Publications by authors named "Manuela Ruzzoli"

23 Publications

  • Page 1 of 1

The phase of Theta oscillations modulates successful memory formation at encoding.

Neuropsychologia 2021 Feb 13;154:107775. Epub 2021 Feb 13.

Center for Brain and Cognition, Computational Neuroscience Group, Department of Information and Communication Technologies, Universitat Pompeu Fabra, Roc Boronat 138, Barcelona, 08018, Spain; Institució Catalana de la Recerca i Estudis Avançats (ICREA), Passeig Lluís Companys 23, Barcelona, 08010, Spain.

Several studies have shown that attention and perception can depend upon the phase of ongoing neural oscillations at stimulus onset. Here, we extend this idea to the memory domain. We tested the hypothesis that ongoing fluctuations in neural activity impact memory encoding in two experiments using a picture paired-associates task in order to gauge episodic memory performance. Experiment 1 was behavioural only and capitalized on the principle of phase resetting. We tested if subsequent memory performance fluctuates rhythmically, time-locked to a resetting cue presented before the to-be-remembered pairs at different time intervals. We found an indication that behavioural performance was periodically and selectively modulated at Theta frequency (~4 Hz). In Experiment 2, we focused on pre-stimulus ongoing activity using scalp EEG while participants performed a paired-associates task. The pre-registered analysis, using large electrode clusters and generic Theta and Alpha spectral ranges, returned null results of the pre-stimulus phase-behaviour correlation. However, as expected from prior literature, we found that variations in stimulus-related Theta-power predicted subsequent memory performance. Therefore, we used this post-stimulus effect in Theta power to guide a post-hoc pre-stimulus phase analysis in terms of scalp and frequency of interest. This analysis returned a correlation between the pre-stimulus Theta phase and subsequent memory. Altogether, these results suggest that pre-stimulus Theta activity at encoding may impact later memory performance.
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http://dx.doi.org/10.1016/j.neuropsychologia.2021.107775DOI Listing
February 2021

Integrating when and what information in the left parietal lobe allows language rule generalization.

PLoS Biol 2020 11 2;18(11):e3000895. Epub 2020 Nov 2.

Cognition and Brain Plasticity Unit, IDIBELL, L'Hospitalet de Llobregat, Spain.

A crucial aspect when learning a language is discovering the rules that govern how words are combined in order to convey meanings. Because rules are characterized by sequential co-occurrences between elements (e.g., "These cupcakes are unbelievable"), tracking the statistical relationships between these elements is fundamental. However, purely bottom-up statistical learning alone cannot fully account for the ability to create abstract rule representations that can be generalized, a paramount requirement of linguistic rules. Here, we provide evidence that, after the statistical relations between words have been extracted, the engagement of goal-directed attention is key to enable rule generalization. Incidental learning performance during a rule-learning task on an artificial language revealed a progressive shift from statistical learning to goal-directed attention. In addition, and consistent with the recruitment of attention, functional MRI (fMRI) analyses of late learning stages showed left parietal activity within a broad bilateral dorsal frontoparietal network. Critically, repetitive transcranial magnetic stimulation (rTMS) on participants' peak of activation within the left parietal cortex impaired their ability to generalize learned rules to a structurally analogous new language. No stimulation or rTMS on a nonrelevant brain region did not have the same interfering effect on generalization. Performance on an additional attentional task showed that this rTMS on the parietal site hindered participants' ability to integrate "what" (stimulus identity) and "when" (stimulus timing) information about an expected target. The present findings suggest that learning rules from speech is a two-stage process: following statistical learning, goal-directed attention-involving left parietal regions-integrates "what" and "when" stimulus information to facilitate rapid rule generalization.
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http://dx.doi.org/10.1371/journal.pbio.3000895DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7660506PMC
November 2020

Can the occipital alpha-phase speed up visual detection through a real-time EEG-based brain-computer interface (BCI)?

Eur J Neurosci 2020 Aug 3. Epub 2020 Aug 3.

