Publications by authors named "Agnese Zazio"

7 Publications

  • Page 1 of 1

Asymmetric transcallosal conduction delay leads to finer bimanual coordination.

Brain Stimul 2021 Feb 10;14(2):379-388. Epub 2021 Feb 10.

Department of Experimental Medicine, Section of Human Physiology, University of Genoa, Genoa, Italy; Ospedale Policlinico San Martino-IRCCS, Genoa, Italy. Electronic address:

It has been theorized that hemispheric dominance and more segregated information processing have evolved to overcome long conduction delays through the corpus callosum (transcallosal conduction delay - TCD) but that this may still impact behavioral performance, mostly in tasks requiring high timing accuracy. Nevertheless, a thorough understanding of the temporal features of interhemispheric communication is lacking. Here, we aimed to assess the relationship between TCD and behavioral performance with a noninvasive directional cortical measure of TCD obtained from transcranial magnetic stimulation (TMS)-evoked potentials (TEPs) in the motor system. Twenty-one healthy right-handed subjects were tested. TEPs were recorded during an ipsilateral silent period (iSP) paradigm and integrated with diffusion tensor imaging (DTI) and an in-phase bimanual thumb-opposition task. Linear mixed models were applied to test relationships between measures. We found TEP indexes of transcallosal communication at ∼15 ms both after primary motor cortex stimulation (M1-P15) and after dorsal premotor cortex stimulation (dPMC-P15). Both M1-and dPMC-P15 were predicted by mean diffusivity in the callosal body. Moreover, M1-P15 was positively related to iSP. Importantly, M1-P15 latency was linked to bimanual coordination with direction-dependent effects, so that asymmetric TCD was the best predictor of bimanual coordination. Our findings support the idea that transcallosal timing in signal transmission is essential for interhemispheric communication and can impact the final behavioral outcome. However, they challenge the view that a short conduction delay is always beneficial. Rather, they suggest that the effect of the conduction delay may depend on the direction of information flow.
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http://dx.doi.org/10.1016/j.brs.2021.02.002DOI Listing
February 2021

Pre-stimulus alpha-band power and phase fluctuations originate from different neural sources and exert distinct impact on stimulus-evoked responses.

Eur J Neurosci 2021 Feb 4. Epub 2021 Feb 4.

Centre for Cognitive Neuroscience, University of Salzburg, Salzburg, Austria.

Ongoing oscillatory neural activity before stimulus onset influences subsequent visual perception. Specifically, both the power and the phase of oscillations in the alpha-frequency band (9-13 Hz) have been reported to predict the detection of visual stimuli. Up to now, the functional mechanisms underlying pre-stimulus power and phase effects on upcoming visual percepts are debated. Here, we used magnetoencephalography recordings together with a near-threshold visual detection task to investigate the neural generators of pre-stimulus power and phase and their impact on subsequent visual-evoked responses. Pre-stimulus alpha-band power and phase opposition effects were found consistent with previous reports. Source localization suggested clearly distinct neural generators for these pre-stimulus effects: Power effects were mainly found in occipital-temporal regions, whereas phase effects also involved prefrontal areas. In order to be functionally relevant, the pre-stimulus correlates should influence post-stimulus processing. Using a trial-sorting approach, we observed that only pre-stimulus power modulated the Hits versus Misses difference in the evoked response, a well-established post-stimulus neural correlate of near-threshold perception, such that trials with stronger pre-stimulus power effect showed greater post-stimulus difference. By contrast, no influence of pre-stimulus phase effects were found. In sum, our study shows distinct generators for two pre-stimulus neural patterns predicting visual perception, and that only alpha power impacts the post-stimulus correlate of conscious access. This underlines the functional relevance of prestimulus alpha power on perceptual awareness, while questioning the role of alpha phase.
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http://dx.doi.org/10.1111/ejn.15138DOI Listing
February 2021

Oscillatory Bursts in Parietal Cortex Reflect Dynamic Attention between Multiple Objects and Ensembles.

