Neural basis of motivational approach and withdrawal behaviors in neurodegenerative disease

Structural and functional correlates of olfactory reward processing in behavioral variant frontotemporal dementia

The behavioral variant of frontotemporal dementia (bvFTD) includes symptoms that reflect altered pursuit of rewards, including food, alcohol, and money. Little is known, however, about how these reward changes relate to atrophy and functional connectivity within reward-related regions. The goal of this study was to examine the structural and functional correlates of valence perception for olfactory rewards in 24 patients with bvFTD. Regression analysis of resting-state brain functional connectivity indicated that more positive valence ratings of olfactory stimuli were predicted by ventral pallidum connectivity to other reward circuit regions, particularly functional connectivity between ventral pallidum and bilateral anterior cingulate cortex/ventromedial prefrontal cortex. Structural analysis showed that atrophy of the anterior cingulate cortex was also significantly associated with perceiving stimuli as more rewarding. Finally, there was a significant interaction between ventral pallidum connectivity and atrophy of the anterior cingulate cortex. More specifically, the ventral pallidum connectivity had a greater effect on the positive perception of olfactory stimuli in the setting of low anterior cingulate cortex volume. These findings indicate that atrophy and functional connectivity within reward-relevant regions exert independent and interacting effects on the perception of pleasantness in bvFTD, potentially due to changes in hedonic "liking" signals.

Social Dysfunction and Apathy: Transdiagnostic Domains in Late-Life Cognitive Disorders

Social dysfunction is a maladaptive process of coping, problem solving, and achieving one's goals. A new definition of apathy was cross-linked to social dysfunction, with a reduced goal-directed behavior and social interaction as a separate dimension. We hypothesized that these two neuropsychiatric symptoms may be included in the mild behavioral impairment diagnostic framework, operationalizing and standardizing late-life neuropsychiatric symptom assessment, to improve risk determination of dementia. Social dysfunction and apathy were transdiagnostic and prodromic for late-life cognitive disorders. A transdiagnostic approach could provide a useful mean for a better understanding of apathy and related conditions such as social behavior.

Awareness impairment in Alzheimer's disease and frontotemporal dementia: a systematic MRI review

This review aims to define awareness impairment and related disturbances in neurodegenerative diseases, including Alzheimer's disease (AD) and frontotemporal lobar degeneration (FTLD) spectrum of disorders. An update of the available scientific literature on the use of magnetic resonance imaging (MRI) in the study of awareness in these disorders is also offered. MRI plays an important role in the characterization of neurodegenerative signatures and can increase our knowledge on brain structural and functional correlates of awareness. In the reviewing process, we established a-priori criteria and we searched the scientific literature for relevant articles on this topic. In summary, we selected 36 articles out of 1340 publications retrieved from PubMed. Based on this selection, this review discusses the multiple terms used to define different or overlapping aspects of awareness impairment, and specifically summarizes recent application of MRI for investigating anosognosia, social cognition, including theory of mind and emotional processing, free will, and autonoetic awareness alterations in different neurodegenerative disorders, with most of these studies focused on AD and FTLD. This systematic review highlights the importance of awareness impairment and related domains in neurodegenerative disorders, especially in AD and FTLD, and it outlines MRI structural and functional correlates in these populations.

White matter tracts alterations underpinning reward and conflict processing

BACKGROUND

Reinforcement sensitivity theory (RST) is proposed as a neurobiological system that eventually led to emotion and motivation-based constructs of personality. Traditionally segmented into the behavioral activation system (BAS) and the behavioral inhibition system (BIS), RST is commonly used to describe personality and behavior. Although there have been studies linking gray matter alterations with BIS/BAS subscales, the role of white matter (WM) alterations is yet controversial. We aimed to investigate the specific WM tracts associated with BIS/BAS scores.

METHODS

220 healthy participants (mean age = 39.14 ± 20.23, 80 (35.7 %) females) were evaluated using the BIS/BAS questionnaire from the LEMON database. Diffusion MRI connectometry (DMRI) was used to investigate the WM correlates of BIS/BAS subscales in each gender group. Multiple regression models with the covariates of age, handedness, and education were fitted to address the correlation of local connectomes with BIS/BAS components.

RESULTS

DMRI connectometry revealed that the quantitative anisotropy (QA) value of the splenium of the corpus callosum, right cerebellum, middle cerebellar peduncle, and superior cerebellar peduncle, had a significant negative correlation with each BIS/BAS subscale. In contrast, the QA value in the body of the corpus callosum and bilateral cingulum showed a positive correlation with BIS/BAS subscales.

