Frontotemporal lobar degeneration (FTLD) has been associated with toxic intracellular aggregates of hyperphosphorylated tau (FTLD‐tau). Moreover, genetic studies identified mutations in the MAPT gene encoding tau in familial cases of the disease. In this review, we cover a range of aspects of tau function, both in the healthy and diseased brain, discussing several in vitro and in vivo models. Tau structure and function in the healthy brain is presented, accentuating its distinct compartmentalization in neurons and its role in microtubule stabilization and axonal transport. Furthermore, tau‐driven pathology is discussed, introducing current concepts and the underlying experimental evidence. Different aspects of pathological tau phosphorylation, the protein's genomic and domain organization as well as its spreading in disease, together with MAPT‐associated mutations and their respective models are presented. Dysfunction related to other post‐transcriptional modifications and their effect on normal neuronal functions such as cell cycle, epigenetics and synapse dynamics are also discussed, providing a mechanistic explanation for the observations made in FTLD‐tau cases, with the possibility for therapeutic intervention.
In this review, we cover aspects of tau function, both in the healthy and diseased brain, referring to different in vitro and in vivo models. In healthy neurons, tau is compartmentalized, with higher concentrations found in the distal part of the axon. Cargo molecules are sensitive to this gradient. A disturbed tau distribution, as found in frontotemporal lobar degeneration (FTLD‐tau), has severe consequences for cellular physiology: tau accumulates in the neuronal soma and dendrites, leading among others to microtubule depolymerization and impaired axonal transport. Tau forms insoluble aggregates that sequester additional molecules stalling cellular physiology. Neuronal communication is gradually lost as toxic tau accumulates in dendritic spines with subsequent degeneration of synapses and synaptic loss. Thus, by providing a mechanistic explanation for the observations made in FTLD‐tau cases, arises a possibility for therapeutic interventions.
This article is part of the Frontotemporal Dementia special issue.
microtubule; phosphorylation; post‐translational; spreading; synapse; transgenic
To contrast the relationships of hormonal eating peptides and hypothalamic volumes to eating behavior and metabolic changes (body mass index [BMI]) in behavioral variant frontotemporal dementia (bvFTD) and semantic variant primary progressive aphasia (svPPA).
Seventy-five patients with dementia (19 bvFTD, 26 svPPA, and 30 Alzheimer disease dementia) and 23 controls underwent fasting blood analyses of leptin, ghrelin, cholecystokinin, peptide tyrosine tyrosine (PYY), and agouti-related peptide (AgRP) levels. On brain MRI anterior, posterior, and total hypothalamic volumes were measured. Relationships between endocrine measures, hypothalamic volumes, eating behaviors, and BMI were investigated.
Levels of AgRP were higher in patients with bvFTD (69 ± 89 pg/mL) and svPPA (62 ± 81 pg/mL) compared with controls (23 ± 19 pg/mL, p < 0.01). No differences were found for leptin, oxytocin, cholecystokinin, ghrelin, and PYY levels. Patients with bvFTD and svPPA had higher scores on questionnaires measuring eating behaviors. Atrophy of the posterior and total hypothalamus was observed in the bvFTD group only. Linear regression modeling revealed that leptin and AgRP levels predicted BMI.
Eating abnormalities are multifactorial in FTD. In bvFTD, they are in part related to hypothalamic degeneration, with potential disintegration of the network connections between the hypothalamus and orbitofrontal cortex/reward pathways. In svPPA, although hypothalamic volumes are preserved, this group experiences elevated AgRP levels similar to bvFTD, which predicts BMI in both groups. This finding highlights the potential key role of AgRP in eating and metabolic changes and provides a potential target for treatment to modify disease progression.
The relationship between behavioral changes and functional decline in frontotemporal dementia (FTD) is not well understood.
Thirty-nine patients (21 behavioral variant FTD [bvFTD], 18 semantic variant primary progressive aphasia [svPPA]) were followed up longitudinally (2–4 years follow-up). Functional (Disability Assessment for Dementia) and behavioral (Cambridge Behavioural Inventory Revised) assessments were included for between-group (pairwise comparisons, mixed model analysis) and within-group analyses (bivariate correlations).
Functionally, patients with bvFTD were more impaired than patients with svPPA at baseline and continued to be at follow-up, despite similar disease duration. By contrast, behavioral impairments differed between patient groups at baseline and at follow-up. At baseline, patients with bvFTD exhibited higher levels of apathy and changes in eating than patients with svPPA; disinhibited and stereotypical behaviors were similar. Over the years, patients with bvFTD showed reduction in disinhibition and stereotypical behavior while apathy and eating changes increased. By contrast, all measured behaviors increased in patients with svPPA over time. Finally, only apathy made longitudinal contributions to functional disability in patients with svPPA, whereas apathy and stereotypical behavior were associated with increased disability in patients with bvFTD.