Departament de Tecnologies de la Informació i les Comunicacions, Center for Brain and Cognition, Universitat Pompeu Fabra, Barcelona, Spain.

Electrical brain oscillations reflect fluctuations in neural excitability. Fluctuations in the alpha band (α, 8-12 Hz) in the occipito-parietal cortex are thought to regulate sensory responses, leading to cyclic variations in visual perception. Inspired by this theory, some past and recent studies have addressed the relationship between α-phase from extra-cranial EEG and behavioural responses to visual stimuli in humans. The latest studies have used offline approaches to confirm α-gated cyclic patterns. However, a particularly relevant implication is the possibility to use this principle online, whereby stimuli are time-locked to specific α-phases leading to predictable outcomes in performance. Here, we aimed at providing a proof of concept for such real-time neurotechnology. Participants performed a speeded response task to visual targets that were presented upon a real-time estimation of the α-phase via an EEG closed-loop brain-computer interface (BCI). According to the theory, we predicted a modulation of reaction times (RTs) along the α-cycle. Our BCI system achieved reliable trial-to-trial phase locking of stimuli to the phase of individual occipito-parietal α-oscillations. Yet, the behavioural results did not support a consistent relation between RTs and the phase of the α-cycle neither at group nor at single participant levels. We must conclude that although the α-phase might play a role in perceptual decisions from a theoretical perspective, its impact on EEG-based BCI application appears negligible.
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http://dx.doi.org/10.1111/ejn.14931DOI Listing
August 2020

From cognitive control to visual incongruity: Conflict detection in surrealistic images.

PLoS One 2020 4;15(6):e0224053. Epub 2020 Jun 4.

Multisensory Research Group, Center for Brain and Cognition, Universitat Pompeu Fabra, Barcelona, Spain.

This study explored brain responses to images that exploit incongruity as a creative technique, often used in advertising (i.e., surrealistic images). We hypothesized that these images would reveal responses akin to cognitive conflict resulting from incongruent trials in typical laboratory tasks (i.e., Stroop Task). Indeed, in many surrealistic images, common visual elements are juxtaposed to create un-ordinary associations with semantically conflicting representations. We expected that these images engage the conflict processing network that has been described in cognitive neuroscience theories. We addressed this hypothesis by measuring the power of mid-frontal Theta oscillations using EEG while participants watched images through a social media-like interface. Incongruent images, compared to controls, produced a significant Theta power increase, as predicted from the cognitive conflict theory. We also found increased memory for incongruent images one week after exposure, compared to the controls. These findings provide evidence for the incongruent images to effectively engage the viewer's cognitive control and boost memorability. The results of this study provide validation of cognitive theories in real-life scenarios (i.e., surrealistic ads or art) and offer insights regarding the use of neural correlates as effectiveness metrics in advertising.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0224053PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7272058PMC
August 2020

The relevance of alpha phase in human perception.

Cortex 2019 11 14;120:249-268. Epub 2019 Jun 14.

Center for Brain and Cognition, Departament de Tecnologies de la Informació i les Comunicacions, Universitat Pompeu Fabra, Barcelona, Spain; Institució Catalana de Recerca i Estudis Avançats (ICREA), Spain. Electronic address:

Neural oscillations in the low frequencies, roughly in the alpha band (α, 5-15 Hz), have been suggested to act as a gateway from sensation to perception. This hypothesis assumes discrete perception. In particular, the amplitude and the phase of the low frequency rhythm entails a cortical mechanism which paces the access of sensory information into the cognitive system. Evidence supporting this idea includes correlations between the phase of neural oscillations and behavioral performance in perception, spatial attention and working memory. Despite a widespread confidence in the theory, these findings have been mostly based on a varied range of exploratory approaches and inferential group statistics. Here, we aimed at validating the involvement of low frequency cortical rhythm in perception and at providing a clear-cut EEG analysis pipeline. Such an analytical pipeline should support the adoption of a hypothesis-driven framework for future replications and applications. The design, the analyses and the statistical power of the present experiment were based on prior studies in which phase opposition was successfully found. However, our results provide evidence for the involvement of pre-stimulus oscillatory alpha amplitude but not phase in perception. We discuss the null findings from the present study within the existing literature.
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http://dx.doi.org/10.1016/j.cortex.2019.05.012DOI Listing
November 2019

Perceptual and Physiological Consequences of Dark Adaptation: A TMS-EEG Study.

