Reduced phonemic fluency in progressive supranuclear palsy is due to dysfunction of dominant BA6

Background

Reduced phonemic fluency is extremely frequent in progressive supranuclear palsy (PSP), but its neural correlate is yet to be defined.

Objective

We explored the hypothesis that poor fluency in PSP might be due to neurodegeneration within a dominant frontal circuit known to be involved in speech fluency, including the opercular area, the superior frontal cortex (BA6), and the frontal aslant tract connecting these two regions.

Methods

We correlated performance on a letter fluency task (F, A, and S, 60 s for each letter) with brain metabolism as measured with Fluoro-deoxy-glucose Positron Emission Tomography, using Statistical Parametric Mapping, in 31 patients with PSP.

Results

Reduced letter fluency was associated with significant hypometabolism at the level of left BA6.

Conclusion

Our finding is the first evidence that in PSP, as in other neurogical disorders, poor self-initiated, effortful verbal retrieval appears to be linked to dysfunction of the dominant opercular-aslant-BA6 circuit.

Morphology and Spatial Probability Maps of the Horizontal Ascending Ramus of the Lateral Fissure

The horizontal ascending ramus of the lateral fissure (half) is a characteristic sulcus of the ventrolateral frontal cortex that forms the morphological boundary between the pars triangularis and the pars orbitalis of the inferior frontal gyrus. The present study examined the morphology of this sulcus to provide a means of identifying it accurately with magnetic resonance imaging (MRI). Voxels within the half were labeled in 50 in vivo MRI volumes (1.5 T) that had been linearly registered to the Montreal Neurological Institute stereotaxic space and the morphology of the half was categorized based on relations with neighboring sulci. The spatial variability and extent of the half were then quantified across subjects using volumetric (MINC Toolkit) and surface (FreeSurfer) spatial probability maps. The half could be identified in 95% of hemispheres, and the main morphological patterns were classified into three categories: Types I, II, and III. There were no statistically significant interhemispheric differences in the frequency of the half or its morphological patterns. Understanding the details of the sulcal morphology of this ventrolateral region is critical for an accurate interpretation of the location of activation peaks generated in functional neuroimaging studies investigating language, working memory, and other cognitive processes.

Beyond language impairment: Profiles of apathy in primary progressive aphasia

Primary progressive aphasia (PPA) is characterised by predominant language and communication impairment. However, behavioural changes, such as apathy, are increasingly recognised. Apathy is defined as a reduction in motivation and goal-directed behaviour. Recent theoretical models have suggested that apathy can be delineated into multiple dimensions: executive apathy (i.e., deficits in maintaining goals and organisation), emotional apathy (i.e., emotional blunting and indifference) and initiation apathy (i.e., reduced self-initiation). Whether the nature of apathy differs between clinical variants of PPA, and across early and late disease stages, remains to be established. Here, carers/informants of 20 semantic variant PPA (svPPA), 15 non-fluent variant PPA (nfvPPA), 16 logopenic variant PPA (lvPPA) and 25 healthy older controls completed the Dimensional Apathy Scale to quantify executive, emotional and initiation apathy. Voxel-based morphometry was used to identify associations between dimensions of apathy and regions of grey matter intensity decrease. Our behavioural results showed greater executive and initiation apathy in late svPPA than in late nfvPPA patients, while late svPPA had greater emotional apathy than both late nfvPPA and late lvPPA groups. Executive and initiation apathy were significantly higher than premorbid levels in all PPA subtypes, while elevated emotional apathy was only seen in early and late svPPA. Distinct neural correlates were identified across apathy dimensions. Executive apathy correlated with grey matter intensity of the left dorsolateral prefrontal and inferior parietal cortices; emotional apathy with the left medial prefrontal, insular and cerebellar regions; and initiation apathy with right parietal areas. Our findings are the first to reveal evidence of the dimensional nature of apathy in PPA, with different clinical signatures observed for each subtype. From a clinical standpoint, these results will inform the development of targeted interventions for specific aspects of apathy which emerge in PPA.