CONCLUSION

The connectivity of WM in certain tracts may contribute to behavioral activation and inhibition. This finding expands the findings on the neural networks associated with risk-taking and reward-seeking behaviors.

Effort avoidance as a core mechanism of apathy in frontotemporal dementia

Apathy is a core symptom in patients with behavioural variant frontotemporal dementia (bvFTD). It is defined by the observable reduction in goal-directed behaviour, but the underlying mechanisms are poorly understood. According to decision theory, engagement in goal-directed behaviour depends on a cost-benefit optimization trading off the estimated effort (related to the behaviour) against the expected reward (related to the goal). In this framework, apathy would thus result from either a decreased appetence for reward, or from an increased aversion to effort. Here, we phenotyped the motivational state of 21 patients with bvFTD and 40 matched healthy controls using computational analyses of behavioural responses in a comprehensive series of behavioural tasks, involving both expression of preference (comparing reward value and effort cost) and optimization of performance (adjusting effort production to the reward at stake). The primary finding was an elevated aversion to effort, consistent across preference and performance tasks in patients with bvFTD compared to controls. Within the bvFTD group, effort avoidance was correlated to cortical atrophy in the dorsal anterior cingulate cortex and to apathy score measured on a clinical scale. Thus, our results highlight elevated effort aversion (not reduced reward appetence) as a core dysfunction that might generate apathy in patients with bvFTD. More broadly, they provide novel behavioural tests and computational tools to identify the dysfunctional mechanisms producing motivation deficits in patients with brain damage.

The architecture of abnormal reward behaviour in dementia: multimodal hedonic phenotypes and brain substrate

Abnormal reward processing is a hallmark of neurodegenerative diseases, most strikingly in frontotemporal dementia. However, the phenotypic repertoire and neuroanatomical substrates of abnormal reward behaviour in these diseases remain incompletely characterized and poorly understood. Here we addressed these issues in a large, intensively phenotyped patient cohort representing all major syndromes of sporadic frontotemporal dementia and Alzheimer's disease. We studied 27 patients with behavioural variant frontotemporal dementia, 58 with primary progressive aphasia (22 semantic variant, 24 non-fluent/agrammatic variant and 12 logopenic) and 34 with typical amnestic Alzheimer's disease, in relation to 42 healthy older individuals. Changes in behavioural responsiveness were assessed for canonical primary rewards (appetite, sweet tooth, sexual activity) and non-primary rewards (music, religion, art, colours), using a semi-structured survey completed by patients' primary caregivers. Changes in more general socio-emotional behaviours were also recorded. We applied multiple correspondence analysis and k-means clustering to map relationships between hedonic domains and extract core factors defining aberrant hedonic phenotypes. Neuroanatomical associations were assessed using voxel-based morphometry of brain MRI images across the combined patient cohort. Altered (increased and/or decreased) reward responsiveness was exhibited by most patients in the behavioural and semantic variants of frontotemporal dementia and around two-thirds of patients in other dementia groups, significantly (P < 0.05) more frequently than in healthy controls. While food-directed changes were most prevalent across the patient cohort, behavioural changes directed toward non-primary rewards occurred significantly more frequently (P < 0.05) in the behavioural and semantic variants of frontotemporal dementia than in other patient groups. Hedonic behavioural changes across the patient cohort were underpinned by two principal factors: a 'gating' factor determining the emergence of altered reward behaviour and a 'modulatory' factor determining how that behaviour is directed. These factors were expressed jointly in a set of four core, trans-diagnostic and multimodal hedonic phenotypes: 'reward-seeking', 'reward-restricted', 'eating-predominant' and 'control-like'-variably represented across the cohort and associated with more pervasive socio-emotional behavioural abnormalities. The principal gating factor was associated (P < 0.05 after correction for multiple voxel-wise comparisons over the whole brain) with a common profile of grey matter atrophy in anterior cingulate, bilateral temporal poles, right middle frontal and fusiform gyri: the cortical circuitry that mediates behavioural salience and semantic and affective appraisal of sensory stimuli. Our findings define a multi-domain phenotypic architecture for aberrant reward behaviours in major dementias, with novel implications for the neurobiological understanding and clinical management of these diseases.

