False recognition of incidentally learned pictures and words in primary progressive aphasia

Transcranial direct current stimulation over the left posterior temporal lobe modulates semantic control: Evidence from episodic memory distortions

Evidence accumulates to show that semantic cognition requires, in addition to semantic representations, control processes that regulate the accessibility and use of semantic knowledge in a task- and time-appropriate fashion. Semantic control has been recently proposed to rely on a distributed network that includes the posterior temporal cortex. Along these lines, recent meta-analyses of neuroimaging data and studies with patients suffering from semantic aphasia have suggested that the left posterior middle temporal gyrus (pMTG) is critically involved whenever situational context must constrain semantic retrieval. In the present experiment, we used transcranial direct current stimulation over the left posterior temporal lobe in an attempt to interfere with semantic control while participants performed a DRM task, a procedure for inducing conceptually-based false recognition that is contingent on both activation and control processes. Paralleling findings with patients suffering from brain damage restricted to the temporoparietal cortex, anodal stimulation (relative to sham stimulation) resulted in increased false recognition but intact true recognition. These findings fit well with the idea that the left pMTG is a key component of a semantic control network, the alteration of which results in memory performance that is affected by the intrusion of contextually-inappropriate semantic information.

Eye movements as a measure of word comprehension deficits in primary progressive aphasia

INTRODUCTION

Eye movement studies can uncover subtle aspects of language processing impairment in individuals with primary progressive aphasia (PPA), who may have difficulty understanding words. This study examined eye movement patterns on a word-object matching task in response to varying levels of word-knowledge in PPA.

METHODS

Participants with semantic and non-semantic PPA completed an object-matching task, where a word was presented and participants then selected the corresponding pictured object from an array. Afterwards, participants defined words for trials to which they incorrectly pointed. Linear mixed-effects analyses examined fixation differences on targets and related and unrelated foils.

RESULTS

On incorrectly-pointed trials, participants demonstrated greater fixation duration on related foils, demonstrating intra-category blurring. For words that could not be defined, there was similar fixation duration on related and unrelated foils, demonstrating inter-category semantic blurring.

DISCUSSION

This study demonstrated that fixation patterns reflect varying levels of word knowledge in PPA.

Semantic Feature Disturbance in Alzheimer Disease: Evidence from an Object Decision Task

BACKGROUND AND OBJECTIVE

It is widely held that semantic disturbance in Alzheimer disease (AD) involves the loss of distinctive features but the relative sparing of nondistinctive features. Many previous studies of semantic feature disturbance have used cognitively challenging tasks with verbal stimuli that allow for potential cognitive confounds. Our objective was to use a task with lower memory demands to investigate distinctive feature disturbance in AD.

METHODS

We used an object decision task to compare the processing of distinctive and nondistinctive semantic features in people with AD and age-matched controls. The task included six conditions based on the relationship between each prime and target object. We tested the processing of distinctive and nondistinctive features by selectively altering distinctive and nondistinctive semantic features between prime and target pairs.

RESULTS

Performance accuracy was significantly lower for participants with AD than for age-matched controls when distinctive features were manipulated, but no difference was found when nondistinctive features were manipulated.

CONCLUSIONS

Our results provide evidence of semantic content disturbance in AD in the context of a task with low cognitive demands.

Selective verbal recognition memory impairments are associated with atrophy of the language network in non-semantic variants of primary progressive aphasia

Primary progressive aphasia (PPA) is clinically defined by an initial loss of language function and preservation of other cognitive abilities, including episodic memory. While PPA primarily affects the left-lateralized perisylvian language network, some clinical neuropsychological tests suggest concurrent initial memory loss. The goal of this study was to test recognition memory of objects and words in the visual and auditory modality to separate language-processing impairments from retentive memory in PPA. Individuals with non-semantic PPA had longer reaction times and higher false alarms for auditory word stimuli compared to visual object stimuli. Moreover, false alarms for auditory word recognition memory were related to cortical thickness within the left inferior frontal gyrus and left temporal pole, while false alarms for visual object recognition memory was related to cortical thickness within the right-temporal pole. This pattern of results suggests that specific vulnerability in processing verbal stimuli can hinder episodic memory in PPA, and provides evidence for differential contributions of the left and right temporal poles in word and object recognition memory.

