Encoding Manual Dexterity through Modulation of Intrinsic α Band Connectivity.

The human hand possesses both consolidated motor skills and remarkable flexibility in adapting to ongoing task demands. However, the underlying mechanisms by which the brain balances stability and flexibility remain unknown. In the absence of external input or behavior, spontaneous (intrinsic) brain connectivity is thought to represent a prior of stored memories. In this study, we investigated how manual dexterity modulates spontaneous functional connectivity in the motor cortex during hand movement. Using magnetoencephalography, in 47 human participants (both sexes), we examined connectivity modulations in the α and ß frequency bands at rest and during two motor tasks (i.e., finger tapping or toe squeezing). The flexibility and stability of such modulations allowed us to identify two groups of participants with different levels of performance (high and low performers) on the nine-hole peg test, a test of manual dexterity. In the α band, participants with higher manual dexterity showed distributed decreases of connectivity, specifically in the motor cortex, increased segregation, and reduced nodal centrality. Participants with lower manual dexterity showed an opposite pattern. Notably, these patterns from the brain to behavior are mirrored by results from behavior to the brain. Indeed, when participants were divided using the median split of the dexterity score, we found the same connectivity patterns. In summary, this experiment shows that a long-term motor skill-manual dexterity-influences the way the motor systems respond during movements.

The Montreal Cognitive Assessment (MoCA): updated norms and psychometric insights into adaptive testing from healthy individuals in Northern Italy.

BACKGROUND: The availability of fine-grained, culture-specific psychometric outcomes can favor the interpretation of scores of the Montreal Cognitive Assessment (MoCA), the most frequently used instrument to screen for mild cognitive dysfunctions in both instrumental and non-instrumental domains. This study thus aimed at providing: (i) updated, region-specific norms for the Italian MoCA, by also (ii) comparing them to pre-existing ones with higher geographical coverage; (iii) information on sensitivity and discriminative capability at the item level. METHODS: Five hundred and seventy nine healthy individuals from Northern Italy (208 males, 371 females; age: 63.4 ± 15, 21-96; education: 11.3 ± 4.6, 1-25) were administered the MoCA. Item Response Theory (IRT) was adopted to assess item difficulty and discrimination. Normative values were derived by means of the Equivalent Scores (ESs) method, applied to the MoCA and its sub-scales. Average ESs were also computed. Agreement with previous ESs classification was assessed via Cohen's k. RESULTS: Age and education significantly predicted all MoCA measures except for Orientation, which was related to age only. No sex differences were detected when tested along with age and education. Substantial disagreements with previous ESs classifications were detected. Several items proved to be scarcely sensitive, especially the place item from Orientation and the letter detection task. Memory items showed high discriminative capability, along with certain items assessing executive functions and orientation. DISCUSSION: Item-level information herewith provided for the Italian MoCA can help interpret its scores by Italian practitioners. Italian practitioners should consider an adaptive use of region-specific norms for the MoCA.

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

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.

Evidence of top-down modulation of the Brentano illusion but not of the glare effect by transcranial direct current stimulation.

Transcranial direct current stimulation (tDCS) has been widely used for modulating sensory, motor and cognitive functions, but there are only few attempts to induce and change illusory perception. Visual illusions have been the most traditional and effective way to investigate visual processing through the comparison between physical reality and subjective reports. Here we used tDCS to modulate two different visual illusions, namely the Brentano illusion and the glare effect, with the aim of uncovering the influence of top-down mechanisms on bottom-up visual perception in two experiments. In Experiment 1, to a first group of subjects, real and sham cathodal tDCS (2 mA, 10 min) were applied over the left and right posterior parietal cortices (PPC). In Experiment 2, real and sham cathodal tDCS were applied to the left and right occipital cortices (OC) to a second group of participants. Results showed that tDCS was effective in modulating only the Brentano illusion, but not the glare effect. tDCS increased the Brentano illusion but specifically for the stimulated cortical area (right PPC), illusion direction (leftward), visual hemispace (left), and illusion length (160 mm). These findings suggest the existence of an inhibitory modulation of top-down mechanisms on bottom-up visual processing specifically for the Brentano illusion, but not for the glare effect. The lack of effect of occipital tDCS should consider the possible role of ocular compensation or of the unstimulated hemisphere, which deserves further investigations.

