selene schintu

National Institutes of Health, NINDS, Post-Doc

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Adaptation to leftward shifting prisms alters motor inter-hemispheric inhibition

Brain Stimulation, Mar 1, 2017

Adaptation to rightward shifting prisms (rightward prism adaptation, RPA) ameliorates neglect sym... more Adaptation to rightward shifting prisms (rightward prism adaptation, RPA) ameliorates neglect symptoms in patients while adaptation to leftward shifting prisms (leftward prism adaptation, LPA) induces neglect-like behaviors in healthy subjects. It has been hypothesized that prism adaptation (PA) modulates interhemispheric balance between the parietal cortices by inhibiting the posterior parietal cortex (PPC) contralateral to the prismatic deviation, but PA's effects on interhemispheric inhibition (IHI) have not been directly investigated. Since there are hyper-excitable connections between the PPC and primary motor cortex (M1) in the left hemisphere of neglect patients, we reasoned that LPA might mimic right hemisphere lesions by reducing parietal IHI, hyper-exciting the left PPC and PPC-M1 connections, and in turn altering IHI at the motor level. Namely, we hypothesized that LPA would increase IHI from the left to the right M1. We examined changes in left-toright and right-to-left IHI between the 2 M1s using the ipsilateral silent period (iSP) before and after either LPA or RPA. The iSP was significantly longer after LPA but only from left-to-right and it did not change at all after RPA. This is the first physiological demonstration that LPA alters IHI in the healthy brain.

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Callosal anisotropy predicts attentional network changes after parietal inhibitory stimulation

NeuroImage, Feb 1, 2021

Hemispatial neglect is thought to result from disruption of interhemispheric equilibrium. Right h... more Hemispatial neglect is thought to result from disruption of interhemispheric equilibrium. Right hemisphere lesions deactivate the right frontoparietal network and hyperactivate the left via release from interhemispheric inhibition. Support for this putative mechanism comes from neuropsychological evidence as well as transcranial magnetic stimulation (TMS) studies in healthy subjects, in whom right posterior parietal cortex (PPC) inhibition causes neglect-like, rightward, visuospatial bias. Concurrent TMS and fMRI after right PPC TMS show task-dependent changes but may fail to identify effects of stimulation in areas not directly activated by the specific task, compli cating interpretations. We used resting-state functional connectivity (RSFC) after inhibitory TMS over the right PPC to examine changes in the networks underlying visuospatial attention and used diffusion-weighted imaging to measure the structural properties of relevant white matter pathways. In a crossover experiment in healthy individuals, we delivered continuous theta burst TMS to the right PPC and vertex as control condition. We hypothesized that PPC inhibitory stimulation would result in a rightward visuospatial bias, decrease frontoparietal RSFC, and increase the PPC RSFC with the attentional network in the left hemisphere. We also expected that individual differences in fractional anisotropy (FA) of the frontoparieta network and the callosal pathway between the PPCs would account for variability of the TMS-induced RSFC changes.

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Dynamic changes in spatial representation within the posterior parietal cortex in response to visuomotor adaptation

Cerebral Cortex, Aug 20, 2022

Recent studies used functional magnetic resonance imaging (fMRI) population receptive field (pRF)... more Recent studies used functional magnetic resonance imaging (fMRI) population receptive field (pRF) mapping to demonstrate that retinotopic organization extends from the primary visual cortex to ventral and dorsal visual pathways, by quantifying visual field maps, receptive field size, and laterality throughout multiple areas. Visuospatial representation in the posterior parietal cortex (PPC) is modulated by attentional deployment, raising the question of whether spatial representation in the PPC is dynamic and f lexible, and whether this f lexibility contributes to visuospatial learning. To answer this question, changes in spatial representation within the PPC and early visual cortex were recorded with pRF mapping before and after prism adaptation (PA)-a well-established visuomotor technique that modulates visuospatial attention according to the direction of the visual displacement. As predicted, results showed that adaptation to left-shifting prisms increases pRF size in left PPC, while leaving space representation in the early visual cortex unchanged. This is the first evidence that PA drives a dynamic reorganization of response profiles in the PPC. These findings show that spatial representations in the PPC not only ref lect changes driven by attentional deployment but dynamically change in response to modulation of external factors such as manipulation of the visuospatial input during visuomotor adaptation.

