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Suppression of premotor cortex disrupts motor coding of peripersonal space
No full textPeripersonal space (PPS) representation depends on the activity of a fronto-parietal network including the Premotor cortex (PMc) and the Posterior Parietal cortex (PPc). PPS representation has a direct effect on the motor system: a stimulus activating the PPS around the hand modulates the excitability of hand representation in the primary motor cortex. However, to date, direct information about the involvement of the PMc-PPc network in the motor mapping of sensory events occurring within PPS is lacking. To address this issue, we used a ‘perturb-and-measure’ paradigm based on the combination of transcranial direct current stimulation (tDCS) and transcranial magnetic stimulation (TMS) techniques. Cathodal tDCS was applied to transiently suppress neural activity in PMc, PPc and primary visual cortex (V1; serving as an active control site); single-pulse TMS was used to induce motor-evoked potentials (MEPs) from hand muscles and so to measure the excitability of the hand motor representation. MEPs were compared when a sound was presented either near the hand or at a distance. In experimental sessions performed after sham-tDCS and after tDCS over the control area V1, we found a spatially dependent modulation of the hand motor representation: sounds presented near the hand induced an inhibitory motor response as compared to sounds presented far apart. Critically, this effect was selectively abolished after tDCS suppression of neural activity in PMc, but not when perturbing the activity of PPc. These findings suggest that PMc has a critical role in mapping sensory representations of space onto the motor system
"Motor resonance and dispositional empathy: single pulse transcranial magnetic stimulation" Poster Presentation - Magstim/University of Oxford TMS Summer School, Oxford.
No full textCompensatory Plasticity in the Action Observation Network: Virtual Lesions of STS Enhance Anticipatory Simulation of Seen Actions
No full textObservation of snapshots depicting ongoing motor acts increases corticospinal motor excitability. Such motor facilitation indexes the anticipatory simulation of observed (implied) actions and likely reflects computations occurring in the parietofrontal nodes of a cortical network subserving action perception (action observation network, AON). However, direct evidence for the active role of AON in simulating the future of seen actions is lacking. Using a perturb-and-measure transcranial magnetic stimulation (TMS) approach, we show that off-line TMS disruption of regions within (inferior frontal cortex, IFC) and upstream (superior temporal sulcus, STS) the parietofrontal AON transiently abolishes and enhances the motor facilitation to observed implied actions, respectively. Our findings highlight the critical role of IFC in anticipatory motor simulation. More importantly, they show that disruption of STS calls into play compensatory motor simulation activity, fundamental for counteracting the noisy visual processing induced by TMS. Thus, short-term plastic changes in the AON allow motor simulation to deal with any gap or ambiguity of ever-changing perceptual worlds. These findings support the active, compensatory, and predictive role of frontoparietal nodes of the AON in the perception and anticipatory simulation of implied actions
Motor properties of peripersonal space in humans.
Full text linkBACKGROUND:A stimulus approaching the body requires fast processing and appropriate motor reactions. In monkeys, fronto-parietal networks are involved both in integrating multisensory information within a limited space surrounding the body (i.e. peripersonal space, PPS) and in action planning and execution, suggesting an overlap between sensory representations of space and motor representations of action. In the present study we investigate whether these overlapping representations also exist in the human brain. METHODOLOGY/PRINCIPAL FINDINGS:We recorded from hand muscles motor-evoked potentials (MEPs) induced by single-pulse of transcranial magnetic stimulation (TMS) after presenting an auditory stimulus either near the hand or in far space. MEPs recorded 50 ms after the near-sound onset were enhanced compared to MEPs evoked after far sounds. This near-far modulation faded at longer inter-stimulus intervals, and reversed completely for MEPs recorded 300 ms after the sound onset. At that time point, higher motor excitability was associated with far sounds. Such auditory modulation of hand motor representation was specific to a hand-centred, and not a body-centred reference frame. CONCLUSIONS/SIGNIFICANCE:This pattern of corticospinal modulation highlights the relation between space and time in the pps representation: an early facilitation for near stimuli may reflect immediate motor preparation, whereas, at later time intervals, motor preparation relates to distant stimuli potentially approaching the body
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
THE ROLE OF FRONTO-PARIETAL AREAS IN THE MOTOR REPRESENTATION OF THE PERIPERSONAL SPACE (PPS)
No full textIntroduction: In order to interact with the external world, our brain integrates multisensory cues about environmental stimuli with information about the body in a coherent representation of the Peripersonal Space (PPS). A network of fronto-parietal regions, involving the ventral premotor cortex (vPMc) and the posterior parietal cortex (PPc), might support this function, since neurons in these areas integrate somatosensory with visual and acoustic stimuli near the body [1,2]. Previous TMS studies have highlighted the motor counterpart of PPS by showing that stimuli presented near or far from the hand are capable of modulating the excitability of the hand representation in the motor cortex (M1) [3,4].
