Stimulus predictability moderates the withdrawal strategy in response to repetitive noxious stimulation in humans

Nociceptive withdrawal reflex (NWR) is a protective reaction to a noxious stimulus, resulting in withdrawal of the affected area and thus preventing potential tissue damage. This involuntary reaction consists of neural circuits, biomechanical strategies, and muscle activity that ensure an optimal withdrawal. Studies of lower limb NWR indicate that the amplitude of the NWR is highly modulated by extrinsic and intrinsic factors, such as stimulation site, intensity, frequency, and supraspinal activity, among others. Whether the predictability of the stimulus has an effect on the biomechanical strategies is still unclear. This study aimed to evaluate how the predictability of impending noxious stimuli modulate the NWR reaction in the lower limb. NWR was evoked on fifteen healthy participants by trains of electrical stimuli on the sole of the foot and was measured in one distal (tibialis anterior) and one proximal (biceps femoris) muscle. The predictability was manipulated by giving participants prior information about the onset of the stimulus trains and the number of delivered stimuli per train. Results showed that the predictability of the incoming stimuli differentially modulates the muscle activity involved in the NWR reaction. For the most unpredictable stimulus train, larger NWR at distal muscles were evoked. Furthermore, the stereotyped temporal summation profile to repeated stimulation was observed when the stimulus train was completely predictable, while it was disrupted in proximal muscles in unpredictable conditions. It is inferred that the reflex response is shaped by descending control, which dynamically tunes the activity of the muscles involved in the resulting reaction. NEW & NOTEWORTHY Innate defensive behaviors such as reflexes are found across all species, constituting preprogrammed responses to external threats that are not anticipated. Previous studies indicated that the excitability of the reflex arcs like spinal nociceptive withdrawal reflex (NWR) pathways in humans are modulated by several cognitive factors. This study assesses how the predictability of a threat affects the biomechanical pattern of the withdrawal response, showing that distal and proximal muscles are differentially modulated by descending control.Fil: Jure, Fabricio A.. Aalborg University; DinamarcaFil: Arguissain, Federico G.. Aalborg University; DinamarcaFil: Biurrun Manresa, José Alberto. Universidad Nacional de Entre Ríos. Instituto de Investigación y Desarrollo en Bioingeniería y Bioinformática - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigación y Desarrollo en Bioingeniería y Bioinformática; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro de Investigaciones y Transferencia de Entre Ríos. Universidad Nacional de Entre Ríos. Centro de Investigaciones y Transferencia de Entre Ríos; Argentina. Aalborg University; DinamarcaFil: Graven Nielsen, Thomas. Aalborg University; DinamarcaFil: Andersen, Ole Kæseler. Aalborg University; Dinamarc

Social foundations of the mathematics curriculum: a rationale for change

The nature of educational aims as criteria for worthwhile curriculum practice is explored and a cross-section of aims for mathematics education is discussed. An aim for mathematics education which emphasises the social aspect of the subject in its being, its conduct and its applications is identified and epistemological foundations for such a view of the nature of the subject are explored. It is argued that such an epistemological perspective of mathematics would be reflected in the social context of the mathematics classroom, arising from a methodology in which the subject would become more problematic and open to change, investigation and hypothesis. The aims of two major mathematics curriculum development projects (the Nuffield Mathematics Project and the School Mathematics Project) are examined to determine the extent to which their aims may take the 'social' nature of mathematics into account. The probable social context of mathematics classrooms using their materials is postulated in an attempt to characterise the nature of the subject as it is reflected in these materials. A view of the nature of mathematics held by practising teachers and by pupils is then established by drawing upon, and extrapolating from, evidence relating to the social context of mathematics classrooms at primary and secondary level. Conclusions follow, which suggest that fundamental change in mathematics education requires, as a first step, the adoption of a new epistemological perspective of the subject in order that the pursuit of the aim which emphasises the social nature of mathematics is achieved. It is suggested that this, in turn, ultimately could lead to the desired balance in the mathematics curriculum which hitherto has been lacking