Despite shared overlapping baseline behavioral symptoms, patients with bvFTD are more functionally impaired than patients with svPPA. Apathy has a strong role in disability for both bvFTD and svPPA, but stereotypical behaviors only contributed to functional deficits in patients with bvFTD. Our findings suggest that rigid/compulsive behaviors may in fact support activity engagement in patients with svPPA. Taken together, our results indicate that interventions to reduce disability in the FTD spectrum require an alternative rationale in comparison to Alzheimer disease dementia, and should carefully weigh the interaction of behavioral symptoms and functional status.
Severe traumatic brain injury (TBI) often leads to deficits in physiological arousal and empathy, which are thought to be linked. This study examined whether injury-related brain volume loss in key limbic system structures is associated with these deficits. Twenty-four adults with TBI and 24 matched Controls underwent MRI scans to establish grey matter volumes in the amygdala, thalamus, and hippocampus. EEG and skin conductance levels were recorded to index basal physiological arousal. Self-report emotional empathy levels were also assessed. The TBI group had reduced brain volumes, topographic alpha differences, and lower emotional empathy compared to Controls. Regional brain volumes were differentially correlated to arousal and self-report empathy. Importantly, lower volume in pertinent brain structures correlated with lower empathy, for participants with and without TBI. Overall we provide new insights into empathic processes after TBI and their relationship to brain volume loss.
•EEG alpha power and SCL provide a stable measure of arousal disturbance following severe traumatic brain injury.•Diminished arousal was associated with reduced volume in the amygdala and thalamus.•Lower affective empathy was associated with reduced volume in the amygdala and hippocampus.•These relationships were found for participants with and without brain injury.
Brain volume loss; Limbic system; Physiological arousal; Empathy; Severe traumatic brain injury
The ability to envisage personally relevant events at a future time point represents an incredibly sophisticated cognitive endeavor and one that appears to be intimately linked to episodic memory integrity. Far less is known regarding the neurocognitive mechanisms underpinning the capacity to envisage non-personal future occurrences, known as semantic future thinking. Moreover the degree of overlap between the neural substrates supporting episodic and semantic forms of prospection remains unclear. To this end, we sought to investigate the capacity for episodic and semantic future thinking in Alzheimer’s disease (n = 15) and disease-matched behavioral-variant frontotemporal dementia (n = 15), neurodegenerative disorders characterized by significant medial temporal lobe (MTL) and frontal pathology. Participants completed an assessment of past and future thinking across personal (episodic) and non-personal (semantic) domains, as part of a larger neuropsychological battery investigating episodic and semantic processing, and their performance was contrasted with 20 age- and education-matched healthy older Controls. Participants underwent whole-brain T1-weighted structural imaging and voxel-based morphometry analysis was conducted to determine the relationship between gray matter integrity and episodic and semantic future thinking. Relative to Controls, both patient groups displayed marked future thinking impairments, extending across episodic and semantic domains. Analyses of covariance revealed that while episodic future thinking deficits could be explained solely in terms of episodic memory proficiency, semantic prospection deficits reflected the interplay between episodic and semantic processing. Distinct neural correlates emerged for each form of future simulation with differential involvement of prefrontal, lateral temporal, and medial temporal regions. Notably, the hippocampus was implicated irrespective of future thinking domain, with the suggestion of lateralization effects depending on the type of information being simulated. Whereas episodic future thinking related to right hippocampal integrity, semantic future thinking was found to relate to left hippocampal integrity. Our findings support previous observations of significant MTL involvement for semantic forms of prospection and point to distinct neurocognitive mechanisms which must be functional to support future-oriented forms of thought across personal and non-personal contexts.
