Semantic dementia: clinical, radiological and pathological perspectives

Socioemotional Dysfunction From Temporal Lobe Involvement in Frontotemporal Dementia: A Preliminary Report

OBJECTIVE

Socioemotional changes, rather than cognitive impairments, are the feature that defines behavioral variant frontotemporal dementia (bvFTD). Investigators have attributed the socioemotional changes in bvFTD and other dementias to frontal lobe dysfunction; however, recent work implies a further contribution from right anterior temporal disease. The authors evaluated relationships between regional brain atrophy and socioemotional changes in both bvFTD and early-onset Alzheimer's disease (EOAD).

METHODS

This study explored the neuroanatomical correlations of performance on the Socioemotional Dysfunction Scale (SDS), an instrument previously shown to document socioemotional changes in bvFTD, among 13 patients with bvFTD not preselected for anterior temporal involvement and 16 age-matched patients with early-onset Alzheimer's disease (EOAD). SDS scores were correlated with volumes of regions of interest assessed with tensor-based morphometric analysis of MRI images.

RESULTS

As expected, the bvFTD group had significantly higher SDS scores overall and smaller frontal regions compared with the EOAD group, which in turn had smaller volumes in temporoparietal regions. SDS scores significantly correlated with lateral anterior temporal lobe (ATL) atrophy, and a regression analysis that controlled for diagnosis indicated that SDS scores predicted lateral ATL volume. Within the bvFTD group, higher SDS scores were associated with smaller lateral and right ATL regions, as well as a smaller orbitofrontal cortex. Within the EOAD group, higher SDS scores were associated with a smaller right parietal cortex.

CONCLUSIONS

This study confirms that, in addition to orbitofrontal disease, there is a prominent right and lateral ATL origin of socioemotional changes in bvFTD and further suggests that right parietal involvement contributes to socioemotional changes in EOAD.

Breakdown of category-specific word representations in a brain-constrained neurocomputational model of semantic dementia

The neurobiological nature of semantic knowledge, i.e., the encoding and storage of conceptual information in the human brain, remains a poorly understood and hotly debated subject. Clinical data on semantic deficits and neuroimaging evidence from healthy individuals have suggested multiple cortical regions to be involved in the processing of meaning. These include semantic hubs (most notably, anterior temporal lobe, ATL) that take part in semantic processing in general as well as sensorimotor areas that process specific aspects/categories according to their modality. Biologically inspired neurocomputational models can help elucidate the exact roles of these regions in the functioning of the semantic system and, importantly, in its breakdown in neurological deficits. We used a neuroanatomically constrained computational model of frontotemporal cortices implicated in word acquisition and processing, and adapted it to simulate and explain the effects of semantic dementia (SD) on word processing abilities. SD is a devastating, yet insufficiently understood progressive neurodegenerative disease, characterised by semantic knowledge deterioration that is hypothesised to be specifically related to neural damage in the ATL. The behaviour of our brain-based model is in full accordance with clinical data-namely, word comprehension performance decreases as SD lesions in ATL progress, whereas word repetition abilities remain less affected. Furthermore, our model makes predictions about lesion- and category-specific effects of SD: our simulation results indicate that word processing should be more impaired for object- than for action-related words, and that degradation of white matter should produce more severe consequences than the same proportion of grey matter decay. In sum, the present results provide a neuromechanistic explanatory account of cortical-level language impairments observed during the onset and progress of semantic dementia.

Primary Progressive Aphasia: Use of Graphical Markers for an Early and Differential Diagnosis

Primary progressive aphasia (PPA) brings together neurodegenerative pathologies whose main characteristic is to start with a progressive language disorder. PPA diagnosis is often delayed in non-specialised clinical settings. With the technologies' development, new writing parameters can be extracted, such as the writing pressure on a touch pad. Despite some studies having highlighted differences between patients with typical Alzheimer's disease (AD) and healthy controls, writing parameters in PPAs are understudied. The objective was to verify if the writing pressure in different linguistic and non-linguistic tasks can differentiate patients with PPA from patients with AD and healthy subjects. Patients with PPA (n = 32), patients with AD (n = 22) and healthy controls (n = 26) were included in this study. They performed a set of handwriting tasks on an iPad® digital tablet, including linguistic, cognitive non-linguistic, and non-cognitive non-linguistic tasks. Average and maximum writing pressures were extracted for each task. We found significant differences in writing pressure, between healthy controls and patients with PPA, and between patients with PPA and AD. However, the classification of performances was dependent on the nature of the tasks. These results suggest that measuring writing pressure in graphical tasks may improve the early diagnosis of PPA, and the differential diagnosis between PPA and AD.

Patient-Tailored, Connectivity-Based Forecasts of Spreading Brain Atrophy

Neurodegenerative diseases appear to progress by spreading via brain connections. Here we evaluated this transneuronal degeneration hypothesis by attempting to predict future atrophy in a longitudinal cohort of patients with behavioral variant frontotemporal dementia (bvFTD) and semantic variant primary progressive aphasia (svPPA). We determined patient-specific "epicenters" at baseline, located each patient's epicenters in the healthy functional connectome, and derived two region-wise graph theoretical metrics to predict future atrophy: (1) shortest path length to the epicenter and (2) nodal hazard, the cumulative atrophy of a region's first-degree neighbors. Using these predictors and baseline atrophy, we could accurately predict longitudinal atrophy in most patients. The regions most vulnerable to subsequent atrophy were functionally connected to the epicenter and had intermediate levels of baseline atrophy. These findings provide novel, longitudinal evidence that neurodegeneration progresses along connectional pathways and, further developed, could lead to network-based clinical tools for prognostication and disease monitoring.

Phenotypic variability and neuropsychological findings associated with C9orf72 repeat expansions in a Bulgarian dementia cohort

BACKGROUND

The GGGGCC repeat expansion in the C9orf72 gene was recently identified as a major cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) in several European populations. The objective of this study was to determine the frequency of C9orf72 repeat expansions in a Bulgarian dementia cohort and to delineate the associated clinical features.

METHODS AND FINDINGS

PCR-based assessments of the C9orf72 hexanucleotide repeat expansion in all study samples (including 82 FTD, 37 Alzheimer's disease (AD), and 16 other neurodegenerative/dementia disorder cases) were performed. We report the clinical, neuropsychological, and neuroimaging findings obtained for the C9orf72 repeat expansion carriers. Of the 135 cases screened, 3/82 (3.7%) of all FTD cases and 1/37 (2.7%) of all clinical AD cases had a C9orf72 repeat expansion. In this cohort, the C9orf72 pathological expansion was found in clinical diagnoses bridging the FTD, parkinsonism, ALS and AD spectrum. Interestingly, we showed early writing errors without aphasia in two subjects with C9orf72 expansions.

CONCLUSIONS

This study represents the first genetic screening for C9orf72 repeat expansions in a Bulgarian dementia cohort. The C9orf72 repeat expansion does not appear to be a common cause of FTD and related disorders. This report confirms the notion that C9orf72 repeat expansions underlie a broad spectrum of neurodegenerative phenotypes. Relatively isolated agraphia in two cases with C9orf72 repeat expansions is a strong motivation to provide detailed and sophisticated oral and written language assessments that can be used to more precisely characterize early cognitive deficits in these heterogeneous conditions.

