degeneration of the anterior temporal lobes in svPPA. These results suggest that focal neurodegeneration can lead to the reorganization of large-scale cognitive networks beyond the primarily affected network(s), possibly contributing to cognitive or behavioral changes that are commonly present as part of the clinical phenotype of svPPA.

Atrophy in Distinct Corticolimbic Networks Subserving Socioaffective Behavior in Semantic Variant Primary Progressive Aphasia

BACKGROUND

Although traditionally conceptualized as a language disorder, semantic variant primary progressive aphasia (svPPA) is often accompanied by significant behavioral and affective symptoms which considerably increase disease morbidity. Specifically, these neuropsychiatric symptoms are characterized by breaches in normative socioaffective function, for example, an inability to read social cues, excessive trusting of others, and decreased empathy. Our prior neuroimaging work identified 3 corticolimbic networks anchored in the amygdala, temporal pole, and frontoinsular cortex: an affiliation network, theorized to mediate social approach behavior; an aversion network, theorized to subserve the appraisal of social threat; and a perception network, theorized to mediate the detection of social cues. We hy-pothesized that degeneration of these networks could provide neuroanatomical substrates for socioaffective deficits in svPPA.

METHODS

We examined hypothesized relationships between subscores on the Social Impairment Rating Scale (SIRS) and atrophy in each of these 3 networks in a group of 16 svPPA patients (using matched cognitively normal controls as a reference).

RESULTS

Consistent with our predictions, the magnitude of atrophy in the affiliation network in svPPA patients correlated with the SIRS subscore of socioemotional detachment, while the magnitude of atrophy in the aversion network in svPPA patients correlated with the SIRS subscore of inappropriate trusting. We did not find the predicted association between perception network atrophy and the SIRS subscore of lack of attention to social cues.

CONCLUSION

These findings highlight specific socioaffective deficits in svPPA and provide a neuroanatomical basis for these impairments by linking them to networks commonly targeted in this disorder.

Focal temporal pole atrophy and network degeneration in semantic variant primary progressive aphasia

A wealth of neuroimaging research has associated semantic variant primary progressive aphasia with distributed cortical atrophy that is most prominent in the left anterior temporal cortex; however, there is little consensus regarding which region within the anterior temporal cortex is most prominently damaged, which may indicate the putative origin of neurodegeneration. In this study, we localized the most prominent and consistent region of atrophy in semantic variant primary progressive aphasia using cortical thickness analysis in two independent patient samples (n = 16 and 28, respectively) relative to age-matched controls (n = 30). Across both samples the point of maximal atrophy was located in the same region of the left temporal pole. This same region was the point of maximal atrophy in 100% of individual patients in both semantic variant primary progressive aphasia samples. Using resting state functional connectivity in healthy young adults (n = 89), we showed that the seed region derived from the semantic variant primary progressive aphasia analysis was strongly connected with a large-scale network that closely resembled the distributed atrophy pattern in semantic variant primary progressive aphasia. In both patient samples, the magnitude of atrophy within a brain region was predicted by that region's strength of functional connectivity to the temporopolar seed region in healthy adults. These findings suggest that cortical atrophy in semantic variant primary progressive aphasia may follow connectional pathways within a large-scale network that converges on the temporal pole.

Consequences of imperfect mixing the Gray-Scott model

We study an autocatalytic reaction-diffusion scheme, the Gray-Scott model, when the mixing processes do not homogenize the reactants. Starting from the master equation, we derive the resulting coupled, nonlinear, stochastic partial differential equations that rigorously include the spatiotemporal fluctuations resulting from the interplay between the reaction and mixing processes. The fields are complex and depend on correlated complex noise terms. We implement a method to solve for these complex fields numerically and extract accurate information about the system evolution and stationary states under different mixing regimes. Through this example, we show how the reaction-induced fluctuations interact with the temporal nonlinearities, leading to results that differ significantly from the mean-field (perfectly mixed) approach. This procedure can be applied to an arbitrary nonlinear reaction diffusion scheme.

Reaction-diffusion model for pattern formation in E. coli swarming colonies with slime

A new experimental colonial pattern and pattern transition observed in E. coli MG1655 swarming cells grown on semisolid agar are described. We present a reaction-diffusion model that, taking into account the slime generated by these cells and its influence on the bacterial differentiation and motion, reproduces the pattern and successfully predicts the observed changes when the colonial collective motility is limited. In spite of having small nonhyperflagellated swarming cells, under these experimental conditions E. coli MG1655 can very rapidly colonize a surface, with a low branching rate, thanks to a strong fluid production and a locally incremented density of motile, lubricating cells.

