Focal cortical presentations of Alzheimer's disease

To determine the frequency of Alzheimer's disease (AD) pathology in patients presenting with progressive focal cortical syndromes, notably posterior cortical atrophy (PCA), corticobasal syndrome (CBS), behavioural variant frontotemporal dementia (bvFTD), progressive non-fluent aphasia (PNFA) (or a mixed aphasia) and semantic dementia (SD); and to compare the age of onset, evolution and prognosis in patients with focal cortical presentations of AD versus more typical AD and those with non AD pathology. From a total of 200 patients with comprehensive prospective clinical and pathological data we selected 120 : 100 consecutive cases with focal cortical syndromes and 20 with clinically typical AD. Clinical files were reviewed blind to pathological diagnosis. Of the 100 patients with focal syndromes, 34 had AD as the primary pathological diagnosis with the following distribution across clinical subtypes: all 7 of the PCA (100%); 6 of 12 with CBS (50%); 2 of 28 with bvFTD (7.1%); 12 of 26 with PNFA (44.1%); 5 of 7 with mixed aphasia (71.4%) and 2 of 20 with SD (10%). Of 20 with clinically typical AD, 19 had pathological AD. Age at both onset and death was greater in the atypical AD cases than those with non-AD pathology, although survival was equivalent. AD is a much commoner cause of focal cortical syndromes than previously recognised, particularly in PCA, PNFA and CBS, but rarely causes SD or bvFTD. The focal syndrome may remain pure for many years. Patients with atypical AD tend to be older than those with non-AD pathology.

How the camel lost its hump: the impact of object typicality on event-related potential signals in object decision

Using an object decision task, event-related potentials (ERPs), and minimum norm current source estimates, we investigated early spatiotemporal aspects of cortical activation elicited by line drawings that were manipulated on two dimensions: authenticity and typicality. Authentic objects were those that match real-world experience, whereas nonauthentic objects were "doctored" by deletion or addition of features (e.g., a camel with its hump removed, a hammer with two handles). The main manipulation of interest for both authentic and nonauthentic objects was the degree of typicality in the object's structure: typical items are composed of parts that have tended to co-occur across many different objects in the perceiver's experience. The ERP pattern revealed a significant typicality effect at 116 msec after stimulus onset. Both atypical authentic objects (e.g., a camel with its hump) and atypical nonauthentic objects (e.g., a jackal with a hump) elicited stronger brain activation than did objects with typical structure. A significant effect of authenticity was observed at 480 msec, with stronger activation for the nonauthentic objects. The factors of typicality and authenticity interacted at 160 and 330 msec. The most prominent source of the typicality effect was the bilateral occipitotemporal cortex, whereas the interaction and the authenticity effects were mainly observed in the more anterior bilateral temporal cortex. These findings support the hypothesis that within the first few hundred milliseconds after stimulus presentation onset, visual-form-related perceptual and conceptual processes represent distinct but interacting stages in object recognition.

Language activation studies with positron emission tomography

Behavioural tasks produce changes in regional cerebral blood flow (rCBF), the result of increased local neural activity. These changes can be measured with positron emission tomography (PET). Language activation studies by means of PET are being used to relate regional patterns of cerebral activation to information-processing models of speech and reading. Significant activation confined to both superior temporal gyri has been observed when normal subjects hear words played backwards, listen to non-words, and perform category judgements on pairs of heard real words. Prestriate cortex is activated by seeing strings of letter-like symbols, consonant strings, pronounceable non-words and real words, with additional activation in left medial prestriate cortex in response to the non-words and real words. Left posterior superior temporal gyrus (PSTG), left dorsolateral prefrontal cortex (DLPFC) and supplementary motor area (SMA) are engaged when subjects retrieve verbs from memory to match nouns. Finally, primary sensorimotor cortex is activated during articulation. There is particular interest at present in the precise roles of left PSTG and DLPFC in single-word comprehension and generation, and interpretation of the results depends critically on the design of the single-word tasks used for behavioural activation.

Effects of age and sex on immunological and virological responses to initial highly active antiretroviral therapy

BACKGROUND

Highly active antiretroviral therapy (HAART) has increased longevity. Currently, women comprise >50% of HIV-infected individuals worldwide. It is not known if there are differences between the sexes in the immunological and virological responses to HAART across the age strata.