Cognitive control of orofacial motor and vocal responses in the ventrolateral and dorsomedial human frontal cortex

In the primate brain, a set of areas in the ventrolateral frontal (VLF) cortex and the dorsomedial frontal (DMF) cortex appear to control vocalizations. The basic role of this network in the human brain and how it may have evolved to enable complex speech remain unknown. In the present functional neuroimaging study of the human brain, a multidomain protocol was utilized to investigate the roles of the various areas that comprise the VLF-DMF network in learning rule-based cognitive selections between different types of motor actions: manual, orofacial, nonspeech vocal, and speech vocal actions. Ventrolateral area 44 (a key component of the Broca's language production region in the human brain) is involved in the cognitive selection of orofacial, as well as, speech and nonspeech vocal responses; and the midcingulate cortex is involved in the analysis of speech and nonspeech vocal feedback driving adaptation of these responses. By contrast, the cognitive selection of speech vocal information requires this former network and the additional recruitment of area 45 and the presupplementary motor area. We propose that the basic function expressed by the VLF-DMF network is to exert cognitive control of orofacial and vocal acts and, in the language dominant hemisphere of the human brain, has been adapted to serve higher speech function. These results pave the way to understand the potential changes that could have occurred in this network across primate evolution to enable speech production.

Neurovascular unit dysregulation, white matter disease, and executive dysfunction: the shared triad of vascular cognitive impairment and Alzheimer disease

Executive dysfunction is the most important predictor for loss of independence in dementia. As executive function involves the coordination of distributed cerebral functions, executive function requires healthy white matter. However, white matter is highly vulnerable to cerebrovascular insults, with executive dysfunction being a core feature of vascular cognitive impairment (VCI). At the same time, cerebrovascular pathology, white matter disease, and executive dysfunction are all increasingly recognized as features of Alzheimer disease (AD). Recent studies have characterized the crucial role of glial cells in the pathological changes observed in both VCI and AD. In comorbid VCI and AD, the glial cells of the neurovascular unit (NVU) emerge as important therapeutic targets for the preservation of white matter integrity and executive function. Our synthesis from current research identifies dysregulation of the NVU, white matter disease, and executive dysfunction as a fundamental triad that is common to both VCI and AD. Further study of this triad will be critical for advancing the prevention and management of dementia.

Beyond a rod through the skull: A systematic review of lesion studies of the human ventromedial frontal lobe

Neuropsychological studies from the past century have associated damage to the ventromedial frontal lobes (VMF) with impairments in a variety of domains, including memory, executive function, emotion, social cognition, and valuation. A central question in the literature is whether these seemingly distinct functions are subserved by different sub-regions within the VMF, or whether VMF supports a broader cognitive process that is crucial to these varied domains. In this comprehensive review of the neuropsychological literature from the last two decades, we present a qualitative synthesis of 184 papers that have examined the psychological impairments that result from VMF damage. We discuss these findings in the context of several theoretical frameworks and advocate for the view that VMF is critical for the formation and representation of schema and cognitive maps.

Exploration Deficits Under Ecological Conditions as a Marker of Apathy in Frontotemporal Dementia

Apathy is one of the six clinical criteria for the behavioral variant of frontotemporal dementia (bvFTD), and it is almost universal in this disease. Although its consequences in everyday life are debilitating, its underlying mechanisms are poorly known, its assessment is biased by subjectivity and its care management is very limited. In this context, we have developed "ECOCAPTURE," a method aimed at providing quantifiable and objective signature(s) of apathy in order to assess it and identify its precise underlying mechanisms. ECOCAPTURE consists of the observation and recording of the patient's behavior when the participant is being submitted to a multiple-phase scenario reproducing a brief real-life situation. It is performed in a functional exploration platform transformed into a fully furnished waiting room equipped with a video and sensor-based data acquisition system. This multimodal method allowed video-based behavior analyses according to predefined behavioral categories (exploration behavior, sustained activities or inactivity) and actigraphy analyses from a 3D accelerometer. The data obtained were also correlated with behavioral/cognitive tests and scales assessing global cognitive efficiency, apathy, cognitive disinhibition, frontal syndrome, depression and anxiety. Here, bvFTD patients (n = 14) were compared to healthy participants (n = 14) during the very first minutes of the scenario, when the participants discovered the room and were encouraged to explore it. We showed that, in the context of facing a new environment, healthy participants first explored it and then engaged in sustained activities. By contrast, bvFTD patients were mostly inactive and eventually explored this new place, but in a more irregular and less efficient mode than normal subjects. This exploration deficit was correlated with apathy, disinhibition and cognitive and behavioral dysexecutive syndromes. These findings led us to discuss the presumed underlying mechanisms responsible for the exploration deficit (an inability to self-initiate actions, to integrate reward valuation and to inhibit involuntary behavior). Altogether, these results pave the way for simple and objective assessment of behavioral changes that represents a critical step for the evaluation of disease progression and efficacy of treatment in bvFTD.

