oalib
Search Results: 1 - 10 of 100 matches for " "
All listed articles are free for downloading (OA Articles)
Page 1 /100
Display every page Item
Inferior parietal lobule volume and schneiderian first-rank symptoms in Antipsychotic-Naive schizophrenia: A 3-Tesla MRI study  [cached]
Danivas Vijay,Kalmady Sunil,Arasappa Rashmi,Behere Rishikesh
Indian Journal of Psychological Medicine , 2009,
Abstract: Background: As per Frith′s neuro-cognitive model, inferior parietal lobule (IPL) is implicated in the pathogenesis of Schneiderian first-rank symptoms (FRS) in schizophrenia. The specific role of IPL structural abnormalities in the pathogenesis of FRS is yet to be ascertained. Materials and Methods: Using 3-tesla MRI scanner, this first-time study examined antipsychotic-naοve schizophrenia patients ( n = 28) (patients with FRS [FRS +]: N = 14, M: F = 7:7; and patients without FRS [FRS-]: N = 14, M: F = 7:7) in comparison with sex-, handedness-, education- and socioeconomic status-matched healthy controls ( n = 14, M: F = 7:7). The volume of IPL was measured using a three-dimensional, interactive, semi-automated analysis, with good inter-rater reliability. Results: FRS + patients showed significant volume deficit in right IPL in comparison with healthy controls (F = 4.0; P=.028) after controlling for the potential confounding effects of age, sex and intracranial volume. Conclusions: Right IPL volume deficit in FRS+patients adds further support to the Frith′s model of FRS in schizophrenia.
Characterization of Visual Percepts Evoked by Noninvasive Stimulation of the Human Posterior Parietal Cortex  [PDF]
Peter J. Fried, Seth Elkin-Frankston, Richard Jarrett Rushmore, Claus C. Hilgetag, Antoni Valero-Cabre
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0027204
Abstract: Phosphenes are commonly evoked by transcranial magnetic stimulation (TMS) to study the functional organization, connectivity, and excitability of the human visual brain. For years, phosphenes have been documented only from stimulating early visual areas (V1–V3) and a handful of specialized visual regions (V4, V5/MT+) in occipital cortex. Recently, phosphenes were reported after applying TMS to a region of posterior parietal cortex involved in the top-down modulation of visuo-spatial processing. In the present study, we systematically characterized parietal phosphenes to determine if they are generated directly by local mechanisms or emerge through indirect activation of other visual areas. Using technology developed in-house to record the subjective features of phosphenes, we found no systematic differences in the size, shape, location, or frame-of-reference of parietal phosphenes when compared to their occipital counterparts. In a second experiment, discrete deactivation by 1 Hz repetitive TMS yielded a double dissociation: phosphene thresholds increased at the deactivated site without producing a corresponding change at the non-deactivated location. Overall, the commonalities of parietal and occipital phosphenes, and our ability to independently modulate their excitability thresholds, lead us to conclude that they share a common neural basis that is separate from either of the stimulated regions.
Orbitofrontal lobe volume deficits in Antipsychotic-Naive schizophrenia: A 3-Tesla MRI study
Behere Rishikesh,Kalmady Sunil,Venkatasubramanian Ganesan,Gangadhar B
Indian Journal of Psychological Medicine , 2009,
Abstract: Background: Prefrontal cortex deficits have been consistently demonstrated in schizophrenia. The orbitofrontal lobe (OFL), a critical component of the prefrontal cortex, subserves social and neuro-cognitive functions. While these functional impairments are established in schizophrenia, the OFL volume deficits have not been well studied, especially in antipsychotic-naοve patients. Aim: To study OFL volume deficits in antipsychotic-naοve schizophrenia patients in comparison with matched healthy controls using high-resolution 3-tesla (3T) magnetic resonance imaging (MRI). Materials and Methods: Fourteen antipsychotic-naοve schizophrenia patients (DSM-IV) and 14 age-, sex-, handedness- and education-matched healthy controls were scanned using 3T MRI. Psychopathology was assessed in the patient group using the scale for assessment of negative symptoms and the scale for assessment of positive symptoms (SAPS). The OFL volume was measured using Region of Interest (ROI)-based manual morphometry technique, with good inter-rater reliability (intra-class correlation coefficient = 0.98). Results: Total OFL volume was significantly smaller in schizophrenia patients (43.3 ± 9.6 mL) in comparison with healthy controls (52.1 ± 12.2 mL) after controlling for the potential confounding effects of age, sex and intracranial volume (F = 5.3, P = .03). Duration of untreated psychosis did not correlate significantly with OFL volumes. There was a trend towards significant negative correlation between the left and total OFL volumes and SAPS scores (r = -0.49, P = .06). Conclusion: OFL volume deficits might underlie the pathogenesis of schizophrenia symptoms with possible neuro-developmental origins.
