Феурра Маттео

Primary motor cortex functionally contributes to language comprehension: An online rTMS study.

2017 · ARTICLE · en

Among various questions pertinent to grounding human cognitive functions in a neurobiological substrate, the association between language and motor brain structures is a particularly debated one in neuroscience and psychology. While many studies support a broadly distributed model of language and semantics grounded, among other things, in the general modality-specific systems, theories disagree as to whether motor and sensory cortex activity observed during language processing is functional or epiphenomenal. Here, we assessed the role of motor areas in linguistic processing by investigating the responses of 28 healthy volunteers to different word types in semantic and lexical decision tasks, following repetitive transcranial magnetic stimulation (rTMS) of primary motor cortex. We found that early rTMS (delivered within 200ms of word onset) produces a left-lateralised and meaning-specific change in reaction speed, slowing down behavioural responses to action-related words, and facilitating abstract words - an effect present only during semantic, but not lexical, decision. We interpret these data in light of action-perception theory of language, bolstering the claim that motor cortical areas play a functional role in language comprehension.

Dynamic changes in prefrontal cortex involvement during verbal episodic memory formation

2017 · ARTICLE · en

During encoding, the neural activity immediately before or during an event can predict whether that event will be later remembered. The contribution of brain activity immediately after an event to memory formation is however less known. Here, we used repetitive Transcranial Magnetic Stimulation (rTMS) to investigate the temporal dynamics of episodic memory encoding with a focus on post-stimulus time intervals. At encoding, rTMS was applied during the online processing of the word, at its offset, or 100, 200, 300 or 400ms thereafter. rTMS was delivered to the left ventrolateral (VLPFC) or dorsolateral prefrontal cortex (DLPFC). VLPFC rTMS during the first few hundreds of milliseconds after word offset disrupted subsequent recognition accuracy. We did not observe effects of DLPFC rTMS at any time point. These results suggest that verbal encoding-related VLPFC engagement starts at a relatively late processing stage, and may reflect brain processes related to the offset of the stimulus.

Effects of Transcranial Alternating Current Stimulation on the Primary Motor Cortex by Online Combined Approach with Transcranial Magnetic Stimulation

2017 · ARTICLE · en

Transcranial Alternating Current Stimulation (tACS) is a neuromodulatory technique able to act through sinusoidal electrical waveforms in a specific frequency and in turn modulate ongoing cortical oscillatory activity. This neurotool allows the establishment of a causal link between endogenous oscillatory activity and behavior. Most of the tACS studies have shown online effects of tACS. However, little is known about the underlying action mechanisms of this technique because of the AC-induced artifacts on Electroencephalography (EEG) signals. Here we show a unique approach to investigate online physiological frequency-specific effects of tACS of the primary motor cortex (M1) by using single pulse Transcranial Magnetic Stimulation (TMS) to probe cortical excitability changes. In our setup, the TMS coil is placed over the tACS electrode while Motor Evoked Potentials (MEPs) are collected to test the effects of the ongoing M1-tACS. So far, this approach has mainly been used to study the visual and motor systems. However, the current tACS-TMS setup can pave the way for future investigations of cognitive functions. Therefore, we provide a step-by-step manual and video guidelines for the procedure.

Effects of tDCS over Broca's area coupled with linguistic training are not specific to language

2017 · ARTICLE · en

Continuous theta-burst stimulation of medial prefrontal cortex enhances schema-linked encoding

2017 · ARTICLE · en

Role of brain hemispheric dominance in anticipatory postural control strategies

2016 · ARTICLE · en

Most of the cerebral functions are asymmetrically represented in the two hemispheres. Moreover, dexterity and coordination of the distal segment of the dominant limbs depend on cortico-motor lateralization. In this study, we investigated whether postural control may be also considered a lateralized hemispheric brain function. To this aim, 15 young subjects were tested in standing position by measuring Center of Pressure (COP) shifts along the antero-posterior axis (COP-Y) during dynamic posturography before and after continuous Theta Burst Stimulation (cTBS) intervention applied to the dominant or non-dominant M1 hand area as well as to the vertex. We show that when subjects were expecting a forward platform translation, the COP-Y was positioned significantly backward or forward after dominant or non-dominant M1 stimulation, respectively. We postulate that cTBS applied on M1 may have disrupted the functional connectivity between intra- and inter-hemispheric areas implicated in the anticipatory control of postural stability. This study suggests a functional asymmetry between the two homologous primary motor areas, with the dominant hemisphere playing a critical role in the selection of the appropriate postural control strategy.

