1,721,080 research outputs found
A feature-based neurocomputational model of semantic memory
No full textAccording with a featural organization of semantic memory, this work is aimed at investigating, through an attractor network, the role of different kinds of features in the representation of concepts, both in normal and neurodegenerative conditions. We implemented new synaptic learning rules in order to take into account the role of partially shared features and of distinctive features with different saliency. The model includes semantic and lexical layers, coding, respectively for object features and word-forms. Connections among nodes are strongly asymmetrical. To account for the feature saliency, asymmetrical synapses were created using Hebbian rules of potentiation and depotentiation, setting different pre-synaptic and post-synaptic thresholds. A variable post-synaptic threshold, which automatically changed to reflect the feature frequency in different concepts (i.e., how many concepts share a feature), was used to account for partially shared features. The trained network solved naming tasks and word recognition tasks very well, exploiting the different role of salient versus marginal features in concept identification. In the case of damage, superordinate concepts were preserved better than the subordinate ones. Interestingly, the degradation of salient features, but not of marginal ones, prevented object identification. The model suggests that Hebbian rules, with adjustable post-synaptic thresholds, can provide a reliable semantic representation of objects exploiting the statistics of input features
Brain networks stimulation in dementia: insights from functional imaging
No full textPurpose of review: Noninvasive brain stimulation (NIBS) is increasingly used in the field of dementia as a therapeutic option; however, evidence of clinical efficacy is limited, and the mechanism of action remains unknown. This review summarizes how functional imaging could contribute to the design of targeted and effective NIBS interventions for dementia. Recent findings: Resting-state functional magnetic resonance imaging (fMRI) has largely contributed to understanding brain dysfunction in dementia by identifying disease-specific networks. Resting-state fMRI might inform on a number of factors critical for the conduction of effective NIBS trials, such as definition of stimulation paradigms and choice of the stimulation target. In addition, fMRI may contribute to the understanding of the mechanisms of action of NIBS, and provide a tool to monitor treatment efficacy. Summary: Functional imaging is a promising approach for the development of hypothesis-driven, targeted stimulation approaches in the field of dementia
Short-term Sahaja Yoga meditation training modulates brain structure and spontaneous activity in the executive control network
Full text linkINTRODUCTION: While cross-sectional studies have shown neural changes in long-term meditators, they might be confounded by self-selection and potential baseline differences between meditators and non meditators. Prospective longitudinal studies of the effects of meditation in naïve subjects are more conclusive with respect to causal inferences, but related evidence is so far limited. METHODS: Here, we assessed the effects of a 4-week Sahaja Yoga meditation training on gray matter density and spontaneous resting-state brain activity in a group of 12 meditation-naïve healthy adults. RESULTS: Compared with 30 control subjects, the participants to meditation training showed increased gray matter density and changes in the coherence of intrinsic brain activity in two adjacent regions of the right inferior frontal gyrus encompassing the anterior component of the executive control network. Both these measures correlated with self-reported well-being scores in the meditation group. CONCLUSIONS: The significant impact of a brief meditation training on brain regions associated with attention, self-control, and self-awareness may reflect the engagement of cognitive control skills in searching for a state of mental silence, a distinctive feature of Sahaja Yoga meditation. The manifold implications of these findings involve both managerial and rehabilitative settings concerned with well-being and emotional state in normal and pathological conditions
Age-related functional changes of prefrontal cortex in long-term memory: A repetitive transcranial magnetic stimulation study
No full textNeuroimaging findings suggest that the lateralization of prefrontal cortex activation associated with episodic memory performance is reduced by aging. It is still a matter of debate whether this loss of asymmetry during encoding and retrieval reflects compensatory mechanisms or de-differentiation processes. We addressed this issue by the transient interference produced by repetitive transcranial magnetic stimulation (rTMS), which directly assesses causal relationships between performance and stimulated regions. We compared the effects of rTMS (a rapid-rate train occurring simultaneously to the presentation of memoranda) applied to the left or right dorsolateral prefrontal cortex (DLPFC) on visuospatial recognition memory in 66 healthy subjects divided in two classes of age (50 years). In young subjects, rTMS of the right DLPFC interfered with retrieval more than left DLPFC stimulation. The asymmetry of the effect progressively vanished with aging, as indicated by bilateral interference effects on recognition performance. Conversely, the predominance of left DLPFC effect during encoding was not abolished in elders, thus probing its causal role for encoding along the life span. Findings confirm that the neural correlates of retrieval modify along aging, suggesting that the bilateral engagement of the DLPFC has a compensatory role on the elders' episodic memory performance
Exploring the syndrome of spatial unilateral neglect through an illusion of length
No full textBoth a neuropsychological syndrome (unilateral spatial neglect) and a visual illusion of length (the Brentano version of the Müller-Lyer illusion) bring about a misjudgement of the subjective centre of a horizontal line, with a unilateral shift. In experiment 1 we investigated, in patients with left unilateral neglect, illusory effects of horizontal length, with the aim of exploring the functional and neural basis of horizontal space perception, and the role of visual processing in shaping the patients' bisection performance. Fourteen right-brain-damaged patients with left spatial unilateral neglect, seven with and seven without left visual half-field deficits (assessed by confrontation, perimetry, and visual event-related potentials), entered this study. Two conditions of manual line bisection were assessed: setting the mid-point of a horizontal line, and of the shaft of the Brentano-Müller-Lyer illusion, with either a left- or a right-sided expansion. Both groups of patients set the subjective midpoint to the right of the objective