Individual differences in white matter microstructure predict semantic control

In everyday conversation, we make many rapid choices between competing concepts and words in order to convey our intent. This process is termed semantic control, and it is thought to rely on information transmission between a distributed semantic store in the temporal lobes and a more discrete region, optimized for retrieval and selection, in the left inferior frontal gyrus. Here, we used diffusion tensor imaging in a group of neurologically normal young adults to investigate the relationship between semantic control and white matter tracts that have been implicated in semantic memory retrieval. Participants completed a verb generation task that taps semantic control (Snyder & Munakata, 2008; Snyder et al., 2010) and underwent a diffusion imaging scan. Deterministic tractography was performed to compute indices representing the microstructural properties of the inferior fronto-occipital fasciculus (IFOF), the uncinate fasciculus (UF), and the inferior longitudinal fasciculus (ILF). Microstructural measures of the UF failed to predict semantic control performance. However, there was a significant relationship between microstructure of the left IFOF and ILF and individual differences in semantic control. Our findings support the view put forth by Duffau (2013) that the IFOF is a key structural pathway in semantic retrieval.

Gustatory Dysfunction as an Early Symptom of Semantic Dementia

OBJECTIVE

To investigate the gustatory function in patients with semantic dementia (SD).

METHODS

Detection and recognition thresholds of the 4 basic tastes (sweet, salty, sour, and bitter), taste discrimination, and taste identification were evaluated in 18 patients with SD, 18 patients with Alzheimer disease (AD), and 22 healthy controls.

RESULTS

Total detection and recognition threshold values were significantly higher in the SD and AD groups than in the control group. Patients with early-stage SD (Clinical Dementia Rating Scale score 0.5) exhibited significantly higher detection and recognition thresholds relative to controls, while increases in recognition threshold were only noted in patients with AD. Patients with SD exhibited significantly higher thresholds for the detection of sweet and salty tastes and the recognition of salty, sour, and bitter tastes, while patients with AD exhibited significantly higher thresholds only for the recognition of salty and sour tastes. Taste discrimination was preserved, whereas taste identification was disturbed, in both the SD and AD groups.

CONCLUSIONS

Gustatory dysfunction at both the sensory and semantic levels may be among the early symptoms of SD. Although patients with SD had difficulty detecting sweet tastes, they more easily recognized these tastes than others, which may explain their strong preference for sweets.

Left Anterior Temporal Lobe and Bilateral Anterior Cingulate Cortex Are Semantic Hub Regions: Evidence from Behavior-Nodal Degree Mapping in Brain-Damaged Patients

The organizational principles of semantic memory in the human brain are still controversial. Although studies have shown that the semantic system contains hub regions that bind information from different sensorimotoric modalities to form concepts, it is unknown whether there are hub regions other than the anterior temporal lobe (ATL). Meanwhile, previous studies have rarely used network measurements to explore the hubs or correlated network indexes with semantic performance, although the most direct supportive evidence of hubs should come from the network perspective. To fill this gap, we correlated the brain-network index with semantic performance in 86 brain-damaged patients. We especially selected the nodal degree measure that reflects how well a node is connected in the network. The measure was calculated as the total number of connections of a given node with other nodes in the resting-state functional MRI network. Semantic ability was measured using the performance of both general and modality-specific (object form, color, motion, sound, manipulation, and function) semantic tasks. We found that the left ATL and the bilateral anterior cingulate cortex could be semantic hubs because the reduced nodal degree values of these regions could effectively predict the deficits in both general and modality-specific semantic performance. Moreover, the effects remained when the analyses were performed only in the patients who did not have lesions in these regions. The two hub regions might support semantic representations and executive control processes, respectively. These data provide empirical evidence for the distributed-plus-hub theory of semantic memory from the network perspective.

SIGNIFICANCE STATEMENT

Although the distributed-plus-hub organization of semantic memory has been proposed for several years, it remains unclear which hubs other than the anterior temporal lobe are included in the semantic system. Here, we identified such hubs from an innovative network perspective. The voxelwise nodal degree values were correlated with the performance of general and modality-specific semantic tasks in 86 patients with brain damage. We observed that the left anterior temporal lobe and bilateral anterior cingulate cortex could be semantic hubs because their decreased nodal degree values were significantly correlated with the severity of the deficit in semantic performance. The two hub regions might contribute to semantic representational and control processes, respectively. These findings offer new evidence for the distributed-plus-hub theory.

Amyloid deposition in semantic dementia: a positron emission tomography study

BACKGROUND

Pittsburgh compound B ([11C]-PIB) identifies amyloid-β (Aβ) deposition in vivo. Asymptomatic Aβ deposition has been reported consistently in some healthy older subjects. Of patients with frontotemporal dementia, those who have later onset have a higher potential for Aβ deposition.

OBJECTIVE

Comparison of Aβ deposition in Alzheimer's disease (AD), healthy older controls, and patients with early- and late-onset semantic dementia (SD), a subtype of frontotemporal dementia.

METHODS

Subjects were recruited from tertiary academic care centers specializing in assessment and management of patients with neurodegenerative disease. We used the radiotracer [11C]-PIB in a high-resolution positron emission tomography scanner to evaluate 11 participants with SD (six with onset before age 65 and five with later onset), 9 with probable AD, and 10 controls over age 60. The main outcome measures were frontal, temporal, parietal, and total [11C]-PIB standardized uptake value ratios to establish PIB-positive (PIB+) cutoff.

RESULTS

The five patients with late-onset SD were PIB-negative. Two of six with early-onset SD, seven of nine with AD, and 1 of 10 controls were PIB+. The SD participants who were PIB+ did not have memory or visuospatial deficits that are typical in AD.

CONCLUSIONS

Aβ deposition does not seem to be associated with late-onset SD. Future larger studies might confirm whether a significant minority of early-onset SD patients exhibit Aβ deposition. Copyright © 2016 John Wiley & Sons, Ltd.

Different effects of anterior temporal lobectomy and selective amygdalohippocampectomy on verbal memory performance of patients with epilepsy

The advantage of selective amygdalohippocampectomy (SAH) over anterior temporal lobectomy (ATL) for the treatment of temporal lobe epilepsy (TLE) remains controversial. Because ATL is more extensive and involves the lateral and medial parts of the temporal lobe, it may be predicted that its impact on memory is more important than SAH, which involves resection of medial temporal structures only. However, several studies do not support this assumption. Possible explanations include task-specific factors such as the extent of semantic and syntactic information to be memorized and failure to control for main confounders. We compared preoperative vs. postoperative memory performance in 13 patients with SAH with 26 patients who underwent ATL matched on side of surgery, IQ, age at seizure onset, and age at surgery. Memory function was assessed using the Logical Memory subtest from the Wechsler Memory Scales - 3rd edition (LM-WMS), the Rey Auditory Verbal Learning Test (RAVLT), the Digit Span subtest from the Wechsler Adult Intelligence Scale, and the Rey-Osterrieth Complex Figure Test. Repeated measures analyses of variance revealed opposite effects of SAH and ATL on the two verbal learning memory tests. On the immediate recall trial of the LM-WMS, performance deteriorated after ATL in comparison with that after SAH. By contrast, on the delayed recognition trial of the RAVLT, performance deteriorated after SAH compared with that after ATL. However, additional analyses revealed that the latter finding was only observed when surgery was conducted in the right hemisphere. No interaction effects were found on other memory outcomes. The results are congruent with the view that tasks involving rich semantic content and syntactical structure are more sensitive to the effects of lateral temporal cortex resection as compared with mesiotemporal resection. The findings highlight the importance of task selection in the assessment of memory in patients undergoing TLE surgery.