J Neurosci 2020 09 4;40(36):6927-6937. Epub 2020 Aug 4.

Centre for Cognitive Neuroscience, University of Salzburg, Salzburg, 5020, Austria.

The visual system uses two complimentary strategies to process multiple objects simultaneously within a scene and update their spatial positions in real time. It either uses selective attention to individuate a complex, dynamic scene into a few focal objects (i.e., object individuation), or it represents multiple objects as an ensemble by distributing attention more globally across the scene (i.e., ensemble grouping). Neural oscillations may be a key signature for focal object individuation versus distributed ensemble grouping, because they are thought to regulate neural excitability over visual areas through inhibitory control mechanisms. We recorded whole-head MEG data during a multiple-object tracking paradigm, in which human participants (13 female, 11 male) switched between different instructions for object individuation and ensemble grouping on different trials. The stimuli, responses, and the demand to keep track of multiple spatial locations over time were held constant between the two conditions. We observed increased α-band power (9-13 Hz) packed into oscillatory bursts in bilateral inferior parietal cortex during multiple-object processing. Single-trial analysis revealed greater burst occurrences on object individuation versus ensemble grouping trials. By contrast, we found no differences using standard analyses on across-trials averaged α-band power. Moreover, the bursting effects occurred only below/at, but not above, the typical capacity limits for multiple-object processing (at ∼4 objects). Our findings reveal the real-time neural correlates underlying the dynamic processing of multiple-object scenarios, which are modulated by grouping strategies and capacity. They support a rhythmic, α-pulsed organization of dynamic attention to multiple objects and ensembles. Dynamic multiple-object scenarios are an important problem in real-world and computer vision. They require keeping track of multiple objects as they move through space and time. Such problems can be solved in two ways: One can individuate a scene object by object, or alternatively group objects into ensembles. We observed greater occurrences of α-oscillatory burst events in parietal cortex for processing objects versus ensembles and below/at versus above processing capacity. These results demonstrate a unique top-down mechanism by which the brain dynamically adjusts its computational level between objects and ensembles. They help to explain how the brain copes with its capacity limitations in real-time environments and may lead the way to technological innovations for time-critical video analysis in computer vision.
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http://dx.doi.org/10.1523/JNEUROSCI.0231-20.2020DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7470925PMC
September 2020

Touch anticipation mediates cross-modal Hebbian plasticity in the primary somatosensory cortex.

Cortex 2020 05 30;126:173-181. Epub 2020 Jan 30.

Department of Psychology & NeuroMi - Milan Center for Neuroscience, University of Milano-Bicocca, Milan, Italy; Laboratory of Neuropsychology, IRCCS Istituto Auxologico Italiano, Milan, Italy. Electronic address:

Paired associative stimulation (PAS) protocols can be used to induce Hebbian plasticity in the human brain. A modified, cross-modal version, of the PAS (cross-modal PAS, cm-PAS) has been recently developed. The cm-PAS consists in the repetitive pairings of a transcranial magnetic stimulation (TMS) pulse over the primary somatosensory cortex (S1) and a visual stimulus depicting a hand being touched; a 20 ms of inter-stimulus interval (ISI) is required to affect S1 plasticity, in turn modulating tactile acuity and somatosensory evoked potentials. The present study explores the role of anticipatory simulation in the cm-PAS efficacy, which could be responsible for such a short ISI. To this aim, we compared the effect of the original, fixed-frequency, cm-PAS to that of a jittered version, in which the time interval between trials was not steady but jittered, hence avoiding the anticipation of the upcoming visual-touch stimulus. Moreover, in the jittered PAS, the ISI between the paired stimulations was varied: it could match the early, somatosensory-driven, activation of S1 (20 ms), or the mirror recruitment of S1 by touch observation (150 ms). Results showed that tactile acuity is enhanced by the fixed-frequency cm-PAS, with an ISI of 20 ms between paired stimulation (visual-touch stimulus and TMS pulse over S1), and also by the jittered cm-PAS but only if the ISI is of 150 ms. These findings suggest that the cm-PAS with a jittered frequency, by preventing an anticipatory pre-activation of S1, delays the timing of the interaction between the visual-touch stimulus and the cortical pulse. On a broader perspective, our study highlights the possible involvement of sensory anticipation, likely through mirror-like simulation mechanisms, in tactile mirroring, as well as its influence of the optimal interval between the afferent and the magnetic pulse during PAS protocols.
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http://dx.doi.org/10.1016/j.cortex.2020.01.008DOI Listing
May 2020

