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Dorsomedial prefrontal hypoexcitability underlies lost empathy in frontotemporal dementia.

ABSTRACT: Empathic function is essential for the well-being of social species. Empathy loss is associated with various brain disorders and represents arguably the most distressing feature of frontotemporal dementia (FTD), a leading form of presenile dementia. The neural mechanisms are unknown. We established an FTD mouse model deficient in empathy and observed that aged somatic transgenic mice expressing GGGGCC repeat expansions in C9orf72, a common genetic cause of FTD, exhibited blunted affect sharing and failed to console distressed conspecifics by affiliative contact. Distress-induced consoling behavior activated the dorsomedial prefrontal cortex (dmPFC), which developed profound pyramidal neuron hypoexcitability in aged mutant mice. Optogenetic dmPFC inhibition attenuated affect sharing and other-directed consolation in wild-type mice, whereas chemogenetically enhancing dmPFC excitability rescued empathy deficits in mutant mice, even at advanced ages when substantial cortical atrophy had occurred. These results establish cortical hypoexcitability as a pathophysiological basis of empathy loss in FTD and suggest a therapeutic strategy.

SUBMITTER: Phillips HL

PROVIDER: S-EPMC10023454 | biostudies-literature | 2023 Mar

REPOSITORIES: biostudies-literature

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Dorsomedial prefrontal hypoexcitability underlies lost empathy in frontotemporal dementia.

Phillips Hannah L HL Dai Huihui H Choi So Yoen SY Jansen-West Karen K Zajicek Alexis S AS Daly Luke L Petrucelli Leonard L Gao Fen-Biao FB Yao Wei-Dong WD

Neuron 20230112 6

Empathic function is essential for the well-being of social species. Empathy loss is associated with various brain disorders and represents arguably the most distressing feature of frontotemporal dementia (FTD), a leading form of presenile dementia. The neural mechanisms are unknown. We established an FTD mouse model deficient in empathy and observed that aged somatic transgenic mice expressing GGGGCC repeat expansions in C9orf72, a common genetic cause of FTD, exhibited blunted affect sharing a ...[more]

PMID: 36638803

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Project description:A lack of empathy, and particularly its affective components, is a core symptom of behavioural variant frontotemporal dementia (bvFTD). Visual exposure to images of a needle pricking a hand (pain condition) and Q-tips touching a hand (control condition) is an established functional magnetic resonance imaging (fMRI) paradigm used to investigate empathy for pain (EFP; pain condition minus control condition). EFP has been associated with increased blood oxygen level dependent (BOLD) signal in regions known to become atrophic in the early stages in bvFTD, including the anterior insula and the anterior cingulate. We therefore hypothesized that patients with bvFTD would display altered empathy processing in the EFP paradigm. Here we examined empathy processing using the EFP paradigm in 28 patients with bvFTD and 28 sex and age matched controls. Participants underwent structural MRI, task-based and resting-state fMRI. The Interpersonal Reactivity Index (IRI) was used as a measure of different facets of empathic function outside the scanner. The EFP paradigm was analysed at a whole brain level and using two regions-of-interest approaches, one based on a metanalysis of affective perceptual empathy versus cognitive evaluative empathy and one based on the controĺs activation pattern. In controls, EFP was linked to an expected increase of BOLD signal that displayed an overlap with the pattern of atrophy in the bvFTD patients (insula and anterior cingulate). Additional regions with increased signal were the supramarginal gyrus and the occipital cortex. These latter regions were the only ones that displayed increased BOLD signal in bvFTD patients. BOLD signal increase under the affective perceptual empathy but not the cognitive evaluative empathy region of interest was significantly greater in controls than in bvFTD patients. The controĺs rating on their empathic concern subscale of the IRI was significantly correlated with the BOLD signal in the EFP paradigm, as were an informantś ratings of the patientś empathic concern subscale. This correlation was not observed on other subscales of the IRI or when using the patient's self-ratings. Finally, controls and patients showed different connectivity patterns in empathy related networks during resting-state fMRI, mainly in nodes overlapping the ventral attention network. Our results indicate that reduced neural activity in regions typically affected by pathology in bvFTD is associated with reduced empathy processing, and a predictor of patientś capacity to experience affective empathy.