episodic memory; semantic memory; imagination; hippocampus; prefrontal cortex; Alzheimer’s disease; frontotemporal dementia; future thinking
Episodic memory recall processes in Alzheimer's disease (AD) and behavioral variant frontotemporal dementia (bvFTD) can be similarly impaired, whereas recognition performance is more variable. A potential reason for this variability could be false-positive errors made on recognition trials and whether these errors are due to amnesia per se or a general over-endorsement of recognition items regardless of memory. The current study addressed this issue by analysing recognition performance on the Rey Auditory Verbal Learning Test (RAVLT) in 39 bvFTD, 77 AD and 61 control participants from two centers (India, Australia), as well as disinhibition assessed using the Hayling test. Whereas both AD and bvFTD patients were comparably impaired on delayed recall, bvFTD patients showed intact recognition performance in terms of the number of correct hits. However, both patient groups endorsed significantly more false-positives than controls, and bvFTD and AD patients scored equally poorly on a sensitivity index (correct hits—false-positives). Furthermore, measures of disinhibition were significantly associated with false positives in both groups, with a stronger relationship with false-positives in bvFTD. Voxel-based morphometry analyses revealed similar neural correlates of false positive endorsement across bvFTD and AD, with both patient groups showing involvement of prefrontal and Papez circuitry regions, such as medial temporal and thalamic regions, and a DTI analysis detected an emerging but non-significant trend between false positives and decreased fornix integrity in bvFTD only. These findings suggest that false-positive errors on recognition tests relate to similar mechanisms in bvFTD and AD, reflecting deficits in episodic memory processes and disinhibition. These findings highlight that current memory tests are not sufficient to accurately distinguish between bvFTD and AD patients.
frontotemporal dementia; Alzheimer's disease; memory; recognition; disinhibition
Frontotemporal dementia (FTD) is a complex disorder characterised by a broad range of clinical manifestations, differential pathological signatures, and genetic variability. Mutations in three genes—MAPT, GRN, and C9orf72—have been associated with FTD. We sought to identify novel genetic risk loci associated with the disorder.
We did a two-stage genome-wide association study on clinical FTD, analysing samples from 3526 patients with FTD and 9402 healthy controls. All participants had European ancestry. In the discovery phase (samples from 2154 patients with FTD and 4308 controls), we did separate association analyses for each FTD subtype (behavioural variant FTD, semantic dementia, progressive non-fluent aphasia, and FTD overlapping with motor neuron disease [FTD-MND]), followed by a meta-analysis of the entire dataset. We carried forward replication of the novel suggestive loci in an independent sample series (samples from 1372 patients and 5094 controls) and then did joint phase and brain expression and methylation quantitative trait loci analyses for the associated (p<5 × 10−8) and suggestive single-nucleotide polymorphisms.
We identified novel associations exceeding the genome-wide significance threshold (p<5 × 10−8) that encompassed the HLA locus at 6p21.3 in the entire cohort. We also identified a potential novel locus at 11q14, encompassing RAB38/CTSC, for the behavioural FTD subtype. Analysis of expression and methylation quantitative trait loci data suggested that these loci might affect expression and methylation incis.
Our findings suggest that immune system processes (link to 6p21.3) and possibly lysosomal and autophagy pathways (link to 11q14) are potentially involved in FTD. Our findings need to be replicated to better define the association of the newly identified loci with disease and possibly to shed light on the pathomechanisms contributing to FTD.
The National Institute of Neurological Disorders and Stroke and National Institute on Aging, the Wellcome/ MRC Centre on Parkinson’s disease, Alzheimer’s Research UK, and Texas Tech University Health Sciences Center.
Motor speech disorders, including apraxia of speech (AOS), account for over 50% of the communication disorders following stroke. Given its prevalence and impact, and the need to understand its neural mechanisms, we used resting state functional MRI to examine functional connectivity within a network of regions previously hypothesized as being associated with AOS (bilateral anterior insula (aINS), inferior frontal gyrus (IFG), and ventral premotor cortex (PM)) in a group of 32 left hemisphere stroke patients and 18 healthy, age-matched controls. Two expert clinicians rated severity of AOS, dysarthria and nonverbal oral apraxia of the patients. Fifteen individuals were categorized as AOS and 17 were AOS-absent. Comparison of connectivity in patients with and without AOS demonstrated that AOS patients had reduced connectivity between bilateral PM, and this reduction correlated with the severity of AOS impairment. In addition, AOS patients had negative connectivity between the left PM and right aINS and this effect decreased with increasing severity of non-verbal oral apraxia. These results highlight left PM involvement in AOS, begin to differentiate its neural mechanisms from those of other motor impairments following stroke, and help inform us of the neural mechanisms driving differences in speech motor planning and programming impairment following stroke.
•Resting state fMRI connectivity of a speech network in apraxia of speech (AOS)•AOS patients had reduced bilateral premotor (PM) connectivity relative to severity.•AOS patients also had reduced left PM–right anterior insula connectivity.•Left PM may drive disordered speech motor planning and programming post-stroke.