The interplay of composition and concept specificity in the left anterior temporal lobe: an MEG study

A fundamental function of natural language is to focus the interlocutor's attention to specific entities and circumstances from the vast set of possibilities in the environment. In other words, as an utterance progresses, the narrower its reference typically becomes. Intriguingly, there is substantial convergence in the neural localization of conceptual specificity effects at the single word level and combinatory effects at the phrasal level, both systematically affecting the left anterior temporal lobe (LATL). However, the relationship between these two types of effects is not well understood. The current study used MEG to characterize the temporal progression of both types of effects in minimal two-word phrases (e.g., tomato soup), where single word specificity was varied in both first and second position (e.g., tomato vs. vegetable; soup vs. dish). These combinatory phrases were further compared to non-combinatory single nouns of high and low specificity. Our most robust result was an effect of the specificity of the first word while processing the second word: responses to the second word were the largest when it was being composed with a more specific as opposed to a more general modifier. In the modifier position, specificity had no reliable effects, while non-combinatory single nouns did show a subtle LATL increase when specific. In all, our findings show that when non-semantic factors such as frequency are controlled for, conceptual specificity weakly modulates LATL activity in non-combinatory situations (i.e., at a single noun), but robustly affects the size of the LATL composition effect. Thus LATL activity appears to be most strongly driven by the composition of concepts as opposed to access to single concepts.

Functional connectivity mapping of regions associated with self- and other-processing

Neuroscience literature increasingly suggests a conceptual self composed of interacting neural regions, rather than independent local activations, yet such claims have yet to be investigated. We, thus, combined task-dependent meta-analytic connectivity modeling (MACM) with task-independent resting-state (RS) connectivity analysis to delineate the neural network of the self, across both states. Given psychological evidence implicating the self's interdependence on social information, we also delineated the neural network underlying conceptual other-processing. To elucidate the relation between the self-/other-networks and their function, we mined the MACM metadata to generate a cognitive-behavioral profile for an empirically identified region specific to conceptual self, the pregenual anterior cingulate (pACC), and conceptual other, posterior cingulate/precuneus (PCC/PC). Mining of 7,200 published, task-dependent, neuroimaging studies, using healthy human subjects, yielded 193 studies activating the self-related seed and were conjoined with RS connectivity analysis to delineate a differentiated self-network composed of the pACC (seed) and anterior insula, relative to other functional connectivity. Additionally, 106 studies activating the other-related seed were conjoined with RS connectivity analysis to delineate a differentiated other-network of PCC/PC (seed) and angular gyrus/temporoparietal junction, relative to self-functional connectivity. The self-network seed related to emotional conflict resolution and motivational processing, whereas the other-network seed related to socially oriented processing and contextual information integration. Notably, our findings revealed shared RS connectivity between ensuing self-/other-networks within the ventromedial prefrontal cortex and medial orbitofrontal cortex, suggesting self-updating via integration of self-relevant social information. We, therefore, present initial neurobiological evidence corroborating the increasing claims of an intricate self-network, the architecture of which may promote social value processing.

Restrictive vs. non-restrictive composition: a magnetoencephalography study

Recent research on the brain mechanisms underlying language processing has implicated the left anterior temporal lobe (LATL) as a central region for the composition of simple phrases. Because these studies typically present their critical stimuli without contextual information, the sensitivity of LATL responses to contextual factors is unknown. In this magnetoencephalography (MEG) study, we employed a simple question-answer paradigm to manipulate whether a prenominal adjective or determiner is interpreted restrictively, i.e., as limiting the set of entities under discussion. Our results show that the LATL is sensitive to restriction, with restrictive composition eliciting higher responses than non-restrictive composition. However, this effect was only observed when the restricting element was a determiner, adjectival stimuli showing the opposite pattern, which we hypothesise to be driven by the special pragmatic properties of non-restrictive adjectives. Overall, our results demonstrate a robust sensitivity of the LATL to high level contextual and potentially also pragmatic factors.

The role of the left anterior temporal lobe in semantic composition vs. semantic memory

The left anterior temporal lobe (LATL) is robustly implicated in semantic processing by a growing body of literature. However, these results have emerged from two distinct bodies of work, addressing two different processing levels. On the one hand, the LATL has been characterized as a 'semantic hub׳ that binds features of concepts across a distributed network, based on results from semantic dementia and hemodynamic findings on the categorization of specific compared to basic exemplars. On the other, the LATL has been implicated in combinatorial operations in language, as shown by increased activity in this region associated with the processing of sentences and of basic phrases. The present work aimed to reconcile these two literatures by independently manipulating combination and concept specificity within a minimal MEG paradigm. Participants viewed simple nouns that denoted either low specificity (fish) or high specificity categories (trout) presented in either combinatorial (spotted fish/trout) or non-combinatorial contexts (xhsl fish/trout). By combining these paradigms from the two literatures, we directly compared the engagement of the LATL in semantic memory vs. semantic composition. Our results indicate that although noun specificity subtly modulates the LATL activity elicited by single nouns, it most robustly affects the size of the composition effect when these nouns are adjectivally modified, with low specificity nouns eliciting a much larger effect. We conclude that these findings are compatible with an account in which the specificity and composition effects arise from a shared mechanism of meaning specification.

Parallel deterioration to language processing in a bilingual speaker

The convergence hypothesis [Green, D. W. (2003). The neural basis of the lexicon and the grammar in L2 acquisition: The convergence hypothesis. In R. van Hout, A. Hulk, F. Kuiken, & R. Towell (Eds.), The interface between syntax and the lexicon in second language acquisition (pp. 197-218). Amsterdam: John Benjamins] assumes that the neural substrates of language representations are shared between the languages of a bilingual speaker. One prediction of this hypothesis is that neurodegenerative disease should produce parallel deterioration to lexical and grammatical processing in bilingual aphasia. We tested this prediction with a late bilingual Hungarian (first language, L1)-English (second language, L2) speaker J.B. who had nonfluent progressive aphasia (NFPA). J.B. had acquired L2 in adolescence but was premorbidly proficient and used English as his dominant language throughout adult life. Our investigations showed comparable deterioration to lexical and grammatical knowledge in both languages during a one-year period. Parallel deterioration to language processing in a bilingual speaker with NFPA challenges the assumption that L1 and L2 rely on different brain mechanisms as assumed in some theories of bilingual language processing [Ullman, M. T. (2001). The neural basis of lexicon and grammar in first and second language: The declarative/procedural model. Bilingualism: Language and Cognition, 4(1), 105-122].

Agraphia in patients with frontotemporal dementia and parkinsonism linked to chromosome 17 with P301L MAPT mutation: dysexecutive, aphasic, apraxic or spatial phenomenon?

OBJECTIVES

Patients with frontotemporal dementia and parkinsonism linked to chromosome 17 (FTDP-17) may be agraphic. The study aimed at characterizing agraphia in individuals with a P301L MAPT mutation.

METHODS

Two pairs of siblings with FTDP-17 were longitudinally examined for agraphia in relation to language and cognitive deficits.

RESULTS

All patients presented with dysexecutive agraphia. In addition, in the first pair of siblings one sibling demonstrated spatial agraphia with less pronounced allographic agraphia and the other sibling had aphasic agraphia. Aphasic agraphia was also present in one sibling from the second pair.

