Knowledge of famous faces and names in semantic dementia

The right temporal lobe variant of frontotemporal dementia

The right temporal variant of frontotemporal lobar degeneration (Rtv-FTLD) is a focal degenerative condition affecting predominantly the right temporal lobe. The aim of this study was to further characterize the profile of cognitive impairment and the neuroanatomical basis of Rtv-FTLD patients without behavioural disturbances. A group of three patients with this syndrome had a detailed neuropsychological assessment, along with Voxel-Based Morphometry (VBM) of their brain to determine location of cortical atrophy. VBM analyses showed a pattern of atrophy that was predominant in the right hemisphere and concerned primarily the right anterior temporal lobe region. Patients carried out a test of famous people in which their ability to recognize, name and provide semantic information about famous persons from their faces, their voices and their names was investigated. They all showed a severe defect in recognizing, naming and identifying famous people irrespective of modality. Therefore, their inability to recognize famous people resulted from a multimodal defect (semantic). These results highlight the semantic nature of the defect, and suggest that the anterior right temporal lobe may have a prominent role in processing person-based semantic knowledge. This study helps in further understanding the neuropsychological profile of patients with Rtv-FTLD.

The natural history of temporal variant frontotemporal dementia

BACKGROUND

The temporal variant of frontotemporal dementia (tvFTD) features asymmetric anterior temporal/amygdala degeneration as well as ventromedial frontal, insular, and inferoposterior temporal involvement. Left temporal atrophy has been linked to loss of semantic knowledge, whereas behavioral symptoms dominate the right temporal variant.

OBJECTIVE

To investigate the first symptoms and the timing of subsequent symptoms in patients with left versus right tvFTD.

METHODS

Twenty-six patients with tvFTD were identified. Six had right > left temporal atrophy (right temporal lobe variant [RTLV]) and were matched with six having comparable left > right temporal atrophy (left temporal lobe variant [LTLV]). Clinical records were reviewed to generate individualized symptom chronologies.

RESULTS

In all patients, first symptoms involved semantics (4/6 LTLV, 1/6 RTLV), behavior (4/6 RTLV, 1/6 LTLV), or both (1 LTLV, 1 RTLV). Semantic loss began with anomia, word-finding difficulties, and repetitive speech, whereas the early behavioral syndrome was characterized by emotional distance, irritability, and disruption of physiologic drives (sleep, appetite, libido). After an average of 3 years, patients developed whichever of the two initial syndromes--semantic or behavioral--that they lacked at onset. A third stage, 5 to 7 years from onset, saw the emergence of disinhibition, compulsions, impaired face recognition, altered food preference, and weight gain. Compulsions in LTLV were directed toward visual, nonverbal stimuli, whereas patients with RTLV were drawn to games with words and symbols.

CONCLUSIONS

The temporal variant of frontotemporal dementia follows a characteristic cognitive and behavioral progression that suggests early spread from one anterior temporal lobe to the other. Later symptoms implicate ventromedial frontal, insular, and inferoposterior temporal regions, but their precise anatomic correlates await confirmation.

Anatomical functional and cognitive determinants of semantic memory disorders

Contemporary debates on the 'semantic memory' construct revolve around three main topics: (1) the functional and anatomical relationships between episodic and semantic memory; (2) the format of semantic representations and their relationships with the underlying sensory-motor processes; (3) the categorical organization of semantic memory. The aim of the present review is to demonstrate that there is a common thread linking these different aspects of semantic memory. This thread is represented by the interdependence of mechanisms involved in the construction of semantic memory and the content of semantic representations. In particular, I suggest there is a continuity between: (a) the mechanisms of acquisition of episodic and semantic memory; (b) semantic representations and sensory-motor processes preliminary to the acquisition of these representations. This continuity has important implications for the format of semantic representations and the brain structures subserving the organisation of various categories of knowledge.

Can episodic memory tasks differentiate semantic dementia from Alzheimer's disease?

The performance of two groups of patients with semantic dementia (SD), with predominant right (SDR) and left temporal lobe atrophy (SDL), was contrasted with that of cases with probable Alzheimer's disease (AD) on a range of standard episodic memory tasks. While the SDL group achieved a good score on a composite visual, but not a verbal, episodic memory measure, the AD and SDR groups were equivalently impaired at visual and verbal memory. The SD, but not the AD, groups were, by definition, impaired on simple tests of semantic memory. Standard verbal episodic memory tests, therefore, failed to discriminate patients with SD from those with probable AD and even visual memory tests may result in misclassification of SDR cases.