Apraxia of speech; Network connectivity; Resting-state fMRI; Stroke
The capacity to remember self-referential past events relies on the integrity of a distributed neural network. Controversy exists, however, regarding the involvement of specific brain structures for the retrieval of recently experienced versus more distant events. Here, we explored how characteristic patterns of atrophy in neurodegenerative disorders differentially disrupt remote versus recent autobiographical memory. Eleven behavioural-variant frontotemporal dementia, 10 semantic dementia, 15 Alzheimer's disease patients and 14 healthy older Controls completed the Autobiographical Interview. All patient groups displayed significant remote memory impairments relative to Controls. Similarly, recent period retrieval was significantly compromised in behavioural-variant frontotemporal dementia and Alzheimer's disease, yet semantic dementia patients scored in line with Controls. Voxel-based morphometry and diffusion tensor imaging analyses, for all participants combined, were conducted to investigate grey and white matter correlates of remote and recent autobiographical memory retrieval. Neural correlates common to both recent and remote time periods were identified, including the hippocampus, medial prefrontal, and frontopolar cortices, and the forceps minor and left hippocampal portion of the cingulum bundle. Regions exclusively implicated in each time period were also identified. The integrity of the anterior temporal cortices was related to the retrieval of remote memories, whereas the posterior cingulate cortex emerged as a structure significantly associated with recent autobiographical memory retrieval. This study represents the first investigation of the grey and white matter correlates of remote and recent autobiographical memory retrieval in neurodegenerative disorders. Our findings demonstrate the importance of core brain structures, including the medial prefrontal cortex and hippocampus, irrespective of time period, and point towards the contribution of discrete regions in mediating successful retrieval of distant versus recently experienced events.
Emotional events gain special priority in how they are remembered, with emotionally arousing events typically recalled more vividly and with greater confidence than non-emotional events. In dementia, memory and emotion processing are affected to varying degrees, however, whether emotional enhancement of memory for complex ecologically-valid events is differentially affected across dementia syndromes remains unclear, with previous studies examining effects of emotion on simple visual recognition only. Here, we examined memory for an emotionally arousing short story and a closely matched, emotionally neutral story in behavioral-variant frontotemporal dementia (bvFTD) (n = 13) and Alzheimer's disease (AD) (n = 14), and contrasted their performance with healthy controls (n = 12). Multiple-choice recognition memory for specific details of the story was assessed after a 1-h delay. While AD and control groups showed enhanced memory for the emotional story, the bvFTD group recalled a similar number of details from the emotional and neutral stories. Voxel-based morphometry analyses revealed emotional enhancement of memory correlated with distinct brain regions in each patient group. In AD, emotional enhancement was associated with integrity of the bilateral hippocampus, parahippocampal gyri, temporal fusiform gyrus and frontal pole, regions typically implicated in memory processes. In contrast in bvFTD, integrity of emotion processing regions, including the orbitofrontal cortex, right amygdala and right insula, correlated with the extent emotion enhanced memory. Our results reveal that integrity of frontal and temporal regions determine the quality and nature of emotional memories. While emotional enhancement of memory is present in mild AD, in bvFTD emotion does not facilitate memory retrieval for complex realistic events. This attenuation of emotional enhancement is due to degradation of emotion processing regions, which may be important for modulating levels of arousal in response to emotional events in these patients.
emotion; episodic memory; dementia; hippocampus; amygdala
Effects of thalamic nuclei damage and related white matter tracts on memory performance are still debated. This is particularly evident for the medio-dorsal thalamus which has been less clear in predicting amnesia than anterior thalamus changes. The current study addresses this issue by assessing 7 thalamic stroke patients with consistent unilateral lesions focal to the left medio-dorsal nuclei for immediate and delayed memory performance on standard visual and verbal tests of anterograde memory, and over the long-term (>24 h) on an object-location associative memory task. Thalamic patients showed selective impairment to delayed recall, but intact recognition memory. Patients also showed accelerated forgetting of contextual details after a 24 h delay, compared to controls. Importantly, the mammillothalamic tract was intact in all patients, which suggests a role for the medio-dorsal nuclei in recall and early consolidation memory processes.
