Gail Robinson

The differing roles of the frontal cortex in fluency tests

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.

A failure of high level verbal response selection in progressive dynamic aphasia

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 Brodmanns Areas 44 and 45. Our findings are discussed with reference to alternative accounts of dynamic aphasia and models of speech production. We interpret our patients 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.

Fractionation of visual memory: Evidence from a case with multiple neurodevelopmental impairments

It is known that the adult visual memory system is fractionable into functionally independent cognitive subsystems, selectively susceptible to brain damage. However, it is unclear whether these cognitive subsystems can fractionate developmentally. The present study describes an investigation of visual memory of a patient (PE) with multiple developmental disorders. PE was congenitally deaf, had Gilles de la Tourette syndrome and autism, with non-verbal ability in the normal range. The patient presented with a recognition memory impairment for unknown human faces. This contrasted with his superior recognition memory for unknown buildings, landscapes and outdoor scenes. PEs memory impairment for faces could not be explained by a general deficit in face processing. Interestingly, PE also showed a recognition memory impairment for animals. These findings indicate that different domains of the visual memory system can be fractionated developmentally. In particular, it demonstrates that topographical memory can develop independently from other aspects of visual memory.

Conceptual proposition selection and the LIFG: Neuropsychological evidence from a focal frontal group

Much debate surrounds the role of the left inferior frontal gyrus (LIFG). Evidence from lesion and neuroimaging studies suggests the LIFG supports a selection mechanism used in single word generation. Single case studies of dynamic aphasic patients with LIFG damage concur with this and extend the finding to selection of sentences at the conceptual preparation stage of language generation. A neuropsychological group with unselected focal frontal and non-frontal lesions is assessed on a sentence generation task that varied the number of possible conceptual propositions available for selection. Frontal patients with LIFG damage when compared to Frontal patients without LIFG damage and Posterior patients were selectively impaired on sentence generation tests only when stimuli activated multiple conceptual propositions that compete with each other for selection. We found that this selective impairment is critical for reduced speech rate, the core deficit of dynamic aphasia, and we would argue it is causative for one form of dynamic aphasia associated with LIFG lesions. These results provide evidence that the LIFG is crucial for selecting among multiple competing conceptual propositions for language generation.

Verbal suppression and strategy use: a role for the right lateral prefrontal cortex?

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.

Selective sparing of verb naming in a case of severe Alzheimer's disease

A patient with severe Alzheimers disease (AD) presented with a severe impairment in naming nouns but selective sparing of the naming of verbs. Her impairment in naming nouns was presented across a wide range of categories investigated. To our knowledge, this is the first case documenting the selective preservation of verb naming in a patient with AD. The implications for the notion of an intrinsic vulnerability of verb naming in AD and for the current knowledge of anatomical correlates of noun/verb processing are discussed.

The selective preservation of colour naming in semantic dementia.

This paper documents a series of seven patients with semantic dementia who showed a selective preservation in colour naming. This was in the context of a pervasive impairment in naming nouns across a wide range of other semantic categories. To our knowledge, this is the first series of patients with semantic dementia documenting a selective preservation of colour naming. These findings are discussed in the light of current theoretical accounts of category-specific effects and the possible contribution of imageability to this selective preservation of colours.

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 Parkinsons disease. MCs language profile was characterised by the hallmark propositional language impairment despite well-preserved naming, reading, repetition and comprehension skills. The severity of MCs 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.

Theory of mind and the social brain: implications for understanding the genetic basis of schizophrenia

Genome‐wide association studies in schizophrenia have recently made significant progress in our understanding of the complex genetic architecture of this disorder. Many genetic loci have been identified and now require functional investigation. One approach involves studying their correlation with neuroimaging and neurocognitive endophenotypes. Theory of Mind (ToM) deficits are well established in schizophrenia and they appear to fulfill criteria for being considered an endophenotype. We aim to review the behavioral and neuroimaging‐based studies of ToM in schizophrenia, assess its suitability as an endophenotype, discuss current findings, and propose future research directions. Suitable research articles were sourced from a comprehensive literature search and from references identified through other studies. ToM deficits are repeatable, stable, and heritable: First‐episode patients, those in remission and unaffected relatives all show deficits. Activation and structural differences in brain regions believed important for ToM are also consistently reported in schizophrenia patients at all stages of illness, although no research to date has examined unaffected relatives. Studies using ToM as an endophenotype are providing interesting genetic associations with both single nucleotide polymorphisms (SNPs) and specific copy number variations (CNVs) such as the 22q11.2 deletion syndrome. We conclude that ToM is an important cognitive endophenotype for consideration in future studies addressing the complex genetic architecture of schizophrenia, and may help identify more homogeneous clinical sub‐types for further study

Age of acquisition effects on spelling in surface dysgraphia

Background: It is not known whether the age of acquisition (AoA) of a word has any significant effect on the spelling performance of normal or impaired speakers. One way to explore this question is to examine the effects of AoA on surface dysgraphia. Aims: We report MK, a patient who suffered herpes simplex viral encephalitis (HSVE) resulting in semantic anomia and surface dysgraphia that we characterise as a tendency to produce a legitimate alternative spelling of a component defined as a LASC error. Methods & Procedures: We describe MKs neuropsychological profile, giving details of impaired naming, spoken and written word comprehension, written picture naming, oral reading, and spelling to dictation, but preserved repetition of whole words. We report experiments designed (1) to test the effect of AoA on spelling by controlling for word frequency as well as other correlated variables using logistic regression and ANOVA, and (2) to test the effects of AoA and sound to spelling predictability on MKs spelling. Outcomes and Results: The results show an effect of AoA but no independent effect of frequency on spelling and an interaction between AoA and predictability, i.e., an effect of AoA on unpredictable word spelling but no effect of AoA on predictable word spelling. Conclusions: We discuss these data with reference to accounts of AoA that locate the effect at the level of mappings between input (phonological) and output (orthographic) representations. We argue that the effect of AoA on spelling is not the result of lexeme activation per se but instead reflects the largely unpredictable mappings between sound and spelling that characterise the majority of English word spellings.