1,721,183 research outputs found
Fractionation of memory in medial temporal lobe amnesia.
No full textWe report a comprehensive investigation of the anterograde memory functions of two patients with memory impairments (RH and JC). RH had neuroradiological evidence of apparently selective right-sided hippocampal damage and an intact cognitive profile apart from selective memory impairments. JC, had neuroradiological evidence of bilateral hippocampal damage following anoxia due to cardiac arrest. He had anomic and "executive" difficulties in addition to a global amnesia, suggesting atrophy extending beyond hippocampal regions. Their performance is compared with that of a previously reported hippocampal amnesic patient who showed preserved recollection and familiarity for faces in the context of severe verbal and topographical memory impairment [VC; Cipolotti, L., Bird, C., Good, T., Macmanus, D., Rudge, P., & Shallice, T. (2006). Recollection and familiarity in dense hippocampal amnesia: A case study. Neuropsychologia, 44, 489-506.] The patients were administered experimental tests using verbal (words) and two types of non-verbal materials (faces and buildings). Receiver operating characteristic analyses were used to estimate the contribution of recollection and familiarity to recognition performance on the experimental tests. RH had preserved verbal recognition memory. Interestingly, her face recognition memory was also spared, whilst topographical recognition memory was impaired. JC was impaired for all types of verbal and non-verbal materials. In both patients, deficits in recollection were invariably associated with deficits in familiarity. JC's data demonstrate the need for a comprehensive cognitive investigation in patients with apparently selective hippocampal damage following anoxia. The data from RH suggest that the right hippocampus is necessary for recollection and familiarity for topographical materials, whilst the left hippocampus is sufficient to underpin these processes for at least some types of verbal materials. Face recognition memory may be adequately subserved by areas outside of the hippocampus
Neuropsychologically plausible models of sequence generation
No full textWe investigate the possibility of incorporating the sequential dynamics of a 'Competitive Queuing' system in a multi-layer perceptron (MLP) architecture. The approach is applied to a model of output processes in spelling, and we show that it provides an explanation for so-called 'Graphemic Buffer Disorder'. We describe a patient with an apparently novel dysgraphia affecting the start of words, and show that this can also be explained in terms of a simple manipulation to the model
The impact of different aetiologies on the cognitive performance of frontal patients.
No full textNeuropsychological group study methodology is considered one of the primary methods to further understanding of the organisation of frontal 'executive' functions. Typically, patients with frontal lesions caused by stroke or tumours have been grouped together to obtain sufficient power. However, it has been debated whether it is methodologically appropriate to group together patients with neurological lesions of different aetiologies. Despite this debate, very few studies have directly compared the performance of patients with different neurological aetiologies on neuropsychological measures. The few that did included patients with both anterior and posterior lesions. We present the first comprehensive retrospective comparison of the impact of lesions of different aetiologies on neuropsychological performance in a large number of patients whose lesion solely affects the frontal cortex. We investigated patients who had a cerebrovascular accident (CVA), high (HGT) or low grade (LGT) tumour, or meningioma, all at the post-operative stage. The same frontal 'executive' (Raven's Advanced Progressive Matrices, Stroop Colour-Word Test, Letter Fluency-S; Trail Making Test Part B) and nominal (Graded Naming Test) tasks were compared. Patients' performance was compared across aetiologies controlling for age and NART IQ scores. Assessments of focal frontal lesion location, lesion volume, global brain atrophy and non-specific white matter (WM) changes were undertaken and compared across the four aetiology. We found no significant difference in performance between the four aetiology subgroups on the 'frontal' executive and nominal tasks. However, we found strong effects of premorbid IQ on all cognitive tasks and robust effects of age only on the frontal tasks. We also compared specific aetiology subgroups directly, as previously reported in the literature. Overall we found no significant differences in the performance of CVA and tumour patients, or LGT and HGT patients or LGT, HGT and meningioma's on our four frontal tests. No difference was found with respect to the location of frontal lesions, lesion volume, global brain atrophy and non-specific WM changes between the subgroups. Our results suggest that the grouping of frontal patients caused by different aetiologies is a pragmatic, justified methodological approach that can help to further understanding of the organisation of frontal executive functions
Dynamic aphasia in progressive supranuclear palsy: A deficit in generating a fluent sequence of novel thought