METHODS

Immunological reconstitution and virological response in the first 6 months of a first HAART regimen in two observational clinical HIV-infected cohorts were compared by both sex and age (>or=50 vs. <50 years old).

RESULTS

A total of 246 individuals (28% women) were included in the study; 63 cases (>or=50 years old) and 183 controls (<50 years old). Over two-thirds of patients had HIV RNA levels <400 HIV-1 RNA copies/mL and CD4 count increases >or=50 cells/microL at 6 months from therapy initiation. There were no differences in immunological reconstitution across age and sex strata (P=0.81) and no differences in virological suppression, even after adjusting for type of HAART (P=0.68) or restricting the analysis to women only (P=0.81). These results suggest that younger and older women and men may have similar short-term initial HAART outcomes.

CONCLUSIONS

Further evaluation of longer term clinical response to initial HAART regimen based on sex and age is indicated, especially with more efficacious and simplified antiretroviral regimens and the associated decrease in mortality.

Semantic dementia and fluent primary progressive aphasia: two sides of the same coin?

Considerable controversy exists regarding the relationship between semantic dementia (SD) and progressive aphasia. SD patients present with anomia and impaired word comprehension. The widely used consensus criteria also include the need for patients to exhibit associative agnosia and/or prosopagnosia: many authors have used the label SD for patients with non-verbal, as well as verbal, semantic deficits on formal testing even if they recognize the objects and people encountered in everyday life; others interpret the criterion of agnosia to require pervasive recognition impairments affecting daily life. According to this latter view, SD patients have pathology that disrupts both a bilateral ventrotemporal-fusiform network (resulting in agnosia) and the left hemisphere language network (resulting in profound aphasia). These authors suggest that this profile is different to that seen in the fluent form of primary progressive aphasia (fPPA), a neurodegenerative disease primarily affecting language function. We present data on seven patients who met the diagnostic criteria for fPPA. All seven showed deficits relative to matched controls on both verbal and non-verbal measures of semantic memory, and these deficits were modulated by degree of anomia, concept familiarity and item typicality. Voxel-based morphometry revealed reduced grey matter density in the temporal lobes bilaterally (more widespread on the left), with the severity of atrophy in the left inferior temporal lobe being significantly related to performance on both the verbal and non-verbal measures. Together these findings suggest that patients who meet the diagnostic criteria for fPPA, can also meet the diagnostic criteria for early-stage SD provided that the impact of concept familiarity and typicality is taken into account. In addition, these findings support a claim that the patients' deficits on both verbal and non-verbal tasks reflect progressive deterioration of an amodal integrative semantic memory system critically involving the rostral temporal lobes, rather than a combination of atrophy in the left language network and a separate bilateral ventrotemporal-fusiform network.

[Q:] When would you prefer a SOSSAGE to a SAUSAGE? [A:] At about 100 msec. ERP correlates of orthographic typicality and lexicality in written word recognition

Using a speeded lexical decision task, event-related potentials (ERPs), and minimum norm current source estimates, we investigated early spatiotemporal aspects of cortical activation elicited by words and pseudo-words that varied in their orthographic typicality, that is, in the frequency of their component letter pairs (bi-grams) and triplets (tri-grams). At around 100 msec after stimulus onset, the ERP pattern revealed a significant typicality effect, where words and pseudo-words with atypical orthography (e.g., yacht, cacht) elicited stronger brain activation than items characterized by typical spelling patterns (cart, yart). At approximately 200 msec, the ERP pattern revealed a significant lexicality effect, with pseudo-words eliciting stronger brain activity than words. The two main factors interacted significantly at around 160 msec, where words showed a typicality effect but pseudo-words did not. The principal cortical sources of the effects of both typicality and lexicality were localized in the inferior temporal cortex. Around 160 msec, atypical words elicited the stronger source currents in the left anterior inferior temporal cortex, whereas the left perisylvian cortex was the site of greater activation to typical words. Our data support distinct but interactive processing stages in word recognition, with surface features of the stimulus being processed before the word as a meaningful lexical entry. The interaction of typicality and lexicality can be explained by integration of information from the early form-based system and lexicosemantic processes.