CONCLUSION

Agraphia associated with FTDP-17 is very heterogeneous.

Anterior temporal lobe degeneration produces widespread network-driven dysfunction

The neural organization of semantic memory remains much debated. A 'distributed-only' view contends that semantic knowledge is represented within spatially distant, modality-selective primary and association cortices. Observations in semantic variant primary progressive aphasia have inspired an alternative model featuring the anterior temporal lobe as an amodal hub that supports semantic knowledge by linking distributed modality-selective regions. Direct evidence has been lacking, however, to support intrinsic functional interactions between an anterior temporal lobe hub and upstream sensory regions in humans. Here, we examined the neural networks supporting semantic knowledge by performing a multimodal brain imaging study in healthy subjects and patients with semantic variant primary progressive aphasia. In healthy subjects, the anterior temporal lobe showed intrinsic connectivity to an array of modality-selective primary and association cortices. Patients showed focal anterior temporal lobe degeneration but also reduced physiological integrity throughout distributed modality-selective regions connected with the anterior temporal lobe in healthy controls. Physiological deficits outside the anterior temporal lobe correlated with scores on semantic tasks and with anterior temporal subregion atrophy, following domain-specific and connectivity-based predictions. The findings provide a neurophysiological basis for the theory that semantic processing is orchestrated through interactions between a critical anterior temporal lobe hub and modality-selective processing nodes.

Extensive left temporal pole damage does not impact on theory of mind abilities

The temporal poles (TPs) are among the brain regions that are often considered as the brain network sustaining our ability to understand other people's mental states or "Theory of Mind" (ToM). However, so far the functional role of the left and right TPs in ToM is still debated, and it is even not clear yet whether these regions are necessary for ToM. In this study, we tested whether the left TP is necessary for ToM by assessing the mentalizing abilities of a patient (C.M.) diagnosed with semantic dementia. Converging evidence from detailed MRI and (18)F-fluoro-2-deoxy-d-glucose PET examinations showed a massive atrophy of the left TP with the right TP being relatively unaffected. Furthermore, C.M.'s atrophy encompassed most regions of the left TP usually activated in neuroimaging studies investigating ToM. Given C.M.'s language impairments, we used a battery of entirely nonverbal ToM tasks. Across five tasks encompassing 100 trials, which probed the patient's ability to attribute various mental states (intentions, knowledge, and beliefs), C.M. showed a totally spared performance. This finding suggests that, despite its consistently observed activation in neuroimaging studies involving ToM tasks, the left TP is not necessary for ToM reasoning, at least in nonverbal conditions and as long as its right counterpart is preserved. Implications for understanding the social abilities of patients with semantic dementia are discussed.

Machine learning approaches to diagnosis and laterality effects in semantic dementia discourse

Advances in automatic text classification have been necessitated by the rapid increase in the availability of digital documents. Machine learning (ML) algorithms can 'learn' from data: for instance a ML system can be trained on a set of features derived from written texts belonging to known categories, and learn to distinguish between them. Such a trained system can then be used to classify unseen texts. In this paper, we explore the potential of the technique to classify transcribed speech samples along clinical dimensions, using vocabulary data alone. We report the accuracy with which two related ML algorithms [naive Bayes Gaussian (NBG) and naive Bayes multinomial (NBM)] categorized picture descriptions produced by: 32 semantic dementia (SD) patients versus 10 healthy, age-matched controls; and SD patients with left- (n = 21) versus right-predominant (n = 11) patterns of temporal lobe atrophy. We used information gain (IG) to identify the vocabulary features that were most informative to each of these two distinctions. In the SD versus control classification task, both algorithms achieved accuracies of greater than 90%. In the right- versus left-temporal lobe predominant classification, NBM achieved a high level of accuracy (88%), but this was achieved by both NBM and NBG when the features used in the training set were restricted to those with high values of IG. The most informative features for the patient versus control task were low frequency content words, generic terms and components of metanarrative statements. For the right versus left task the number of informative lexical features was too small to support any specific inferences. An enriched feature set, including values derived from Quantitative Production Analysis (QPA) may shed further light on this little understood distinction.

“Object Categorization: Reversals and Explanations of the Basic-Level Advantage” (Rogers & Patterson, 2007): A simplicity account

T. T. Rogers and K. Patterson (2007), in their article “Object Categorization: Reversals and Explanations of the Basic-Level Advantage” ( Journal of Experimental Psychology: General, 136, 451–469), reported an impressive set of results demonstrating a reversal of the highly robust basic-level advantage both in patients with semantic dementia and in healthy individuals engaged in a speeded categorization task. To explain their results, as well as the usual basic-level advantage seen in healthy individuals, the authors employed a parallel distributed processing theory of conceptual knowledge. In this paper, we introduce an alternative way of explaining the results of Rogers and Patterson, which is premised on a more restricted set of assumptions born from standard categorization theory. Specifically, we provide evidence that their results can be accounted for based on the predictions of the simplicity model of unsupervised categorization.

The time course of neurolinguistic and neuropsychological symptoms in three cases of logopenic primary progressive aphasia

Primary progressive aphasia (PPA) is a rare clinical dementia syndrome affecting predominantly language abilities. Word-finding difficulties and comprehension deficits despite relatively preserved cognitive functions are characteristic symptoms during the first two years, and distinguish PPA from other dementia types like Alzheimer's disease. However, the dynamics of changes in language and non-linguistic abilities are not well understood. Most studies on progression used cross-sectional designs, which provide only limited insight into the course of the disease. Here we report the results of a longitudinal study in three cases of logopenic PPA over a period of 18 months, with exemplary longitudinal data from one patient even over 46 months. A comprehensive battery of neurolinguistic and neuropsychological tests was applied four times at intervals of six months. Over this period, deterioration of verbal abilities such as picture naming, story retelling, and semantic word recall was found, and the individual decline was quantified and compared between the three patients. Furthermore, decrease in non-verbal skills such as divided attention and increasing apraxia was observed in all three patients. In addition, inter-subject variability in the progression with different focuses was observed, with one patient developing a non-fluent PPA variant. The longitudinal, multivariate investigation of logopenic PPA thus provides novel insights into the progressive deterioration of verbal as well as non-verbal abilities. These deficits may further interact and thus form a multi-causal basis for the patients' problems in every-day life which need to be considered when planning individually targeted intervention in PPA.

Visual rating versus volumetry to detect frontotemporal dementia

BACKGROUND/AIMS

Automated, volumetrically defined atrophy in the left anterior cingulate (LAC) and anterior temporal regions (LAT) on MRI can be used to distinguish most patients with frontotemporal dementia (FTD) from controls. FTD and Alzheimer's disease (AD) can differ in the degree of anterior temporal atrophy. We explored whether clinicians can visually detect this atrophy pattern and whether they can use it to classify the 2 groups of dementia patients with the same accuracy.

METHODS

Four neurologists rated atrophy in the LAC and LAT regions on MRI slices from 21 FTD, 21 controls, and 14 AD participants. Inter-rater reliability and diagnostic accuracy were assessed.

RESULTS

All 4 raters agreed on the presence of clinically significant atrophy, and their atrophy scoring correlated with the volumes, but without translation into high inter-rater diagnostic agreement.

CONCLUSIONS

Volumetric analyses are difficult to translate into routine clinical practice.