Declarative memory impairments in Alzheimer's disease and semantic dementia

Semantic dementia (SD) and Alzheimer's disease (AD) are both disorders in which early pathology affects the temporal lobe yet they produce distinct syndromes of declarative memory impairment-loss of established semantic knowledge with relatively preserved episodic memory in the former and the converse in the latter. Groups with mild SD and mild AD who showed a double dissociation in these two aspects of declarative memory were studied-the SD group's episodic memory and the AD group's semantic knowledge each being comparable to controls. Positron emission tomography and volumetric magnetic resonance imaging were used to map deficits in regional cerebral metabolic rate and mesial temporal lobe (MTL) atrophy, respectively. Episodic memory impairment in AD was associated with dysfunction of an integrated network (mesial temporal lobe, mamillary bodies, dorso-mesial thalamus and posterior cingulate). Semantic memory impairment in SD was associated with bilateral rostral temporal lobe hypometabolism. The SD group had comparable MTL atrophy and hypometabolism to that found in AD but the remainder of their limbic-diencephalic network was preserved suggesting that the latter explains their ability to acquire new episodic memories. The results challenge the view that amnesia in early AD can be explained by the degree of MTL damage alone while showing that semantic impairment can occur with damage restricted to the rostral temporal lobes.

Dissociable roles of the bilateral anterior temporal lobe in face-name associations: an event-related fMRI study

Previous studies have suggested the importance of bilateral anterior temporal regions in face-name associations, but there is little evidence concerning their precise role. In this fMRI study, we investigated the effects of person-related semantics (PS) and repeated learning (R) on activations in these regions during the retrieval of face-name associations. For encoding stimuli, we prepared four lists of faces. To control the factor of PS, people's and occupation names were attached to the faces in lists A and B, whereas only people's names were attached to the faces in lists C and D. To control the factor of R, the stimuli in lists A and C were learned twice, whereas the stimuli in lists B and D were learned seven times during encoding before fMRI. During fMRI after the encoding, subjects participated in the retrieval task of people's names from faces or in the retrieval task of faces from people's names. The left anterior temporal lobe was significantly activated during the retrieval of people's names from faces encoded with, compared to without, PS; whereas the right anterior temporal lobe was activated during the retrieval of people's faces from names, compared to without, this encoding. Also, activation of the left (but not the right) anterior temporal lobe was significantly reduced after R of face-name associations. These findings suggest that the three components of faces, names, and PS may be mutually mediated by the bilateral anterior temporal lobe, whose activity may be dynamically changed by the level of consolidation of face-name associations.

Hyperfamiliarité stéréotypée pour les visages au cours d’une démence fronto-temporale avec prosopagnosie

INTRODUCTION

The association of prosopagnosia and false recognition of faces is unusual and contributes to our understanding of the generation of facial familiarity.

METHOD

A 67-year-old man with a left prefrontal traumatic lesion, developed a temporal variety of fronto-temporal dementia (semantic dementia) with amyotrophic lateral sclerosis. Cerebral imagery demonstrated a bilateral, temporal anterior atrophy predominating in the right hemisphere. The main cognitive signs consisted in severe difficulties to recognize faces of familiar people (prosopagnosia), associated with systematic false recognition of unfamiliar people.

RESULT

Neuropsychological testing indicated that the prosopagnosia probably resulted from the association of an associative/mnemonic mechanism (inability to activate the Face Recognition Units (FRU) from the visual input) and a semantic mechanism (degradation of semantic/biographical information or deconnexion between FRU and this information). At the early stage of the disease, the patient could activate residual semantic information about individuals from their names, but after a 4-year course, he failed to do so. This worsening could be attributed to the extension of the degenerative lesions to the left temporal lobe. Familiar and unfamiliar faces triggered a marked feeling of knowing. False recognition concerned all the unfamiliar faces, and the patient claimed spontaneously that they corresponded to actors, but he could not provide any additional information about their specific identities. The coexistence of prosopagnosia and false recognition suggests the existence of different interconnected systems processing face recognition, one intended to identification of individuals, and the other producing the sense of familiarity. Dysfunctions at different stages of one or the other of these two processes could result in distortions in the feeling of knowing.

CONCLUSION

From this case and others reported in literature, we propose to complete the classical model of face processing by adding a pathway linked to limbic system and frontal structures. This later pathway could normally emit signals for familiarity, essentially autonomic, in response to the familiar faces. These signals, primitively unconscious, secondly reach consciousness and are then integrated by a central supervisor system which evaluates and verifies identity-specific biographical information in order to make a decision about the sense of familiarity.