Verbal and nonverbal memory in primary progressive aphasia: the Three Words-Three Shapes Test

OBJECTIVES

To investigate cognitive components and mechanisms of learning and memory in primary progressive aphasia (PPA) using a simple clinical measure, the Three Words Three Shapes Test (3W3S).

BACKGROUND

PPA patients can complain of memory loss and may perform poorly in standard tests of memory. The extent to which these signs and symptoms reflect dysfunction of the left hemisphere language versus limbic memory network remains unknown.

METHODS

3W3S data from 26 patients with a clinical diagnosis of PPA were compared with previously published data from patients with typical dementia of the Alzheimer type (DAT) and cognitively healthy elders.

RESULTS

PPA patients showed two bottlenecks in new learning. First, they were impaired in the effortless (but not effortful) on-line encoding of verbal (but not non-verbal) items. Second, they were impaired in the retrieval (but not retention) of verbal (but not non-verbal) items. In contrast, DAT patients had impairments also in effortful on-line encoding and retention of verbal and nonverbal items.

CONCLUSIONS

PPA selectively interferes with spontaneous on-line encoding and subsequent retrieval of verbal information. This combination may underlie poor memory test performance and is likely to reflect the dysfunction of the left hemisphere language rather than medial temporal memory network.

A clinical, neurolinguistic, and radiological study of a Chinese follow-up case with primary progressive aphasia

Primary progressive aphasia (PPA) is a progressive neurodegenerative disorder characterized by the deterioration of language functions. The Han language bears some unique features from the Latin languages; however, the features of PPA in the Han language-speaking population are not well understood. In this study, we performed a 3-year follow-up on a Han language-speaking PPA patient with corresponding changes in magnetic resonance imaging (MRI). During the early stage, linguistic analysis revealed several symptoms including difficulty with auditory comprehension, right-left disorientation, reading disorders, and agraphia, specifically the execution of serial oral instructions. This Chinese PPA patient presented with a reading disorder, but his word comprehension ability remained intact. There are two different possible modalities of incorrect writing in this case. The patient also presented with noun-verb double dissociation. The early-stage MRI showed atrophy of the left frontal lobe, which was most severe in the inferior frontal gyrus. Three years later, the patient was found to have progressive atrophy in the parietal, frontal, and temporal lobes, among which the frontal lobe remained the most severely affected region. The brain imaging of the Chinese-speaking PPA patient showed changes similar to those of a Latin language-speaking PPA patient. The prominent change was asymmetrical atrophy in the frontal and temporal lobes. This is the first report of noun-verb double dissociation existing in a Chinese-language speaking PPA patient. The dissociation may be related to an impaired function of the inferior frontal gyrus, which is likely associated with verb-naming in Chinese-speaking people. Several unique features were observed in this case, including impairment in writing ability.

Covert processing of words and pictures in nonsemantic variants of primary progressive aphasia

The inability to name objects (anomia) is one of the most common findings in the neurologic examination of primary progressive aphasia (PPA). In the semantic variant of PPA, the anomia is profound and reflects a combination of object naming and word comprehension deficits. In contrast, nonsemantic variants of PPA display a more selective impairment of object naming, without corresponding impairments of word comprehension. The aim of the present study was to explore the nature of the anomia in nonsemantic variants of PPA with a sensitive chronometric test of covert word/picture association. We tested priming effects in 12 patients with nonsemantic variant of PPA and 18 controls. Stimuli consisted of written words and line pictures of concrete objects. Within-format (word-word and picture-picture) and cross-format (word-picture and picture-word) priming effects were assessed by measuring the shortening of response times to the second versus initial presentation of corresponding stimulus pairs. In addition to the expected impairment of picture-to-word priming, a condition simulating object naming, the nonsemantic PPA patients also showed unexpected impairments of word-to-picture and word-to-word priming. Picture-to-picture priming was preserved, demonstrating the selectivity of the deficit for lexical processing. These findings show that the information processing bottleneck in patients with nonsemantic variants of PPA is not confined to the stage of lexical access but that it also extends into the prior levels of lexical semantics. The boundaries between the semantic and nonsemantic variants are therefore far from rigid.

An update on primary progressive aphasia

Primary progressive aphasia is a neurodegenerative syndrome characterized by a relentless dissolution of language but relative sparing of other cognitive domains during the initial stages of the disease. Substantial progress has been made in understanding the clinical characteristics, imaging, genetics, and neuropathology of this syndrome. This article reviews the clinical criteria for diagnosing primary progressive aphasia and some of the more recent research advances in this field.