Recency Effects in the Inferior Parietal Lobe during Verbal Recognition Memory  [PDF]
Bradley R. Buchsbaum,Donald Ye,Mark D’Esposito
Frontiers in Human Neuroscience , 2011, DOI: 10.3389/fnhum.2011.00059
Abstract: The most recently encountered information is often most easily remembered in psychological tests of memory. Recent investigations of the neural basis of such “recency effects” have shown that activation in the lateral inferior parietal cortex (LIPC) tracks the recency of a probe item when subjects make recognition memory judgments. A key question regarding recency effects in the LIPC is whether they fundamentally reflect the storage (and strength) of information in memory, or whether such effects are a consequence of task difficulty or an upswing in resting state network activity. Using functional magnetic resonance imaging we show that recency effects in the LIPC are independent of the difficulty of recognition memory decisions, that they are not a by-product of an increase in resting state network activity, and that they appear to dissociate from regions known to be involved in verbal working memory maintenance. We conclude with a discussion of two alternative explanations – the memory strength and “expectancy” hypotheses, respectively – of the parietal lobe recency effect.
Neuronal Chains for Actions in the Parietal Lobe: A Computational Model  [PDF]
Fabian Chersi, Pier Francesco Ferrari, Leonardo Fogassi
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0027652
Abstract: The inferior part of the parietal lobe (IPL) is known to play a very important role in sensorimotor integration. Neurons in this region code goal-related motor acts performed with the mouth, with the hand and with the arm. It has been demonstrated that most IPL motor neurons coding a specific motor act (e.g., grasping) show markedly different activation patterns according to the final goal of the action sequence in which the act is embedded (grasping for eating or grasping for placing). Some of these neurons (parietal mirror neurons) show a similar selectivity also during the observation of the same action sequences when executed by others. Thus, it appears that the neuronal response occurring during the execution and the observation of a specific grasping act codes not only the executed motor act, but also the agent's final goal (intention). In this work we present a biologically inspired neural network architecture that models mechanisms of motor sequences execution and recognition. In this network, pools composed of motor and mirror neurons that encode motor acts of a sequence are arranged in form of action goal-specific neuronal chains. The execution and the recognition of actions is achieved through the propagation of activity bursts along specific chains modulated by visual and somatosensory inputs. The implemented spiking neuron network is able to reproduce the results found in neurophysiological recordings of parietal neurons during task performance and provides a biologically plausible implementation of the action selection and recognition process. Finally, the present paper proposes a mechanism for the formation of new neural chains by linking together in a sequential manner neurons that represent subsequent motor acts, thus producing goal-directed sequences.
