The effect of lexical content on sentence production in nonfluent aphasia

<p>Individuals with nonfluent aphasia are able to produce many words in isolation, but have great difficulty producing sentences. Most research to date has compared accuracy across different types of sentence structures, focussing on grammatical aspects that may be compromised in nonfluent aphasia. However, based on the premise that lexical elements activate their associated grammatical frames as well as vice versa, lexical content may also be of vital importance. For example, rapid access to lexical elements – particularly ones appearing early in the sentence - may be crucial, especially if the sentence plan is weakly activated or rapidly decaying. The current study investigated the effect of different aspects of lexical content on nonfluent aphasic sentence production. Five participants with nonfluent aphasia, four participants with fluent aphasia and eight controls completed two picture description tasks eliciting subject-verb-object sentences (e.g., the dog is chasing the fox). Based on existing evidence suggesting that common words are accessed more rapidly than rarer ones, Experiment 1 manipulated the frequency of sentence nouns, thereby varying their speed of lexical retrieval by varying the frequency of sentence nouns. Nonfluent participants' accuracy was consistently higher for sentences commencing with a high frequency subject noun, even when errors on those nouns were themselves excluded. This was not the case for the fluent participants. Experiment 2 manipulated the semantic relationship between subject and object nouns. Previous research suggests that phrases containing related words may be challenging for individuals with nonfluent aphasia, possibly because lexical representations are inadequately tied to appropriate structural representations. The nonfluent participants produced sentences less accurately when they contained related lexical items, even when those items were in different noun phrases. The fluent participants exhibited the opposite trend. Finally, the relationship between the patterns observed in Experiment 1 and 2 and lesion location in the aphasic participants was explored by analysing magnetic resonance scans. We discuss the implications of our findings for theoretical accounts of sentence production more generally, and of nonfluent aphasia in particular. More precisely, we propose that individuals with nonfluent aphasia are disproportionately reliant on activated lexical representations to drive the sentence generation process, an idea we call the Content Drives Structure (COST) hypothesis.</p>

Why Can't Individuals with Nonfluent Aphasia Produce Sentences? Exploring the Role of Lexical Availability

<p>Nonfluent aphasia is a language disorder characterised by sparse, fragmented speech. Individuals with this disorder often produce single words accurately (for example, they can name pictured objects), but have great difficulty producing sentences. An important research goal is to understand why sentences are so difficult for these individuals. To produce a sentence, a speaker must not only retrieve its lexical elements, but also integrate them into a grammatically well-formed sentence. Indeed, most research to date has focused on this grammatical integration process. However, recent studies suggest that the noun and/or verb content of the sentence can also be an important determinant of success (e.g., Raymer & Kohen, 2006; Speer & Wilshire, 2014). In this thesis, I explore the role of noun availability on sentence production accuracy using an identity priming paradigm. Participants are asked to describe a pictured event using a single sentence (e.g., “The fish is kissing the turtle”). In the critical condition, an auditory prime word is presented just prior to the picture, which is identical to one of the nouns in the target sentence (e.g., fish). The rationale is that the prime will enhance the availability of its counterpart when the person comes to produce the target sentence. Participants were four individuals with mild nonfluent aphasia, two individuals with fluent aphasia, and six older, healthy controls. Consistent with our hypotheses, the nonfluent participants as a group were more accurate at producing sentences when one of its nouns – either the subject or object - was primed in this way. Importantly, in the primed subject noun condition, these results held even when accuracy on the primed element itself was excluded, suggesting it had a broad effect on sentence production accuracy. The primed nouns had no effect on sentence production accuracy for the fluent individuals or the controls. We interpret these findings within models of sentence production that allow for considerable interplay between the processes of lexical content retrieval and sentence structure generation.</p>

Why Can't Individuals with Nonfluent Aphasia Produce Sentences? Exploring the Role of Lexical Availability

<p>Nonfluent aphasia is a language disorder characterised by sparse, fragmented speech. Individuals with this disorder often produce single words accurately (for example, they can name pictured objects), but have great difficulty producing sentences. An important research goal is to understand why sentences are so difficult for these individuals. To produce a sentence, a speaker must not only retrieve its lexical elements, but also integrate them into a grammatically well-formed sentence. Indeed, most research to date has focused on this grammatical integration process. However, recent studies suggest that the noun and/or verb content of the sentence can also be an important determinant of success (e.g., Raymer & Kohen, 2006; Speer & Wilshire, 2014). In this thesis, I explore the role of noun availability on sentence production accuracy using an identity priming paradigm. Participants are asked to describe a pictured event using a single sentence (e.g., “The fish is kissing the turtle”). In the critical condition, an auditory prime word is presented just prior to the picture, which is identical to one of the nouns in the target sentence (e.g., fish). The rationale is that the prime will enhance the availability of its counterpart when the person comes to produce the target sentence. Participants were four individuals with mild nonfluent aphasia, two individuals with fluent aphasia, and six older, healthy controls. Consistent with our hypotheses, the nonfluent participants as a group were more accurate at producing sentences when one of its nouns – either the subject or object - was primed in this way. Importantly, in the primed subject noun condition, these results held even when accuracy on the primed element itself was excluded, suggesting it had a broad effect on sentence production accuracy. The primed nouns had no effect on sentence production accuracy for the fluent individuals or the controls. We interpret these findings within models of sentence production that allow for considerable interplay between the processes of lexical content retrieval and sentence structure generation.</p>