centre of the line, consistent with the presence of left neglect. Patients with neglect and left hemianopia showed no illusory effects and a greater bisection error. The effects of the illusion, by contrast, were fully present in neglect patients without hemianopia, in both illusory conditions, adding to, or subtracting from, the rightward bisection bias. Anatomoclinical correlations revealed an association of damage to the occipital regions with the lack of illusory effects. Conversely, more anterior damage, sparing these regions, did not disrupt the illusion, revealing a dissociation between visual and spatial processing of extension. These findings suggest that processing of the Müller-Lyer illusion of length is likely to occur in the occipital cortex, at a retinotopic level of representation. In neglect patients with left homonymous hemianopia the visual deficit adds to the spatial bias, yielding a greater error in line bisection, but not in other visual exploratory tasks, such as cancellation, where the contribution of retinotopic frames is likely to be comparatively minor. Experiment 2 showed preserved illusory effects in patients with homonymous visual field defects without spatial unilateral neglect, suggesting that preserved spatial processing may compensate for unilateral visual field defects
Mortality of alzheimer’s disease in Italy from 1980 to 2015
Full text linkObjective: To evaluate mortality for Alzheimer's Disease (AD) in Italy over more than three decades (1980-2015) and discuss the possible role of general and specific contributing factors. Methods: Mortality data were extracted by the Italian National Institute of Statistics: crude mortality rates were computed for sex and age, considering the whole country and its five main geographical sub-areas. Rates were standardized in two ways: directly (annual mortality rates AMRs) and indirectly (standardized mortality rates, SMRs). SMRs were then used to evaluate geographical differences; to study mortality trend, AMRs and joinpoint linear regression analysis were used. Results: Considering the entire period and the whole country, mortality rates were similar for females and males and for geographical regions, with the exception of the older age groups where mortality for AD in females slightly prevailed. In these older patients, a steep increase of mortality was seen starting from the current century. The increase in male mortality mirrored the national trend in North-West and Central Italy, but not in North-East, South, and the Islands, where it did not surge until the mid to late 1990s. Conclusions: the general increase of mortality is in line with international data and it reflects the increasing prevalence of the disease, likely due to increasing longevity, and to improvements in diagnostic accuracy. In addition, the accuracy of death certificate compilation could account for both geographical and temporal differences. Currently available drugs for AD do not seem to have an impact on mortality rates
Effectiveness of language training and non-invasive brain stimulation on oral and written naming performance in Primary Progressive Aphasia: a meta-analysis and systematic review
No full textThe aim of this systematic review and meta-analysis is to examine the efficacy of language training, alone or in combination with non-invasive brain stimulation techniques, designed to improve oral and written naming abilities in Primary Progressive Aphasia (PPA), and to investigate whether gains can be maintained over time and generalize to untrained items. An electronic database search was conducted up to 31st of May 2019. Forty-three articles on language training alone and seven articles on the combined treatment fitted the inclusion criteria for the systematic review. Results indicated that language training, alone or in combination with transcranial direct current stimulation (tDCS), improves oral naming accuracy for trained items in patients with PPA, with a long-term maintenance of the gain over time. Only language training combined with tDCS improves oral naming accuracy for untrained items. Considering written naming abilities, language training combined with tDCS improves performance for both trained and untrained items, immediately after training and at follow-up
Effectiveness of an Innovative Cognitive Treatment and Telerehabilitation on Subjects With Mild Cognitive Impairment: A Multicenter, Randomized, Active-Controlled Study
No full textBackground: In recent years, the potential usefulness of cognitive training procedures in normal aging and mild cognitive impairment (MCI) have received increased attention.
Objective: The main aim of this study was to evaluate the efficacy of the face-to-face cognitive virtual reality rehabilitation system (VRRS) and to compare it to that of face-to-face cognitive treatment as usual for individuals with MCI. Moreover, we assessed the possibility of prolonging the effects of treatment with a telerehabilitation system.
Methods: A total of 49 subjects with MCI were assigned to 1 of 3 study groups in a randomized controlled trial design: (a) those who received face-to-face cognitive VRRS (12 sessions of individualized cognitive rehabilitation over 4 weeks) followed by telerehabilitation (36 sessions of home-based cognitive VRRS training, three sessions for week); (b) those who received face-to-face cognitive VRRS followed by at-home unstructured cognitive stimulation (36 sessions of home-based unstructured cognitive stimulation, three sessions for week); and (c) those who received face-to-face cognitive treatment as usual (12 sessions of face-to-face cognitive treatment as usual).
Results: An improvement in memory, language and visuo-constructional abilities was observed after the end of face-to-face VRRS treatment compared to face-to-face treatment as usual. The application of home-based cognitive VRRS telerehabilitation seems to induce more maintenance of the obtained gains than home-based unstructured stimulation.
Discussion: The present study provides preliminary evidence in support of individualized VRRS treatment and telerehabilitation delivery for cognitive rehabilitation and should pave the way for future studies aiming at identifying optimal cognitive treatment protocols in subjects with MCI
Aprassia degli arti
No full textL’aprassia è un disturbo primitivo dell’attività motoria che insorge durante l’esecuzione di un movimento finalizzato, avviato intenzionalmente per compiere un’azione o un gesto, sulla scorta di uno scopo. Il disturbo aprassico può manifestarsi in assenza di deficit di input, quali alterazioni degli organi di senso (sordità, cecità, anestesia tattile) o della presenza di afasia (deficit di comprensione) o di agnosia visiva o tattile. Può emergere anche in assenza di deficit di output (per es., paresi, tremore, atassia, ipocinesia o ipercinesia), di deficit di orientamento spaziale, deficit di schema corporeo o inerzia frontale
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