Elaboration versus Suppression of Cued Memories: Influence of Memory Recall Instruction and Success on Parietal Lobe, Default Network, and Hippocampal Activity  [PDF]
Sarah I. Gimbel, James B. Brewer
PLOS ONE , 2014, DOI: 10.1371/journal.pone.0089037
Abstract: Functional imaging studies of episodic memory retrieval consistently report task-evoked and memory-related activity in the medial temporal lobe, default network and parietal lobe subregions. Associated components of memory retrieval, such as attention-shifts, search, retrieval success, and post-retrieval processing also influence regional activity, but these influences remain ill-defined. To better understand how top-down control affects the neural bases of memory retrieval, we examined how regional activity responses were modulated by task goals during recall success or failure. Specifically, activity was examined during memory suppression, recall, and elaborative recall of paired-associates. Parietal lobe was subdivided into dorsal (BA 7), posterior ventral (BA 39), and anterior ventral (BA 40) regions, which were investigated separately to examine hypothesized distinctions in sub-regional functional responses related to differential attention-to-memory and memory strength. Top-down suppression of recall abolished memory strength effects in BA 39, which showed a task-negative response, and BA 40, which showed a task-positive response. The task-negative response in default network showed greater negatively-deflected signal for forgotten pairs when task goals required recall. Hippocampal activity was task-positive and was influenced by memory strength only when task goals required recall. As in previous studies, we show a memory strength effect in parietal lobe and hippocampus, but we show that this effect is top-down controlled and sensitive to whether the subject is trying to suppress or retrieve a memory. These regions are all implicated in memory recall, but their individual activity patterns show distinct memory-strength-related responses when task goals are varied. In parietal lobe, default network, and hippocampus, top-down control can override the commonly identified effects of memory strength.
Somatosensory aura in mesial temporal lobe epilepsy: semiologic characteristics, MRI findings and differential diagnosis with parietal lobe epilepsy
Rahal, Márcio Andriani;Araújo Filho, Gerardo Maria de;Caboclo, Luís Otávio Sales Ferreira;Rosa, Vivianne Pellegrino;Centeno, Ricardo da Silva;Carrete Jr, Henrique;Garzon, Eliana;Sakamoto, Américo Ceiki;Yacubian, Elza Márcia Targas;
Journal of Epilepsy and Clinical Neurophysiology , 2006, DOI: 10.1590/S1676-26492006000500008
Abstract: introduction: somatosensory auras (ssas) are more usually described in patients with parietal lobe epilepsy (ple), producing more commonly a localized cutaneous tingling sensation, involving hands and fingers followed by tonic or clonic focal seizures. these usually originate in the contralateral hemisphere. etiology includes dysplasias, tumours, ischemic or postencephalitic gliosis. however, other focal epilepsies, such as frontal and temporal, may also originate ssas. although this type of aura is reported as rare in patients with mesial temporal lobe epilepsy (mtle), this association has not been systematically studied. objectives: the aim of this article was to describe the cases of four patients with refractory mtle and ssas, reporting their clinical characteristics and mri findings. we discuss the localizing and lateralizing value of ssas, particularly in the context of mtle. methods and results: four patients with refractory mtle and ssas followed-up in the outpatient's clinic at the epilepsy section, universidade federal de s?o paulo, were submitted to presurgical evaluation and corticoamygdalohippocampectomy. mri in all cases showed unilateral mesial temporal sclerosis (mts). regarding seizure semiology, tingling sensation involving the upper extremity was the most prevalent symptom. three of the four patients had ssas contralateral to the mts. following the ssas all patients most of the time presented other symptoms such as autonomic or psychic auras evolving to psychomotor seizures. after surgical treatment, two of the patients presented infrequent auras, and two were rendered seizure-free. conclusion: although rare, ssas can be present in mtle. the characteristics of autonomic or psychic auras, psychomotor seizures, neuropsychological deficits, and typical neurophysiologic and mri findings may help differentiate patients with mtle from those with ple.
The Continuous Wagon Wheel Illusion and the ‘When’ Pathway of the Right Parietal Lobe: A Repetitive Transcranial Magnetic Stimulation Study  [PDF]
Rufin VanRullen, Alvaro Pascual-Leone, Lorella Battelli
PLOS ONE , 2008, DOI: 10.1371/journal.pone.0002911
Abstract: A continuous periodic motion stimulus can sometimes be perceived moving in the wrong direction. These illusory reversals have been taken as evidence that part of the motion perception system samples its inputs as a series of discrete snapshots –although other explanations of the phenomenon have been proposed, that rely on the spurious activation of low-level motion detectors in early visual areas. We have hypothesized that the right inferior parietal lobe (‘when’ pathway) plays a critical role in timing perceptual events relative to one another, and thus we examined the role of the right parietal lobe in the generation of this “continuous Wagon Wheel Illusion” (c-WWI). Consistent with our hypothesis, we found that the illusion was effectively weakened following disruption of right, but not left, parietal regions by low frequency repetitive transcranial magnetic stimulation (1 Hz, 10 min). These results were independent of whether the motion stimulus was shown in the left or the right visual field. Thus, the c-WWI appears to depend on higher-order attentional mechanisms that are supported by the ‘when’ pathway of the right parietal lobe.
