The Time Course of Language Production as Revealed by Pattern Classification of MEG Sensor Data.

Language production involves a complex set of computations, from conceptualization to articulation, which are thought to engage cascading neural events in the language network. However, recent neuromagnetic evidence suggests simultaneous meaning-to-speech mapping in picture naming tasks, as indexed by early parallel activation of frontotemporal regions to lexical semantic, phonological, and articulatory information. Here we investigate the time course of word production, asking to what extent such "earliness" is a distinctive property of the associated spatiotemporal dynamics. Using MEG, we recorded the neural signals of 34 human subjects (26 males) overtly naming 134 images from four semantic object categories (animals, foods, tools, clothes). Within each category, we covaried word length, as quantified by the number of syllables contained in a word, and phonological neighborhood density to target lexical and post-lexical phonological/phonetic processes. Multivariate pattern analyses searchlights in sensor space distinguished the stimulus-locked spatiotemporal responses to object categories early on, from 150 to 250 ms after picture onset, whereas word length was decoded in left frontotemporal sensors at 250-350 ms, followed by the latency of phonological neighborhood density (350-450 ms). Our results suggest a progression of neural activity from posterior to anterior language regions for the semantic and phonological/phonetic computations preparing overt speech, thus supporting serial cascading models of word production.SIGNIFICANCE STATEMENT Current psycholinguistic models make divergent predictions on how a preverbal message is mapped onto articulatory output during the language planning. Serial models predict a cascading sequence of hierarchically organized neural computations from conceptualization to articulation. In contrast, parallel models posit early simultaneous activation of multiple conceptual, phonological, and articulatory information in the language system. Here we asked whether such earliness is a distinctive property of the neural dynamics of word production. The combination of the millisecond precision of MEG with multivariate pattern analyses revealed subsequent onset times for the neural events supporting semantic and phonological/phonetic operations, progressing from posterior occipitotemporal to frontal sensor areas. The findings bring new insights for refining current theories of language production.

Parallel or sequential? Decoding conceptual and phonological/phonetic information from MEG signals during language production.

Speaking requires the temporally coordinated planning of core linguistic information, from conceptual meaning to articulation. Recent neurophysiological results suggested that these operations involve a cascade of neural events with subsequent onset times, whilst competing evidence suggests early parallel neural activation. To test these hypotheses, we examined the sources of neuromagnetic activity recorded from 34 participants overtly naming 134 images from 4 object categories (animals, tools, foods and clothes). Within each category, word length and phonological neighbourhood density were co-varied to target phonological/phonetic processes. Multivariate pattern analyses (MVPA) searchlights in source space decoded object categories in occipitotemporal and middle temporal cortex, and phonological/phonetic variables in left inferior frontal (BA 44) and motor cortex early on. The findings suggest early activation of multiple variables due to intercorrelated properties and interactivity of processing, thus raising important questions about the representational properties of target words during the preparatory time enabling overt speaking.

Idea Formulation for Spoken Language Production: The Interface of Cognition and Language.

BACKGROUND: Language and communication are fundamental to the human experience, and, traditionally, spoken language is studied as an isolated skill. However, before propositional language (i.e., spontaneous, voluntary, novel speech) can be produced, propositional content or 'ideas' must be formulated. OBJECTIVE: This review highlights the role of broader cognitive processes, particularly 'executive attention', in the formulation of propositional content (i.e., 'ideas') for propositional language production. CONCLUSIONS: Several key lines of evidence converge to suggest that the formulation of ideas for propositional language production draws on executive attentional processes. Larger-scale clinical research has demonstrated a link between attentional processes and language, while detailed case studies of neurological patients have elucidated specific idea formulation mechanisms relating to the generation, selection and sequencing of ideas for expression. Furthermore, executive attentional processes have been implicated in the generation of ideas for propositional language production. Finally, neuroimaging studies suggest that a widely distributed network of brain regions, including parts of the prefrontal and parietal cortices, supports propositional language production. IMPLICATIONS: Theoretically driven experimental research studies investigating mechanisms involved in the formulation of ideas are lacking. We suggest that novel experimental approaches are needed to define the contribution of executive attentional processes to idea formulation, from which comprehensive models of spoken language production can be developed. Clinically, propositional language impairments should be considered in the context of broader executive attentional deficits.