Brain Topogr 2019 09 10;32(5):773-782. Epub 2019 May 10.

Institute of Neuroscience and Psychology, University of Glasgow, Glasgow, UK.

Existing literature on sensory deprivation suggests that short-lasting periods of dark adaptation (DA) can cause changes in visual cortex excitability. DA cortical effects have previously been assessed through phosphene perception, i.e., the ability to report visual sensations when a transcranial magnetic stimulation (TMS) pulse is delivered over the visual cortex. However, phosphenes represent an indirect measure of visual cortical excitability which relies on a subjective report. Here, we aimed at overcoming this limitation by assessing visual cortical excitability by combining subjective (i.e., TMS-induced phosphenes) and objective (i.e., TMS-evoked potentials - TEPs) measurements in a TMS-EEG protocol after 30 min of DA. DA effects were compared to a control condition, entailing 30 min of controlled light exposure. TMS was applied at 11 intensities in order to estimate the psychometric function of phosphene report and explore the relationship between TEPs and TMS intensity. Compared to light adaptation, after DA the slope of the psychometric function was significantly steeper, and the amplitude of a TEP component (P60) was lower, only for high TMS intensities. The perceptual threshold was not affected by DA. These results support the idea that DA leads to a change in the excitability of the visual cortex, accompanied by a behavioral modification of visual perception. Furthermore, this study provides a first valuable description of the relationship between TMS intensity and visual TEPs.
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http://dx.doi.org/10.1007/s10548-019-00715-xDOI Listing
September 2019

The phase of pre-stimulus brain oscillations correlates with cross-modal synchrony perception.

Eur J Neurosci 2019 01 24;49(2):150-164. Epub 2018 Oct 24.

Multisensory Research Group, Center for Brain and Cognition, Universitat Pompeu Fabra, Barcelona, Spain.

In everyday life multisensory events, such as a glass crashing on the floor, the different sensory inputs are often experienced as simultaneous, despite the sensory processing of sound and sight within the brain are temporally misaligned. This lack of cross-modal synchrony is the unavoidable consequence of different light and sound speeds, and their different neural transmission times in the corresponding sensory pathways. Hence, cross-modal synchrony must be reconstructed during perception. It has been suggested that spontaneous fluctuations in neural excitability might be involved in the temporal organisation of sensory events during perception and account for variability in behavioural performance. Here, we addressed the relationship between ongoing brain oscillations and the perception of cross-modal simultaneity. Participants performed an audio-visual simultaneity judgement task while their EEG was recorded. We focused on pre-stimulu activity, and found that the phase of neural oscillations at 13 ± 2 Hz 200 ms prior to the stimulus correlated with subjective simultaneity of otherwise identical sound-flash events. Remarkably, the correlation between EEG phase and behavioural report occurred in the absence of concomitant changes in EEG amplitude. The probability of simultaneity perception fluctuated significantly as a function of pre-stimulus phase, with the largest perceptual variation being accounted for phase angles nearly 180º apart. This pattern was strongly reliable for sound-flash pairs but not for flash-sound pairs. Overall, these findings suggest that the phase of ongoing brain activity might underlie internal states of the observer that influence cross-modal temporal organisation between the senses and, in turn, subjective synchrony.
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http://dx.doi.org/10.1111/ejn.14186DOI Listing
January 2019

The breakdown of the Simon effect in cross-modal contexts: EEG evidence.

Eur J Neurosci 2018 04;47(7):832-844

Center for Brain and Cognition, Departament de Tecnologies de la Informació i les Comunicacions, Universitat Pompeu Fabra, Edifici Mercè Rodoreda, carrer Ramon Trias Fargas 25-27, 08005, Barcelona, Spain.