Frontotemporal dementia: A unique window on the functional role of the temporal lobes

Frontotemporal dementia (FTD) is an umbrella term covering a plethora of progressive changes in executive functions, motor abilities, behavior, and/or language. Different clinical syndromes have been described in relation to localized atrophy, informing on the functional networks that underlie these specific cognitive, emotional, and behavioral processes. These functional declines are linked with the underlying neurodegeneration of frontal and/or temporal lobes due to diverse molecular pathologies. Initially, the accumulation of misfolded proteins targets specifically susceptible cell assemblies, leading to relatively focal neurodegeneration that later spreads throughout large-scale cortical networks. Here, we discuss the most recent clinical, neuropathological, imaging, and genetics findings in FTD-spectrum syndromes affecting the temporal lobe. We focus on the semantic variant of primary progressive aphasia and its mirror image, the right temporal variant of FTD. Incipient focal atrophy of the left anterior temporal lobe (ATL) manifests with predominant naming, word comprehension, reading, and object semantic deficits, while cases of predominantly right ATL atrophy present with impairments of socioemotional, nonverbal semantic, and person-specific knowledge. Overall, the observations in FTD allow for crucial clinical-anatomic inferences, shedding light on the role of the temporal lobes in both cognition and complex behaviors. The concerted activity of both ATLs is critical to ensure that percepts are translated into concepts, yet important hemispheric differences should be acknowledged. On one hand, the left ATL attributes meaning to linguistic, external stimuli, thus supporting goal-oriented, action-related behaviors (e.g., integrating sounds and letters into words). On the other hand, the right ATL assigns meaning to emotional, visceral stimuli, thus guiding socially relevant behaviors (e.g., integrating body sensations into feelings of familiarity).

Sex Differences in the Behavioral Inhibition System and Ventromedial Prefrontal Cortex Connectivity

The reinforcement sensitivity theory proposes brain–behavioral systems that underlie individual differences in sensitivity to punishment and reward. Such trait sensitivity is assessed using the behavioral inhibition/activation system (BIS/BAS) scales. Recent studies have reported sex-linked neuroanatomical correlates of the BIS/BAS, especially in the regions belonging to the valuation and salience networks that are associated with the representation of subjective value (SV), whereas less effort has been focused on investigating the neurofunctional aspects associated with sex differences in the BIS/BAS. We tested whether functional connectivity (FC) of the regions associated with the representation of SV mediates the relationship between sex and BIS sensitivity in healthy young adults by using resting-state functional magnetic resonance imaging data and self-reported BIS/BAS measures. Compared with males, females had heightened BIS sensitivity and increased FC between the ventromedial prefrontal cortex (vmPFC) seed and posterior parietal areas; this FC mediated the impact of sex on BIS sensitivity. Given that the observed vmPFC FC maps are considered part of the default-mode network, which is involved in ruminative processes, and that the BIS is associated with rumination and negative affect, our results may have implications for psychiatric disorders such as depression and anxiety, both of which have high incidence in females.

Social Behavior Observer Checklist: Patterns of Spontaneous Behaviors Differentiate Patients With Neurodegenerative Disease From Healthy Older Adults

Neurodegenerative disease syndromes often affect personality and interpersonal behavior in addition to cognition, but there are few structured observational measures of altered social demeanor validated for this population. We developed the Social Behavior Observer Checklist (SBOCL), a 3-min checklist tool, to facilitate identification of patterns of interpersonal behavior that are diagnostically relevant to different neurodegenerative syndromes. Research assistants without formal clinical training in dementia used the SBOCL to describe participants' behavior, including 125 healthy older adults and 357 patients diagnosed with one of five neurodegenerative disease syndromes: 135 behavioral variant frontotemporal dementia (bvFTD), 57 semantic variant primary progressive aphasia (svPPA), 51 non-fluent variant PPA (nfvPPA), 65 progressive supranuclear palsy (PSP), and 49 amyloid-positive Alzheimer's disease syndrome (AD), all of whom had concurrent 3D T1 MRI scans available for voxel-based morphometry analysis. SBOCL item interrater reliability ranged from moderate to very high, and score elevations showed syndrome-specific patterns. Subscale scores derived from a degree*frequency product of the items had excellent positive predictive value for identifying patients. Specifically, scores above 2 on the Disorganized subscale, and above 3 on the Reactive and Insensitive subscales, were not seen in any healthy controls but were found in many patients with bvFTD, svPPA, nfvPPA, PSP, and AD syndromes. Both the Disorganized and Reactive subscale scores showed significant linear relationships with frontal and temporal gray matter volume that generalized across syndromes. With these initial psychometric characteristics, the SBOCL may be a useful measure to help non-experts identify patients who are appropriate for additional specialized dementia evaluation, without adding time to patient encounters or requiring the presence of an informant.