thalamus; anterograde memory; stroke; mammillothalamic tract; MRI
Frontotemporal dementia (FTD) is associated with motor neurone disease (FTD-MND), corticobasal syndrome (CBS) and progressive supranuclear palsy syndrome (PSPS). Together, this group of disorders constitutes a major cause of young-onset dementia. One of the three clinical variants of FTD is progressive nonfluent aphasia (PNFA), which is focused on in this study. The steroid hormone progesterone (PROG) is known to have an important role as a neurosteroid with potent neuroprotective and promyelination properties. In a case-control study of serum samples (39 FTD, 91 controls), low serum PROG was associated with FTD overall. In subgroup analysis, low PROG levels were significantly associated with FTD-MND and CBS, but not with PSPS or PNFA. PROG levels of >195 pg/ml were significantly correlated with lower disease severity (frontotemporal dementia rating scale) for individuals with CBS. In the human neuroblastoma SK-N-MC cell line, exogenous PROG (9300–93,000 pg/ml) had a significant effect on overall Tau and nuclear TDP-43 levels, reducing total Tau levels by ∼1.5-fold and increasing nuclear TDP-43 by 1.7- to 2.0-fold. Finally, elevation of plasma PROG to a mean concentration of 5870 pg/ml in an Ala315Thr (A315T) TARDBP transgenic mouse model significantly reduced the rate of loss of locomotor control in PROG-treated, compared with placebo, mice. The PROG treatment did not significantly increase survival of the mice, which might be due to the limitation of the transgenic mouse to accurately model TDP-43-mediated neurodegeneration. Together, our clinical, cellular and animal data provide strong evidence that PROG could be a valid therapy for specific related disorders of FTD.
The recently discovered hexanucleotide repeat expansion, C9ORF72, has been shown to be among the most common cause of familial behavioural variant frontotemporal dementia (bvFTD) and to be present in a significant minority of apparently sporadic cases. While mounting evidence points to prominent episodic memory dysfunction in bvFTD cases, recent reports have also suggested an amnestic profile in C9ORF72 mutation carriers. No study to date, however, has formally characterised the extent to which episodic memory is impaired in C9ORF72 mutation versus sporadic cases, or the underlying neural substrates of such deficits. We conducted a comparison of C9ORF72 (n = 8) and sporadic (n = 15) bvFTD cases using a battery of verbal and visual episodic memory tasks, and contrasted their performance with that of Alzheimer's disease (AD, n = 15) and healthy older control (n = 15) participants. Behaviourally, the two bvFTD groups displayed comparable episodic memory profiles, irrespective of task administered, with prominent impairments evident relative to Controls. Whole-brain voxel-based morphometry analyses revealed distinct neural correlates of episodic memory dysfunction in each patient group. Widespread atrophy in medial prefrontal, medial and lateral temporal cortices correlated robustly with episodic memory dysfunction in sporadic bvFTD cases. In contrast, atrophy in a distributed set of regions in the frontal, temporal, and parietal lobes including the posterior cingulate cortex, was implicated in episodic memory dysfunction in C9ORF72 cases. Our results demonstrate that while episodic memory is disrupted to the same extent irrespective of genetic predisposition in bvFTD, distinct neural changes specific to each patient group are evident. The involvement of medial and lateral parietal regions in episodic memory dysfunction in C9ORF72 cases is of particular significance and represents an avenue of considerable interest for future studies.
•We assessed episodic memory in bvFTD patients with and without C9ORF72 mutations.•Episodic memory deficits were present in C9ORF72 cases relative to Controls.•C9ORF72 and sporadic bvFTD cases showed equivalent episodic memory profiles.•Neural substrates of memory disruption differed contingent on mutation status.•Medial and lateral parietal involvement in C9ORF72 memory deficits is notable.
Episodic memory; Frontotemporal dementia; Alzheimer's disease; C9ORF72 mutation; Neuroimaging
Patients with frontotemporal dementia have pervasive changes in emotion recognition and social cognition, yet the neural changes underlying these emotion processing deficits remain unclear. The multimodal system model of emotion proposes that basic emotions are dependent on distinct brain regions, which undergo significant pathological changes in frontotemporal dementia. As such, this syndrome may provide important insight into the impact of neural network degeneration upon the innate ability to recognise emotions. This study used voxel-based morphometry to identify discrete neural correlates involved in the recognition of basic emotions (anger, disgust, fear, sadness, surprise and happiness) in frontotemporal dementia. Forty frontotemporal dementia patients (18 behavioural-variant, 11 semantic dementia, 11 progressive nonfluent aphasia) and 27 healthy controls were tested on two facial emotion recognition tasks: The Ekman 60 and Ekman Caricatures. Although each frontotemporal dementia group showed impaired recognition of negative emotions, distinct associations between emotion-specific task performance and changes in grey matter intensity emerged. Fear recognition was associated with the right amygdala; disgust recognition with the left insula; anger recognition with the left middle and superior temporal gyrus; and sadness recognition with the left subcallosal cingulate, indicating that discrete neural substrates are necessary for emotion recognition in frontotemporal dementia. The erosion of emotion-specific neural networks in neurodegenerative disorders may produce distinct profiles of performance that are relevant to understanding the neurobiological basis of emotion processing.