In everyday life, we often must coordinate information across spatial locations and different senses for action. It is well known, for example, that reactions are faster when an imperative stimulus and its required response are congruent than when they are not, even if stimulus location itself is completely irrelevant for the task (the so-called Simon effect). However, because these effects have been frequently investigated in single-modality scenarios, the consequences of spatial congruence when more than one sensory modality is at play are less well known. Interestingly, at a behavioral level, the visual Simon effect vanishes in mixed (visual and tactile) modality scenarios, suggesting that irrelevant spatial information ceases to exert influence on vision. To shed some light on this surprising result, here we address the expression of irrelevant spatial information in EEG markers typical of the visual Simon effect (P300, theta power modulation, LRP) in mixed-modality contexts. Our results show no evidence for the visual-spatial information to affect performance at behavioral and neurophysiological levels. The absence of evidence of the neural markers of visual S-R conflict in the mixed-modality scenario implies that some aspects of spatial representations that are strongly expressed in single-modality scenarios might be bypassed.
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http://dx.doi.org/10.1111/ejn.13882DOI Listing
April 2018

Modality-switching in the Simon task: The clash of reference frames.

J Exp Psychol Gen 2017 Oct 22;146(10):1478-1497. Epub 2017 Jun 22.

Center for Brain and Cognition, Departament de Tecnologies de la Informació i les Comunicacions, Universitat Pompeu Fabra.

The representation of spatial information related to an event can influence behavior even when location is task-irrelevant, as in the case of Stimulus-Response (S-R) compatibility effects on the Simon task. However, unlike single-modality situations, which are often used to study the Simon effect, in real-life scenarios various sensory modalities provide spatial information coded in different coordinate systems. Here, we address the expression of S-R compatibility effects in mixed-modality contexts, where events can occur in 1 of various sensory modalities (i.e., vision, touch or audition). The results confirm that, in single-modality cases, Simon effects in vision are expressed in an external spatial frame of reference, while touch information is coded anatomically. Remarkably, when mixing visual and tactile trials in an unpredictable way, the Simon effect disappeared in vision whereas tactile Simon effects remained expressed in their own (anatomical) frame of reference. Mixing visual and auditory stimuli did not obliterate the visual Simon effect and S-R compatibility effects in an external reference frame were evident for both modalities. The extinction of visual Simon effects as a result of mixing visual and tactile modalities can be interpreted as a consequence of the dynamic reorganization of the weights associated to the different sources of spatial information at play. (PsycINFO Database Record
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http://dx.doi.org/10.1037/xge0000342DOI Listing
October 2017

Reliability of TMS phosphene threshold estimation: Toward a standardized protocol.

Brain Stimul 2017 May - Jun;10(3):609-617. Epub 2017 Feb 2.

Center for Brain and Cognition, Universitat Pompeu Fabra, Barcelona, Spain. Electronic address:

Background: Phosphenes induced by transcranial magnetic stimulation (TMS) are a subjectively described visual phenomenon employed in basic and clinical research as index of the excitability of retinotopically organized areas in the brain.

Objective: Phosphene threshold estimation is a preliminary step in many TMS experiments in visual cognition for setting the appropriate level of TMS doses; however, the lack of a direct comparison of the available methods for phosphene threshold estimation leaves unsolved the reliability of those methods in setting TMS doses. The present work aims at fulfilling this gap.

Methods: We compared the most common methods for phosphene threshold calculation, namely the Method of Constant Stimuli (MOCS), the Modified Binary Search (MOBS) and the Rapid Estimation of Phosphene Threshold (REPT). In two experiments we tested the reliability of PT estimation under each of the three methods, considering the day of administration, participants' expertise in phosphene perception and the sensitivity of each method to the initial values used for the threshold calculation.

Results: We found that MOCS and REPT have comparable reliability when estimating phosphene thresholds, while MOBS estimations appear less stable.

