RESUMO
Neuroimaging studies in humans have shown that different working memory (WM) tasks recruit a common bilateral fronto-parietal cortical network. Animal studies as well as neuroimaging studies in humans have suggested that this network, in particular the prefrontal cortex, is preferentially recruited when material from different domains (e.g. spatial information or verbal/object information) has to be memorized. Early imaging studies have suggested qualitative dissociations in the prefrontal cortex for spatial and object/verbal WM, either in a left-right or a ventral-dorsal dimension. However, results from different studies are inconsistent. Moreover, recent fMRI studies have failed to find evidence for domain dependent dissociations of WM-related activity in prefrontal cortex. Here we present evidence from two independent fMRI studies using physically identical stimuli in a verbal and spatial WM task showing that domain dominance for WM does indeed exist, although only in the form of quantitative differences in activation and not in the form of a dissociation with different prefrontal regions showing mutually exclusive activation in different domains. Our results support a mixed dimension model of domain dominance for WM within the prefrontal cortex, with left ventral prefrontal cortex (PFC) supporting preferentially verbal WM and right dorsal PFC supporting preferentially spatial WM. The concept of domain dominance is discussed in the light of recent theories of prefrontal cortex function.
Assuntos
Mapeamento Encefálico , Dominância Cerebral/fisiologia , Lobo Frontal/fisiologia , Memória de Curto Prazo/fisiologia , Lobo Parietal/fisiologia , Adulto , Feminino , Humanos , Imageamento por Ressonância Magnética , Masculino , Rede Nervosa/fisiologia , Estimulação Luminosa , Tempo de Reação/fisiologia , Valores de Referência , Percepção Espacial/fisiologia , Comportamento Espacial/fisiologia , Aprendizagem Verbal/fisiologiaRESUMO
Hypofrontality and decreased lateralization have been two major, albeit controversial, results from functional neuroimaging studies of schizophrenia. We used fMRI to study cortical activation during a verbal and spatial working memory (WM) task (2-back) in 15 inpatients acutely ill with schizophrenia and 15 matched control subjects. We hypothesized (i) hypofrontality in patients in both tasks and (ii) decreased lateralization of prefrontal activation in patients under the assumption that, in controls, left prefrontal cortex (PFC) is engaged preferentially in the verbal task (verbal domain dominance) and the right prefrontal cortex is engaged preferentially in the spatial task (spatial domain dominance). Our results showed no significant differences in frontal activation between controls and patients, i.e. no hypofrontality in patients, even at a very liberal threshold (p<0.01). This may be explained by the fact that nearly all patients studied received atypical neuroleptics. Nonetheless, we found evidence for more subtle, domain-related prefrontal dysfunction. Whereas controls showed verbal WM domain dominance in left inferior frontal cortex and spatial WM domain dominance in right prefrontal cortex, these domain dominance effects were absent in the patient group, i.e. there were no lateralization effects. Finally, only patients showed an inverse correlation between performance and right prefrontal activation in verbal WM. We conclude that the finding of hypofrontality may depend on the medication of the patients and that there is prefrontal dysfunction even in the absence of hypofrontality.
Assuntos
Lobo Frontal/fisiopatologia , Processamento de Imagem Assistida por Computador , Imageamento Tridimensional , Imageamento por Ressonância Magnética , Memória de Curto Prazo/fisiologia , Orientação/fisiologia , Reconhecimento Visual de Modelos/fisiologia , Córtex Pré-Frontal/fisiopatologia , Esquizofrenia/fisiopatologia , Psicologia do Esquizofrênico , Aprendizagem Verbal/fisiologia , Adulto , Mapeamento Encefálico , Feminino , Humanos , Masculino , Testes Neuropsicológicos , Esquizofrenia/diagnóstico , Aprendizagem Seriada/fisiologiaRESUMO
Episodic memory performance varies in older subjects but underlying biological correlates remain as yet ambiguous. We investigated episodic memory in healthy older individuals (n=24; mean age: 64.4+/-6.7 years) without subjective memory complaints or objective cognitive impairment. Episodic memory was assessed with repetitive learning and recall of abstract geometric patterns during fMRI. Group analysis of brain activity during initial learning and maximum recall revealed hippocampal activation. Correlation analysis of brain activation and task performance demonstrated significant hippocampal activity during initial learning and maximum recall in a success-dependent manner. Neither age nor gray matter densities correlated with hippocampal activation. Functional imaging of episodic memory thus permits to detect objectively variability in hippocampal recruitment in healthy aged individuals without subjective memory complaints. Correlation analysis of brain activation and performance during an episodic memory task may be used to determine and follow-up hippocampal malfunction in a very sensitive manner.
Assuntos
Envelhecimento/fisiologia , Hipocampo/fisiologia , Imageamento por Ressonância Magnética , Memória/fisiologia , Idoso , Mapeamento Encefálico/métodos , Feminino , Humanos , Processamento de Imagem Assistida por Computador , Masculino , Pessoa de Meia-Idade , Testes Neuropsicológicos , Reconhecimento Visual de Modelos , Padrões de ReferênciaRESUMO
PURPOSE: To evaluate the frequency and significance of thromboembolic complications following endovascular treatment of aortic aneurysms. METHODS: One hundred seventy-four patients (153 men; mean 71.4 years, range 26-90) underwent endovascular repair of aneurysms of the thoracic (n = 38) or abdominal (n = 136) aorta using a variety of endografts. All patients were examined preprocedurally using 3-phase helical computed tomography (CT) to determine appropriate endograft size. To exclude the occurrence of infarction in parenchymal organs, the first postprocedural CT scan was compared with preoperative findings. Newly recognized perfusion deficits were taken as evidence of procedure-related infarction. RESULTS: Infarctions were detected in 16 (9.2%) patients: 13 in the kidneys, 2 in the spleen, with 1 in the mesentery; only the mesenteric infarction was clinically symptomatic. Both splenic infarctions were associated with deployment of stent-grafts in the thoracic aorta (5.3% of the 38 patients), while the mesenteric and 13 renal infarctions were seen in patients with infrarenal abdominal aortic aneurysms (0.7% and 9.6%, respectively, of 136 patients). One patient experienced complete thromboembolic occlusion of a renal artery, which was partially recanalized with intraoperative lysis. CONCLUSIONS: Thromboembolic complications of endovascular aortic aneurysm repairs are not uncommon, and although usually asymptomatic, these sequelae have the potential to be life threatening. Perfusion abnormalities may respond to immediate lytic therapy with complete dissolution of the thrombus in certain isolated cases.