Apathy: a neurocircuitry model based on frontotemporal dementia

Apathy is a symptom shared among many neurological and psychiatric disorders. However, the underlying neurocircuitry remains incompletely understood. Apathy is one of the core features of behavioural variant frontotemporal dementia (bvFTD), a neurodegenerative disease presenting with heterogeneous combinations of socioaffective symptoms and executive dysfunction. We reviewed all neuroimaging studies of apathy in frontotemporal dementia (FTD) attempting to refine a neurocircuitry model and inform clinical definitions. Levels of apathy have been consistently shown to correlate with the severity of executive dysfunctions across a wide range of diseases, including FTD. Some authors view 'energisation'-the loss of which is central in apathy-as a core executive function. Apathy in FTD is most robustly associated with atrophy, hypometabolism and/or hypoperfusion in the dorsolateral prefrontal cortex, the anterior and middle cingulate cortex, the orbitofrontal cortex and the medial and ventromedial superior frontal gyri. Data also suggest that abnormalities in connecting white matter pathways and functionally connected more posterior cortical areas could contribute to apathy. There is a lack of consistency across studies due to small samples, lenient statistical thresholds, variable measurement scales and the focus on apathy as a unitary concept. Integrating findings across studies, we revise a neurocircuitry model of apathy divided along three subcomponents (cognition/planning, initiation, emotional-affective/motivation) with specific neuroanatomical and cognitive substrates. To increase consistency in clinical practice, a recommendation is made to modify the bvFTD diagnostic criteria of apathy/inertia. More generally, we argue that bvFTD constitutes a disease model to study the neurocircuitry of complex behaviours as a 'lesion-based' approach to neuropsychiatric symptoms observed across diagnostic categories.

Comparison of animal, action and phonemic fluency in aphasia

BACKGROUND

The ability to generate words that follow certain constraints, or verbal fluency, is a sensitive indicator of neurocognitive impairment, and is impacted by a variety of variables.

AIMS

To investigate the effect of post-stroke aphasia, elicitation category and linguistic variables on verbal fluency performance.

METHODS & PROCEDURES

Twenty-eight persons with aphasia (PWA) with a single left-hemisphere lesion and 40 age-matched neurotypical community-dwelling adults were administered three verbal fluency tasks: two semantic (animals and actions) and one phonemic (the letters F, A and S). Data analysis included comparison of total scores, clusters and perseverations. Individual responses were coded for frequency of occurrence, age of acquisition and syllable length to investigate qualitative differences in word generation.

OUTCOMES & RESULTS

PWA performed worse than neurotypical participants across all verbal fluency tasks, and animal fluency scores were farthest from neurotypical performance. PWAs' animal and action fluency were correlated with other language measures, while phonemic fluency was uncorrelated with language measures. While some PWAs showed dissociations between verbal fluency tasks, the dissociations did not pattern along with aphasia fluency. PWAs produced fewer clusters and responses with higher word frequency across all three verbal fluency tasks. Responses had earlier age of acquisition and shorter word length for animal and phonemic fluency, but not action fluency.

CONCLUSIONS & IMPLICATIONS

Verbal fluency, particularly animal fluency, is sensitive to even mild aphasia. PWA produced lexically simpler responses than their neurotypical peers. This study identifies the relevance of qualitative analysis of verbal fluency responses.

The frontal assessment battery in clinical practice: a systematic review

BACKGROUND

The frontal assessment battery (FAB) is a brief tool designed to evaluate executive function. Some studies have particularly focused on assessing its applicability addressing two issues: first, on detecting the brain regions responsible for the FAB performance, and second, on determining its capability for differential diagnosis. Our aim was to summarize and analyze critically the studies that assessed the neuroanatomical correspondence and the differential diagnostic value of the FAB in several study populations suffering from different pathologies.

METHODS

We completed a literature search in MEDLINE (via PubMed) database by using the term "frontal assessment battery" and the combination of this term with "applicability" or "use" or "usefulness". The search was limited to articles in English or Spanish languages, published between 1 September 2000 and 30 September 2016, human studies, and journal articles.