Conclusions: Based on our results, researchers and clinicians can estimate phosphene threshold according to MOCS or REPT equally reliably, depending on their specific investigation goals. We suggest several important factors for consideration when calculating phosphene thresholds and describe strategies to adopt in experimental procedures.
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http://dx.doi.org/10.1016/j.brs.2017.01.582DOI Listing
December 2017

The mismatch negativity as an index of cognitive decline for the early detection of Alzheimer's disease.

Sci Rep 2016 09 12;6:33167. Epub 2016 Sep 12.

Cognitive Neuroscience Section, IRCCS Centro San Giovanni di Dio Fatebenefratelli, Brescia, Italy.

Evidence suggests that Alzheimer's disease (AD) is part of a continuum, characterized by long preclinical phases before the onset of clinical symptoms. In several cases, this continuum starts with a syndrome, defined as mild cognitive impairment (MCI), in which daily activities are preserved despite the presence of cognitive decline. The possibility of having a reliable and sensitive neurophysiological marker that can be used for early detection of AD is extremely valuable because of the incidence of this type of dementia. In this study, we aimed to investigate the reliability of auditory mismatch negativity (aMMN) as a marker of cognitive decline from normal ageing progressing from MCI to AD. We compared aMMN elicited in the frontal and temporal locations by duration deviant sounds in short (400 ms) and long (4000 ms) inter-trial intervals (ITI) in three groups. We found that at a short ITI, MCI showed only the temporal component of aMMN and AD the frontal component compared to healthy elderly who presented both. At a longer ITI, aMMN was elicited only in normal ageing subjects at the temporal locations. Our study provides empirical evidence for the possibility to adopt aMMN as an index for assessing cognitive decline in pathological ageing.
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http://dx.doi.org/10.1038/srep33167DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5018736PMC
September 2016

Confounders in the detection of minimal hepatic encephalopathy: a neuropsychological and quantified EEG study.

Liver Int 2015 May 23;35(5):1524-32. Epub 2014 Jul 23.

Department of Medicine (DIMED), University of Padua, Padua, Italy.

Background & Aims: Chronic alcohol misuse, HCV infection and cirrhosis may cause cognitive alterations. The aim of the present study was to assess the influence of alcohol misuse, HCV infection and cirrhosis per se on the neuropsychological and electroencephalogram (EEG) profile and to evaluate the role of alcohol misuse and HCV infections as potential confounding factors in the detection of minimal hepatic encephalopathy.

Methods: A comprehensive neuropsychological profile and EEG spectral parameters were obtained in six age-matched groups of 30 subjects each: (i) HCV-related hepatitis without cirrhosis, (ii) chronic alcohol abusers, (iii) patients with HCV-related cirrhosis, (iv) alcohol-related cirrhosis, (v) cirrhosis not related to alcohol or HCV and (vi) healthy subjects. Cirrhotic patients were matched for MELD score.

Results: The factor 'cirrhosis' was associated with low Phonemic Verbal Fluency (PVF) and Difference between Trail Making Test B and A (TMT) (B-A) (P < 0.001). Chronic alcohol misuse was associated with low PVF, TMT (B-A), Memory with Interference Task at 10 (ITM 10) and 30 s (ITM 30) (all P < 0.05). An interaction was found between the factors 'cirrhosis', 'alcohol misuse' and tests (P < 0.01). HCV hepatitis reduced ITM 10 (P < 0.05), but no interaction was found between 'cirrhosis', 'HCV infection' and tests (P = 0.14). The EEG parameters were mainly influenced by 'cirrhosis' (P < 0.05), and EEG alterations were more pronounced in patients with alcoholic cirrhosis (P = 0.04).

Conclusions: Cirrhosis per se, chronic alcohol misuse and HCV infection were found to be associated with cognitive dysfunction. In patients with cirrhosis, the interaction with alcohol misuse further impinged on brain dysfunction.
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http://dx.doi.org/10.1111/liv.12635DOI Listing
May 2015

Alpha stimulation of the human parietal cortex attunes tactile perception to external space.

Curr Biol 2014 Feb 16;24(3):329-32. Epub 2014 Jan 16.