Here we test whether M1 modulation due to PPS representation relies on the activity of two key nodes of the PPS fronto-parietal network, namely vPMc and PPc. To this aim we used a ‘perturb-and-measure’ paradigm [5]: transcranial direct current stimulation (tDCS) was applied to transiently suppress activity in vPMc or PPc; then single-pulse TMS was used to measure the excitability of the hand motor representation, when an acoustic stimulus was presented either near the hand or in the far space.
Methods: 15 minutes of cathodal, inhibitory, tDCS were applied to target areas (vPMc and PPc) or to V1, serving as a control site. Single-pulse TMS was applied to the hand area of M1 and motor-evoked potentials (MEPs) from FDI muscle were recorded after presenting a sound either at ≈5 cm (NEAR sounds) or at ≈100 cm (FAR sounds) from the hand. TMS pulses were delivered at 120% of resting motor threshold (rMT), at 3 different intervals (50, 175, and 300 ms) after sound presentation. In Experiment 1 (16 subjects), we compared MEPs after Real-tDCS over vPMc (test) or after Sham-tDCS over the same site (sham control). In Experiment 2 (12 subjects), we compared the effect of Real-tDCS over PPc (test) or over V1 (active control).
Results: After the sham stimulation, we found a space-specific modulation of the hand motor representation: MEP amplitudes recorded at 300 ms after the onset of near sounds were lower than those recorded after far sounds, confirming that stimuli near the hand may suppress hand M1 excitability [3,4]. This motor modulation disappeared after Real-tDCS over vPMc. In contrast, Real-tDCS over PPc or V1 did not affect the space-specific modulation of M1: MEPs recorded at 300ms from sound onset were again lower when a near, compared to a far sound, was presented.
Conclusions: PPS representation implies both (multi)sensory (processing external stimuli potentially approaching the body) and motor functions (preparing appropriate motor responses) [1-4]. By using a tDCS-TMS perturb-and-measure paradigm [5] we showed that inhibitory motor response to sounds presented near the body was disrupted by suppression of vPMc, but not of PPc or V1. Our findings suggest a crucial role of vPMc in the motor representation of the PPS. Thus, the two nodes of the fronto-parietal network representing the PPS have partially dissociable functions, being vPMc, rather than PPc, mainly involved in transforming sensory representations of space in motor responses.
References:
1. Graziano MS, Cooke DF (2006) Parieto-frontal interactions, personal space, and defensive behavior. Neuropsychologia 44, 845-859.
2. Bremmer F, Schlack A, Shah NJ, Zafiris O, Kubischik M, Hoffmann K, et al. (2001) Polymodal Motion Processing in Posterior Parietal and Premotor Cortex: A Human fMRI Study Strongly Implies Equivalencies between Humans and Monkeys. Neuron 29, 287-296
3. Serino A, Annella L, Avenanti A (2009) Motor Properties of Peripersonal Space in Humans. PLoS ONE 4, e6582.
4. Makin TR, Holmes NP, Brozzoli C, Rossetti Y, Farnè A (2009) Coding of visual space during motor preparation: Approaching objects rapidly modulate corticospinal excitability in hand-centered coordinates. Journal of Neuroscience 29, 11841-51.
5. Avenanti A, Bolognini N, Maravita A, Aglioti SM (2007) Somatic and motor components of action simulation. Current Biology 17, 2129-35
"Suppression of left ventral premotor cortex impairs action prediction: transcranial direct current stimulation" Poster Presentation - CAOS Workshop, Rovereto-Italy, May 19-22, 2011.
No full textVariations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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