scholarly journals Oscillatory Characteristics of Nociceptive Responses in the SII Cortex

2008 ◽  
Vol 35 (5) ◽  
pp. 630-637 ◽  
Author(s):  
Fu-Jung Hsiao ◽  
Wei-Ta Chen ◽  
Kwong-Kum Liao ◽  
Zin-An Wu ◽  
Low-Tone Ho ◽  
...  
Keyword(s):  
Statistical Power ◽  
Stimulus Onset ◽  
Pain Level ◽  
Thulium Laser ◽  
Current Dipole ◽  
Left Hand ◽  
Power Difference ◽  
Nociceptive Responses ◽  
Cortical Responses ◽  
Pain Stimuli

Objective:This study is aimed to explore the frequency characteristics of pain-evoked neuromagnetic responses in the secondary somatosensory (SII) cortices.Methods:Thulium-laser nociceptive stimuli to the left hand dorsum of 10 right-handed healthy adults. The pain stimuli were rated as mild, moderate, and severe levels according to subjects' reports on a 10-point visual analog scale. We analyzed their cortical responses with wavelet-based frequency analyses and equivalent current dipole (ECD) modeling.Results:For each pain level, we found an increase of theta (4-8 Hz) and alpha (8-13 Hz) power in bilateral SII areas at 180-210 ms after stimulus onset. The power was larger for the moderate than for the mild pain level (p < 0.05), but there was no statistical power difference of these oscillations between moderate and severe pain stimulus conditions (p = 0.7). Within the SII area, we did not observe particular difference in theta and alpha ECD locations between varying pain level conditions.Conclusions:The 4-13 Hz activities, peaking from 180 to 210 ms, are oscillatory correlates of SII activation in response to nociceptive stimulation, but their power may code the magnitude of pain stimuli only up to moderate level, as rated subjectively. This measure could be potentially used to evaluate SII activation in further pain studies.

Non-Linear Interactions in Cortical Responses to Bilateral vs Unilateral Visual Field Stimulation

Perception ◽  
1997 ◽  
Vol 26 (1_suppl) ◽  
pp. 62-62
Author(s):  
S P Ahlfors ◽  
J J Foxe ◽  
R J Ilmoniemi ◽  
G V Simpson
Keyword(s):  
Visual Field ◽  
Evoked Potentials ◽  
Normal Subjects ◽  
Stimulus Onset ◽  
Current Dipole ◽  
Field Patterns ◽  
Cortical Responses ◽  
Bilateral Case ◽  
Multichannel Recordings ◽  
Onset Asynchrony

Stimuli in different parts of the visual field can be perceived as independent entities and as conjoined wholes. It is of interest to determine whether there are cortical representations of the left and right hemifields which remain as independent entities when both hemifields are stimulated simultaneously and/or whether they interact to form a conjoined representation. We examined whether cortical processing of visual stimuli depends on whether they occur in isolation in one hemifield (unilaterally) or simultaneously in both hemifields (bilaterally). Visual evoked potentials of six normal subjects were recorded from 128 scalp sites. Wedge-shaped chequerboard stimuli, extending 1 – 4 deg eccentricity, were presented to quadrants of the visual field. Stimulus duration was 250 ms; the stimulus onset asynchrony was random, 500 – 750 ms. The evoked potentials revealed multiple peaks of activity with different surface topography. Prominent deflections occurred around 80, 120 – 180, and 230 ms. The response to bilateral stimuli was compared with the sum of the responses to unilateral stimuli. On the basis of the multichannel recordings, nonlinear interactions were characterised as either (a) modulations (same generators, but different amplitude) or (b) interactions originating from different generators. Modulation occurred at 230 ms, the response being suppressed for the bilateral case. At 120 – 180 ms, the field patterns suggested that at least some of the sources of the interaction effect are different from the source of the bilateral response. Underlying generators of the evoked responses and the interaction effects were further explored with the use of an equivalent current dipole model.

scholarly journals Distinct Patterns of P1 and C2 VEP Potentiation and Attenuation in Visual Snow: A Case Report

2021 ◽  
Vol 12 ◽  
Author(s):  
Alison M. Harris
Keyword(s):  
Visual Processing ◽  
Stimulus Presentation ◽  
Stimulus Onset ◽  
Pattern Reversal ◽  
Current Dipole ◽  
Opposite Pattern ◽  
Cortical Responses ◽  
Pattern Onset Vep ◽  
Foveal Stimulation

Visual snow syndrome, characterized by persistent flickering dots throughout the visual field, has been hypothesized to arise from abnormal neuronal responsiveness in visual processing regions. Previous research has reported a lack of typical VEP habituation to repeated stimulus presentation in patients with visual snow. Yet these studies generally used pattern-reversal paradigms, which are suboptimal for measuring cortical responses to the onset of foveal stimulation. Instead, these responses are better indexed by the C2, a pattern-onset VEP peaking 100–120 ms after stimulus onset. In this case study, we analyzed the C2 and its adaptation profile in data previously collected from a single patient with visual snow using a “double-pulse” presentation paradigm. In controls, shorter intervals between stimulus pairs were associated with greater attenuation of the C2 VEP, with recovery from adaptation at longer stimulus onset asynchronies (SOAs). However, the visual snow patient showed the opposite pattern, with reduced C2 amplitude at longer SOAs despite distinct C2 peaks at the shortest SOAs. These results stand in contrast not only to the pattern of C2 VEP attenuation in controls, but also to a lack of adaptation previously reported for the pattern-onset P1 VEP in this patient. Exploratory source localization using equivalent current dipole fitting further suggested that P1 and C2 VEPs in the visual snow patient arose from distinct sources in extrastriate visual cortex. While preliminary, these results support differential patterns of VEP attenuation and potentiation within the same individual, potentially pointing toward multiple mechanisms of abnormal neuronal responsiveness in visual snow syndrome.