Center for Brain and Cognition, Departament de Tecnologies de la Informació i les Comunicacions, Universitat Pompeu Fabra, 08018 Barcelona, Spain; Institució Catalana de Recerca i Estudis Avançats (ICREA), 08010 Barcelona, Spain.

An intriguing question in neuroscience concerns how somatosensory events on the skin are represented in the human brain. Since Head and Holmes' [1] neuropsychological dissociation between localizing touch on the skin and localizing body parts in external space, touch is considered to operate in a variety of spatial reference frames [2]. At least two representations of space are in competition during orienting to touch: a somatotopic one, reflecting the organization of the somatosensory cortex (S1) [3], and a more abstract, external reference frame that factors postural changes in relation to body parts and/or external space [4, 5]. Previous transcranial magnetic stimulation (TMS) studies suggest that the posterior parietal cortex (PPC) plays a key role in supporting representations as well as orienting attention in an external reference frame [4, 6]. Here, we capitalized on the TMS entrainment approach [7, 8], targeting the intraparietal sulcus (IPS). We found that frequency-specific (10 Hz) tuning of the PPC induced spatially specific enhancement of tactile detection that was expressed in an external reference frame. This finding establishes a tight causal link between a concrete form of brain activity (10 Hz oscillation) and a specific type of spatial representation, revealing a fundamental property of how the parietal cortex encodes information.
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http://dx.doi.org/10.1016/j.cub.2013.12.029DOI Listing
February 2014

Transcranial stimulation and cognition.

Handb Clin Neurol 2013 ;116:739-50

Department of Clinical and Experimental Sciences, National Institute of Neuroscience, University of Brescia, Brescia, Italy; Cognitive Neuroscience Section, IRCCS Centro San Giovanni di Dio Fatebenefratelli, Brescia, Italy. Electronic address:

Noninvasive brain stimulation (NIBS) is a unique method for studying cognitive function. For the study of cognition, NIBS has gained popularity as a complementary method to functional neuroimaging. By bypassing the correlative approaches of standard imaging techniques, it is possible to establish a putative relationship between brain cognition. In fact, functional neuroimaging data cannot demonstrate the actual role of a particular cortical activation in a specific function because an activated area may simply be correlated with task performance, rather than being responsible for it. NIBS can induce a temporary modification of performance only if the stimulated area is causally engaged in the task. In analogy with lesion studies, NIBS can provide information about where and when a particular process occurs. Based on this assumption, NIBS has been used in many different cognitive domains. However, one of the most interesting questions in neuroscience may not be where and when, but how cognitive activity occurs. Beyond localization approaches, NIBS can be employed to study brain mechanisms. NIBS techniques have the potential to influence behavior transiently by altering neuronal activity, which may have facilitatory or inhibitory behavioral effects. NIBS techniques include transcranial magnetic stimulation (TMS) and transcranial electrical stimulation (tES). TMS has been shown transiently to modulate neural excitability in a manner that is dependent mainly on the timing and frequency of stimulation (high versus low). The mechanism underlying tES is a change in neuronal membrane potentials that appears to be dependent mainly on the direction of current flow (anodal versus cathodal). Nevertheless, the final effects induced by TMS or tES depend on many technical parameters used during stimulation, such as the intensity of stimulation, coil orientation, site of the reference electrode, and time of application. Moreover, an important factor is the possible interactions between these factors and the physiological and cognitive state of the subject. To use NIBS in cognition, it is important to understand not only how NIBS functions but also the brain mechanisms being studied and the features of the area of interest. To describe better the advanced knowledge provided by NIBS in cognition, we will treat each NIBS technique separately and underline the related hypotheses beyond applications.
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http://dx.doi.org/10.1016/B978-0-444-53497-2.00056-5DOI Listing
April 2014

Modelling non-invasive brain stimulation in cognitive neuroscience.

Neurosci Biobehav Rev 2013 Sep 1;37(8):1702-12. Epub 2013 Jul 1.