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Hedonic and autonomic responses in promoting affective touch

Scientific Reports

Interpersonal touch is intrinsically reciprocal since it entails a person promoting and another r... more Interpersonal touch is intrinsically reciprocal since it entails a person promoting and another receiving the touch. While several studies have investigated the beneficial effects of receiving affective touch, the affective experience of caressing another individual remains largely unknown. Here, we investigated the hedonic and autonomic responses (skin conductance and heart rate) in the person promoting affective touch. We also examined whether interpersonal relationship, gender, and eye contact modulate these responses. As expected, caressing the partner was perceived as more pleasant than caressing a stranger, especially if the affective touch occurred together with mutual eye contact. Promoting affective touch to the partner also resulted in a decrease of both autonomic responses and anxiety levels, suggesting the occurrence of a calming effect. Additionally, these effects were more pronounced in females compared to males, indicating that hedonic and autonomic aspects of affecti...

format_quoteParticipants rated pleasantness significantly higher for partners than strangers (F(1, 48) = 114.29, p < 0.001).format_quote

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Editorial: Uncovering the neural correlates of prism adaptation: Evidence from the brain network approach

Frontiers in Psychology

Eye dominance modulates visuospatial attention

Neuropsychologia, 2019

Visuospatial attention has an inherent asymmetry: the leftward bias called pseudoneglect. In typi... more Visuospatial attention has an inherent asymmetry: the leftward bias called pseudoneglect. In typical line bisection tasks, healthy individuals tend to judge the center of a line leftward of the true center, an effect attributed to the right hemisphere dominance in visuospatial attention. Since it has been shown that information perceived by the dominant eye strongly activates the ipsilateral visual cortex, we hypothesized that eye dominance may modulate visuospatial attention bias. Because activation of the left hemisphere induced by left eye dominance should mitigate the right hemisphere dominance in attention, we predicted that right-handed individuals with left dominant eye would show smaller amount of pseudoneglect than right-handed individuals with right dominant eye. We compared the performance at both the perceptual (Landmark) and manual line bisection task of forty right-handed healthy individuals, half of whom had a right dominant eye and the other half a left dominant eye. As predicted, the left eyed dominant group showed smaller, actually not significant pseudoneglect, which was thus greater in the right eye dominant group. The influence of eye dominance on visuospatial attention was present in the Landmark but not the manual line bisection task, in which the amount of visuospatial bias correlated with participants' degree of (right) handedness. This is the first report of the effect of eye dominance on visuospatial attention within a right-handed population. This finding, by showing the influence of eye dominance on visuospatial cognition, not only helps in better defining intact visuospatial cognition mechanism but also encourages further research to pinpoint the neural basis of such interaction.

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Effective connectivity underlying neural and behavioral components of prism adaptation

Frontiers in Psychology

Prism adaptation (PA) is a form of visuomotor training that produces both sensorimotor and cognit... more Prism adaptation (PA) is a form of visuomotor training that produces both sensorimotor and cognitive aftereffects depending on the direction of the visual displacement. Recently, a neural framework explaining both types of PA-induced aftereffects has been proposed, but direct evidence for it is lacking. We employed Structural Equation Modeling (SEM), a form of effective connectivity analysis, to establish directionality among connected nodes of the brain network thought to subserve PA. The findings reveal two distinct network branches: (1) a loop involving connections from the parietal cortices to the right parahippocampal gyrus, and (2) a branch linking the lateral premotor cortex to the parahippocampal gyrus via the cerebellum. Like the sensorimotor aftereffects, the first branch exhibited qualitatively different modulations for left versus right PA, and critically, changes in these connections were correlated with the magnitude of the sensorimotor aftereffects. Like the cognitive...

