PubMed Health⌕ Search

Biomedical subjects

Narinder Kapur

Publications and source records attributed to Narinder Kapur.

9 recordsLinked to original sources
PubMed2005

Specialization in the medial temporal lobe for processing of objects and scenes.

There has been considerable debate as to whether the hippocampus and perirhinal cortex may subserve both memory and perception. We administered a series of oddity tasks, in which subjects selected the odd stimulus from a visual array, to amnesic patients with either selective hippocampal damage (HC group) or more extensive medial temporal damage, including the perirhinal cortex (MTL group). All patients performed normally when the stimuli could be discriminated using simple visual features, even if faces or complex virtual reality scenes were presented. Both patient groups were, however, severely impaired at scene discrimination when a significant demand was placed on processing spatial information across viewpoint independent representations, while only the MTL group showed a significant deficit in oddity judgments of faces and objects when object viewpoint independent perception was emphasized. These observations provide compelling evidence that the human hippocampus and perirhinal cortex are critical to processes beyond long-term declarative memory and may subserve spatial and object perception, respectively.

Aged↗
PubMed2005

Perceptual deficits in amnesia: challenging the medial temporal lobe 'mnemonic' view.

Recent animal studies suggest that the medial temporal lobe (MTL), which is thought to subserve memory exclusively, may support non-mnemonic perceptual processes, with the hippocampus and perirhinal cortex contributing to spatial and object perception, respectively. There is, however, no support for this view in humans, with human MTL lesions causing prominent memory deficits in the context of apparently normal perception. We assessed visual discrimination in amnesic cases to reveal that while selective hippocampal damaged patients could discriminate faces, objects, abstract art and colour, they were significantly poorer in discriminating spatial scenes. By contrast, patients with MTL damage, including perirhinal cortex, were significantly impaired in discriminating scenes, faces, and to a lesser extent objects, with relatively intact discrimination of art and colour. These novel observations imply that the human MTL subserves both perceptual and mnemonic functions, with the hippocampus and perirhinal cortex playing distinct roles in spatial and object discrimination, respectively.

Aged↗
PubMed2004

Dissociating person-specific from general semantic knowledge: roles of the left and right temporal lobes.

The cognitive architecture and neural underpinnings of different semantic domains remains highly controversial. We report two patients with focal temporal lobe atrophy who presented with contrasting and theoretically informative dissociations of person-specific versus general semantic knowledge. Subject J.P. showed severely impaired person-specific semantics, with relative preservation of knowledge about objects and animals, while subject M.A. exhibited the opposite pattern of performance (good knowledge of people in the context of impoverished general semantics). Voxel-based morphometric analysis of MR images in the two cases established predominantly right temporal atrophy associated with J.P.'s deficit for person knowledge and predominantly left temporal atrophy in M.A. who was impaired in general conceptual knowledge.

Atrophy↗
PubMed2003

Unexpected amnesia: are there lessons to be learned from cases of amnesia following unilateral temporal lobe surgery?

Cases of amnesia following unilateral temporal lobe surgery are rare, but they may provide important insights into human brain functioning. Such cases are reconsidered here in the light of recent developments in clinical and cognitive neuroscience. Descriptions of preoperative seizure activity in these cases indicate the potentially valuable role of ictal semiology in localizing the source of epileptiform discharges. Cases of amnesia after unilateral temporal lobectomy illustrate the complexity of intra- and inter-hemispheric propagation of epileptiform discharges and highlight possible neurophysiological mechanisms underlying false localization of abnormal EEG activity. This review points to the value of preoperative neuropsychological assessment in providing information on the likely primary locus of pathology and in predicting outcome after surgery. The analysis of cases upholds the benefits of the Wada procedure, but it highlights the variability in Wada test procedures and the fact that Wada test scores themselves may be open to varying interpretation. These cases of postoperative amnesia are further considered in the context of the cognitive neuroscience of human memory and, in particular, mechanisms underlying the human amnesic syndrome. They confirm the critical role of bilateral medial temporal lobe structures in anterograde memory, but they also highlight the complexity in teasing apart neural mechanisms underlying remote memory loss.

Amnesia↗
PubMed2003

Dissociating medial temporal and basal ganglia memory systems with a latent learning task.

The medial temporal (MT) lobes and basal ganglia have both been implicated as brain substrates of associative learning. Here, we show a dissociation between medial temporal and basal ganglia damage using a latent learning task, in which prior exposure to cues, uncorrelated with each other, slows subsequent learning of an association between them. Consistent with prior work, we found a robust exposure effect in healthy controls, with exposed controls learning more slowly than non-exposed controls. This effect was abolished in medial temporal amnesia: both exposed and non-exposed amnesic patients learned at the same speed. A group of patients with basal ganglia damage due to Parkinson's disease showed a reversal of the effect: exposed subjects learned faster than non-exposed subjects. Our findings point to distinct and dissociable contributions of medial temporal lobe and basal ganglia structures to learning and memory.

Adult↗
PubMed2003

Routes to remembering: the brains behind superior memory.

Why do some people have superior memory capabilities? We addressed this age-old question by examining individuals renowned for outstanding memory feats in forums such as the World Memory Championships. Using neuropsychological measures, as well as structural and functional brain imaging, we found that superior memory was not driven by exceptional intellectual ability or structural brain differences. Rather, we found that superior memorizers used a spatial learning strategy, engaging brain regions such as the hippocampus that are critical for memory and for spatial memory in particular. These results illustrate how functional neuroimaging might prove valuable in delineating the neural substrates of mnemonic techniques, which could broaden the scope for memory improvement in the general population and the memory-impaired.

Adult↗
PubMed2003

Advanced brain imaging procedures and human memory disorder.

The impact of advanced brain imaging procedures in the field of human memory disorder is reviewed, with particular emphasis on current and potential applications that may impact upon the diagnosis and management of memory-disordered patients. While both advanced structural, resting physiological and functional physiological brain imaging procedures have been applied to conditions where memory disorder is a major feature, the specific implications of research findings for diagnosis and treatment in routine clinical practice remain tentative and promising, but not yet substantive enough to inform clinical decisions to a significant degree. In terms of diagnostic applications, several promising areas include dementia, epilepsy, and transient amnesic states. In the case of applications in treatment settings, advanced brain imaging procedures may help to monitor neural correlates of spontaneous recovery or progression of memory function, and may also help in the planning and monitoring of therapeutic intervention.

Brain↗