Department of Clinical and Experimental Sciences, National Neuroscience Institute, University of Brescia, Brescia, Italy; Cognitive Neuroscience Section, IRCCS Centro San Giovanni di Dio Fatebenefratelli, Brescia, Italy. Electronic address:

Non-invasive brain stimulation (NIBS) is a method for the study of cognitive function that is quickly gaining popularity. It bypasses the correlative approaches of other imaging techniques, making it possible to establish a causal relationship between cognitive processes and the functioning of specific brain areas. Like lesion studies, NIBS can provide information about where a particular process occurs. However, NIBS offers the opportunity to study brain mechanisms beyond process localisation, providing information about when activity in a given brain region is involved in a cognitive process, and even how it is involved. When using NIBS to explore cognitive processes, it is important to understand not only how NIBS functions but also the functioning of the neural structures themselves. We know that NIBS techniques have the potential to transiently influence behaviour by altering neuronal activity, which may have facilitatory or inhibitory behavioural effects, and these alterations can be used to understand how the brain works. Given that NIBS necessarily involves the relatively indiscriminate activation of large numbers of neurons, its impact on a neural system can be easily understood as modulation of neural activity that changes the relation between noise and signal. In this review, we describe the mutual interactions between NIBS and brain activity and provide an updated and precise perspective on the theoretical frameworks of NIBS and their impact on cognitive neuroscience. By transitioning our discussion from one aspect (NIBS) to the other (cognition), we aim to provide insights to guide future research.
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http://dx.doi.org/10.1016/j.neubiorev.2013.06.014DOI Listing
September 2013

Is transcranial alternating current stimulation effective in modulating brain oscillations?

PLoS One 2013 14;8(2):e56589. Epub 2013 Feb 14.

Cognitive Neuroscience Section, IRCCS Centro San Giovanni di Dio Fatebenefratelli, Brescia, Italy.

Transcranial alternating current stimulation (tACS) is a promising tool for modulating brain oscillations, as well as a possible therapeutic intervention. However, the lack of conclusive evidence on whether tACS is able to effectively affect cortical activity continues to limit its application. The present study aims to address this issue by exploiting the well-known inhibitory alpha rhythm in the posterior parietal cortex during visual perception and attention orientation. Four groups of healthy volunteers were tested with a Gabor patch detection and discrimination task. All participants were tested at the baseline and selective frequencies of tACS, including Sham, 6 Hz, 10 Hz, and 25 Hz. Stimulation at 6 Hz and 10 Hz over the occipito-parietal area impaired performance in the detection task compared to the baseline. The lack of a retinotopically organised effect and marginal frequency-specificity modulation in the detection task force us to be cautious about the effectiveness of tACS in modulating brain oscillations. Therefore, the present study does not provide significant evidence for tACS reliably inducing direct modulations of brain oscillations that can influence performance in a visual task.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0056589PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3573000PMC
August 2013

The neural basis of the Enigma illusion: a transcranial magnetic stimulation study.

Neuropsychologia 2011 Nov 19;49(13):3648-55. Epub 2011 Sep 19.

Department of Neurological, Neuropsychological, Morphological and Motor Sciences, University of Verona, Verona, Italy.

The aim of this study was to test the role of the visual primary (V1) and the middle temporal area (V5/MT) in the illusory motion perception evoked by the Enigma figure. The Enigma figure induces a visual illusion that is characterized by apparent rotatory motion in the presence of a static figure. By means of repetitive transcranial magnetic stimulation (rTMS) we show that V5/MT is causally linked to the illusory perception of motion. When rTMS was applied bilaterally over V5/MT just prior to presentation of the Enigma figure, the perception of illusory motion was disrupted for approximately 400 ms resulting in a delayed illusion onset. In contrast, rTMS applied over V1 did not have any effect on the illusory perception of motion. These results show that V5/MT, a visual cortical area associated with real motion perception, is also important for the perception of illusory motion, while V1 appears not to be functionally involved in illusory motion perception.
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http://dx.doi.org/10.1016/j.neuropsychologia.2011.09.020DOI Listing
November 2011

Accurate and rapid estimation of phosphene thresholds (REPT).

