1,721,004 research outputs found
Real-Time Blind Independent Component Extraction from fMRI Experimental Data
No full textNew York, June 18-22, 2003, published on CD-Rom in NeuroImage, 19(2), 2003 (abstract 882
Cortico-spinal modularity in the parieto-frontal system: a new perspective on action control
Full text link: Classical neurophysiology suggests that the motor cortex (MI) has a unique role in action control. In contrast, this review presents evidence for multiple parieto-frontal spinal command modules that can bypass MI. Five observations support this modular perspective: (i) the statistics of cortical connectivity demonstrate functionally-related clusters of cortical areas, defining functional modules in the premotor, cingulate, and parietal cortices; (ii) different corticospinal pathways originate from the above areas, each with a distinct range of conduction velocities; (iii) the activation time of each module varies depending on task, and different modules can be activated simultaneously; (iv) a modular architecture with direct motor output is faster and less metabolically expensive than an architecture that relies on MI, given the slow connections between MI and other cortical areas; (v) lesions of the areas composing parieto-frontal modules have different effects from lesions of MI. Here we provide examples of six cortico-spinal modules and functions they subserve: module 1) arm reaching, tool use and object construction; module 2) spatial navigation and locomotion; module 3) grasping and observation of hand and mouth actions; module 4) action initiation, motor sequences, time encoding; module 5) conditional motor association and learning, action plan switching and action inhibition; module 6) planning defensive actions. These modules can serve as a library of tools to be recombined when faced with novel tasks, and MI might serve as a recombinatory hub. In conclusion, the availability of locally-stored information and multiple outflow paths supports the physiological plausibility of the proposed modular perspective
Functional Responses in the Human Spinal Cord during Willed Motor Actions: Evidence for Side- and Rate-Dependent Activity
No full textAlthough the spinal cord is the output station of the central motor system, little is known about the relationships between its functionalactivity and willed movement parameters in humans. We investigated here blood oxygenation level-dependent functional magneticresonance imaging (fMRI) signal changes in the cervical spinal cord during a simple finger-to-thumb opposition task in 13 right-handedvolunteers, using a dedicated array of 16 receive-only surface coils on a 3 Tesla MRI system. In a first experiment, we found significantfMRI signal increases on both sides of the lower cervical spinal cord while subjects performed the motor task at a comfortable pace (0.5Hz) using either hand. Both the spatial extent of movement-related clusters and peak signal increases were significantly higher on the sideof the cord ipsilateral to the moving hand than on the contralateral side. Movement-related activity was consistently larger than signalfluctuations during rest. In a second experiment, we recorded spinal cord responses while the same motor sequence was performed usingthe dominant hand at two different rates (0.5 or 1 Hz). The intensity but not the spatial extent of the response was larger during higherrates, and it was higher on the ipsilateral side of the cord. Notwithstanding the limited spatial resolving power of the adopted technique,the present results clearly indicate that the finger movement-related fMRI signals recorded from the spinal cord have a neural origin andthat as a result of recent technological advances, fMRI can be used to obtain novel and quantitative physiological information on theactivity of spinal circuit
Adelta nociceptor response to laser stimuli: selective effect of stimulus duration on skin temperature, brain potentials and pain perception
No full textObjective: To disclose a possible effect of duration of pulsed laser heat stimuli on Ad nociceptor responses, skin temperature profiles,
brain evoked potentials and pain perception.
Methods:We used a laser stimulator which works in the millisecond range and allows us to change the duration of the pulse while keeping
the total energy of the stimulus constant. In 10 healthy volunteers, we measured the intensity of perceived pain with a 0–10 scale and the
latency and amplitude of the early N1 and late N2 components of the scalp potentials evoked by laser pulses of equal energy and three
different stimulus durations (2, 10, and 20 ms). Using a specifically developed pyrometer with a temporal resolution lower than 1 ms we also
measured stimulus-induced changes of skin temperature.
Results: Stimulus duration significantly influenced temperature rise times, pain perception, and brain potentials. Shorter stimulus
durations yielded steeper slopes in the skin temperature profiles and higher pain ratings, shortened the latency of the N1 and N2 components,
and increased the amplitude of N1.
Conclusions and significance: The shorter stimulus duration shortens receptor activation times and yields a more synchronous afferent
volley, thus providing a stronger spatial–temporal summation at central synapses that enhances intensity of first pain and brain potentials.
This may prove useful in clinical applications
How the senses guide goal-directed and defensive actions. Common principles of organization
No full textHigh-level motor functions such as reaching, grasping, object construction and tool use are classically described as being subserved by internal models which combine sensory signals with motor outflow operations. In contrast, internal models of rapid defensive behavior have been mostly considered to be minimally accessible to cognitive control, and thus rarely discussed in the context of motor cognition. In this chapter we propose, instead, that injury avoidance is based on cortical areas, anatomical connections and functional motifs similar to those described for goal-directed actions
Comparing data-driven to hypothesis-driven techniques for analyzing fMRI data of music perception.
No full text
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
Variations 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
- …