The Relationship Between Anxiety and Alzheimer's Disease

Although Alzheimer’s disease (AD) is primarily a neurocognitive disorder, it also results in prominent neuropsychiatric symptoms (NPS). Much literature has investigated the NPS of apathy and depression in association with AD, but relatively less is known regarding anxiety, the third most common NPS in this disorder. The prevalence of anxiety symptoms in AD is about 40%, and it can be a prelude of AD. Anxiety can be especially present among patients with mild cognitive impairment, mild dementia, or early-onset forms of the disease, and can promote progression or conversion to Alzheimer’s clinical syndrome. A number of studies have established that anxiety is associated with positive amyloid scans, mesial temporal changes with atrophy and hypometabolism in the entorhinal region, and neurofibrillary tangles present on pathological examination of this region. In addition to psychosocial factors, proposed neurobiological mechanisms for increased anxiety in AD include decreased sensorimotor gating, relatively increased activation of amygdalae or the Salience Network, and the presence of comorbid pathology, particularly Lewy bodies. Having management strategies for anxiety in patients with AD is important as anxiety can worsen cognitive deficits. Interventions involve psychological support, behavioral management, and the judicious use of the psychiatric armamentarium of medications.

Degenerative dementias: Alterations of emotions and mood disorders

Degenerative dementias such as Alzheimer's disease and frontotemporal dementia result in distinct alterations in emotional processing, emotional experiences, and mood. The neuropathology of these dementias extends to structures involved in emotional processing, including the basolateral limbic network (orbitofrontal cortex, anterior temporal lobe, amygdala, and thalamus), the insula, and ventromedial frontal lobe. Depression is the most common emotion and mood disorder affecting patients with Alzheimer's disease. The onset of depression can be a prodromal sign of this dementia. Anxiety can also be present early in the course of Alzheimer's disease and especially among patients with early-onset forms of the disease. In contrast, patients with behavioral variant frontotemporal dementia demonstrate hypoemotionality, deficits in the recognition of emotion, and decreased psychophysiological reactivity to emotional stimuli. They typically have a disproportionate impairment in emotional and cognitive empathy. One other unique feature of behavioral variant frontotemporal dementia is the frequent occurrence of bipolar disorder. The management strategies for these alterations of emotion and mood in degenerative dementias primarily involve the judicious use of the psychiatric armamentarium of medications.

Motivational Sensitivities Linked to Impulsive Motor Errors in Parkinson's Disease

OBJECTIVES

We investigated how broad motivational tendencies are related to the expression and suppression of action impulses in Parkinson's disease (PD).

METHODS

Sixty-nine participants with PD completed a Simon response conflict task and Behavioral Inhibition System (BIS) and Behavioral Activation System (BAS) scales based on Gray's (1987) reinforcement sensitivity theory. Analyses determined relationships between BIS, BAS, and the susceptibility to making impulsive action errors and the proficiency of inhibiting interference from action impulses.

RESULTS

BIS scores correlated positively with rates of impulsive action errors, indicating that participants endorsing low BIS tendencies were much more susceptible to acting on strong motor impulses. Analyses of subgroups with high versus low BIS scores confirmed this pattern and ruled out alternative explanations in terms of group differences in speed-accuracy tradeoffs. None of the scores on the BIS or BAS scales correlated with reactive inhibitory control.

CONCLUSIONS

PD participants who endorse diminished predilection toward monitoring and avoiding aversive experiences (low BIS) show much greater difficulty restraining fast, impulsive motor errors. Establishing relationships between motivational sensitivities and cognitive control processes may have important implications for treatment strategies and positive health outcomes in participants with PD, particularly those at risk for falling and driving difficulties related to impulsive reactions. (JINS, 2018, 24, 128-138).