Episodic memory refers to a complex and multifaceted process which enables the retrieval of richly detailed evocative memories from the past. In contrast, semantic memory is conceptualized as the retrieval of general conceptual knowledge divested of a specific spatiotemporal context. The neural substrates of the episodic and semantic memory systems have been dissociated in healthy individuals during functional imaging studies, and in clinical cohorts, leading to the prevailing view that episodic and semantic memory represent functionally distinct systems subtended by discrete neurobiological substrates. Importantly, however, converging evidence focusing on widespread neural networks now points to significant overlap between those regions essential for retrieval of autobiographical memories, episodic learning, and semantic processing. Here we review recent advances in episodic memory research focusing on neurodegenerative populations which has proved revelatory for our understanding of the complex interplay between episodic and semantic memory. Whereas episodic memory research has traditionally focused on retrieval of autobiographical events from the past, we also include evidence from the recent paradigm shift in which episodic memory is viewed as an adaptive and constructive process which facilitates the imagining of possible events in the future. We examine the available evidence which converges to highlight the pivotal role of semantic memory in providing schemas and meaning whether one is engaged in autobiographical retrieval for the past, or indeed, is endeavoring to construct a plausible scenario of an event in the future. It therefore seems plausible to contend that semantic processing may underlie most, if not all, forms of episodic memory, irrespective of temporal condition.
semantic dementia; autobiographical memory; future thinking; Alzheimer’s disease; episodic memory; anterior temporal lobes; semantic memory
Aging is associated with a decline in episodic memory function. This is accompanied by degradation of and functional changes in the medial temporal lobe (MTL) which subserves mnemonic processing. To date no study has investigated age-related functional change in MTL substructures during specific episodic memory processes such as intra-item associative memory. The aim of this study was to characterize age-related change in the neural correlates of intra-item associative memory processing. Sixteen young and 10 older subjects participated in a compound word intra-item associative memory task comprising a measure of associative recognition memory and a measure of recognition memory. There was no difference in performance between groups on the associative memory measure but each group recruited different MTL regions while performing the task. The young group recruited the left anterior hippocampus and posterior parahippocampal gyrus whereas the older participants recruited the hippocampus bilaterally. In contrast, recognition memory was significantly worse in the older subjects. The left anterior hippocampus was recruited in the young group during successful recognition memory whereas the older group recruited a more posterior region of the left hippocampus and showed a more bilateral activation of frontal brain regions than was observed in the young group. Our results suggest a reorganization of the neural correlates of intra-item associative memory in the aging brain.
associative memory; medial temporal lobe; hippocampus; perirhinal cortex; aging
Frontotemporal dementia (FTD) is classically considered to be a neurodegenerative disease with cortical changes. Recent structural imaging findings, however, highlight that subcortical and in particular striatal regions are also affected in the FTD syndrome. The influence of striatal pathology on cognitive and behavioural changes in FTD is virtually unexplored. In the current study we employ the Weather Prediction Task (WPT), a probabilistic learning task which taps into striatal dysfunction, in a group of FTD patients. We also regressed the patients' behavioural performance with their grey matter atrophy via voxel-based morphometry (VBM) to identify the grey matter contributions to WPT performance in FTD. Based on previous studies we expected to see striatal and frontal atrophy to be involved in impaired probabilistic learning. Our behavioural results show that patients performed on a similar level to controls overall, however, there was a large variability of patient performance in the first 30 trials of the task, which are critical in the acquisition of the probabilistic learning rules. A VBM analysis covarying the performance for the first 30 trials across participants showed that atrophy in striatal but also frontal brain regions correlated with WPT performance in these trials. Closer inspection of performance across the first 30 trials revealed a subgroup of FTD patients that performed significantly poorly than the remaining patients and controls on the WPT, despite achieving the same level of probabilistic learning as the other groups in later trials. Additional VBM analyses revealed that the subgroup of FTD patients with poor early probabilistic learning in the first 30 trials showed greater striatal atrophy compared to the remaining FTD patients and controls. These findings suggest that the integrity of fronto-striatal regions is important for probabilistic learning in FTD, with striatal integrity in particular, determining the acquisition learning rate. These findings will therefore have implications for developing an easily administered version of the probabilistic learning task which can be used by clinicians to assess striatal functioning in neurodegenerative syndromes.