Self-other distinction modulates the social softness illusion

Psychological Research

The social softness illusion (i.e., the tendency to perceive another person's skin as softer ... more The social softness illusion (i.e., the tendency to perceive another person's skin as softer than our own) is thought to promote the sharing of social-emotional experiences because of the rewarding properties of receiving and giving social affective touch. Here we investigated whether the ability to distinguish someone else’s body from our own modulates the social softness illusion. In particular, we tested whether the spatial perspective taken by the participants and seeing or not the touched arms could alter this illusion. Pairs of female participants were assigned the roles of either the giver (i.e., delivering the touches) or the receiver (i.e., being touched). We manipulated the location of the touch (palm or forearm), the spatial perspective of the receiver’s body with respect to the giver’s body (egocentric or allocentric perspective), and the vision of the touched body part (the giver could either see both her own and the receiver’s body part, or she was blindfolded). Co...

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Dynamic changes in spatial representation within the posterior parietal cortex in response to visuomotor adaptation

Recent studies used fMRI population receptive field (pRF) mapping to demonstrate that retinotopic... more Recent studies used fMRI population receptive field (pRF) mapping to demonstrate that retinotopic organization extends from primary visual cortex to ventral and dorsal visual pathways by quantifying visual field maps, receptive field size, and laterality throughout multiple areas. Visuospatial representation in the posterior parietal cortex (PPC) is modulated by attentional deployment, raising the question of whether spatial representation in the PPC is dynamic and flexible and that this flexibility contributes to visuospatial learning. To answer this question, changes in spatial representation within PPC, as measured with pRF mapping, were recorded before and after visuomotor adaptation. Visuospatial input was laterally manipulated, rightward or leftward, via prism adaptation, a well-established visuomotor technique that modulates visuospatial performance. Based on existing models of prism adaptation mechanism of action, we predicted left prism adaptation to produce a right visuosp...

Changing your body changes your eating attitudes: embodiment of a slim virtual avatar induces avoidance of high-calorie food

Heliyon

Left-shifting prism adaptation boosts reward-based learning

Cortex

Callosal anisotropy predicts attentional network changes after parietal inhibitory stimulation

Prismatic adaptation modulates inter-hemispheric balance with a subsequent change in visual field coverage

Journal of Vision

Prism adaptation modulates connectivity of the intraparietal sulcus with multiple brain networks

Prism adaptation (PA) alters spatial cognition according to the direction of visual displacement ... more Prism adaptation (PA) alters spatial cognition according to the direction of visual displacement by temporarily modifying sensorimotor mapping. Right-shifting prisms (right PA) improve neglect of left space in patients, possibly by decreasing activity in the left hemisphere and increasing it in the right. Left PA shifts attention to the right in healthy individuals by an opposite mechanism. However, functional imaging studies of PA are inconsistent, perhaps because of differing activation tasks. We measured resting-state functional connectivity (RSFC) in healthy individuals before and after PA. Right, vs. left, PA decreased RSFC in the navigation network defined by the right posterior parietal cortices (PPCs), hippocampus, and cerebellum. Right PA, relative to baseline, increased RSFC between regions within both PPCs and between the PPCs and the right middle frontal gyrus, whereas left PA decreased RSFC between these regions. These results show that right PA modulates connectivity w...

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Neuropsychological aspects of Asperger Syndrome in adults: a review

Neuropsychological Trends

Despite distinctive clinical characteristics, Asperger Syndrome (AS) is actually included in the ... more Despite distinctive clinical characteristics, Asperger Syndrome (AS) is actually included in the broad spectrum of Autism Spectrum Disorder. Usually, to evaluate AS in adulthood, diagnostic tools are referred to autistic traits; furthermore, AS' neuropsychological profile features are still unclear. The aim of the present review is to shed light on the cognitive characteristics of adults with AS. Limited number of studies have investigated the neuropsychological profile of adults with AS: individuals with AS have intellectual abilities in the normal range and show strengths in verbal memory, inhibitory control and decision making. Disagreement exists about the presence of deficits in attentional functions, visual-spatial memory, cognitive flexibility, planning and verbal fluency. The present work underlines the need for a neuropsychological assessment in order to delineate the cognitive profile of adults with AS, which could help in the diagnosis of AS in adulthood and to design rehabilitative protocols.