Project description:BackgroundReduced empathy is a common symptom in frontotemporal dementia (FTD). Although empathy deficits have been extensively researched in sporadic cases, few studies have explored the differences in familial forms of FTD.MethodsEmpathy was examined using a modified version of the Interpersonal Reactivity Index (mIRI) in 676 participants from the Genetic FTD Initiative: 216 mutation-negative controls, 192 C9orf72 expansion carriers, 193 GRN mutation carriers and 75 MAPT mutation carriers. Using global scores from the CDR® plus NACC FTLD, mutation carriers were divided into three groups, asymptomatic (0), very mildly symptomatic/prodromal (.5), or fully symptomatic (1 or more). The mIRI Total score, as well as the subscores of Empathic Concern (EC) and Perspective Taking (PT) were assessed. Linear regression models with bootstrapping were used to assess empathy ratings across genetic groups, as well as across phenotypes in the symptomatic carriers. Neural correlates of empathy deficits were examined using a voxel-based morphometry (VBM) analysis.ResultsAll fully symptomatic groups scored lower on the mIRI Total, EC, and PT when compared to controls and their asymptomatic or prodromal counterparts (all p < .001). Prodromal C9orf72 expansion carriers also scored significantly lower than controls on the mIRI Total score (p = .046). In the phenotype analysis, all groups (behavioural variant FTD, primary progressive aphasia and FTD with amyotrophic lateral sclerosis) scored significantly lower than controls (all p < .007). VBM revealed an overlapping neural correlate of the mIRI Total score across genetic groups in the orbitofrontal lobe but with additional involvement in the temporal lobe, insula and basal ganglia in both the GRN and MAPT groups, and uniquely more posterior regions such as the parietal lobe and thalamus in the GRN group, and medial temporal structures in the MAPT group.ConclusionsSignificant empathy deficits present in genetic FTD, particularly in symptomatic individuals and those with a bvFTD phenotype, while prodromal deficits are only seen using the mIRI in C9orf72 expansion carriers.

Project description:Frontotemporal dementia (FTD) encompasses a spectrum of neurodegenerative diseases with heterogeneous clinical presentations and two predominant types of underlying neuropathology. FTD typically comprises three distinct clinical syndromes: behavioral variant frontotemporal dementia (bvFTD), semantic variant primary progressive aphasia (svPPA), and nonfluent variant primary progressive aphasia (nfvPPA). FTD also frequently overlaps both clinically and neuropathologically with three other neurodegenerative syndromes: corticobasal syndrome (CBS), progressive supranuclear palsy (PSP), and amyotrophic lateral sclerosis (ALS). Each syndrome can be associated with one or more underlying neuropathological diagnoses and are referred to as frontotemporal lobar degeneration (FTLD). Although the various FTD syndromes can substantially differ in terms of clinical symptoms and underlying pathology, the symptoms can be broadly categorized into behavioral, cognitive and motor domains. Currently there are no Food and Drug Administration (FDA) approved therapies for the above syndromes except riluzole for ALS. FTD treatment strategies generally rely on off-label use of medications for symptomatic management, and most therapies lack quality evidence from randomized, placebo-controlled clinical trials. For behavioral symptoms, selective serotonin reuptake inhibitors may be effective, while case reports hint at possible efficacy with antipsychotics or anti-epileptics, but use of these latter agents is limited due to concerns regarding side effects. There are no effective therapies for cognitive complaints in FTD, which frequently involve executive function, memory, and language. Motor difficulties associated with FTD may present with parkinsonian symptoms or motor neuron disease, for which riluzole is indicated as therapy. Compared to idiopathic Parkinson's disease, FTD-related atypical parkinsonism is generally not responsive to dopamine replacement therapies, but a small percentage of patients may experience improvement with a trial of carbidopa-levodopa. Physical and occupational therapy remain an important corner stone of motor symptom management in FTD. Speech therapy may also help patients manage symptoms associated with aphasia, apraxia, and dysarthria. Recent advances in the understanding of FTLD pathophysiology and genetics have led to development of potentially disease-modifying therapies as well as symptomatic therapies aimed at ameliorating social and behavioral deficits.

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Dorsomedial prefrontal hypoexcitability underlies lost empathy in frontotemporal dementia.

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Dorsomedial prefrontal hypoexcitability underlies lost empathy in frontotemporal dementia.

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