Repetition priming and hyperpriming in semantic dementia

Evidence from neurologically normal subjects suggests that repetition priming (RP) is independent of semantic processing. Therefore, we may expect patients with a selective deficit to conceptual knowledge to exhibit RP for words regardless of the integrity of their semantic representations. We tested six patients with semantic dementia (SD) on a lexical decision task that incorporated four different lags between first (baseline) and second (primed) presentation of repeated words. The patients exhibited significant RP that was greater for words that were categorised as semantically 'degraded' than for words categorised as 'known.' This RP advantage for semantically degraded words declined as lag increased. The patients also demonstrated hyperpriming, and a significant correlation was identified between baseline response time and RP in SD but not in controls. These findings indicate that level of semantic knowledge about a word influences both baseline lexical decision performance and RP of that word. The observed hyperpriming can be parsimoniously explained by a cognitive slowing account.

Survival trends for advanced colorectal cancer (CRC): Are improvements only for patients in clinical trials?

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Background: Significant improvements in the outcome for patients with advanced CRC have been achieved. We have reviewed the prospective CRC database at our institution from 1992 to 2004 to explore whether the availability of new chemotherapy drugs (irinotecan & oxaliplatin) and surgical advances has impacted on survival in the normal population. Earlier results had suggested a trend to improved survival (1). Methods: In Australia the first of these drugs became available at the end of 1997 thus we have taken this as the time point to compare outcomes pre and post. Disease-specific survivals were analysed from the date of diagnosis for stage D, and from the date of distant recurrence for stages A, B and C, with a date of censoring of live cases at December 31st, 2004. The Kaplan-Meier product-limit estimate was used for univariate analyses and Cox proportional hazards regression for multivariable analyses. Results: The current analysis is of 744 patients; 92–97 n=313, 98–04 n=431. Survival for the respective time periods were 47.6% and 54.9% 12 mths; 28.0% and 34.8% 24 mths; 18.9% and 23.0% 36 mths; 12.6% and 17.2% 48 mths; and 10.4% and 14.9% 60 mths. Cox proportional hazards regression indicated a lower risk of case fatality for 1998–2004 than 1992–1997 cases (p=0.048) after adjusting for age measured in years. The key predictors of case fatality in a multivariate analysis were found to be period (i.e., 1992–97/1998–04), age, and stage of disease at time of initial diagnosis. While an upward trend in survival was recorded for all ages, it was most pronounced for 70–79 year olds (n=272), where the increase in 24 mth survival was from 21.1% for 1992–97 to 36.1% for 1998–2004 (p=0.015). For patients aged 80 years and over (1992–97 n=40 & 1998–2004 n=67) the 24mth survivals were 18.6% (6.7%) and 26.4% (6.9%) respectively (p>0.200). Conclusions: Clinical trials have shown improvements in survival for highly selected patients. This current analysis confirms an improvement in survival over time for advanced CRC and this is seen in unselected patients including the elderly. Preliminary data has suggested that a number of factors have contributed to the trend of improved survival. Final analysis, including updated chemotherapy trends, will be presented at the meeting. (1) Proc ASCO 2004, #3707

No significant financial relationships to disclose.

A horse of a different colour: Do patients with semantic dementia recognise different versions of the same object as the same?

Ten patients with semantic dementia resulting from bilateral anterior temporal lobe atrophy, and 10 matched controls, were tested on an object recognition task in which they were invited to choose (from a four-item array) the picture representing "the same thing" as an object picture that they had just inspected and attempted to name. The target in the response array was never physically identical to the studied picture but differed from it - in the various conditions - in size, angle of view, colour or exemplar (e.g. a different breed of dog). In one test block for each patient, the response array was presented immediately after the studied picture was removed; in another block, a 2 min filled delay was inserted between study and test. The patients performed relatively well when the studied object and target response differed only in the size of the picture on the page, but were significantly impaired as a group in the other three type-of-change conditions, even with no delay between study and test. The five patients whose structural brain imaging revealed major right-temporal atrophy were more impaired overall, and also more affected by the 2 min delay, than the five patients with an asymmetric pattern characterised by predominant left-sided atrophy. These results are interpreted in terms of a hypothesis that successful classification of an object token as an object type is not a pre-semantic ability but rather results from interaction of perceptual and conceptual processing.