PLoS One 2011 22;6(7):e22342. Epub 2011 Jul 22.

School of Psychology, The University of Sydney, Sydney, New South Wales, Australia.

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.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0022342PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3142147PMC
December 2011

The effect of TMS on visual motion sensitivity: an increase in neural noise or a decrease in signal strength?

J Neurophysiol 2011 Jul 4;106(1):138-43. Epub 2011 May 4.

Department of Neurological, Neuropsychological, Morphological and Motor Sciences, University of Verona, Verona, Italy.

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.
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http://dx.doi.org/10.1152/jn.00746.2010DOI Listing
July 2011

Sensory memory during physiological aging indexed by mismatch negativity (MMN).

Neurobiol Aging 2012 Mar 6;33(3):625.e21-30. Epub 2011 May 6.

Cognitive Neuroscience Section, IRCCS San Giovanni di Dio Fatebenefratelli, Brescia, Italy.

Physiological aging affects early sensory-perceptual processes. The aim of this experiment was to evaluate changes in auditory sensory memory in physiological aging using the Mismatch Negativity (MMN) paradigm as index. The MMN is a marker recorded through the electroencephalogram and is used to evaluate the integrity of the memory system. We adopted a new, faster paradigm to look for differences between 3 groups of subjects of different ages (young, middle age and older adults) as a function of short or long intervals between stimuli. We found that older adults did not show MMN at long interval condition and that the duration of MMN varied according to the participants' age. The current study provides electrophysiological evidence supporting the theory that the encoding of stimuli is preserved during normal aging, whereas the maintenance of sensory memory is impaired. Considering the advantage offered by the MMN paradigm used here, these data might be a useful reference point for the assessment of auditory sensory memory in pathological aging (e.g., in neurodegenerative diseases).
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http://dx.doi.org/10.1016/j.neurobiolaging.2011.03.021DOI Listing
March 2012

The neural mechanisms of the effects of transcranial magnetic stimulation on perception.

J Neurophysiol 2010 Jun 24;103(6):2982-9. Epub 2010 Mar 24.

Department of Neurological and Vision Sciences, University of Verona, Verona, Italy.

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.
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http://dx.doi.org/10.1152/jn.01096.2009DOI Listing
June 2010

The mechanism of transcranial magnetic stimulation in cognition.

Cortex 2010 Jan 21;46(1):128-30. Epub 2009 Mar 21.

Department of Biomedical Sciences and Biotechnology, National Institute of Neuroscience, University of Brescia, Italy.

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http://dx.doi.org/10.1016/j.cortex.2009.03.004DOI Listing
January 2010

Effects of right parietal transcranial magnetic stimulation on object identification and orientation judgments.

J Cogn Neurosci 2008 May;20(5):916-26

School of Psychology, University of Sydney, Australia.

We investigated the role played by the right parietal lobe in object identification and the ability to interpret object orientation, using transcranial magnetic stimulation (TMS) to momentarily interfere with ongoing cortical activity. Short trains of TMS pulses (12 Hz) were applied to a site overlying the right intraparietal sulcus/inferior parietal lobe while subjects performed either object identification tasks (i.e., picture-word verification and categorizing objects as natural or manufactured) or object orientation judgment tasks (i.e., picture-arrow verification and deciding whether an object was rotated clockwise or counterclockwise). Across different tasks, right parietal TMS impaired orientation judgments, but facilitated object identification, compared to TMS applied to a brain vertex control site. These complementary findings demonstrate that the right parietal lobe--a region belonging to the dorsal visual stream--is critical for processing the spatial attributes of objects, but not their identity. The observed improvement in object recognition, however, suggests an indirect role for the right parietal lobe in object recognition. We propose that this involves the creation of a spatial reference frame for the object, which allows interaction with the object and the individuation of specific viewing instances.
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http://dx.doi.org/10.1162/jocn.2008.20513DOI Listing
May 2008