No full textWe report a patient (KAS) who presented with pure dynamic aphasia in the context of progressive supranuclear palsy (PSP). KAS had the hallmark propositional language impairment in the context of preserved naming, reading, repetition and comprehension skills. The severity of KAS's propositional language deficit was demonstrated to be comparable to other dynamic aphasic patients. Remarkably, despite virtually abolished propositional speech, KAS was unimpaired on word and sentence level generation tasks that required a single response. This dissociation was further investigated on two discourse level generation tasks that required the generation of multiple connected sentences. Quantitative production analysis and novelty measures demonstrated that her performance was extremely reduced and characterised by a lack of novel words and sentences and a tendency to perseverate. This pattern of performance suggests that there may be two subtypes of dynamic aphasia. Patients with the more documented first subtype have language-specific deficits, fail word and sentence level generation tests and have left inferior frontal gyrus lesions. Patients with the second subtype, like KAS, pass word and sentence level generation tests and fail discourse level generation tests. They have a verbal and non-verbal generation deficit and bilateral frontal and subcortical damage. Our findings are discussed with reference to executive functioning accounts of dynamic aphasia and models of speech production. We interpret our patients' impairment as being underpinned by a deficit in one set of mechanisms involved in discourse generation; namely the generation of a fluent sequence of novel thought. (c) 2006 Elsevier Ltd. All rights reserved
Cognitive and social cognitive functioning in spinocerebellar ataxia: a preliminary characterization
No full textIntroduction The spinocerebellar ataxias (SCAs), are rare neurodegenerative disorders caused by distinct genetic mutations. Clinically, the SCAs are characterised by progressive ataxia and a variety of other features, including cognitive dysfunction. The latter is consistent with a growing body of evidence supporting a cognitive as well as motor role for the cerebellum. Recent suggestions of cerebellar involvement in social cognition have not been extensively explored in these conditions. The availability of definitive molecular diagnosis allows genetically defined subgroups of SCA patients, with distinct patterns of cerebellar and extracerebellar involvement, to be tested comparatively using a common battery of tests of general, social and emotional cognition. Methods: Nine patients with SCA6, and 6 with SCA3 were assessed using a comprehensive battery of neuropsychological instruments, encompassing domains of memory, language, visuo-spatial skills, calculation, attention and executive function, emotional processing and theory of mind (ToM). Results There were no deficits in visuo-spatial processing or calculation in either group, while individuals with naming and attentional difficulties were seen in both. Deficits in memory and executive function were present in both conditions, albeit more pronounced in SCA3. By contrast, both groups demonstrated consistently poor performance on ToM tests, and normal attribution of social and emotional responses. Conclusion The data support the hypothesis that the cerebellum is important for cognitive as well as motor activity. The pattern of overlap of domain impairments provides tentative preliminary evidence that there is a cerebellar contribution to aspects of memory and executive function and ToM, and that other domains depend more on neural system outside the cerebellum. The findings relating to ToM are relevant to the possibility of cerebellar involvement in autism
Towards a unified process model for graphemic buffer disorder and deep dysgraphia
No full textModels based on the competitive queuing (CQ) approach can explain many of the effects on
dysgraphic patients’ spelling attributed to disruption of the “graphemic output buffer”. Situating
such a model in the wider spelling system, however, raises the question of what happens when
input to the buffer (e.g., from a semantic system) is degraded while the buffer remains intact. We
present a preliminary exploration of predictions following from the CQ approach. We show that
the CQ account of the graphemic buffer predicts and explains the finding that deep dysgraphic
patients generally show features of graphemic buffer disorder, as disrupted input from a damaged
semantic system has an inevitable effect upon the functioning of the buffer. The approach also explains
the most salient differences between the two syndromes, which are seen as consequences of the differ-
ence between an intact sequence generation system operating on degraded input versus a damaged
sequencing system operating on intact input
The role of the prefrontal cortex in familiarity and recollection processes during verbal and non verbal recognition memory: a rTMS study.
Full text linkNeuroimaging and lesion studies have documented the involvement of the frontal lobes in recognition memory. However, the precise nature of prefrontal contributions to verbal and non-verbal memory and to familiarity and recollection processes remains unclear. The aim of the current rTMS study was to investigate for the first time the role of the DLPFC in encoding and retrieval of non-verbal and verbal memoranda and its contribution to recollection and familiarity processes. Recollection and familiarity processes were studied using the ROC and unequal variance signal detection methodologies. We found that rTMS delivered over left and right DLPFC at encoding resulted in material specific laterality effects with a disruption of recognition of verbal and non-verbal memoranda. Interestingly, rTMS over DLPFCs at encoding significantly affected both recollection and familiarity. However, at retrieval rTMS did not affect recollection and familiarity. Our results suggest that DLPFC has a degree of functional specialisation and plays an important role in the encoding of verbal and non-verbal memoranda
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