Increased resting-state perfusion after repeated encoding is related to later retrieval of declarative associative memories

Electrophysiological studies in animals have shown coordinated reactivation of neuronal ensembles during a restricted time period of behavioral inactivity that immediately followed active encoding. In the present study we directly investigated off-line processing of associative memory formation in the human brain. Subjects' regional cerebral blood flow (rCBF) as a surrogate marker of neural activity during rest was measured by MR-based perfusion imaging in a sample of 14 healthy male subjects prior to (Pre2) and after (Post) extensive learning of 24 face-name associations within a selective reminding task (SR). Results demonstrated significant Post-Pre2 rCBF increases in hippocampal and temporal lobe regions, while in a control comparison of two perfusion scans with no learning task in-between (Pre2-Pre1) no differences in rCBF emerged. Post perfusion scanning was followed by a surprise cued associative recall task from which two types of correctly retrieved names were obtained: older names already correctly retrieved at least once during one of the SR blocks, and recent names acquired during the last SR block immediately prior to the Post scan. In the anterior hippocampus individual perfusion increases were correlated with both correct retrievals of older and recent names. By contrast, older but not recently learned names showed a significant correlation with perfusion increases in the left lateral temporal cortex known to be associated with long-term memory. Recent, but not older names were correlated with dopaminergic midbrain structures reported to contribute to the persistence of memory traces for novel information. Although the direct investigation of off-line memory processing did not permit concomitant experimental control, neither intentional rehearsal, nor substantial variations in subjects' states of alertness appear to contribute to present results. We suggest that the observed rCBF increases might reflect processes that possibly contribute to the long-term persistence of memory traces.

Heterogeneity of the left temporal lobe in semantic representation and control: priming multiple versus single meanings of ambiguous words

Semantic judgments involve both representations of meaning plus executive mechanisms that guide knowledge retrieval in a task-appropriate way. These 2 components of semantic cognition—representation and control—are commonly linked to left temporal and prefrontal cortex, respectively. This simple proposal, however, remains contentious because in most functional neuroimaging studies to date, the number of concepts being activated and the involvement of executive processes during retrieval are confounded. Using functional magnetic resonance imaging, we examined a task in which semantic representation and control demands were dissociable. Words with multiple meanings like “bank” served as targets in a double-prime paradigm, in which multiple meaning activation and maximal executive demands loaded onto different priming conditions. Anterior inferior temporal gyrus (ITG) was sensitive to the number of meanings that were retrieved, suggesting a role for this region in semantic representation, while posterior middle temporal gyrus (pMTG) and inferior frontal cortex showed greater activation in conditions that maximized executive demands. These results support a functional dissociation between left ITG and pMTG, consistent with a revised neural organization in which left prefrontal and posterior temporal areas work together to underpin aspects of semantic control.

Visual and semantic processing of living things and artifacts: an FMRI study

We carried out an fMRI study with a twofold purpose: to investigate the relationship between networks dedicated to semantic and visual processing and to address the issue of whether semantic memory is subserved by a unique network or by different subsystems, according to semantic category or feature type. To achieve our goals, we administered a word-picture matching task, with within-category foils, to 15 healthy subjects during scanning. Semantic distance between the target and the foil and semantic domain of the target-foil pairs were varied orthogonally. Our results suggest that an amodal, undifferentiated network for the semantic processing of living things and artifacts is located in the anterolateral aspects of the temporal lobes; in fact, activity in this substrate was driven by semantic distance, not by semantic category. By contrast, activity in ventral occipito-temporal cortex was driven by category, not by semantic distance. We interpret the latter finding as the effect exerted by systematic differences between living things and artifacts at the level of their structural representations and possibly of their lower-level visual features. Finally, we attempt to reconcile contrasting data in the neuropsychological and functional imaging literature on semantic substrate and category specificity.

Intuition, insight, and the right hemisphere: Emergence of higher sociocognitive functions

Intuition is the ability to understand immediately without conscious reasoning and is sometimes explained as a 'gut feeling' about the rightness or wrongness of a person, place, situation, temporal episode or object. In contrast, insight is the capacity to gain accurate and a deep understanding of a problem and it is often associated with movement beyond existing paradigms. Examples include Darwin, Einstein and Freud's theories of natural selection, relativity, or the unconscious; respectively. Many cultures name these concepts and acknowledge their value, and insight is recognized as particularly characteristic of eminent achievements in the arts, sciences and politics. Considerable data suggests that these two concepts are more related than distinct, and that a more distributed intuitive network may feed into a predominately right hemispheric insight-based functional neuronal architecture. The preparation and incubation stages of insight may rely on the incorporation of domain-specific automatized expertise schema associated with intuition. In this manuscript the neural networks associated with intuition and insight are reviewed. Case studies of anomalous subjects with ability-achievement discrepancies are summarized. This theoretical review proposes the prospect that atypical localization of cognitive modules may enhance intuitive and insightful functions and thereby explain individual achievement beyond that expected by conventionally measured intelligence tests. A model and theory of intuition and insight's neuroanatomical basis is proposed which could be used as a starting point for future research and better understanding of the nature of these two distinctly human and highly complex poorly understood abilities.

Theory of mind ability in the behavioural variant of frontotemporal dementia: an analysis of the neural, cognitive, and social levels

The paper reviews convergent evidence on the ability to attribute mental states to one's self and to others (i.e., theory of mind, ToM) in patients affected by the behavioural variant of frontotemporal dementia (bv-FTD). This disease represents a particular challenge for researchers and clinicians, due to its insidious onset and ambiguous clinical features, which frequently render difficult a precise and timely diagnosis. The paper proposes a way to shed new light on the hypothesis that the neuropsychiatric profile of individuals with bv-FTD can be at least partially explained by a deficit in ToM ability. We examined both neuroimaging data on the neural correlates of ToM ability in healthy participants and studies investigating the progressive cerebral atrophy in patients with bv-FTD. Our findings suggest a link between the progressive degeneration of the anterior regions of medial frontal structures characterising the early stages of the bv-FTD and the ToM deficit these patients show. They also suggest the importance of using ToM tests during the diagnostic process of bv-FTD.

Selective attention to semantic and syntactic features modulates sentence processing networks in anterior temporal cortex

Numerous studies have identified an anterior temporal lobe (ATL) region that responds preferentially to sentence-level stimuli. It is unclear, however, whether this activity reflects a response to syntactic computations or some form of semantic integration. This distinction is difficult to investigate with the stimulus manipulations and anomaly detection paradigms traditionally implemented. The present functional magnetic resonance imaging study addresses this question via a selective attention paradigm. Subjects monitored for occasional semantic anomalies or occasional syntactic errors, thus directing their attention to semantic integration, or syntactic properties of the sentences. The hemodynamic response in the sentence-selective ATL region (defined with a localizer scan) was examined during anomaly/error-free sentences only, to avoid confounds due to error detection. The majority of the sentence-specific region of interest was equally modulated by attention to syntactic or compositional semantic features, whereas a smaller subregion was only modulated by the semantic task. We suggest that the sentence-specific ATL region is sensitive to both syntactic and integrative semantic functions during sentence processing, with a smaller portion of this area preferentially involved in the later. This study also suggests that selective attention paradigms may be effective tools to investigate the functional diversity of networks involved in sentence processing.

