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Association Areas (association + area)
Selected AbstractsFunctional topography of the human nonREM sleep electroencephalogramEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 12 2001Luca A. Finelli Abstract The sleep EEG of healthy young men was recorded during baseline and recovery sleep after 40 h of waking. To analyse the EEG topography, power spectra were computed from 27 derivations. Mean power maps of the nonREM sleep EEG were calculated for 1-Hz bins between 1.0 and 24.75 Hz. Cluster analysis revealed a topographic segregation into distinct frequency bands which were similar for baseline and recovery sleep, and corresponded closely to the traditional frequency bands. Hallmarks of the power maps were the frontal predominance in the delta and alpha band, the occipital predominance in the theta band, and the sharply delineated vertex maximum in the sigma band. The effect of sleep deprivation on EEG topography was determined by calculating the recovery/baseline ratio of the power spectra. Prolonged waking induced an increase in power in the low-frequency range (1,10.75 Hz) which was largest over the frontal region, and a decrease in power in the sigma band (13,15.75 Hz) which was most pronounced over the vertex. The topographic pattern of the recovery/baseline power ratio was similar to the power ratio between the first and second half of the baseline night. These results indicate that changes in sleep propensity are reflected by specific regional differences in EEG power. The predominant increase of low-frequency power in frontal areas may be due to a high ,recovery need' of the frontal heteromodal association areas of the cortex. [source] Neural substrates of tactile object recognition: An fMRI studyHUMAN BRAIN MAPPING, Issue 4 2004Catherine L. Reed Abstract A functional magnetic resonance imaging (fMRI) study was conducted during which seven subjects carried out naturalistic tactile object recognition (TOR) of real objects. Activation maps, conjunctions across subjects, were compared between tasks involving TOR of common real objects, palpation of "nonsense" objects, and rest. The tactile tasks involved similar motor and sensory stimulation, allowing higher tactile recognition processes to be isolated. Compared to nonsense object palpation, the most prominent activation evoked by TOR was in secondary somatosensory areas in the parietal operculum (SII) and insula, confirming a modality-specific path for TOR. Prominent activation was also present in medial and lateral secondary motor cortices, but not in primary motor areas, supporting the high level of sensory and motor integration characteristic of object recognition in the tactile modality. Activation in a lateral occipitotemporal area associated previously with visual object recognition may support cross-modal collateral activation. Finally, activation in medial temporal and prefrontal areas may reflect a common final pathway of modality-independent object recognition. This study suggests that TOR involves a complex network including parietal and insular somatosensory association cortices, as well as occipitotemporal visual areas, prefrontal, and medial temporal supramodal areas, and medial and lateral secondary motor cortices. It confirms the involvement of somatosensory association areas in the recognition component of TOR, and the existence of a ventrolateral somatosensory pathway for TOR in intact subjects. It challenges the results of previous studies that emphasize the role of visual cortex rather than somatosensory association cortices in higher-level somatosensory cognition. Hum. Brain Mapping 21:236,246, 2004. © 2004 Wiley-Liss, Inc. [source] Alcohol intoxication effects on visual perception: An fMRI studyHUMAN BRAIN MAPPING, Issue 1 2004Vince D. Calhoun Abstract We examined the effects of two doses of alcohol (EtOH) on functional magnetic resonance imaging (fMRI) activation during a visual perception task. The Motor-Free Visual Perception Test,Revised (MVPT-R) provides measures of overall visual perceptual processing ability. It incorporates different cognitive elements including visual discrimination, spatial relationships, and mental rotation. We used the MVPT-R to study brain activation patterns in healthy controls (1) sober, and (2) at two doses of alcohol intoxication with event-related fMRI. The fMRI data were analyzed using a general linear model approach based upon a model of the time course and a hemodynamic response estimate. Additionally, a correlation analysis was performed to examine dose-dependent amplitude changes. With regard to alcohol-free task-related brain activation, we replicate our previous finding in which SPM group analysis revealed robust activation in visual and visual association areas, frontal eye field (FEF)/dorsolateral prefrontal cortex (DLPFC), and the supplemental motor area (SMA). Consistent with a previous study of EtOH and visual stimulation, EtOH resulted in a dose-dependent decrease in activation amplitude over much of the visual perception network and in a decrease in the maximum contrast-to-noise ratio (in the lingual gyrus). Despite only modest behavior changes (in the expected