Erectile function after anterior urethroplasty

PURPOSE

We ascertained the impact of anterior urethroplasty on male sexual function.

MATERIALS AND METHODS

A validated questionnaire was mailed to 200 men who underwent anterior urethroplasty to evaluate postoperative sexual function. Questions addressed the change in erect penile length and angle, patient satisfaction with erection, preoperative and postoperative coital frequency, and change in erection noted by the sexual partner. Results were stratified by the urethral reconstruction method, namely anastomosis, buccal mucosal graft, penile flap and all others, and compared with those in a similar group of men who underwent circumcision only.

RESULTS

Of the 200 men who underwent urethroplasty 152 who were 17 to 83 years old (mean age 45.7) completed the questionnaire. Average followup was 36 months (range 3 to 149). Overall there was a similar incidence of sexual problems after urethroplasty and circumcision. Penile skin flap urethroplasty was associated with a slightly higher incidence of impaired sexual function than other procedures (p >0.05). Men with a longer stricture were most likely to report major changes in erectile function and penile length (p <0.05) but improvement was evident with time in 61.8%.

CONCLUSIONS

Overall anterior urethral reconstruction appears no more likely to cause long-term postoperative sexual dysfunction than circumcision. Men with a long stricture may be at increased risk for transient erectile changes.

Heat kernel regularization of the effective action for stochastic reaction-diffusion equations

The presence of fluctuations and nonlinear interactions can lead to scale dependence in the parameters appearing in stochastic differential equations. Stochastic dynamics can be formulated in terms of functional integrals. In this paper we apply the heat kernel method to study the short distance renormalizability of a stochastic (polynomial) reaction-diffusion equation with real additive noise. We calculate the one-loop effective action and its ultraviolet scale dependent divergences. We show that for white noise a polynomial reaction-diffusion equation is one-loop finite in d=0 and d=1, and is one-loop renormalizable in d=2 and d=3 space dimensions. We obtain the one-loop renormalization group equations and find they run with scale only in d=2.

Renormalization group analysis of a quivering string model of posture control

Scaling concepts and renormalization group methods are applied to a simple linear model of human posture control consisting of a trembling or quivering string subject to damping and restoring forces. The string is driven by uncorrelated white Gaussian noise, intended to model the corrections of the physiological control system. We find that adding a weak quadratic nonlinearity to the posture control model opens up a rich and complicated phase space (representing the dynamics) with various nontrivial fixed points and basins of attraction. The transition from diffusive to saturated regimes of the linear model is understood as a crossover phenomenon, and the robustness of the linear model with respect to weak nonlinearities is confirmed. Correlations in posture fluctuations are obtained in both time and space domains. There is an attractive fixed point identified with falling. The scaling of the correlations in the front-back displacement, which can be measured in the laboratory, is predicted for both large-separation (along the string) and long-time regimes of posture control.

Interstitial fibrosis of unilateral ureteral obstruction is exacerbated in kidneys of mice lacking the gene for inducible nitric oxide synthase

Unilateral ureteral obstruction (UUO) is characterized by decreases in renal function and increases in interstitial fibrosis. Previous studies have indicated that pharmacologic manipulations that increase nitric oxide (NO) are beneficial to the obstructed kidneys. NO is produced from arginine by nitric oxide synthase (NOS), an enzyme that exists in both constitutive and inducible (iNOS) forms. To determine the role of the inducible form of NOS in UUO, we used mice with a targeted deletion of iNOS (iNOS -/- mice) and compared them with wild-type (WT) mice. Kidneys were obstructed for 2 weeks in both WT and iNOS -/- mice, and were then removed and bisected. Half of the kidney was embedded in paraffin and tissue sections were examined for interstitial volume or the presence of macrophages. The remainder was flash-frozen and samples were used to measure tissue collagen (hydroxyproline) or transforming growth factor-beta (TGF-beta). This study demonstrates that both cortex and medulla of obstructed kidneys of iNOS -/- mice exhibit significantly increased interstitial volume and interstitial macrophages as compared with their WT counterparts. Furthermore tissue collagen was increased to 9.2+/-1.3 microg/mg tissue in WT obstructed kidneys, whereas in iNOS -/- kidneys, collagen was increased to 13.2+/-0.8 microg/mg tissue. The profibrotic cytokine TGF-beta was also significantly increased in obstructed kidneys of iNOS -/- mice, as compared with WT mice. No differences were noted between the unobstructed kidneys of iNOS -/- mice compared with WT mice in any of the parameters examined. These results demonstrate that targeted deletion of the iNOS results in exacerbation of fibrotic events in the obstructed kidney. These results confirm previous pharmacologic studies, and suggest that NO produced via the inducible NOS normally serves a protective function in UUO.

