Speech production: Wernicke, Broca and beyond

Abstract

We investigated the brain systems engaged during propositional speech (PrSp) and two forms of non- propositional speech (NPrSp): counting and reciting overlearned nursery rhymes. Bilateral cerebral and cerebellar regions were involved in the motor act of articulation, irrespective of the type of speech. Three additional, left-lateralized regions, adjacent to the Sylvian sulcus, were activated in common: the most posterior part of the supratemporal plane, the lateral part of the pars opercularis in the posterior inferior frontal gyrus and the anterior insula. Therefore, both NPrSp and PrSp were dependent on the same discrete subregions of the anatomically ill-defined areas of Wernicke and Broca. PrSp was also dependent on a predominantly left-lateralized neural system distributed between multi-modal and amodal regions in posterior inferior parietal, anterolateral and medial temporal and medial prefrontal cortex. The lateral prefrontal and paracingulate cortical activity observed in previous studies of cued word retrieval was not seen with either NPrSp or PrSp, demonstrating that normal brain- language representations cannot be inferred from explicit metalinguistic tasks. The evidence from this study indicates that normal communicative speech is dependent on a number of left hemisphere regions remote from the classic language areas of Wernicke and Broca. Destruction or disconnection of discrete left extrasylvian and perisylvian cortical regions, rather than the total extent of damage to perisylvian cortex, will account for the qualitative and quantitative differences in the impaired speech production observed in aphasic stroke patients.

Verbal adynamia in parkinsonian syndromes: behavioral correlates and neuroanatomical substrate

“…Anatomical small volumes were derived from the Oxford–Harvard brain maps (Desikan et al, 2006) in FSL view (Jenkinson, Beckmann, Behrens, Woolrich, & Smith, 2012), comprising key brain regions previously implicated in generation of propositional language output (Blank et al, 2002; Braun et al, 2001; Wagner et al, 2001) (left inferior and superior frontal, left posterior superior temporal gyri).…”

“…Here, we refer to speech as exemplified by everyday conversation, in which we are generally required to create a verbal message, however banal. Deficits of propositional speech output we subsume under the general term “verbal adynamia;” in its most well-defined and selective form, impaired generation of novel verbal messages leads to a characteristic, specific language disorder, “dynamic aphasia.” Dynamic aphasia is characterized by disproportionate impoverishment of propositional speech despite relatively preserved ability to produce speech in specific contexts such as naming, repetition, or reading; the core cognitive deficit has been variously held to reflect impaired construction of a sentence scheme, generation of novel verbal ideas, fluent sequencing of verbal thought, or selection among prepotent verbal alternatives (Costello & Warrington, 1989; Blank, Scott, Murphy, Warburton, & Wise, 2002; Esmonde, Giles, Xuereb, & Hodges, 1996; Robinson, Shallice, & Cipolotti, 2006; Wagner, Pare-Blagoev, Clark, & Poldrack, 2001; Warren, Warren, Fox, & Warrington, 2003). These formulations are not mutually incompatible and more than one cognitive mechanism may operate, particularly in the setting of strategic or diffuse brain damage (Esmonde et al, 1996; Robinson et al, 2006; Robinson, Spooner, & Harrison, 2015).…”

“…Dynamic aphasia has been documented in association with various focal brain lesions involving the dominant frontal lobe and its connections (Blank et al, 2002; Braun, Guillemin, Hosey, & Varga, 2001; Robinson, 2013; Wagner et al, 2001) as well as neurodegenerative syndromes implicating this circuitry, notably PSP (Bak, Hodges, & Thomas, 2008; ; Esmonde et al, 1996; Litvan et al, 1996; Robinson, 2013; Robinson et al, 2015; Warren et al, 2003). Propositional speech production is mediated by a distributed neural network including left superior and inferior frontal gyri, frontal operculum, and posterior superior temporal cortex (Blank et al, 2002; Braun et al, 2001; Wagner et al, 2001).…”

“…Propositional speech production is mediated by a distributed neural network including left superior and inferior frontal gyri, frontal operculum, and posterior superior temporal cortex (Blank et al, 2002; Braun et al, 2001; Wagner et al, 2001). Disruption of these fronto-subcortical networks and, more particularly, dopaminergic projection pathways is clearly a candidate substrate for development of verbal adynamia across parkinsonian disorders (Robinson, 2013).…”

“…Second, we hypothesized on clinical and neuroanatomical grounds that verbal adynamia (as an index of reduced processing flexibility in fronto-subcortical brain networks) would differentiate parkinsonian syndromes: we predicted that verbal generation deficits would be more severe in PSP and CBS than in PDD, but would also show greater sensitivity to dopaminergic modulation than other cognitive deficits in PDD. Finally, we hypothesized a neuroanatomical correlate of verbal adynamia in dominant hemisphere circuits previously implicated in the generation of propositional speech (Blank et al, 2002; Braun et al, 2001). …”