CT slice index and thickness: impact on organ contouring in radiation treatment planning for prostate cancer

Objective: To assess the impact of CT slice index and thickness (3 mm versus 5 mm) on (i) prostate volume, dimensions, and isocenter coordinates, (ii) bladder and rectal volumes, and (iii) DRR quality, in the treatment of prostate cancer. Methods: 16 patients with prostate cancer underwent two planning CT‐scans using 3 and 5 mm slice index/thickness. Prostate, bladder, and rectum were outlined on all scans. Prostate isocenter coordinates, maximum dimensions, and volumes were compared along with bladder and rectal volumes. Bladder volumes and maximum diameters were further investigated using a second observer. A comparative analysis of DRR quality was conducted as well as a dosimetric analysis using DVH. Results: The differences in measurements of prostate volume, isocenter coordinates and maximum dimensions between the 3 and 5 mm scans, were small and not statistically significant. Similar finding was seen for rectal volume. However, bladder volume was always larger on the 3 mm scan (mean difference=27.9 cc;  SE=4.8 cc;  95% CI:  17.7−38.2 cc;  p<0.001) and the findings were reproduced with the second observer (mean difference=31.9 cc;  SE=4.7 cc;  95% CI:  21.9−41.9 cc;  p<0.001). The differences in volume are caused by a slight increase in (1) the measurement of the longitudinal dimensions on the 3 mm scans, and (2) the slice by slice measured bladder area on the 3 mm scans. The latter is due to partial volume effect. The 3 mm DRR were slightly better than the 5 mm DRR. The bladder DVH differed significantly in some patients. Conclusion: Bladder volume is significantly larger on the 3 mm scans. Differences in contoured areas may be accounted for, in part, by the partial volume effect.

PACS number(s): 87.57.–s, 87.53.–j

An effective approach to violence prevention: traditional martial arts in middle school

This study replicated and extended the design and outcome measures of several small studies. In these studies, juveniles at high risk for violence and delinquency showed decreased violence and positive changes in psychological risk factors after being required to take a school-linked course in traditional martial arts. In the present study, 60 boys in a large urban middle school were required to take a traditional martial arts course in their school. They were paired on problematic behavior profiles and assigned to a treatment group or to a wait-list control group. Thirty classes, three per week (45 minutes each), were taught by a master of Koga Ha Kosho Shorei Ryu Kempo and his assistant (neither was a public school teacher). Results are reported here for 14 variables from the following measures: four teacher rating scales from the Sutter-Eyberg Student Behavior Inventory, five self-report scales of the Piers-Harris Self-Concept Scale, four computerized measures of attentional self-control from the Intermediate Visual and Auditory Continuous Performance Test, and a count of permanent expulsions from school. The treatment students improved over baseline on 12 variables, while the controls improved on 5 by small amounts and deteriorated from baseline on 8, including teacher-rated violence. There were significant differences between the groups on self-reported happiness and schoolwork and on one measure of attention. After controls took the course, their scores resembled the postcourse scores of the treatment group. Importantly, the control group's increase in teacher-rated violence was reversed. Both groups were then pooled to compare baseline and postcourse teacher ratings. Their scores improved significantly in the areas of resistance to rules, impulsiveness, and inappropriate social behavior. There was also improvement in regard to violence, but the change in scores was not statistically significant. Follow-up on teachers' ratings showed that improvement remained, and in some cases increased, four months after completion of the course. Interestingly, all 6 permanent expulsions were among the control group students who had not yet taken, or had only begun taking, the martial arts course.

Expansion of CD4+ T cells with a cytotoxic phenotype in patients with B-chronic lymphocytic leukaemia (B-CLL)

Abnormal CD4/CD8 ratios and T-cell function have previously been shown in patients with B-chronic lymphocytic leukaemia (B-CLL). We have demonstrated that CD4+ T cells containing both serine esterase and perforin (PF) are increased in the blood of these patients. Using flow cytometry, we have shown that the CD4+ PF+ cells were CD57+ but lacked expression of CD28, suggesting a mature population. The same phenotype in CD8+ T cells is characteristic of mature cytotoxic T cells. However, in contrast to the CD8+ T cells, the CD4+ T cells were more frequently CD45RO positive than CD45RA positive, indicating prior antigen experience. In contrast, this population lacked expression of either CD69 or HLA-DR, arguing that they were not activated or that they are an abnormal population of T cells. Their constitutive cytokine levels showed them mainly to contain IL4 and not IFNgamma, suggesting a Th2 phenotype. The role of the CD4+ PF+ T-cell population is at present uncertain. However, this potentially cytotoxic T-cell population could contribute both to enhancing survival of the B-CLL tumour cells through production of IL4, and to the immunodeficient state frequently seen in patients with this tumour, independent of drug treatment.