direction), significant dose-dependent activation increases were observed in insula, DLPFC, and precentral regions, whereas dose-dependent activation decreases were observed in anterior and posterior cingulate, precuneus, and middle frontal areas. Some areas (FEF/DLPFC/SMA) became more diffusely activated (i.e., increased in spatial extent) at the higher dose. Alcohol, thus, appears to have both global and local effects upon the neural correlates of the MVPT-R task, some of which are dose dependent. Hum. Brain Mapping 21:15,26, 2004. © 2003 Wiley-Liss, Inc. [source] The role of neuroimaging in mild cognitive impairmentNEUROPATHOLOGY, Issue 6 2007Hiroshi Matsuda The main purposes of neuroimaging in Alzheimer's disease (AD) have been moved from diagnosis of advanced AD to diagnosis of very early AD at a prodromal stage of mild cognitive impairment, prediction of conversion from mild cognitive impairment (MCI) to AD, and differential diagnosis from other diseases causing dementia. Structural MRI studies and functional studies using F-18 fluorodeoxyglucose-positron emission tomography (FDG-PET) and brain perfusion single-photon emission computed tomography (SPECT) are widely used in diagnosis of AD. Outstanding progress in diagnostic accuracy of these neuroimaging modalities has been obtained using statistical analysis on a voxel-by-voxel basis after spatial normalization of individual scans to a standardized brain-volume template instead of visual inspection or a conventional region of interest technique. In a very early stage of AD, this statistical approach revealed gray matter loss in the entorhinal and hippocampal areas and hypometabolism or hypoperfusion in the posterior cingulate cortex and precuneus. These two findings might be related in view of anatomical knowledge that the regions are linked through the circuit of Papez. This statistical approach also offers prediction of conversion from MCI to AD. Presence of hypometabolism or hypoperfusion in parietal association areas and entorhinal atrophy at the MCI stage has been reported to predict rapid conversion to AD. [source] Neurobiological basis of behavioral and psychological symptoms in dementia of the Alzheimer typePSYCHIATRY AND CLINICAL NEUROSCIENCES, Issue 6 2000Kazuhiro Shinosaki MD Abstract Recent dementia studies indicate that behavioral and psychological symptoms of dementia (BPSD) are not merely an epiphenomenon of cognitive impairment, but could be attributed to specific biological brain dysfunction. We describe findings from different research modalities related with BPSD (psychopathological, neuropsychological, neurochemical, and psychophysiological strategies), and attempt to reconcile them into the more integrated form. Characteristics of delusions in dementia patients should be studied in more detail from a psychopathological aspect, aiming for the integration of psychopathology and neurobiology. Imperfect integration of memory function and cognitive function, assigned to the limbic systems and association areas, respectively, may result in BPSD. More intimate collaboration of psychopathological and neurobiological study would be fruitful to promote the research in psychological basis of BPSD. Neurochemical studies indicated that density of extracellular tangles and/or PHF-tau protein have relationships with delusion or misidentification. These changes in neurochemical parameters should be the key to understanding the pathogenesis of BPSD. More importantly, neurochemical and psychological study could be linked by the research in psychophysiology. Computer-assisted electroencephalogram analysis suggests that the right posterior hemisphere shows significant age-associated change earlier than the left in the elderly. Cerebral metabolic rate by positron emission tomography study indicates that paralimbic, left medial temporal, and left medial occipital area are involved in pathogenesis of BPSD in some dementia patients. [source] The natural endocast of Taung (Australopithecus africanus): Insights from the unpublished papers of Raymond Arthur DartAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue S49 2009Dean Falk Abstract Dart's 1925 announcement of Australopithecus africanus (Dart: Nature 115 [1925] 195,199) was highly controversial, partly because of an interpretation of the Taung natural endocast that rested on an erroneous identification of the lambdoid suture as the lunate sulcus. Unpublished materials from the University of Witwatersrand Archives (Dart, unpublished material) reveal that Dart reacted to the controversy by: 1) describing and illustrating the entire sulcal pattern on the Taung endocast, in contrast to just two sulcal identifications in 1925, 2) identifying a hypothetical part of the lambdoid suture and revising his description of the lunate sulcus, and 3) bolstering his argument that Taung's brain was advanced by detailing expansions in three significant cortical association areas. Four unpublished illustrations of Dart's identifications for sulci and sutures on the Taung endocast are compared here with those published by Keith (Keith: New discoveries relating to the antiquity of man (1931)), Schepers (Schepers: The endocranial casts of the