The effect of lexical content on sentence production in nonfluent aphasia

<p>Individuals with nonfluent aphasia are able to produce many words in isolation, but have great difficulty producing sentences. Most research to date has compared accuracy across different types of sentence structures, focussing on grammatical aspects that may be compromised in nonfluent aphasia. However, based on the premise that lexical elements activate their associated grammatical frames as well as vice versa, lexical content may also be of vital importance. For example, rapid access to lexical elements – particularly ones appearing early in the sentence - may be crucial, especially if the sentence plan is weakly activated or rapidly decaying. The current study investigated the effect of different aspects of lexical content on nonfluent aphasic sentence production. Five participants with nonfluent aphasia, four participants with fluent aphasia and eight controls completed two picture description tasks eliciting subject-verb-object sentences (e.g., the dog is chasing the fox). Based on existing evidence suggesting that common words are accessed more rapidly than rarer ones, Experiment 1 manipulated the frequency of sentence nouns, thereby varying their speed of lexical retrieval by varying the frequency of sentence nouns. Nonfluent participants' accuracy was consistently higher for sentences commencing with a high frequency subject noun, even when errors on those nouns were themselves excluded. This was not the case for the fluent participants. Experiment 2 manipulated the semantic relationship between subject and object nouns. Previous research suggests that phrases containing related words may be challenging for individuals with nonfluent aphasia, possibly because lexical representations are inadequately tied to appropriate structural representations. The nonfluent participants produced sentences less accurately when they contained related lexical items, even when those items were in different noun phrases. The fluent participants exhibited the opposite trend. Finally, the relationship between the patterns observed in Experiment 1 and 2 and lesion location in the aphasic participants was explored by analysing magnetic resonance scans. We discuss the implications of our findings for theoretical accounts of sentence production more generally, and of nonfluent aphasia in particular. More precisely, we propose that individuals with nonfluent aphasia are disproportionately reliant on activated lexical representations to drive the sentence generation process, an idea we call the Content Drives Structure (COST) hypothesis.</p>

Focal Cognitive Syndromes

The neurologic results of cortical lesions reflect the structural properties of the affected region. Lesions affecting primary sensorimotor cortices result in primary sensorimotor deficits that are qualitatively all-or-nothing, such as blindness (hemianopia) and paralysis (hemiparesis). Quantitatively, though, the severity of the deficit depends on the extent of the lesion (so that a hemiparetic patient may not be completely paralyzed but simply weak). Lesions affecting modality-specific association regions result in conceptually more complex disorders that are confined to a single modality, such as nonfluent aphasia (a form of motor speech disorder reflecting the language-dominant hemisphere) or prosopagnosia (a visual disorder impairing the ability to disambiguate visually similar entities, specifically faces, reflecting the “what” visual pathway in inferotemporal cortices).

MNI-FTD templates, unbiased average templates of frontotemporal dementia variants

Standard templates are widely used in human neuroimaging processing pipelines to facilitate group-level analyses and comparisons across subjects/populations. MNI-ICBM152 template is the most commonly used standard template, representing an average of 152 healthy young adult brains. However, in patients with neurodegenerative diseases such as frontotemporal dementia (FTD), high atrophy levels lead to significant differences between individuals’ brain shapes and MNI-ICBM152 template. Such differences might inevitably lead to registration errors or subtle biases in downstream analyses and results. Disease-specific templates are therefore desirable to reflect the anatomical characteristics of the populations of interest and reduce potential registration errors. Here, we present MNI-FTD136, MNI-bvFTD70, MNI-svFTD36, and MNI-pnfaFTD30, four unbiased average templates of 136 FTD patients, 70 behavioural variant (bv), 36 semantic variant (sv), and 30 progressive nonfluent aphasia (pnfa) variant FTD patients and a corresponding age-matched template of 133 controls (MNI-CN133), along with probabilistic tissue maps for each template. Public availability of these templates will facilitate analyses of FTD cohorts and enable comparisons between different studies in an appropriate common standardized space.

Rapid Progressive Glioblastoma despite Radiation in a Patient with Myelodysplastic Syndrome

The rapidity of glioblastoma progression can be exacerbated by impaired systemic immune surveillance. We describe an elderly woman with advanced 5q– myelodysplastic syndrome (MDS) associated with trilineage dysfunction in hematopoiesis. She also developed multiple solid tumor malignancies including ER/PR-positive and HER2-negative breast cancer, probable lung cancer without histologic confirmation, and primary glioblastoma with a high proliferation index of 80%. Because of low platelet counts of 20,000–30,000/µL that required periodic transfusion and a reduced white cell count of 600–900/µL, she was deemed unsafe to take concomitant daily temozolomide during radiation and her glioblastoma was treated with a shortened course of radiotherapy alone. Her baseline absolute neutrophil count was 110–390/µL, and CD4+ and CD8+ lymphocyte counts were 235/µL and 113/µL, respectively. During the last week of radiation, the patient developed a nonfluent aphasia, increased fatigue, and aspiration pneumonia. A gadolinium-enhanced head MRI, obtained 2 days after completion of radiation and 39 days after biopsy, demonstrated near tripling of the size of the left frontal tumor with a significant amount of adjacent cerebral edema. This case raises the possibility that advanced MDS is a negative immunomodulatory condition that can accelerate glioblastoma progression.