Very early semantic dementia with progressive temporal lobe atrophy: an 8-year longitudinal study

BACKGROUND

Semantic dementia is a syndrome within the spectrum of frontotemporal lobar degenerations characterized by fluent progressive aphasia (particularly anomia) and loss of word meaning.

OBJECTIVE

To report a unique case of very early semantic dementia with a slowly progressive course, allowing insights into the early natural history of this disorder.

DESIGN

Case report.

SETTING

A tertiary care center.

PATIENT

A 62-year-old woman who presented with "memory loss" complaints.

MAIN OUTCOME MEASURES

Clinical course, neuropsychological data, and magnetic resonance imaging results.

RESULTS

The patient was first evaluated when the results of standard neuropsychological measures were normal but subtle left anterior temporal lobe atrophy was present. During the follow-up period of 8 years, she developed profound anomia and loss of word meaning associated with progressive left anterior temporal lobe atrophy, consistent with semantic dementia. In more recent years, anterograde memory impairment and mild prosopagnosia evolved in association with left hippocampal atrophy and subtle atrophy in the homologous gyri of the right anterior temporal lobe. She remains functionally independent despite her current deficits.

CONCLUSIONS

Early identification of patients who will develop semantic dementia is difficult and might be missed with standard clinical, neuropsychological, and structural neuroimaging evaluations. Recognition of this relatively rare syndrome is important for early diagnosis and prognostication and particularly for therapeutic interventions in the future.

Basic pathologies of neurodegenerative dementias and their relevance for state-of-the-art molecular imaging studies

INTRODUCTION

Rising life-expectancy in the modern society has resulted in a rapidly growing prevalence of dementia, particularly of Alzheimer's disease (AD). Dementia turns into one of the most common age-related disorders with deleterious consequences for the concerned patients and their relatives, as well as worrying effects on the socio-economic systems. These facts justify strengthened scientific efforts to identify the pathologic origin of dementing disorders, to improve diagnosis, and to interfere therapeutically with the disease progression.

BASIC PATHOLOGIES

In the recent years, remarkable progress has been made concerning the identification of molecular mechanisms underlying the pathology of neurodegenerative disorders. Growing evidence indicates that a common basis of many neurodegenerative dementias can be found in increased production, misfolding and pathological aggregation of proteins, such as beta-amyloid, tau protein, a-synuclein, or the recently described ubiquitinated TDP-43. This progressive insight in pathological processes is paralleled by the development of new therapeutic approaches. However, the exact contribution or mechanism of different pathologies with regard to the development of disease is not yet sufficiently clear. Considerable overlap of pathologies has been documented in different types of clinically defined dementias post mortem, and it has been difficult to correlate post mortem histopathology data with disease-expression during life. Molecular imaging procedures may play a valuable role to circumvent this limitation.

RELEVANCE FOR IMAGING STUDIES

In general, methods of molecular imaging have recently experienced an impressive advance, with numerous new and improved technologies emerging. These exciting tools may play a key role in the future regarding the evaluation of pathomechanisms, preclinical evaluation of new diagnostic procedures in animal models, selection of patients for clinical trials, and therapy monitoring. In this overview, molecular key pathologies, which are currently regarded to be strongly associated with the development of different dementias, will be shortly summarized; it will also be discussed how state-of-the-art imaging technology can assist to visualize these processes now and in the future.

Atrophy measurement of the anterior commissure and substantia innominata with 3T high-resolution MR imaging: does the measurement differ for patients with frontotemporal lobar degeneration and Alzheimer disease and for healthy subjects?

BACKGROUND AND PURPOSE

The anterior commissure (AC) and substantia innominata (SI) can be clearly demonstrated at 3T high-resolution MR imaging. Our aim was to investigate if atrophy of the AC and SI on 3T MR imaging differs among patients with frontotemporal lobar degeneration (FTLD) and Alzheimer dementia (AD) and healthy subjects.

MATERIALS AND METHODS

Seven consecutive patients with FTLD, 20 patients with AD, and 16 age-matched control subjects were enrolled. MR imaging was performed at 3T. The AC thickness as well as the SI thickness was measured on a thin-section coronal T2-weighted image, and the AC area was measured on a sagittal T1-weighted image. The measurement differences among the participants were analyzed with the Kruskal-Wallis test. A correlation of the measurement with the Mini-Mental State Examination (MMSE) score was obtained with the Spearman rank correlation test.

RESULTS

Thinning of the AC was significantly more prominent in FTLD than in AD (P < .001). Although the right SI thickness was significantly decreased in patients with AD as compared with control subjects (P < .05), there was no significant difference, with a substantial overlap of the average SI thickness among the 3 groups. The thickness and the area of the AC were positively correlated with the MMSE score (rho = 0.612, P < .001, and rho = 0.659, P < .001, respectively). In contrast, the average SI thickness showed a weak positive correlation with the MMSE score (rho = 0.325, P < .05).

CONCLUSION

Measurement of AC atrophy with 3T MR imaging may provide additional diagnostic clues for FTLD and AD. Conversely, SI atrophy measurement does not provide an additional benefit in the evaluation of FTLD and AD, owing to a considerable overlap in the average thickness of bilateral SI.

Differentiation of semantic dementia and Alzheimer's disease using the Addenbrooke's Cognitive Examination (ACE)

BACKGROUND

The Addenbrooke's Cognitive Examination (ACE) is a simple diagnostic tool bridging the gap between the very brief Mini Mental State Exam (MMSE) and much longer test batteries used by neuropsychologists which has proven extremely popular internationally.

OBJECTIVE

We aimed to assess the ability of the ACE to differentiate semantic dementia (SD) from Alzheimer's disease (AD).

METHODS

The ACE was administered to three groups: SD patients (n = 40) and two separate groups of AD patients (n = 40 in each), matched for overall ACE or MMSE score.

RESULTS

Significant differences were found between SD and both AD groups for the ACE sub-scores of naming, reading and orientation in time. Discriminant analysis (SD versus AD) led to the formulation of a 'semantic index' (naming plus reading minus scores for serial-7s, orientation in time and drawing). Application of the semantic index to the patient data found values of less than zero to be predictive of SD rather than AD with 88% sensitivity and 90% specificity. Validation analysis in an independent sample of 24 SD and AD patients proved even more favourable.

CONCLUSIONS

The overall ACE score is known to be a sensitive, and specific, indicator of early neurodegenerative dementia; this study shows that the ACE can also be used to detect SD through application of the semantic index.

DTI tractography of the human brain's language pathways

Diffusion Tensor Imaging (DTI) tractography has been used to detect leftward asymmetries in the arcuate fasciculus, a pathway that links temporal and inferior frontal language cortices. In this study, we more specifically define this asymmetry with respect to both anatomy and function. Twenty right-handed male subjects were scanned with DTI, and the arcuate fasciculus was reconstructed using deterministic tractography. The arcuate was divided into 2 segments with different hypothesized functions, one terminating in the posterior superior temporal gyrus (STG) and another terminating in the middle temporal gyrus (MTG). Tractography results were compared with peak activation coordinates from prior functional neuroimaging studies of phonology, lexical-semantic processing, and prosodic processing to assign putative functions to these pathways. STG terminations were strongly left lateralized and overlapped with phonological activations in the left but not the right hemisphere, suggesting that only the left hemisphere phonological cortex is directly connected with the frontal lobe via the arcuate fasciculus. MTG terminations were also strongly left lateralized, overlapping with left lateralized lexical-semantic activations. Smaller right hemisphere MTG terminations overlapped with right lateralized prosodic activations. We combine our findings with a recent model of brain language processing to explain 6 aphasia syndromes.