South African ape-men. In: Broom R, Schepers GWH, editors. The South African fossil ape-men; the Australopithecinae [1946] p 155,272), and Falk (Falk: Am J Phys Anthropol 53 [1980] 525,539), and the thorny issue of the location of the lunate sulcus is revisited in light of new information. Archival materials reveal that Dart believed that Taung's brain was reorganized globally rather than in a mosaic manner, and that the shapes of certain cortical association areas showed that Australopithecus was closer to Pithecanthropus than to the living apes. Although a few of Dart's hitherto-unpublished sulcal identifications, including his revision for the lunate sulcus, were questionable, his claim that the Taung endocast reproduced a shape that was advanced toward a human condition in its prefrontal cortex and caudally protruded occipital lobe was correct. Yrbk Phys Anthropol 52:49,65, 2009. © 2009 Wiley-Liss, Inc. [source] Decreased GAD65 mRNA levels in select subpopulations of neurons in the cerebellar dentate nuclei in autism: an in situ hybridization studyAUTISM RESEARCH, Issue 1 2009Jane Yip Abstract The laterally positioned dentate nuclei lie in a key position in the cerebellum to receive input from Purkinje cells in the lateral cerebellar hemisphere participating in both motor and cognitive functions. Although neuropathology of the four cerebellar nuclei using Nissl staining has been qualitatively reported in children and adults with autism, surprisingly the dentate nuclei appeared less affected despite reported reductions in Purkinje cells in the posterolateral cerebellar hemisphere. To determine any underlying abnormalities in the critically important GABAergic system, the rate-limiting GABA synthesizing enzyme, glutamic acid decarboxylase (GAD) type 65 was measured via in situ hybridization histochemistry in dentate somata. GAD65 mRNA labeling revealed two distinct subpopulations of neurons in adult control and autism postmortem brains: small-sized cells (about 10,12,µm in diameter, presumed interneurons) and larger-sized neurons (about 18,20,µm in diameter, likely feedback to inferior olivary neurons). A mean 51% reduction in GAD65 mRNA levels was found in the larger labeled cells in the autistic group compared with the control group (P=0.009; independent t -test) but not in the smaller cell subpopulation. This suggests a disturbance in the intrinsic cerebellar circuitry in the autism group potentially interfering with the synchronous firing of inferior olivary neurons, and the timing of Purkinje cell firing and inputs to the dentate nuclei. Disturbances in critical neural substrates within these key circuits could disrupt afferents to motor and/or cognitive cerebral association areas in the autistic brain likely contributing to the marked behavioral consequences characteristic of autism. [source] When brains expand: mind and the evolution of cortexACTA NEUROPSYCHIATRICA, Issue 3 2007Matthew T. K. Kirkcaldie Objective:, To critically examine the relationship between evolutionary and developmental influences on human neocortex and the properties of the conscious mind it creates. Methods:, Using PubMed searches and the bibliographies of several monographs, we selected 50 key works, which offer empirical support for a novel understanding of the organization of the neocortex. Results:, The cognitive gulf between humans and our closest primate relatives has usually been taken as evidence that our brains evolved crucial new mechanisms somehow conferring advanced capacities, particularly in association areas of the neocortex. In this overview of neocortical development and comparative brain morphometry, we propose an alternative view: that an increase in neocortical size, alone, could account for novel and powerful cognitive capabilities. Other than humans' very large brain in relation to the body weight, the morphometric relations between neocortex and all other brain regions show remarkably consistent exponential ratios across the range of primate species, including humans. For an increase in neocortical size to produce new abilities, the developmental mechanisms of neocortex would need to be able to generate an interarchy of functionally diverse cortical domains in the absence of explicit specification, and in this respect, the mammalian neocortex is unique: its relationship to the rest of the nervous system is unusually plastic, allowing great changes in cortical organization to occur in relatively short periods of evolution. The fact that even advanced abilities like self-recognition have arisen in species from different mammalian orders suggests that expansion of the neocortex quite naturally generates new levels of cognitive sophistication. Our cognitive and behavioural sophistication may, therefore, be attributable to these intrinsic mechanisms' ability to generate complex interarchies when the neocortex reaches a sufficient size. Conclusion:, Our analysis offers a parsimonious explanation for key properties of the human mind based on evolutionary influences and developmental processes. This view is perhaps surprising in its simplicity, but offers a fresh perspective on the evolutionary basis of mental complexity. [source] | |||||||||||||