► Probabilistic association memory was investigated in FTD patients. ► FTD patients with slow acquisition rates showed greater striatal atrophy. ► Striatal dysfunction in FTD can be functionally assessed via such tests.
Frontotemporal dementia; Probabilistic learning; Weather Prediction Task; Striatum; Orbitofrontal cortex; Voxel-based morphometry
Based on the recent literature and collective experience, an international consortium developed revised guidelines for the diagnosis of behavioural variant frontotemporal dementia. The validation process retrospectively reviewed clinical records and compared the sensitivity of proposed and earlier criteria in a multi-site sample of patients with pathologically verified frontotemporal lobar degeneration. According to the revised criteria, ‘possible’ behavioural variant frontotemporal dementia requires three of six clinically discriminating features (disinhibition, apathy/inertia, loss of sympathy/empathy, perseverative/compulsive behaviours, hyperorality and dysexecutive neuropsychological profile). ‘Probable’ behavioural variant frontotemporal dementia adds functional disability and characteristic neuroimaging, while behavioural variant frontotemporal dementia ‘with definite frontotemporal lobar degeneration’ requires histopathological confirmation or a pathogenic mutation. Sixteen brain banks contributed cases meeting histopathological criteria for frontotemporal lobar degeneration and a clinical diagnosis of behavioural variant frontotemporal dementia, Alzheimer’s disease, dementia with Lewy bodies or vascular dementia at presentation. Cases with predominant primary progressive aphasia or extra-pyramidal syndromes were excluded. In these autopsy-confirmed cases, an experienced neurologist or psychiatrist ascertained clinical features necessary for making a diagnosis according to previous and proposed criteria at presentation. Of 137 cases where features were available for both proposed and previously established criteria, 118 (86%) met ‘possible’ criteria, and 104 (76%) met criteria for ‘probable’ behavioural variant frontotemporal dementia. In contrast, 72 cases (53%) met previously established criteria for the syndrome (P < 0.001 for comparison with ‘possible’ and ‘probable’ criteria). Patients who failed to meet revised criteria were significantly older and most had atypical presentations with marked memory impairment. In conclusion, the revised criteria for behavioural variant frontotemporal dementia improve diagnostic accuracy compared with previously established criteria in a sample with known frontotemporal lobar degeneration. Greater sensitivity of the proposed criteria may reflect the optimized diagnostic features, less restrictive exclusion features and a flexible structure that accommodates different initial clinical presentations. Future studies will be needed to establish the reliability and specificity of these revised diagnostic guidelines.
behavioural variant frontotemporal dementia; diagnostic criteria; frontotemporal lobar degeneration; FTD; pathology
It is well established that healthy aging is accompanied by structural changes in many brain regions and functional decline in a number of cognitive domains. The goal of this study was to determine 1) whether the regional distribution of age-related brain changes is similar in gray matter (GM) and white matter (WM) regions, or whether these two tissue types are affected differently by aging, and 2) whether measures of cognitive performance are more closely linked to alterations in the cerebral cortex or in the underlying WM in older adults (OA). To address these questions, we collected high-resolution MRI data from a large sample of healthy young adults (YA; aged 18–28) and OA (aged 61–86 years). In addition, the OA completed a series of tasks selected to assess cognition in three domains: cognitive control, episodic memory, and semantic memory. Using advanced techniques for measuring cortical thickness and WM integrity, we found that healthy aging was accompanied by deterioration of both GM and WM, but with distinct patterns of change: Cortical thinning occurred primarily in primary sensory and motor cortices, whereas WM changes were localized to regions underlying association cortices. Further, in OA, we found a striking pattern of region-specific correlations between measures of cognitive performance and WM integrity, but not cortical thickness. Specifically, cognitive control correlated with integrity of frontal lobe WM, whereas episodic memory was related to integrity of temporal and parietal lobe WM. Thus, age-related impairments in specific cognitive capacities may arise from degenerative processes that affect the underlying connections of their respective neural networks.
aging; white matter; cortical thickness; DTI; MRI; cognitive control processes; episodic memory
Inflammatory changes are a prominent feature of brains affected by Alzheimer's disease (AD). Activated glial cells release inflammatory cytokines which modulate the neurodegenerative process. These cytokines are encoded by genes representing several interleukins and TNFA, which are associated with AD. The gene coding for HLA-B associated transcript 1 (BAT1) lies adjacent to TNFA in the central major histocompatibility complex (MHC). BAT1, a member of the DEAD-box family of RNA helicases, appears to regulate the production of inflammatory cytokines associated with AD pathology. In the current study TNFA and BAT1 promoter polymorphisms were analysed in AD and control cases and BAT1 mRNA levels were investigated in brain tissue from AD and control cases.
