Fluency tasks have been widely used to tap the voluntary generation of responses. The anatomical correlates of fluency tasks and their sensitivity and specificity have been hotly debated. However, investigation of the cognitive processes involved in voluntary generation of responses and whether generation is supported by a common, general process (e.g. fluid intelligence) or specific cognitive processes underpinned by particular frontal regions has rarely been addressed. This study investigates a range of verbal and non-verbal fluency tasks in patients with unselected focal frontal (n=47) and posterior (n=20) lesions. Patients and controls (n=35) matched for education, age and sex were administered fluency tasks including word (phonemic/semantic), design, gesture and ideational fluency as well as background cognitive tests. Lesions were analysed by standard anterior/posterior and left/right frontal subdivisions as well as a finer-grained frontal localization method. Thus, patients with right and left lateral lesions were compared to patients with superior medial lesions. The results show that all eight fluency tasks are sensitive to frontal lobe damage although only the phonemic word and design fluency tasks were specific to the frontal region. Superior medial patients were the only group to be impaired on all eight fluency tasks, relative to controls, consistent with an energization deficit. The most marked fluency deficits for lateral patients were along material specific lines (i.e. left-phonemic and right-design). Phonemic word fluency that requires greater selection was most severely impaired following left inferior frontal damage. Overall, our results support the notion that frontal functions comprise a set of specialized cognitive processes, supported by distinct frontal regions.

In this study we report a patient (A.N.G.) who, following a malignant left frontal meningioma impinging upon Brodmann area 45, presented a 'pure' dynamic aphasia. Her spontaneous speech was markedly reduced in the absence of any syntactical impairment. Her naming, repetition and reading skills were completely normal. Two experimental investigations were carried out. The first investigation found that A.N.G. had a profound impairment in phrase and sentence generation tasks given a verbal context. However, her verbal generative skills were normal when she was asked to describe pictorial scenes and complex actions. Moreover, it was found that A.N.G. had no difficulty ordering the constituent words of a sentence. Thus, it was concluded that her verbal planning skills were intact. The second investigation tested a hypothesis that dynamic aphasia is due to an inability to select a verbal response option whenever the stimulus activates many competing verbal responses. Predictions based upon this hypothesis were confirmed on three different verbal generation tasks. It was found that our patient's grave verbal generative impairment was present for tasks involving stimuli which activate many potential responses. However, it was absent for tasks involving stimuli which activate few or only a single 'prepotent' response. The findings are discussed with reference to traditional interpretations of dynamic aphasia and more general interpretations of prefrontal cortex functioning. On the basis of a computational model of prefrontal cortex functioning, we propose that pure dynamic aphasia may be caused by damage to a 'context' module containing units responsible for selection of verbal response options. Moreover, it is suggested that our findings support the view that Brodmann area 45 is involved in verbal response generation to stimuli which activate many potential response options.

Brain malformations involving the corpus callosum are common in children with developmental disabilities. We identified DCC mutations in four families and five sporadic individuals with isolated agenesis of the corpus callosum (ACC) without intellectual disability. DCC mutations result in variable dominant phenotypes with decreased penetrance, including mirror movements and ACC associated with a favorable developmental prognosis. Possible phenotypic modifiers include the type and location of mutation and the sex of the individual.

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Different theoretical interpretations have been offered in order to account for a specific language impairment termed dynamic aphasia. We report a patient (CH) who presented with a dynamic aphasia in the context of nonfluent progressive aphasia. CH had the hallmark of reduced spontaneous speech in the context of preserved naming, reading, and single word repetition and comprehension. Articulatory and grammatical difficulties were also present. CH had a very severe verbal generation impairment despite being able to describe pictorial scenes and action sequences well. In the experimental investigations CH was severely impaired in word, phrase, and sentence generation tasks when many competing responses were activated by a stimulus. By contrast, he could generate verbal responses satisfactorily when a dominant response was activated by a stimulus. For the first time, we demonstrated that the verbal generation impairment was specific to the production of language. Strikingly, our patient was unimpaired on a number of nonverbal generation tasks (e.g., design fluency, gesture fluency, and motor movement generation). MRI revealed focal left frontal atrophy that predominantly affected Brodmann's Areas 44 and 45. Our findings are discussed with reference to alternative accounts of dynamic aphasia and models of speech production. We interpret our patient's impairment as being underpinned by an inability to select between competing verbal response options. This interpretation converges with evidence from the neuroimaging literature, which implicates the left inferior frontal gyrus in the selection of a response among competing information. We conclude that the left posterior inferior frontal gyrus is involved in the generation of verbal output, and specifically in the selection between competing verbal responses.

Neuropsychological deficits are prevalent at all points of recovery from anti-NMDAR encephalitis, although improvement in cognitive outcomes can be expected as patients recover. Some cognitive deficits may be less likely than others to resolve. Close neuropsychological monitoring is warranted in this population. Longitudinal studies of neuropsychological functioning of patients with anti-NMDAR encephalitis are needed to accurately inform prognosis.

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.

Verbal initiation, suppression and strategy generation/use are cognitive processes widely held to be supported by the frontal cortex. The Hayling Test was designed to tap these cognitive processes within the same sentence completion task. There are few studies specifically investigating the neural correlates of the Hayling Test but it has been primarily used to detect frontal lobe damage. This study investigates the components of the Hayling Test in a large sample of patients with unselected focal frontal (n = 60) and posterior (n = 30) lesions. Patients and controls (n = 40) matched for education, age and sex were administered the Hayling Test as well as background cognitive tests. The standard Hayling Test clinical measures (initiation response time, suppression response time, suppression errors and overall score), composite errors scores and strategy-based responses were calculated. Lesions were analysed by classical frontal/posterior subdivisions as well as a finer-grained frontal localization method and a specific contrast method that is somewhat analogous to voxel-based lesion mapping methods. Thus, patients with right lateral, left lateral and superior medial lesions were compared to controls and patients with right lateral lesions were compared to all other patients. The results show that all four standard Hayling Test clinical measures are sensitive to frontal lobe damage although only the suppression error and overall scores were specific to the frontal region. Although all frontal patients produced blatant suppression errors, a specific right lateral frontal effect was revealed for producing errors that were subtly wrong. In addition, frontal patients overall produced fewer correct responses indicative of developing an appropriate strategy but only the right lateral group showed a significant deficit. This problem in strategy attainment and implementation could explain, at least in part, the suppression error impairment. Contrary to previous studies there was no specific frontal effect for verbal initiation. Overall, our results support a role for the right lateral frontal region in verbal suppression and, for the first time, in strategy generation/use.