Longitudinal profiles of semantic impairment for living and nonliving concepts in dementia of Alzheimer's type

Two types of theoretical account have been proposed to explain the phenomenon of category-specific impairment in tests of semantic memory: One stresses the importance of different cortical regions to the representation of living and nonliving categories, while the other emphasize the importance of statistical relationships among features of concepts belonging to these two broad semantic domains. Theories of the latter kind predict that the direction of a domain advantage will be determined in large part by the overall damage to the semantic system, and that the profiles of patients with progressive impairments of semantic memory are likely to include a point at which an advantage for one domain changes to an advantage for the other. The present series of three studies employed semantic test data from two separate cohorts of patients with probable dementia of Alzheimer's type (DAT) to look for evidence of such a crossover. In the first study, longitudinal test scores from a cohort of 58 patients were examined to confirm the presence of progressive semantic deterioration in this group. In the second study, Kaplan-Meier survival curves based on serial naming responses and plotted separately for items belonging to living and nonliving domains indicated that the representations of living concepts (as measured by naming) deteriorated at a consistently and significantly faster rate than those of nonliving concepts. A third study, carried out to look in detail at the performance of mildly affected patients, employed an additional cross-sectional cohort of 20 patients with mild DAT and utilized a graded naming assessment. This study also revealed no evidence for a crossover in the advantage of one domain over the other as a function of disease severity. Taken together with the model of anatomical progression in DAT based on the work of Braak and Braak (1991), these findings are interpreted as evidence for the importance of regional cerebral anatomy to the genesis of semantic domain effects in DAT.

Angiogenic proteins in the lungs of children after cavopulmonary anastomosis

OBJECTIVE

Pulmonary arteriovenous malformations may cause progressive cyanosis after cavopulmonary anastomosis and may develop as a result of abnormal angiogenesis. We used immunohistochemistry to determine whether angiogenic proteins are increased in the lungs of children after cavopulmonary anastomosis.

METHODS

Lung specimens were obtained from 13 children after cavopulmonary anastomosis and from 6 control subjects. Specimens were stained with antibodies against vascular endothelial growth factor and its receptor (flk-1/KDR), basic fibroblast growth factor, alpha-smooth muscle actin, CD31, collagen IV, fibronectin, and proliferating cell nuclear antigen. Staining was graded on a scale of 0 to 3. Vessels positive for proliferating cell nuclear antigen were counted in 10 fields per specimen, and the results were averaged.

RESULTS

After cavopulmonary anastomosis, patients demonstrated increased staining for vascular endothelial growth factor (P =.03) and its receptor (P =.03) and decreased staining for CD31 (P =.004). Proliferating cell nuclear antigen staining in patients was equivalent to that for control subjects (P =.9).

CONCLUSIONS

Lung biopsy specimens from children after cavopulmonary anastomosis demonstrate increased expression of vascular endothelial growth factor and its receptor. These data confirm earlier findings that blood vessels forming after cavopulmonary anastomosis may have reduced intercellular junctions (decreased CD31 staining). Despite the increased numbers of pulmonary vessels that are present in these patients, these vessels are not highly proliferative (proliferating cell nuclear antigen staining equivalent to that of control subjects). These results suggest that vascular endothelial growth factor may be a mediator of angiogenesis in the lungs of children after cavopulmonary anastomosis; however, other factors, such as vascular dilation and remodeling, may also be important.

Large, colorful, or noisy? Attribute- and modality-specific activations during retrieval of perceptual attribute knowledge

Position emission tomography was used to investigate whether retrieval of perceptual knowledge from long-term memory activates unique cortical regions associated with the modality and/or attribute type retrieved. Knowledge about the typical color, size, and sound of common objects and animals was probed, in response to written words naming the objects. Relative to a nonsemantic control task, all the attribute judgments activated similar left temporal and frontal regions. Visual (color, size) knowledge selectively activated the right posterior inferior temporal (PIT) cortex, whereas sound judgments elicited selective activation in the left posterior superior temporal gyrus and the adjacent parietal cortex. All of the attribute judgments activated a left PIT region, but color retrieval generated more activation in this area. Size judgments activated the right medial parietal cortex. These results indicate that the retrieval of perceptual semantic information activates not only a general semantic network, but also cortical areas specialized for the modality and attribute type of the knowledge retrieved.