format_quoteAsperger Syndrome's delayed diagnosis leads to higher rates of comorbid psychiatric issues, emphasizing the need for distinct clinical approaches.format_quote

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The asymmetrical effect of leftward and rightward prisms on intact visuospatial cognition

Cortex

Motor cortex inhibition by TMS reduces cognitive non-motor procedural learning when immediate incentives are present

Cortex; a journal devoted to the study of the nervous system and behavior, Dec 1, 2017

Inhibitory repetitive transcranial magnetic stimulation (rTMS) of the primary motor area (M1) imp... more Inhibitory repetitive transcranial magnetic stimulation (rTMS) of the primary motor area (M1) impairs motor sequence-learning, but not basic motor function. It is unknown if this is specific for motor forms of procedural learning or a more general effect. To investigate, we tested the effect of M1-inhibition on the weather prediction task (WPT), a learning task with minimal motor learning component. In the WPT, participants learn arbitrary, probabilistic, associations between sets of meaningless cues and fictional outcomes. In our "Feedback" (FB) condition, they received monetary rewards/punishments during learning. In the "paired associate" (PA) condition they learned the same information by passive observation of associations. The observational and feedback learning conditions were matched for their non-learning-specific motor demands. In each of two FB or PA sessions, we delivered Real (inhibitory) or Sham continuous theta-burst (cTBS) to the left-M1, before 1...

Prismatic Adaptation Boosts Feedback-Based Learning

Journal of Vision

Adaptation to Leftward Shifting Prisms Alters Motor Interhemispheric Inhibition

Cerebral Cortex, 2016

Adaptation to rightward shifting prisms (rightward prism adaptation, RPA) ameliorates neglect sym... more Adaptation to rightward shifting prisms (rightward prism adaptation, RPA) ameliorates neglect symptoms in patients while adaptation to leftward shifting prisms (leftward prism adaptation, LPA) induces neglect-like behaviors in healthy subjects. It has been hypothesized that prism adaptation (PA) modulates interhemispheric balance between the parietal cortices by inhibiting the posterior parietal cortex (PPC) contralateral to the prismatic deviation, but PA's effects on interhemispheric inhibition (IHI) have not been directly investigated. Since there are hyper-excitable connections between the PPC and primary motor cortex (M1) in the left hemisphere of neglect patients, we reasoned that LPA might mimic right hemisphere lesions by reducing parietal IHI, hyper-exciting the left PPC and PPC-M1 connections, and in turn altering IHI at the motor level. Namely, we hypothesized that LPA would increase IHI from the left to the right M1. We examined changes in left-toright and right-to-left IHI between the 2 M1s using the ipsilateral silent period (iSP) (Meyer et al. 1995) before and after either LPA or RPA. The iSP was significantly longer after LPA but only from left-to-right and it did not change at all after RPA. This is the first physiological demonstration that LPA alters IHI in the healthy brain.

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Paired-Pulse Parietal-Motor Stimulation Differentially Modulates Corticospinal Excitability across Hemispheres When Combined with Prism Adaptation

Neural plasticity, 2016

Rightward prism adaptation ameliorates neglect symptoms while leftward prism adaptation (LPA) ind... more Rightward prism adaptation ameliorates neglect symptoms while leftward prism adaptation (LPA) induces neglect-like biases in healthy individuals. Similarly, inhibitory repetitive transcranial magnetic stimulation (rTMS) on the right posterior parietal cortex (PPC) induces neglect-like behavior, whereas on the left PPC it ameliorates neglect symptoms and normalizes hyperexcitability of left hemisphere parietal-motor (PPC-M1) connectivity. Based on this analogy we hypothesized that LPA increases PPC-M1 excitability in the left hemisphere and decreases it in the right one. In an attempt to shed some light on the mechanisms underlying LPA's effects on cognition, we investigated this hypothesis in healthy individuals measuring PPC-M1 excitability with dual-site paired-pulse TMS (ppTMS). We found a left hemisphere increase and a right hemisphere decrease in the amplitude of motor evoked potentials elicited by paired as well as single pulses on M1. While this could indicate that LPA bi...

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