Frequency-specific insight into short-term memory capacity

2016 · ARTICLE · en

The digit span is one of the most widely used memory tests in clinical and experimental neuropsychology for reliably measuring short-term memory capacity. In the forward version, sequences of digits of increasing length have to be reproduced in the order in which they are presented, whereas in the backward version items must be reproduced in the reversed order. Here, we assessed whether transcranial alternating current stimulation (tACS) increases the memory span for digits of young and midlife adults. Imperceptibly weak electrical currents in the alpha (10 Hz), beta (20 Hz), theta (5 Hz) and gamma (40 Hz) range, as well as a sham stimulation, were delivered over the left posterior parietal cortex, a cortical region thought to sustain maintenance processes in short-term memory through oscillatory brain activity in the beta range. We showed a frequency-specific effect of beta-tACS that robustly increased the forward memory span of young, but not middle-aged, healthy individuals. The effect correlated with age: the younger the subjects, the greater the benefit arising from parietal beta stimulation. Our results provide evidence of a short-term memory capacity improvement in young adults by online frequency-specific tACS application.

Commentary: Duration-dependent effects of the BDNF Val66Met polymorphism on anodal tDCS induced motor cortex plasticity in older adults: a group and individual perspective

2015 · ARTICLE · en

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(McHughen et al., 2010) 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showed that during a simple right index finger movement task, Val/Met carriers exhibited reduced activation volumes on different brain regions (including motor cortex, premotor cortex, supplementary motor area) with respect to Val/Val carriers. Interestingly, after training, Val/Val showed a greater activation volume expansion whereas Val/Met carriers a greater activation volume reduction. Moreover, inside a driving-based motor learning task, subjects with polymorphism benefitted less from training. All together, these findings highlight that differences in volume activation, accordingly to the polymorphism, increase with presence of training. Recently, it has been shown that Transcranial Direct Current Stimulation (tDCS), might be an optimal tool to investigate the role of BDNF polymorphism in activity-dependent plasticity (Fritsch et al., 2010). In the human motor system, tDCS induces long-lasting and polarity-specific changes in the excitability of the motor cortex (Nitsche and Paulus, 2000). Anodal tDCS induces facilitatory effect by a membrane depolarization and by an increase in the excitability of corticospinal axons (Di Lazzaro et al., 2013), while cathodal tDCS induces inhibitory effects by a membrane hyperpolarization (Wagner et al., 2007). Animal models showed that tDCS modify thalamocortical synapses at presynaptic sites by changes in the membrane potential of cortical neurons (Marquez-Ruiz et al., 2012). -->

Individual and sex-related differences in pain and relief responsiveness are associated with differences in resting-state functional networks in healthy volunteers

2015 · ARTICLE · en

Pain processing is associated with neural activity in a number of wide-spread brain regions. Here, we investigated whether functional connectivity at rest between these brain regions is associated with individual and sex-related differences in thermal pain and relief responsiveness. Twenty healthy volunteers (ten females) were scanned with functional magnetic resonance imaging in resting condition. Half an hour after scanning, we administered thermal pain on the back of their right hand, and collected pain and relief ratings in two separate runs of twelve stimulations each. Across the whole group, mean pain ratings were associated with decreased connectivity at rest between brain regions belonging to the default mode and the visual resting-state network. In men, pain measures correlated with increased connectivity within the visual resting-state network. In women instead, decreased connectivity between this network and parietal and prefrontal brain regions implicated in affective cognitive control were associated with both pain and relief ratings. Our findings indicate that the well documented individual variability and sex-differences in pain sensitivity may be explained, at least in part, by network dynamics at rest in these brain regions.

Differential effects of acute cortisol administration on deep and shallow episodic memory traces: a study on healthy males

2014 · ARTICLE · en

We aimed at investigating rapid effects of plasma cortisol elevations on the episodic memory phase of encoding or retrieval, and on the strength of the memory trace. Participants were asked either to select a word containing the letter "e" (shallow encoding task) or to judge if a word referred to a living entity (deep encoding task). We intravenously administered a bolus of 20mg of cortisol either 5 min before encoding or 5 min before retrieval, in a between-subjects design. The study included only male participants tested in the late afternoon, and neutral words as stimuli. When cortisol administration occurred prior to retrieval, a main effect of group emerged. Recognition accuracy was higher for individuals who received cortisol compared to placebo. The higher discrimination accuracy for the cortisol group was significant for words encoded during deep but not shallow task. Cortisol administration before encoding did not affect subsequent retrieval performance (either for deep or shallow stimuli) despite a facilitatory trend. Because genomic mechanisms take some time to develop, such a mechanism cannot apply to our findings where the memory task was performed shortly after the enhancement of glucocorticoid levels. Therefore, glucocorticoids, through non-genomic fast effects, determine an enhancement in episodic memory if administered immediately prior to retrieval. This effect is more evident if the memory trace is laid down through deep encoding operations involving the recruitment of specific neural networks.