Differing patterns of temporal atrophy in Alzheimer's disease and semantic dementia

OBJECTIVE

To characterize and quantify the patterns of temporal lobe atrophy in AD vs semantic dementia and to relate the findings to the cognitive profiles. Medial temporal lobe atrophy is well described in AD. In temporal variant frontotemporal dementia (semantic dementia), clinical studies suggest polar and inferolateral temporal atrophy with hippocampal sparing, but quantification is largely lacking.

METHODS

A volumetric method for quantifying multiple temporal structures was applied to 26 patients with probable AD, 18 patients with semantic dementia, and 21 matched control subjects.

RESULTS

The authors confirmed the expected bilateral hippocampal atrophy in AD relative to controls, with involvement of the amygdala bilaterally and the right parahippocampal gyrus. Contrary to expectations, patients with semantic dementia had asymmetric hippocampal atrophy, more extensive than AD on the left. As predicted, the semantic dementia group showed more severe involvement of the temporal pole bilaterally and the left amygdala, parahippocampal gyrus (including the entorhinal cortex), fusiform gyrus, and the inferior and middle temporal gyri. Performance on semantic association tasks correlated with the size of the left fusiform gyrus, whereas naming appeared to depend upon a wider left temporal network. Episodic memory measures, with the exception of recognition memory for faces, did not correlate with temporal measures.

CONCLUSIONS

Hippocampal atrophy is not specific for AD but is also seen in semantic dementia. Distinguishing the patients with semantic dementia was the severe global but asymmetric (left > right) atrophy of the amygdala, temporal pole, and fusiform and inferolateral temporal gyri. These findings have implications for diagnosis and understanding of the cognitive deficits in AD and semantic dementia.

No right to speak? The relationship between object naming and semantic impairment: neuropsychological evidence and a computational model

The processes required for object naming were addressed in a study of patients with semantic dementia (a selective decline of semantic memory resulting from progressive temporal lobe atrophy) and in a computational model of single-word production. Although all patients with semantic dementia are impaired in both single-word production and comprehension, previous reports had indicated two different patterns: (a) a parallel decline in accuracy of naming and comprehension, with frequent semantic naming errors, suggesting a purely semantic basis for the anomia and (b) a dramatic progressive anomia without commensurate decline in comprehension, which might suggest a mainly postsemantic source of the anomia. Longitudinal data for 16 patients with semantic dementia reflected these two profiles, but with the following additional important specifications: (1) despite a few relatively extreme versions of one or other profile, the full set of cases formed a continuum in the extent of anomia for a given degree of degraded comprehension; (2) the degree of disparity between these two abilities was associated with relative asymmetry in laterality of atrophy: a parallel decline in the two measures characterized patients with greater right- than left-temporal atrophy, while disproportionate anomia occurred with a predominance of atrophy in the left-temporal lobe. In an implemented computational model of naming, semantic representations were distributed across simulated left- and right-temporal regions, but the semantic units on the left were more strongly connected to left-lateralized phonological representations. Asymmetric damage to semantic units reproduced the longitudinal patient profiles of naming relative to comprehension, plus additional characteristics of the patients' naming performance. On the basis of both the neuropsychological and computational evidence, we propose that semantic impairment alone can account for the full range of word production deficits described here.

Deficits in irregular past-tense verb morphology associated with degraded semantic knowledge

Two distinct mechanisms are often considered necessary to account for generation of the past-tense of English verbs: a lexical associative process for irregular forms like speak-->spoke, and a rule-governed process ("add -ed") for regular and novel forms like talk-->talked and wug-->wugged. An alternative account based on a parallel-distributed processing approach proposes that one complex procedure processes all past-tense types. In this alternative view, neuropsychological dissociations are explained by reduced input from word meaning that plays a greater role in successful generation of the past-tense for lower frequency irregular verbs, and by phonological deficits that disproportionately affect regular and novel forms. Only limited evidence has been available concerning the relationship between knowledge of word meaning and verb-tense processing. The study reported here evaluated the past-tense verb abilities of 11 patients with semantic dementia, a neurodegenerative condition characterised by degraded semantic knowledge. We predicted and confirmed that the patients would have essentially normal ability to generate and recognise regular (and novel) past-tense forms, but a marked and frequency-modulated deficit on irregular verbs. Across the set of 11 patients, the degree of impairment for the irregular past-tense was significantly correlated with the degree of comprehension impairment as measured by verb synonym judgements. These results, plus other features of the data such as the nature of the errors to irregular verbs, are discussed in relation to currently developing theories of the language system.