Selective nociceptor activation in volunteers by infrared diode laser

<p>Abstract</p> <p>Background</p> <p>Two main classes of peripheral sensory neurons contribute to thermal pain sensitivity: the unmyelinated C fibers and thinly myelinated Aδ fibers. These two fiber types may differentially underlie different clinical pain states and distinctions in the efficacy of analgesic treatments. Methods of differentially testing C and Aδ thermal pain are widely used in animal experimentation, but these methods are not optimal for human volunteer and patient use. Thus, this project aimed to provide psychophysical and electrophysiological evidence that whether different protocols of infrared diode laser stimulation, which allows for direct activation of nociceptive terminals deep in the skin, could differentially activate Aδ or C fiber thermonociceptors in volunteers.</p> <p>Results</p> <p>Short (60 ms), high intensity laser pulses (SP) evoked monomodal "pricking" pain which was not enhanced by topical capsaicin, whereas longer, lower power pulses (LP) evoked monomodal "burning" pain which was enhanced by topical capsaicin. SP also produced cortical evoked EEG potentials consistent with Aδ mediation, the amplitude of which was directly correlated with pain intensity but was not affected by topical capsaicin. LP also produced a distinct evoked potential pattern the amplitude of which was also correlated with pain intensity, which was enhanced by topical capsaicin, and the latency of which could be used to estimate the conduction velocity of the mediating nociceptive fibers.</p> <p>Conclusions</p> <p>Psychophysical and electrophysiological data were consistent with the ability of short high intensity infrared laser pulses to selectively produce Aδ mediated pain and of longer pulses to selectively produce C fiber mediated thermal pain. Thus, the use of these or similar protocols may be useful in developing and testing novel therapeutics based on the differential molecular mechanisms underlying activation of the two fiber types (e.g., TRPV1, TRPV2, etc). In addition, these protocol may be useful in determining the fiber mediation of different clinical pain types which may, in turn be useful in treatment choice.</p

Attention spatiale auditive et visuelle chez des patients héminégligents et des sujets normaux : étude clinique, comportementale et électrophysiologique

L'attention est une fonction cognitive à la base d'un grand nombre de nos comportements, elle permet le déroulement d'autres fonctions comme la mémoire ou le raisonnement. L'objectif principal de ces études était de déterminer les caractéristiques anatomiques et fonctionnelles des processus attentionnels automatiques et contrôlés, dans les modalités auditives et visuelles. Lors de tâches de détection de cibles auditives ou visuelles, latéralisées à gauche ou à droite, nous avons recueilli des indices comportementaux et électrophysiologiques chez des sujets sains et des patients héminégligents affectés de lésions temporo-pariétales droites. Ces études ont mis en évidence une organisation cérébrale différente, d'une part entre les processus attentionnels automatiques et contrôlés, et d'autre part entre les modalités auditives et visuelles. Ces travaux confirment l'implication primordiale de la région pariétale droite dans les processus attentionnels et spécifient que cette asymétrie hémisphérique serait plus importante pour les processus attentionnels contrôlés que pour les processus attentionnels automatiques

An immersive virtual reality tool for assessing left and right unilateral spatial neglect

The reported rate of the occurrence of unilateral spatial neglect (USN) is highly variable likely due to the lack of validity and low sensitivity of classical tools used to assess it. Virtual reality (VR) assessments try to overcome these limitations by proposing immersive and complex environments. Nevertheless, existing VR‐based tasks are mostly focused only on near space and lack analysis of psychometric properties and/or clinical validation. The present study evaluates the clinical validity and sensitivity of a new immersive VR‐based task to assess USN in the extra‐personal space and examines the neuronal correlates of deficits of far space exploration. The task was administrated to two groups of patients with right ( N = 28) or left ( N = 11) hemispheric brain lesions, also undergoing classical paper‐and‐pencil assessment, as well as a group of healthy participants. Our VR‐based task detected 44% of neglect cases compared to 31% by paper‐and‐pencil tests in the total sample. Importantly, 30% of the patients (with right or left brain lesions) with no clear sign of USN on the paper‐and‐pencil tests performed outside the normal range in the VR‐based task. Voxel lesion‐symptom mapping revealed that deficits detected in VR were associated with lesions in insular and temporal cortex, part of the neural network involved in spatial processing. These results show that our immersive VR‐based task is efficient and sensitive in detecting mild to strong manifestations of USN affecting the extra‐personal space, which may be undetected using standard tools

Virtual reality-based sensorimotor adaptation shapes subsequent spontaneous and naturalistic stimulus-driven brain activity

Our everyday life summons numerous novel sensorimotor experiences, to which our brain needs to adapt in order to function properly. However, tracking plasticity of naturalistic behavior and associated brain modulations is challenging. Here, we tackled this question implementing a prism adaptation-like training in virtual reality (VRPA) in combination with functional neuroimaging. Three groups of healthy participants (N&nbsp;= 45) underwent VRPA (with a shift either to the left/right side, or with no shift), and performed functional magnetic resonance imaging (fMRI) sessions before and after training. To capture modulations in free-flowing, task-free brain activity, the fMRI sessions included resting-state and free-viewing of naturalistic videos. We found significant decreases in spontaneous functional connectivity between attentional and default mode (DMN)/fronto-parietal networks, only for the adaptation groups, more pronouncedly in the hemisphere contralateral to the induced shift. In addition, VRPA was found to bias visual responses to naturalistic videos: Following rightward adaptation, we found upregulation of visual response in an area in the parieto-occipital sulcus (POS) only in the right hemisphere. Notably, the extent of POS upregulation correlated with the size of the VRPA-induced after-effect measured in behavioral tests. This study demonstrates that a brief VRPA exposure can change large-scale cortical connectivity and correspondingly bias visual responses to naturalistic sensory inputs

Modulation of visual attention by prismatic adaptation.

Visuo-motor adaptation via rightward-deviating prisms has been repeatedly shown to alleviate lateralized deficits in neglect, including detection of targets as well as endogenous and exogenous orienting of attention. We review here evidence relevant to the underlying neural mechanisms. Rightward prismatic adaptation was shown to shift visual field representation from right to left inferior parietal lobule, changing thus hemispheric dominance within the ventral attentional system. This change is likely to redirect visual input to the dorsal attentional system and to re-install balance between its left- and right-hemispheric components in neglect. We propose a model based on the shift in hemispheric dominance within the ventral attentional system (SHD-VAS), which offers a parsimonious explanation for the effect of rightward prismatic adaptation on spatial bias in neglect and on behavioral data in normal subjects