Reward deficits in behavioural variant frontotemporal dementia include insensitivity to negative stimuli

During reward processing individuals weigh positive and negative features of a stimulus to determine whether they will pursue or avoid it. Though patients with behavioural variant frontotemporal dementia display changes in their pursuit of rewards, such as food, alcohol, money, and sex, the basis for these shifts is not clearly established. In particular, it is unknown whether patients' behaviour results from excessive focus on rewards, insensitivity to punishment, or to dysfunction in a particular stage of reward processing, such as anticipation, consumption, or action selection. Our goal was to determine the nature of the reward deficit in behavioural variant frontotemporal dementia and its underlying anatomy. We devised a series of tasks involving pleasant, unpleasant, and neutral olfactory stimuli, designed to separate distinct phases of reward processing. In a group of 25 patients with behavioural variant frontotemporal dementia and 21 control subjects, diagnosis by valence interactions revealed that patients with behavioural variant frontotemporal dementia rated unpleasant odours as less aversive than did controls and displayed lower skin conductance responses when anticipating an upcoming aversive odour. Subjective pleasantness ratings and skin conductance responses did not differ between behavioural variant frontotemporal dementia and controls for pleasant or neutral smells. In a task designed to measure the effort subjects would expend to smell or avoid smelling a stimulus, patients with behavioural variant frontotemporal dementia were less motivated, and therefore less successful than control subjects, at avoiding what they preferred not to smell, but had equivalent success at obtaining stimuli they found rewarding. Voxel-based morphometry of patients with behavioural variant frontotemporal dementia revealed that the inability to subjectively differentiate the valence of pleasant and unpleasant odours correlated with atrophy in right ventral mid-insula and right amygdala. High pleasantness ratings of unpleasant stimuli correlated with left dorsal anterior insula and frontal pole atrophy. These findings indicate that insensitivity to negative information may be a key component of the reward-seeking behaviours in behavioural variant frontotemporal dementia, and may relate to degeneration of structures that are involved in representing the emotional salience of sensory information.

Anatomical brain difference of subthreshold depression in young and middle-aged individuals

BACKGROUND

Subthreshold depression (StD) is associated with substantial functional impairments due to depressive symptoms that do not fully meet the diagnosis of major depressive disorder (MDD). Its high incidence in the general population and debilitating symptoms has recently put it at the forefront of mood disorder research.

AIM

In this study we investigated common volumetric brain changes in both young and middle-aged StD patients.

METHODS

Two cohorts of StD patients, young and middle-aged, (n = 57) and matched controls (n = 76) underwent voxel-based morphometry (VBM).

RESULTS

VBM analysis found that: 1) compared with healthy controls, StD patients showed decreased gray matter volume (GMV) in the bilateral globus pallidus and precentral gyrus, as well as increased GMV in the left thalamus and right rostral anterior cingulate cortex/medial prefrontal cortex; 2) there is a significant association between Center for Epidemiological Studies Depression Scale scores and the bilateral globus pallidus (negative) and left thalamus (positive); 3) there is no interaction between age (young vs. middle-age) and group (StD vs. controls).

CONCLUSIONS

Our findings indicate significant VBM brain changes in both young and middle-aged individuals with StD. Individuals with StD, regardless of age, may share common neural characteristics.

Apathy in Frontotemporal Degeneration: Neuroanatomical Evidence of Impaired Goal-directed Behavior

Background: Apathy, the major manifestation of impaired goal-directed behavior (GDB), is the most common neuropsychiatric syndrome associated with behavioral variant frontotemporal degeneration (bvFTD). The behavioral and biological mechanisms of apathy, however, are not well understood. We hypothesized that GDB has multiple components—including at least initiation, planning and motivation—and that GDB is supported by a network of multiple frontal brain regions. In this study, we examined this hypothesis by evaluating the selective breakdown of GDB in bvFTD, and relating these deficits to gray matter (GM) atrophy and white matter (WM) integrity.

Methods: Eighteen apathetic bvFTD participants and 17 healthy controls completed the Philadelphia Apathy Computerized Test (PACT). This test quantifies each of three components of GDB hypothesized to contribute to apathy. We then used regression analyses to relate PACT scores to GM atrophy and reduced white matter (WM) fractional anisotropy (FA) in bvFTD.

Results: Compared to controls, bvFTD participants demonstrated significant impairments in each of the three hypothesized components of GDB that contribute to apathy. Regression analyses related each component to disease in specific GM structures and associated WM tracts. Poor initiation thus was related to GM atrophy in anterior cingulate and reduced FA in the cingulum. Planning impairment was related to GM atrophy in dorsolateral prefrontal cortex and reduced FA in superior longitudinal fasciculus. Poor motivation was related to GM atrophy in orbitofrontal cortex (OFC) and reduced FA in uncinate fasciculus (UNC).

Conclusions: bvFTD patients have difficulty with initiation, planning and motivation components of GDB. These findings are consistent with the hypotheses that GDB encompasses at least three processes, that these are supported by a large-scale neural network within specific portions of the frontal lobe, and that degradation of any one of these prefrontal regions in bvFTD may contribute to apathy.