Cortical dynamics underpinning the self-other distinction of touch: A TMS-EEG study.

Touch supports processes crucial to human social behaviour, adding a bodily dimension to the perception and understanding of others' feelings. Mirror cortical activity was proposed to underpin the interpersonal sharing of touch, allowing an automatic and unconscious simulation of others' somatic states. However, recent evidence questioned the existence of a tactile shared representation in the primary somatosensory cortex (S1), and the neural correlates of self-other distinction in the somatosensory system remains unknown. We address these issues by exploring S1 reactivity, and the associated neural network oscillations and connectivity, to self and others' touch. Transcranial Magnetic Stimulation combined with Electroencephalography (TMS-EEG) recordings were performed during tactile perception and observation, looking for differences in cortical activation and connectivity between felt and seen touch. The sight of a touch directed to a human body part, but not to an object, triggered an early activation of S1 as a felt touch did, which, in both conditions, propagated to fronto-parietal regions. Critically, touch perception and observation shared an effective connectivity network generated in the beta band, which is typically associated to unconscious tactile processing. Conversely, alpha band connectivity, a marker of conscious tactile processing, was detected only for real tactile stimulation. Alpha connectivity within a fronto-parietal pathway seems to underpin the ability to distinguish self and others' somatosensory states, controlling and distinguishing shared tactile representations in S1.

Rewiring the evolution of the human hand: How the embodiment of a virtual bionic tool improves behavior.

Humans are the most versatile tool users among animals. Accordingly, our manual skills evolved alongside the shape of the hand. In the future, further evolution may take place: humans may merge with their tools, and technology may integrate into our biology in a way that blurs the line between the two. So, the question is whether humans can embody a bionic tool (i.e., experience it as part of their body) and thus if this would affect behavior. We investigated in virtual reality how the substitution of the hand with a virtual grafting of an end-effector, either non-naturalistic (a bionic tool) or naturalistic (a hand), impacts embodiment and behavior. Across four experiments, we show that the virtual grafting of a bionic tool elicits a sense of embodiment similar to or even stronger than its natural counterpart. In conclusion, the natural usage of bionic tools can rewire the evolution of human behavior.

The Reading the Mind in the Eyes Test, Iowa Gambling Task and Interpersonal Reactivity Index: Normative Data in an Italian Population Sample.

OBJECTIVE: Social cognition and executive deficits are frequent in neurological and neuropsychiatric disorders. Yet, there is a paucity of standardized domain-specific psychometric tools for the assessment of complex decision-making, social cognition (i.e., Theory of Mind), and empathy. To this aim, this study intended at providing normative data in an Italian population sample for the Iowa Gambling Task, the Reading the Mind in the Eyes Test, and the Interpersonal Reactivity Index. METHOD: The Iowa Gambling Task, the Reading the Mind in the Eyes Test, and the Interpersonal Reactivity Index were administered to 462 healthy Italian participants aged between 18 and 91 years, considering demographic factors. A confirmatory factor analysis was run to test for unidimensionality. Normative values were derived by means of the Equivalent Scores method. RESULTS: Education predicted all tests' scores, age influenced scores at the Interpersonal Reactivity Index and the Reading the Mind in the Eyes Test, gender predicted empathic abilities only. The three tests did not underpin a unidimensional structure. CONCLUSIONS: The present work provides demographically adjusted Italian normative data for a set of tests assessing real-life decision-making, emotion recognition and empathy, filling a gap within II-level, domain-specific, neuropsychological testing. For the first time, the Interpersonal Reactivity Index is proposed as an adjuvant neuropsychological tool, while the standardization of the Iowa Gambling Task offers a new scoring system for advantageous/disadvantageous choices.

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

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.