The underlying mechanisms of semantic memory loss in Alzheimer's disease and semantic dementia

Patients with Alzheimer's disease (AD) and patients with semantic dementia (SD) both exhibit deficits on explicit tasks of semantic memory such as picture naming and category fluency. These deficits have been attributed to a degradation of the stored semantic network. An alternative explanation attributes the semantic deficit in AD to an impaired ability to consciously retrieve items from the semantic network. The present study used an implicit lexical-decision priming task to examine the integrity of the underlying semantic network in AD and SD patients matched for degree of impairment on explicit semantic memory tasks. The AD (n=11) and SD (n=11) patient groups were matched for age, education, level of dementia and impairment on four explicit semantic memory tasks. Healthy elderly participants (n=22) were matched for age and education. Semantic priming effects were evaluated for three types of semantic relationships (attributes, category coordinates, and category superordinates) and compared to lexical associative priming. Healthy controls showed significant priming across all conditions. In contrast, AD patients showed normal superordinate priming, and significant (although somewhat reduced) coordinate priming, but no attribute priming. SD patients showed no priming effect for any semantic relationship. All groups showed significant associative priming. The results indicate that SD patients do indeed have substantial degradation of semantic memory, while AD patients have a partially intact network, accounting for priming in superordinate and coordinate conditions. These findings suggest that AD patients' impairment on explicit semantic tasks is the product of deficient explicit retrieval in combination with a partially degraded semantic network.

Towards a nosology for frontotemporal lobar degenerations—A meta-analysis involving 267 subjects

Frontotemporal lobar degeneration is the second most common diagnosis of dementia in individuals younger than 65 years. We conducted a systematic and quantitative meta-analysis to examine neural correlates of frontotemporal lobar degeneration and its subtypes and to place the disease in a framework of cognitive neuropsychiatry. MedLine and Current Contents search engines were used to identify functional and anatomical imaging studies investigating frontotemporal lobar degeneration between 1980 and 2005. Studies were included, if they were peer-reviewed, applied internationally recognized diagnostic criteria, were original studies, and had results normalized to a stereotactic space. 19 studies were identified reporting either atrophy or decreases in glucose utilization. Finally, the analysis involved 267 subjects suffering from frontotemporal lobar degeneration and 351 control subjects. A quantitative meta-analysis was performed. Maxima of the studies resulted in activation likelihood estimates. The meta-analysis revealed specific neural networks for each of the three clinically defined subtypes of frontotemporal lobar degeneration, namely frontotemporal dementia, semantic dementia, and progressive non-fluent aphasia. Networks did not overlap as shown by a conjunction analysis, and they corresponded to clinical characteristics. The study relates the clinical features of each subtype of frontotemporal lobar degeneration specifically to its neural substrate. By 'triple dissociating' frontotemporal lobar degenerations into three clinicoanatomical prototypes, the study contributes to placing these disorders in cognitive neuropsychiatry and suggests a respective nosology.

Clinical significance of lobar atrophy in frontotemporal dementia: application of an MRI visual rating scale

BACKGROUND/AIMS

The status of imaging findings in the clinical diagnosis of frontotemporal dementia (FTD) remains uncertain; while they may be supportive of a diagnosis of frontotemporal dementia, they are not mandatory. Our aim was to assess patterns of lobar atrophy in a large sample of clinically defined, prospectively studied, patients using a magnetic resonance image (MRI) rating scale, to (1) determine whether imaging findings warrant a more prominent position in FTD diagnosis and (2) correlate the extent of lobar atrophy with clinical data.

METHODS

We adapted a recently devised post mortem rating scale for FTD to rate lobar atrophy on MRI scans. The areas rated included the frontal cortex and both anterior and posterior temporal regions bilaterally. All available brain scans from all patients seen in the Cambridge Dementia Clinic (n = 258) diagnosed as having FTD, together with controls (n = 20), were used to assess the reliability of the method. A subset of these (n = 121) were used for clinico-anatomic analysis.

RESULTS

The scale proved quick and reliable (intra-, inter-rater k = 0.80, 0.67). MRI scans were abnormal in the majority of patients (75%), with focal atrophy present in 100% of semantic dementia (SD) patients. By contrast, nearly half (47%) of the patients with clinical behavioural variant FTD had scans within the normal range. Behavioural cases with normal scans generally had fewer cognitive deficits and milder functional impairment than those with abnormal scans, yet displayed a clinically indistinguishable behavioural syndrome. They were not, however, simply at an earlier stage of the disease.

CONCLUSIONS

MRI findings should form part of the diagnostic criteria for SD; the absence of atrophy on MRI in many behavioural cases raises the prospect that the behavioural syndrome of FTD is not specific for patients with a neurodegenerative disease.

Driving abilities in frontotemporal dementia patients

OBJECTIVE

To evaluate driving competency and the relationship between neuropsychiatric symptoms and driving behavior in frontotemporal dementia (FTD) patients.

METHODS

Fifteen patients with a diagnosis of FTD and 15 healthy controls were administered a driving simulation task. Measures of driving performance and neuropsychiatric symptoms were assessed.

RESULTS

The FTD patients received more speeding tickets, ran more stop signs and were involved in more off-road crashes and collisions than the controls. The patients' overall average speed was significantly higher. Driving performance was correlated with agitated behavior.

CONCLUSIONS

Behavioral changes characteristic of FTD patients have an impact on their driving skills leading to inappropriate driving behavior.

Longitudinal changes of cerebral glucose metabolism in semantic dementia

BACKGROUND

Semantic dementia (SD).

OBJECTIVE

To identify the pattern of decline of cerebral glucose metabolism in SD using cerebral (18)F-fluoro-2-desoxy-D-glucose positron emission tomography scanning ((18)F-FDG-PET).

METHODS

Eight patients with SD underwent (18)F-FDG-PET at baseline and at re-examination in average 15 months later.

RESULTS

Compared with healthy control subjects, patients with SD showed a significant asymmetrical (left > right) hypometabolism of the temporal lobes, particularly of the anterior poles, at baseline. At follow-up, we observed a deterioration of cognitive abilities. However, in addition to the temporal lobes no other cortical or subcortical region showed a significant reduction of glucose metabolism except the anterior cingulate cortex (pcorr < 0.05).

CONCLUSION

Subtle functional changes suffice to produce significant neuropsycho- logical deterioration.

Orbitofrontal dysfunction related to both apathy and disinhibition in frontotemporal dementia

Orbitofrontal metabolic impairment is characteristic of the frontal variant of frontotemporal dementia (fv-FTD), as are early changes in emotional and social conduct. Two main types of behavioral disturbances have been distinguished in fv-FTD patients: apathetic and disinhibited manifestations. In this study, we searched for relationships between brain metabolism and presence of apathetic or disinhibited behavior. Metabolic activity and behavioral data were collected in 41 fv-FTD patients from European PET centers. A conjunction analysis of the PET data showed an expected impairment of metabolic activity in the anterior cingulate, ventromedial and orbital prefrontal cortex, the dorsolateral prefrontal cortex and the left anterior insula in fv-FTD subjects compared to matched controls. A correlation was observed between disinhibition scores on the Neuropsychiatric Inventory scale and a cluster of voxels located in the posterior orbitofrontal cortex (6, 28, -24). Comparison of brain activity between apathetic and nonapathetic fv-FTD patients from two centers also revealed a specific involvement of the posterior orbitofrontal cortex in apathetic subjects (4, 22, -22). The results confirm that the main cerebral metabolic impairment in fv-FTD patients affects areas specializing in emotional evaluation and demonstrate that decreased orbitofrontal activity is related to both disinhibited and apathetic syndromes in fv-FTD.