Analysis of naming processing stages in patients with mild Alzheimer.

In the evaluation of the nature of naming disorders, there is a rapid increase of anomia with the progression of Alzheimer's disease (AD), which is associated with whole brain atrophy. Although numerous studies have investigated this naming disorder, there is limited information on naming procedures in these patients. Reaction time (RT) is highly sensitive to dementia and provides an accurate measurement. The present study investigated the RT of each underlying level of naming in patients with mild AD and identified the nature of anomia in these patients. The study consisted of 24 healthy elderly and 22 mild AD patients who participated in experiments that were designed for evaluating each level of Levelt's model. Responses were divided into three groups of correct, false, and no-response and their RTs were calculated. The statistical analyses showed significant differences between healthy elderly and patients with mild AD in terms of access to the concept and the phonological form of the words. Moreover, significant differences in the type of responses were observed between correct and false responses of both groups. There was a significant difference between the no-response cases except in the case of lemma access for singular and plural names in other tasks. The results suggest that patients with mild AD have problems at the conceptual stage and access to the phonological form of a word.

Left frontal aslant tract and lexical selection: Evidence from frontal lobe lesions.

The frontal aslant tract (FAT) is a white-matter tract connecting the inferior frontal gyrus (IFG) and the supplementary motor complex (SMC). Damage to either component of the network causes spontaneous speech dysfluency, indicating its critical role in language production. However, spontaneous speech dysfluency may stem from various lower-level linguistic deficits, precluding inferences about the nature of linguistic processing subserved by the IFG-SMC network. Since the IFG and the SMC are attributed a role in conceptual and lexical selection during language production, we hypothesized that these processes rely on the IFG-SMC connectivity via the FAT. We analysed the effects of FAT volume on conceptual and lexical selection measures following frontal lobe stroke. The measures were obtained from the sentence completion task, tapping into conceptual and lexical selection, and the picture-word interference task, providing a more specific measure of lexical selection. Lower FAT volume was not associated with lower conceptual or lexical selection abilities in our patient cohort. Current findings stand in marked discrepancy with previous lesion and neuroimaging evidence for the joint contribution of the IFG and the SMC to lexical and conceptual selection. A plausible explanation reconciling this discrepancy is that the IFG-SMC connectivity via the FAT does contribute to conceptual and/or lexical selection but its disrupted function undergoes reorganisation over the course of post-stroke recovery. Thus, our negative findings stress the importance of testing the causal role of the FAT in lexical and conceptual selection in patients with more acute frontal lobe lesions.

Age-related differences in idea generation and selection for propositional language.

Conceptual preparation mechanisms such as novel idea generation and selection from amongst competing alternatives are critical for language production and may contribute to age-related language deficits. This study investigated whether older adults show diminished idea generation and selection abilities, compared to younger adults. Twenty younger (18-35 years) and 20 older (60-80 years) adults completed two novel experimental tasks, an idea generation task and a selection task. Older participants were slower than younger participants overall on both tasks. Importantly, this difference was more pronounced for task conditions with greater demands on generation and selection. Older adults were also significantly reduced on a semantic, but not phonemic, word fluency task. Overall, the older group showed evidence of age-related decline specific to idea generation and selection ability. This has implications for the message formulation stage of propositional language decline in normal aging.

Improved conceptual generation and selection with transcranial direct current stimulation in older adults.

INTRODUCTION: Normal aging is associated with deficits in various aspects of spoken language production, including idea generation and selection, and involves activity in frontal brain areas including left inferior frontal cortex (LIFG). These conceptual preparation processes, largely involving executive control, precede formulation and articulation stages and are critical for language production. Noninvasive brain stimulation (e.g., transcranial direct current stimulation, tDCS) has proven beneficial for age-related fluency and naming deficits, but this has not been extended to conceptual preparation mechanisms. METHOD: We investigated whether tDCS could facilitate idea generation and selection in 24 older adults aged 60-80 years. In the first phase, participants completed an idea generation test and a selection test with no stimulation. In the second phase they completed an alternate version of the tests in conjunction with either active or sham stimulation. Active stimulation applied 1-mA anodal tDCS over LIFG for the test duration (10 min). RESULTS: Responses were faster following active stimulation than following sham. Furthermore, improvements were specific to test conditions involving novel generation (p = .030) and selection (p = .001) and were not observed in control conditions for which these mechanisms were minimally involved. CONCLUSIONS: We concluded that tDCS benefits conceptual preparation mechanisms. This preliminary evidence is an important step for addressing age-related decline in propositional language generation, which is integral to conversational speech. This approach could also be extended toward rehabilitation in neurological patients with deficits in these processes.

