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Caroli A.,LENITEM Laboratory of Epidemiology | Caroli A.,Mario Negri Institute for Pharmacological Research | Lorenzi M.,LENITEM Laboratory of Epidemiology | Geroldi C.,LENITEM Laboratory of Epidemiology | And 7 more authors.
Dementia and Geriatric Cognitive Disorders | Year: 2010

Background/Aims: The aim of this study was to map metabolic compensation and depression in Alzheimer's disease (AD) on a voxel-by-voxel basis. Methods: Twenty-one healthy elderly subjects and 25 AD patients underwent cerebral MR and FDG-PET imaging. All images were processed with SPM2, and whole-brain gray matter (GM) atrophy and hypometabolism maps were computed. Metabolic compensation and depression were assessed using Biological Parametric Mapping software. Results: GM atrophy and hypometabolism mapped to similar regions, with varying degrees of severity. Significant metabolic compensation was found in the amygdala, while exceeding hypometabolism was mainly located in the posterior cingulate cortex. Conclusion: Metabolic depression can be due to both distant effects of atrophy and to additional hypometabolism-inducing factors, such as amyloid deposition. Conversely, metabolic compensation could reflect spared synaptic plasticity of the surviving neurons. The investigation of the metabolic compensation mechanism could help in the comprehension of the AD underlying pathology. Copyright © 2010 S. Karger AG, Basel.

Ruzzoli M.,University of Verona | Marzi C.A.,University of Verona | Miniussi C.,Cognitive Neuroscience Section | Miniussi C.,University of Brescia
Journal of Neurophysiology | Year: 2010

Transcranial magnetic stimulation (TMS) is a technique used to study perceptual, motor, and cognitive functions in the human brain. Its effects have been likened to a "virtual brain lesion," but a direct test of this assumption is lacking. To verify this hypothesis, we measured psychophysically the interaction between the neural activity induced by a visual motion-direction discrimination task and that induced by TMS. The visual stimulus featured two elements: a visual signal (dots that moved coherently in one direction) and visual noise (dots that moved randomly in many directions). Three hypotheses were tested to explain the impairment in performance as a result of TMS: 1) a decrease in signal strength; 2) an induction of randomly distributed neural noise with an accompanying decrement in system sensitivity; and 3) a suppression of relevant information processing and addition of neural noise. We provide evidence in favor of the second hypothesis by showing that TMS basically acts by adding neural noise to the perceptual process. Copyright © 2010 The American Physiological Society.

Abrahamyan A.,University of Sydney | Clifford C.W.G.,University of Sydney | Ruzzoli M.,Cognitive Neuroscience Section | Phillips D.,The Magstim Company Ltd | And 2 more authors.
PLoS ONE | Year: 2011

To calibrate the intensity of transcranial magnetic stimulation (TMS) at the occipital pole, the phosphene threshold is used as a measure of cortical excitability. The phosphene threshold (PT) refers to the intensity of magnetic stimulation that induces illusory flashes of light (phosphenes) on a proportion of trials. The existing PT estimation procedures lack the accuracy and mathematical rigour of modern threshold estimation methods. We present an improved and automatic procedure for estimating the PT which is based on the well-established Ψ Bayesian adaptive staircase approach. To validate the new procedure, we compared it with another commonly used procedure for estimating the PT. We found that our procedure is more accurate, reliable, and rapid when compared with an existing PT measurement procedure. The new procedure is implemented in Matlab and works automatically with the Magstim Rapid 2 stimulator using a convenient graphical user interface. The Matlab program is freely available for download. © 2011 Abrahamyan et al.

Thut G.,University of Glasgow | Miniussi C.,Cognitive Neuroscience Section | Miniussi C.,University of Brescia | Gross J.,University of Glasgow
Current Biology | Year: 2012

Oscillations in brain activity have long been known, but many fundamental aspects of such brain rhythms, particularly their functional importance, have been unclear. As we review here, new insights into these issues are emerging from the application of intervention approaches. In these approaches, the timing of brain oscillations is manipulated by non-invasive brain stimulation, either through sensory input or transcranially, and the behavioural consequence then monitored. Notably, such manipulations have led to rapid, periodic fluctuations in behavioural performance, which co-cycle with underlying brain oscillations. Such findings establish a causal relationship between brain oscillations and behaviour, and are allowing novel tests of longstanding models about the functions of brain oscillations. © 2012 Elsevier Ltd All rights reserved.

Ruzzoli M.,University of Verona | Abrahamyan A.,University of Sydney | Clifford C.W.G.,University of Sydney | Marzi C.A.,University of Verona | And 3 more authors.
Journal of Neurophysiology | Year: 2011

The underlying mechanisms of action of transcranial magnetic stimulation (TMS) are still a matter of debate. TMS may impair a subject's performance by increasing neural noise, suppressing the neural signal, or both. Here, we delivered a single pulse of TMS (spTMS) to V5/MT during a motion direction discrimination task while concurrently manipulating the level of noise in the motion stimulus. Our results indicate that spTMS essentially acts by suppressing the strength of the relevant visual signal. We suggest that TMS may induce a pattern of neural activity that complements the ongoing activation elicited by the sensory signal in a manner that partially impoverishes that signal © 2011 the American Physiological Society.

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