Anatomical Substrates of the Alerting, Orienting and Executive Control Components of Attention: Focus on the Posterior Parietal Lobe  [PDF]
Xuntao Yin, Lu Zhao, Junhai Xu, Alan C. Evans, Lingzhong Fan, Haitao Ge, Yuchun Tang, Budhachandra Khundrakpam, Jian Wang, Shuwei Liu
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0050590
Abstract: Both neuropsychological and functional neuroimaging studies have identified that the posterior parietal lobe (PPL) is critical for the attention function. However, the unique role of distinct parietal cortical subregions and their underlying white matter (WM) remains in question. In this study, we collected both magnetic resonance imaging and diffusion tensor imaging (DTI) data in normal participants, and evaluated their attention performance using attention network test (ANT), which could isolate three different attention components: alerting, orienting and executive control. Cortical thickness, surface area and DTI parameters were extracted from predefined PPL subregions and correlated with behavioural performance. Tract-based spatial statistics (TBSS) was used for the voxel-wise statistical analysis. Results indicated structure-behaviour relationships on multiple levels. First, a link between the cortical thickness and WM integrity of the right inferior parietal regions and orienting performance was observed. Specifically, probabilistic tractography demonstrated that the integrity of WM connectivity between the bilateral inferior parietal lobules mediated the orienting performance. Second, the scores of executive control were significantly associated with the WM diffusion metrics of the right supramarginal gyrus. Finally, TBSS analysis revealed that alerting performance was significant correlated with the fractional anisotropy of local WM connecting the right thalamus and supplementary motor area. We conclude that distinct areas and features within PPL are associated with different components of attention. These findings could yield a more complete understanding of the nature of the PPL contribution to visuospatial attention.
Six-month treatment with atypical antipsychotic drugs decreased frontal-lobe levels of glutamate plus glutamine in early-stage first-episode schizophrenia
Goto N,Yoshimura R,Kakeda S,Nishimura J
Neuropsychiatric Disease and Treatment , 2012,
Abstract: Naoki Goto1, Reiji Yoshimura1, Shingo Kakeda2, Joji Nishimura2, Junji Moriya2, Kenji Hayashi1, Asuka Katsuki1, Hikaru Hori1, Wakako Umene-Nakano1, Atsuko Ikenouchi-Sugita1, Yukunori Korogi2, Jun Nakamura11Department of Psychiatry, University of Occupational and Environmental Health, Kitakyushu, Fukuoka, Japan; 2Department of Radiology, University of Occupational and Environmental Health, Kitakyushu, Fukuoka, JapanObjective: To study the effects of treatment with atypical antipsychotic drugs on brain levels of glutamate plus glutamine in early-stage first-episode schizophrenia.Participants: Sixteen patients (eight males, eight females; aged 30 ± 11 years) completed the study.Methods: We used administered 6 months of atypical antipsychotic drugs and used proton magnetic resonance spectroscopy to evaluate the results.Results: We found that the administration of atypical antipsychotic drugs for 6 months decreased the glutamate plus glutamine/creatine ratio in the frontal lobe. These results suggest that the administration of atypical antipsychotic drugs for at least 6 months decreased glutamatergic neurotransmissions in the frontal lobe in early-stage first-episode schizophrenia, but there was no difference in frontal-lobe levels between patients and control subjects before administration.Conclusion: Taking these findings into account, the glutamatergic and GABAergic neurons are implicated in early-stage first-episode schizophrenia, but in complex ways.Keywords: Proton magnetic resonance spectroscopy, creatine, frontal lobe, parieto-occipital node, left basal ganglia
Page 1 /100
Display every page Item


Home
Copyright © 2008-2017 Open Access Library. All rights reserved.