Novel surface electrode design for preferential activation of cutaneous nociceptors

Objective.Small area electrodes enable preferential activation of nociceptive fibers. It is debated, however, whether co-activation of large fibers still occurs for the existing electrode designs. Moreover, existing electrodes are limited to low stimulation intensities, for which behavioral and physiological responses may be considered less reliable. A recent optimization study showed that there is a potential for improving electrode performance and increase the range of possible stimulation intensities. Based on those results, the present study introduces and tests a novel planar concentric array electrode design for small fiber activation in healthy volunteers.Approach.Volunteers received electrical stimulation with the planar concentric array electrode and a regular patch electrode. Perception thresholds (PT) were estimated at the beginning and the end of the experiment. Evoked cortical potentials were recorded in blocks of 30 stimuli. For the patch, stimulation current intensity was set to two times PT, while three intensities, two, five, and ten times PT, were applied with the planar concentric array electrode. Sensation quality, numerical-rating scores, and reaction times were obtained for each PT estimation and during each block of evoked potential recordings.Main results.Stimulation with the patch electrode was characterized as dull, while stimulation with the planar concentric array electrode was characterized as sharp, with increased sharpness for increasing stimulus current intensity. Likewise, scores of the numerical rating scale were higher for the planar concentric array electrode compared to the patch and increased with increasing stimulation current intensity. Reaction times and ERP latencies were longer for the planar concentric array electrode compared to the patch.Significance.The presented novel planar concentric array electrode is a small, non-invasive, and single-use electrode that has the potential to investigate small fiber neuropathy and pain mechanisms, as it is small fiber preferential for a wide range of stimulation intensities

Quantitative agreement in the detection of the N1 peak (primary outcomes).

<p>The boundaries of the boxes indicate the 25^th and 75^th percentiles, the line within the box marks the median, the whiskers indicate the 10^th and 90^th percentiles and the circles above and below represent outliers (<i>n</i> = 16 for each index). Horizontal lines on top of the bars represent statistically significant post hoc differences between pairings (Student-Newman-Keuls, <i>p</i> < 0.05). LoA: limits of agreement, CV: coefficient of variation.</p

Effects of stimulation intensity on event-related potential (ERP) recordings.

<p>Each panel shows the average ERP of all available trials from each subject (color-coded) for a single stimulation intensity. The overlapping thick black line represents the grand average of all subjects (<i>n</i> = 16). RTh: nociceptive withdrawal reflex threshold.</p

Categorical agreement in the detection of the N1 peak (primary outcomes).

<p>The boundaries of the boxes indicate the 25^th and 75^th percentiles, the line within the box marks the median, the whiskers indicate the 10^th and 90^th percentiles and the circles above and below represent outliers (<i>n</i> = 16 for each index). Horizontal lines on top of the bars represent statistically significant post hoc differences between pairings (Student-Newman-Keuls, <i>p</i> < 0.05). <i>p</i>_<i>pos</i>: positive percent agreement, <i>p</i>_<i>neg</i>: negative percent agreement, κ: Cohen’s kappa.</p

Comparison of manual and automated ERP feature detection/estimation methods.

<p><b>A)</b> Trial-by-trial image of ERP responses of a single subject elicited with the highest stimulation intensity (20 trials). <b>B-E)</b> Performance of OBS1, OBS2, DRIV and WVLT methods, respectively, on the detection/estimation of single-trial ERP features of a single subject elicited with the highest stimulation intensity. Crosses, circles and asterisks represent single-trial N1, N2 and P2 features, respectively, while the blue trace is the average of 20 trials. Note that WVLT algorithm did not detect the N2 peak in <b>E)</b>.</p

Single-trial peak amplitude and latency values and number of peaks detected with each method, averaged across stimulation intensities and subjects.

<p>Values are presented as mean ± SD.</p><p>Single-trial peak amplitude and latency values and number of peaks detected with each method, averaged across stimulation intensities and subjects.</p