Knowing 7 x 8, but not the meaning of 'elephant': evidence for the dissociation between numerical and non-numerical semantic knowledge

Patients affected by semantic dementia (SD) and other severe cognitive deficits may show preserved numerical skills, including the retrieval of multiplication facts from long-term memory. No studies so far specifically investigated the network of arithmetic facts in semantic dementia. Thus, it is unknown whether preserved multiplication in SD truly reflects intact semantic knowledge or preserved retrieval of verbal sequences (just as the recitation of rhymes or poems). In the present study a patient (SG) with SD underwent an extensive assessment of number processing and calculation abilities. In particular, multiplication knowledge was investigated through a series of computerised tasks (production task, multiple-choice task, number bisection task with multiplicative triplets, number-matching task). SG demonstrated excellent performance in all number processing and calculation tasks. In computerised tasks tapping multiplication fact knowledge, SG was as accurate and fast as healthy controls. Analyses on individual regression slopes indicated that SG's reaction time effects (problem-size effect, problem-difficulty effect, interference effects, and facilitation effect) were comparable to those found in controls in each task. These results add new evidence to the independence of numerical knowledge from other semantic information and provide further insight into the organisation of stored arithmetic knowledge.

"Dementia unmasked": atypical, acute aphasic, presentations of neurodegenerative dementing disease

Acute onset of aphasia is most commonly due to a cerebrovascular event in the territory of the dominant hemisphere middle cerebral artery. An isolated and slowly progressive aphasia may occasionally be the presenting feature of a dementia syndrome. The longitudinal clinical, neuropsychological and neuroimaging findings of two patients with an acute, perioperative, onset of aphasia are reported, to show that acute aphasia may on occasion be the presenting feature of neurodegenerative dementing disorders, notwithstanding clinical diagnostic exclusion criteria for these conditions.

Integrating automatic and controlled processes into neurocognitive models of social cognition

Interest in the neural systems underlying social perception has expanded tremendously over the past few decades. However, gaps between behavioral literatures in social perception and neuroscience are still abundant. In this article, we apply the concept of dual-process models to neural systems in an effort to bridge the gap between many of these behavioral studies and neural systems underlying social perception. We describe and provide support for a neural division between reflexive and reflective systems. Reflexive systems correspond to automatic processes and include the amygdala, basal ganglia, ventromedial prefrontal cortex, dorsal anterior cingulate cortex, and lateral temporal cortex. Reflective systems correspond to controlled processes and include lateral prefrontal cortex, posterior parietal cortex, medial prefrontal cortex, rostral anterior cingulate cortex, and the hippocampus and surrounding medial temporal lobe region. This framework is considered to be a working model rather than a finished product. Finally, the utility of this model and its application to other social cognitive domains such as Theory of Mind are discussed.

The role of semantic distance in category-specific impairments for living things: evidence from a case of semantic dementia

In this paper, we describe a patient (LI) suffering from semantic dementia who showed a category-specific naming impairment for living things over and above the effects of several nonsemantic confounding variables. We investigated the characteristics of LI's impairment to address the following three issues raised in three different accounts of category-specific impairments: (i) the role of an imbalance in the loss of sensory compared to nonsensory features (assumed by the Sensory Functional Theory [Warrington, E. K., & Shallice, T. (1984). Category-specific semantic impairments. Brain, 107, 829-859]); (ii) the role of cross domain differences in Feature Correlation (assumed by the Conceptual Structure Account [Moss, H., Tyler, L. K., & Devlin, J. T. (2002). The emergence of category-specific deficits in a distributed semantic system. In: E. M. E. Forde & G. W. Humphreys (Eds.), Category Specificity in Brain and Mind (pp. 115-147). New York: Psychology Press]); (iii) the role of semantic distance (proposed by Cree and McRae [Cree, G. S., & McRae, K. (2003). Analyzing the factors underlying the structure and computation of the meaning of chipmunk, cherry, chisel, cheese, and cello (and many other such concrete nouns). Journal of Experimental Psychology: General, 132, 163-201]). We found that semantic distance was the only factor causally linked to LI's poorer performance on living things. In fact, her naming performance was less accurate on items that had many semantic neighbours, which is typical of living things. On the contrary, a feature listing task revealed that the features available to LI were not predicted by their level of correlation, as expected by the Conceptual Structure Account. Finally, at variance with the Sensory Functional Theory, although LI quoted sensory features less accurately than nonsensory ones, this did not give rise to a disproportionate loss of semantic features in the living domain.

Neuropsychology in Alzheimer's disease and other dementia research

PURPOSE OF REVIEW

This review describes a variety of neuropsychological dementia studies published between January 2004 and June 2005. In selecting articles for description in the present paper, our goal was not a comprehensive review of what is an enormous and growing literature, but rather to select and describe individual interesting studies from a sufficient range of dementia-related topics to permit illustration of some of the important questions for which a neuropsychological perspective aids in the understanding of dementias.

RECENT FINDINGS

Findings in the studies reviewed include a variety of different topics. Some of the themes include the following: (a) Alzheimer's disease is the most common cause of dementia, but a large body of research documents that there are important cognitive differences among various types of dementia, (b) the emerging research is also important in demonstrating the need for more sensitive clinical screening measures, (c) cognitive data are strongly predictive of functional decline, and (d) subtle declines in verbal learning appear to precede clinical Alzheimer's disease.

SUMMARY

Neuropsychological data are key to progress in understanding and developing more effective treatments for Alzheimer's disease and other dementia. For instance, efforts to identify early markers of dementia will be a key component to development of early intervention strategies.

Presymptomatic semantic impairment in a case of fronto-temporal lobar degeneration associated with the +16 mutation in MAPT

We describe a patient who came to neurological attention because of his at-risk status for the +16 exon 10 splice mutation in the tau gene (microtubule associated protein tau, MAPT), which had given rise to progressive behavioural disturbances in two of his siblings. The patient began to exhibit early signs of behavioural disturbance at around the age of symptom onset in both of his siblings. Although he did not spontaneously complain of difficulties in the domain of language, he met clinical, radiological and neuropsychological criteria for semantic dementia. On the assumption that his illness is mediated by the same pathological process as those of his siblings, we propose that this clinical picture represents the earliest changes of a semantic impairment - a phase of the illness that is often retrospectively described by patients and their relations, but has never previously been documented at first hand. Although typical of semantic dementia in many respects, the illness had several interesting and atypical features that emerged on detailed testing: first, he exhibited no insight into his difficulties; secondly, progression over a twelve-month interval was unusually slow; thirdly, he evinced a striking and consistent advantage for nonliving over living concepts; fourthly, a differential impairment of distinctive over shared knowledge did not emerge except when items that he could still name were compared with those for which he was anomic. Finally, the availability of post mortem pathological analysis from the brains of both of his affected siblings allowed us to attribute his illness to a specific pathological process which is considered unusual for patients with this clinical phenotype.