Frontal dynamic aphasia in progressive supranuclear palsy: Distinguishing between generation and fluent sequencing of novel thoughts.

Frontal dynamic aphasia is characterised by a profound reduction in spontaneous speech despite well-preserved naming, repetition and comprehension. Since Luria (1966, 1970) designated this term, two main forms of dynamic aphasia have been identified: one, a language-specific selection deficit at the level of word/sentence generation, associated with left inferior frontal lesions; and two, a domain-general impairment in generating multiple responses or connected speech, associated with more extensive bilateral frontal and/or frontostriatal damage. Both forms of dynamic aphasia have been interpreted as arising due to disturbances in early prelinguistic conceptual preparation mechanisms that are critical for language production. We investigate language-specific and domain-general accounts of dynamic aphasia and address two issues: one, whether deficits in multiple conceptual preparation mechanisms can co-occur; and two, the contribution of broader cognitive processes such as energization, the ability to initiate and sustain response generation over time, to language generation failure. Thus, we report patient WAL who presented with frontal dynamic aphasia in the context of progressive supranuclear palsy (PSP). WAL was given a series of experimental tests that showed that his dynamic aphasia was not underpinned by a language-specific deficit in selection or in microplanning. By contrast, WAL presented with a domain-general deficit in fluent sequencing of novel thoughts. The latter replicated the pattern documented in a previous PSP patient (Robinson, et al., 2006); however, unique to WAL, generating novel thoughts was impaired but there was no evidence of a sequencing deficit because perseveration was absent. Thus, WAL is the first unequivocal case to show a distinction between novel thought generation and subsequent fluent sequencing. Moreover, WAL's generation deficit encompassed verbal and non-verbal responses, showing a similar (but more profoundly reduced) pattern of performance to frontal patients with an energization deficit. In addition to impaired generation of novel thoughts, WAL presented with a concurrent strategy generation deficit, both falling within the second form of dynamic aphasia comprised of domain-general conceptual preparation mechanisms. Thus, within this second form of dynamic aphasia, concurrent deficits can co-occur. Overall, WAL presented with the second form of dynamic aphasia and was impaired in the generation of novel thoughts and internally-generated strategies, in the context of PSP and bilateral frontostriatal damage.

An unusual presentation of probable dementia: rhyming, associations, and verbal disinhibition.

We report a case of probable Alzheimer's disease who presented with the unusual feature of disinhibited rhyming. Core language skills were largely intact but generative language was characterized by semantic-based associations, evident in tangential and associative content, and phonology-based associations, evident in rhyming, in the context of prominent executive dysfunction. We suggest this pattern is underpinned by a failure to terminate or inhibit verbal associations resulting in a 'loosening' of associations at the level of conceptual preparation for spoken language.

Primary progressive dynamic aphasia and Parkinsonism: generation, selection and sequencing deficits.

MC is the first reported case of dynamic aphasia in the context of non-fluent progressive aphasia and Parkinson's disease. MC's language profile was characterised by the hallmark propositional language impairment despite well-preserved naming, reading, repetition and comprehension skills. The severity of MC's propositional language deficit was comparable to other dynamic aphasic patients. Word and sentence generation performance was severely impaired only when many competing responses were activated by a stimulus. Thus, when a dominant response was available verbal generation was satisfactory. MC also presented with a deficit in idea generation and fluent sequencing of novel thoughts as discourse generation was extremely reduced and perseverative. In addition, non-verbal generation was impaired although dissociations emerged. MC was able to generate novel designs and gestures but his performance was highly perseverative, and his motor movement selection was abnormal, resembling a non-random pattern. MC is the first dynamic aphasic case with concurrent deficits in three mechanisms thought crucial for conceptual preparation processes; namely impaired selection, impaired generation of ideas and impaired fluent sequencing of novel thoughts. The findings are discussed in relation to conceptual preparation processes and their organisation, accounts of dynamic aphasia and the roles of the left inferior frontal and basal ganglia regions in conceptual preparation processes for verbal and non-verbal generation.