The expression pattern of Epstein-Barr virus latent genes in vivo is dependent upon the differentiation stage of the infected B cell

Epstein-Barr virus-infected B cells in vivo demonstrate three distinct patterns of latent gene expression, depending on the differentiation stage of the cell. Tonsillar naive B cells express the EBNA2-dependent lymphoblastoid phenotype, characteristic of direct infection. Germinal center centroblasts and centrocytes as well as tonsillar memory B cells express a more restricted pattern of latent genes (EBNA1(Q-K)+, LMP1+, LMP2+, EBNA2-) that has only been seen previously in EBV-positive tumors. Peripheral memory cells express an even more restricted pattern where no latent genes are expressed, with the possible exception of LMP2. These results are consistent with a model where EBV uses the normal biology of B lymphocytes to gain access to and persist within the long-lived memory B cell compartment.

Effective action for stochastic partial differential equations

Stochastic partial differential equations (SPDEs) are the basic tool for modeling systems where noise is important. SPDEs are used for models of turbulence, pattern formation, and the structural development of the universe itself. It is reasonably well known that certain SPDEs can be manipulated to be equivalent to (nonquantum) field theories that nevertheless exhibit deep and important relationships with quantum field theory. In this paper we systematically extend these ideas: We set up a functional integral formalism and demonstrate how to extract all the one-loop physics for an arbitrary SPDE subject to arbitrary Gaussian noise. It is extremely important to realize that Gaussian noise does not imply that the field variables undergo Gaussian fluctuations, and that these nonquantum field theories are fully interacting. The limitation to one loop is not as serious as might be supposed: Experience with quantum field theories (QFTs) has taught us that one-loop physics is often quite adequate to give a good description of the salient issues. The limitation to one loop does, however, offer marked technical advantages: Because at one loop almost any field theory can be rendered finite using zeta function technology, we can sidestep the complications inherent in the Martin-Siggia-Rose formalism (the SPDE analog of the Becchi-Rouet-Stora-Tyutin formalism used in QFT) and instead focus attention on a minimalist approach that uses only the physical fields (this "direct approach" is the SPDE analog of canonical quantization using physical fields). After setting up the general formalism for the characteristic functional (partition function), we show how to define the effective action to all loops, and then focus on the one-loop effective action and its specialization to constant fields: the effective potential. The physical interpretation of the effective action and effective potential for SPDEs is addressed and we show that key features carry over from QFT to the case of SPDEs. An important result is that the amplitude of the two-point function governing the noise acts as the loop-counting parameter and is the analog of Planck's constant in this SPDE context. We derive a general expression for the one-loop effective potential of an arbitrary SPDE subject to translation-invariant Gaussian noise, and compare this with the one-loop potential for QFT.

Incidental prostatic adenocarcinoma in patients undergoing radical cystoprostatectomy for bladder cancer

To determine if patients with bladder cancer have a higher incidence of unsuspected prostate cancer, 40 cases were studied. All except one case had no evidence of prostate cancer on preoperative clinical assessment. Detailed pathological evaluation of cystoprostatectomy specimens with sections at 2- to 3-mm intervals was done. Adenocarcinoma of the prostate was identified in 18 of 40 patients (45%). Multifocal prostatic intraepithelial neoplasia (PIN) was present in 19 cases (47.5%); 4 (10%) without an associated prostate cancer and 15 (37.5%) in conjunction with adenocarcinoma of the prostate. Twelve cases of unsuspected prostate cancer were stage pT1a, 4 were pT1b, and 2 were pT3. No patients exhibited nodal or distance metastases by the prostate cancer. At a mean follow-up of 15.2 months (range 3-34 months), 37 of the 40 patients are alive. Among prostate cancer patients, no clinical or biochemical evidence of disease recurrence or prostate cancer related mortality has been observed. Our findings support the previously reported high incidence rate of prostate cancer in patients undergoing cystoprostatectomy for bladder cancer. This, though, may not be higher than the observed incidence in an age-matched general population. We recommend DRE and PSA as part of the bladder cancer workup in males, and complete removal of the prostate at cystoprostatectomy to prevent the dilemma of residual prostate cancer.