Modelling the effects of ongoing alpha activity on visual perception: The oscillation-based probability of response.

Neurosci Biobehav Rev 2020 05 2;112:242-253. Epub 2020 Feb 2.

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

Substantial evidence has shown that ongoing neural activity significantly contributes to how the brain responds to upcoming stimuli. In visual perception, a considerable portion of trial-to-trial variability can be accounted for by prestimulus magneto/electroencephalographic (M/EEG) alpha oscillations, which play an inhibitory function by means of cross-frequency interactions with gamma-band oscillations. Despite the fundamental theories on the role of oscillations in perception and cognition, the current literature lacks a clear theorization of the neural mechanisms underlying the effects of prestimulus activity, including electrophysiological phenomena at different scales (e.g., local field potentials and macro-scale M/EEG). Here, we present a model called the oscillation-based probability of response (OPR), which directly assesses the link between meso-scale neural mechanisms, macro-scale M/EEG, and behavioural outcome. The OPR includes distinct meso-scale mechanisms through which alpha oscillations modulate M/EEG gamma activity, namely, by decreasing a) the amplitude and/or b) neural synchronization of gamma oscillations. Crucially, the OPR makes specific predictions on the effects of these mechanisms on visual perception, as assessed through the psychometric function. SIGNIFICANCE STATEMENT: The oscillation-based probability of response (OPR) is grounded on a psychophysical approach focusing on the psychometric function estimation and may be highly informative in the study of ongoing brain activity, because it provides a tool for distinguishing different neural mechanisms of alpha-driven modulation of sensory processing.
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http://dx.doi.org/10.1016/j.neubiorev.2020.01.037DOI Listing
May 2020

Hebbian associative plasticity in the visuo-tactile domain: A cross-modal paired associative stimulation protocol.

Neuroimage 2019 11 17;201:116025. Epub 2019 Jul 17.

Department of Psychology & NeuroMi - Milan Center for Neuroscience, University of Milano-Bicocca, Milano, Italy; Laboratory of Neuropsychology, IRCCS Istituto Auxologico Italiano, Milano, Italy. Electronic address:

We developed and assessed the effects of a novel cross-modal protocol aimed at inducing associative (Hebbian-like) plasticity in the somatosensory cortical system through vision. Associative long-term potentiation can be induced in the primary somatosensory cortex (S1) by means of paired associative stimulation (PAS), in which a peripheral electrical stimulation of the median nerve is repeatedly paired with a transcranial magnetic stimulation (TMS) pulse over S1. Considering the mirror proprieties of S1, the cross-modal PAS (cm-PAS) consists of repetitive observation of bodily tactile stimulations, paired with TMS pulses over the contralateral S1. Through three experiments in healthy participants, we demonstrate that the cm-PAS is able to induce excitatory plastic effects with functional significance in S1, improving somatosensory processing at both behavioral (tactile acuity) and neurophysiological (somatosensory-evoked potentials) levels. The plastic effects induced by cm-PAS depend on the interval (20 ms) between the visual stimulus and the magnetic pulse, the targeted cortical site (S1), and the tactile content of the visual stimulus, which must represent a touch event. Such specificity implies the involvement of cross-modal, mirror-like, mechanisms in S1, which are able to visually promote associative synaptic plasticity in S1 likely through the recruitment of predictive coding processes.
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http://dx.doi.org/10.1016/j.neuroimage.2019.116025DOI 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