RESULTS

A total of 32 studies met inclusion criteria. Seventeen studies were aimed at identifying the brain regions or the neural substrates involved in executive functions measured by the FAB and 15 studies at verifying that the FAB was an appropriate tool for the differential diagnosis in neurological diseases.

CONCLUSION

Our study showed that the FAB may be an adequate assessment tool for executive function and may provide useful information for differential diagnosis in several diseases. Given that the FAB takes short time and is easy to administer, its usage may be of great interest as part of a full neuropsychological assessment in clinical settings. Copyright © 2017 John Wiley & Sons, Ltd.

Disrupted Intrinsic Local Synchronization in Poststroke Aphasia

Evidence has accumulated from the task-related and task-free (i.e., resting state) studies that alternations of intrinsic neural networks exist in poststroke aphasia (PSA) patients. However, information is lacking on the changes in the local synchronization of spontaneous functional magnetic resonance imaging blood-oxygen level-dependent fluctuations in PSA at rest. We investigated the altered intrinsic local synchronization using regional homogeneity (ReHo) on PSA (n = 17) and age- and sex-matched healthy controls (HCs) (n = 20). We examined the correlations between the abnormal ReHo values and the aphasia severity and language performance in PSA. Compared with HCs, the PSA patients exhibited decreased intrinsic local synchronization in the right lingual gyrus, the left calcarine, the left cuneus, the left superior frontal gyrus (SFG), and the left medial of SFG. The local synchronization (ReHo value) in the left medial of SFG was positively correlated with aphasia severity (r = 0.55, P = 0.027) and the naming scores of Aphasia Battery of Chinese (r = 0.66, P = 0.005). This result is consistent with the important role of this value in language processing even in the resting state. The pathogenesis of PSA may be attributed to abnormal intrinsic local synchronous in multiple brain regions.

Ventrolateral and dorsomedial frontal cortex lesions impair mnemonic context retrieval

The prefrontal cortex appears to contribute to the mnemonic retrieval of the context within which stimuli are experienced, but only under certain conditions that remain to be clarified. Patients with lesions to the frontal cortex, the temporal lobe and neurologically intact individuals were tested for context memory retrieval when verbal stimuli (words) had been experienced across multiple (unstable context condition) or unique (stable context condition) contexts; basic recognition memory of these words-in-contexts was also tested. Patients with lesions to the right ventrolateral prefrontal cortex (VLPFC) were impaired on context retrieval only when the words had been seen in multiple contexts, demonstrating that this prefrontal region is critical for active retrieval processing necessary to disambiguate memory items embedded across multiple contexts. Patients with lesions to the left dorsomedial prefrontal region were impaired on both context retrieval conditions, regardless of the stability of the stimulus-to-context associations. Conversely, prefrontal lesions sparing the ventrolateral and dorsomedial regions did not impair context retrieval. Only patients with temporal lobe excisions were impaired on basic recognition memory. The results demonstrate a basic contribution of the left dorsomedial frontal region to mnemonic context retrieval, with the VLPFC engaged, selectively, when contextual relations are unstable and require disambiguation.

Utilization behavior after lesions restricted to the frontal cortex

Utilization behavior, which refers to the tendency of patients to use objects presented to them out of context and in the absence of instructions to use them, has been ascribed to dysfunction of the frontal cortex. However, careful examination of the reports of patients presenting utilization behavior shows that these patients had sustained widespread cerebral lesions extending beyond the frontal cortex and often involving massive subcortical damage. The present study examined whether utilization behavior can be observed in patients with lesions restricted to the prefrontal cortex and no more than the immediately subjacent white matter. All patients had surgical excisions, except for three patients in the frontal group who had sustained a cerebrovascular accident. A group of patients with excisions in the temporal lobe and a group of healthy participants were also studied for comparison. The investigation of utilization behavior took place in the context of a broader neuropsychological examination. There was no difference in the presence of utilization behavior in patients with lesions restricted to the prefrontal cortex in comparison with patients with temporal lobe lesions and carefully matched neurologically intact individuals. The results suggest that, in previous studies, the exhibition of utilization behavior by patients with extensive damage to the anterior part of the brain may have been due to damage to subcortical structures or to the prefrontal cortex in conjunction with subcortical damage.