Genotyping was performed for polymorphisms at positions -850 and -308 in the proximal promoter of TNFA and position -22 in the promoter of BAT1. These were investigated singly or in haplotypic association in a cohort of Australian AD patients with AD stratified on the basis of their APOE ε4 genotype. Semi-quantitative RT-PCR was also performed for BAT1 from RNA isolated from brain tissue from AD and control cases.
APOE ε4 was associated with an independent increase in risk for AD in individuals with TNFA -850*2, while carriage of BAT1 -22*2 reduced the risk for AD, independent of APOE ε4 genotype. Semi-quantitative mRNA analysis in human brain tissue showed elevated levels of BAT1 mRNA in frontal cortex of AD cases.
These findings lend support to the application of TNFA and BAT1 polymorphisms in early diagnosis or risk assessment strategies for AD and suggest a potential role for BAT1 in the regulation of inflammatory reactions in AD pathology.
Behavioral-variant frontotemporal dementia (bvFTD) is a progressive neurodegenerative brain disorder, clinically characterized by changes in cognition, personality, and behavior. Marked disturbances in eating behavior, such as overeating and preference for sweet foods, are also commonly reported. The hypothalamus plays a critical role in feeding regulation, yet the relation between pathology in this region and eating behavior in FTD is unknown. This study aimed to address this issue using 2 complementary approaches.
First, 18 early stage bvFTD patients and 16 healthy controls underwent high-resolution structural magnetic resonance imaging and assessment of eating behavior. Hypothalamic volumes were traced manually on coronal images. Second, postmortem analyses of 12 bvFTD cases and 6 matched controls were performed. Fixed hypothalamic tissue sections were stained for a cell marker and for peptides regulating feeding behaviors using immunohistochemistry. Stereological estimates of the hypothalamic volume and the number of neurons and glia were performed.
Significant atrophy of the hypothalamus in bvFTD was present in both analyses. Patients with high feeding disturbance exhibited significant atrophy of the posterior hypothalamus. Neuronal loss, which was observed only in bvFTD cases with Tar DNA protein-43 deposition, was also predominant posteriorly. In contrast, orexin (hypocretin), neuropeptide Y, cocaine- and amphetamine-regulating transcript, and vasopressin-containing neurons that regulate appetite were spared in posterior nuclei known to participate in feeding regulation.
Degeneration and consequent dysregulation within the hypothalamus relates to significant feeding disturbance in bvFTD. These findings provide a basis for the development of therapeutic models. Ann Neurol 2011
Background: Anecdotal evidence indicates that some patients with dementia exhibit novel or increased positive behaviors, such as painting or singing, after the disease onset. Due to the lack of objective measures, however, the frequency and nature of these changes has not been formally investigated.
Objective: This study aimed to systematically identify changes in these behaviors in the two most common younger-onset dementia syndromes: Alzheimer’s disease (AD) and behavioral-variant frontotemporal dementia (bvFTD).
Methods: Sixty-three caregivers of patients with dementia (32 caregivers of AD patients and 31 caregivers of bvFTD patients) participated in the study. Caregivers rated the presence and frequency of positive and negative behavior changes after the onset of dementia using the Hypersensory and Social/Emotional Scale (HSS) questionnaire, focusing on three domains: sensory processing, cognitive skills, and social/emotional processing. Six composites scores were obtained reflecting these three domains (two composite scores for each domain). Differences across scores and ratios of increased and decreased behaviors were analyzed between AD and bvFTD, at different disease severity levels.
Results: After disease onset, significant changes in the sensory processing domain were observed across disease severity levels, particularly in AD. Composite scores of the other domains did not change significantly. Importantly, however, some novel or increased positive behaviors were present in between 10% (Music activities) and 70% (Hypersensitivity) of AD and bvFTD patients, regardless of disease severity.
Conclusions: We provide the first systematic investigation of positive behaviors in AD and bvFTD. The newly developed HSS questionnaire is a valid measure to characterize changes and progression of positive behaviors in patients with dementia.
Alzheimer’s disease; behavioral symptoms; caregivers; factor analysis; frontotemporal dementia; progression; questionnaire development