The phase of prestimulus alpha oscillations affects tactile perception

2014 ◽  
Vol 111 (6) ◽  
pp. 1300-1307 ◽  
Author(s):  
Lei Ai ◽  
Tony Ro
Keyword(s):  
Brain Activity ◽  
Brain Regions ◽  
Stimulus Onset ◽  
Tactile Perception ◽  
Alpha Power ◽  
Perceptual Awareness ◽  
Alpha Oscillations ◽  
Left Hand ◽  
Tactile Stimuli ◽  
Significant Difference

Previous studies have shown that neural oscillations in the 8- to 12-Hz range influence sensory perception. In the current study, we examined whether both the power and phase of these mu/alpha oscillations predict successful conscious tactile perception. Near-threshold tactile stimuli were applied to the left hand while electroencephalographic (EEG) activity was recorded over the contralateral right somatosensory cortex. We found a significant inverted U-shaped relationship between prestimulus mu/alpha power and detection rate, suggesting that there is an intermediate level of alpha power that is optimal for tactile perception. We also found a significant difference in phase angle concentration at stimulus onset that predicted whether the upcoming tactile stimulus was perceived or missed. As has been shown in the visual system, these findings suggest that these mu/alpha oscillations measured over somatosensory areas exert a strong inhibitory control on tactile perception and that pulsed inhibition by these oscillations shapes the state of brain activity necessary for conscious perception. They further suggest that these common phasic processing mechanisms across different sensory modalities and brain regions may reflect a common underlying encoding principle in perceptual processing that leads to momentary windows of perceptual awareness.

scholarly journals Convergence of Submodality-Specific Input Onto Neurons in Primary Somatosensory Cortex

2009 ◽  
Vol 102 (3) ◽  
pp. 1843-1853 ◽  
Author(s):  
Yu-Cheng Pei ◽  
Peter V. Denchev ◽  
Steven S. Hsiao ◽  
James C. Craig ◽  
Sliman J. Bensmaia
Keyword(s):  
Somatosensory Cortex ◽  
Cortical Neurons ◽  
Stimulus Onset ◽  
Sustained Response ◽  
Primary Somatosensory Cortex ◽  
Stimulus Interval ◽  
Specific Input ◽  
Afferent Fibers ◽  
Cortical Responses ◽  
Different Populations

At the somatosensory periphery, slowly adapting type 1 (SA1) and rapidly adapting (RA) afferents respond very differently to step indentations: SA1 afferents respond throughout the entire stimulus interval (sustained response), whereas RA afferents respond only at stimulus onset (on response) and offset (off response). We recorded the responses of cortical neurons to step indentations and found many neurons in areas 3b and 1 to exhibit properties that are intermediate between these two extremes: These neurons responded during the sustained portion of the stimulus and also at the offset of the stimulus. Several lines of evidence indicate that these neurons, which exist in large proportions even at these early stages of somatosensory cortical processing, receive input from both populations of afferents. First, we show that many cortical neurons have both a significant sustained response and a significant off response. Second, the strength of the off response is uncorrelated with that of the sustained response, which is to be expected if sustained and off responses stem from different populations of afferent fibers. Third, the bulk of the variance in cortical responses to step indentations can be accounted for using a linear combination of both SA1 and RA responses. Finally, we show that the off response in cortical neurons does not reflect rebound from inhibition. We conclude that the convergence of modality specific input onto individual neurons is common in primary somatosensory cortex and discuss how this conclusion might be reconciled with previous findings.

Evoked and Event-Related Responses

2017 ◽  
pp. 189-199
Author(s):  
Riitta Hari ◽  
Aina Puce
Keyword(s):  
Motor Planning ◽  
Auditory Brainstem ◽  
Stimulus Onset ◽  
Evoked Responses ◽  
Cognitive Operations ◽  
Long Duration ◽  
Cortical Responses ◽  
Steady State Responses ◽  
Eeg Recordings ◽  
General Aspects

This chapter discusses general aspects of evoked and event-related responses in MEG and EEG recordings. The earliest evoked responses occur within milliseconds from stimulus onset (for example in the auditory brainstem) and cortical responses continue for many hundreds of milliseconds poststimulus. Sustained potentials and fields can be recorded during long-duration stimuli, or during tasks involving motor planning, attention, and other cognitive operations. Interstimulus interval and physical stimulus characteristics can dramatically affect amplitudes and latencies of evoked responses. A distinction is made between transient and steady-state responses. Various nomenclatures adopted in literature for different types of evoked responses are discussed and recommendations are given for more consistency in nomenclature.

scholarly journals Comparison of Two Measures of Missing Cofactor in Cofactor-Dependent Enzymes: Proportion Versus Relative Increase

2012 ◽  
Vol 5 (1) ◽  
pp. 16-21 ◽  
Author(s):  
Tomas Hansson
Keyword(s):  
Statistical Power ◽  
Relative Increase ◽  
Statistical Properties ◽  
Sensitive Measure ◽  
Power Difference ◽  
Two Measures

The degree of missing cofactor in a cofactor-dependent enzyme is widely used as a biomarker of cofactor defi-ciency. The degree of missing cofactor can be expressed either as the proportion of enzyme without cofactor, or as the rel-ative increase in enzyme with cofactor after addition of excess cofactor to the sample. Especially for enzymes with thia-mine pyrophosphate (TPP) as a cofactor, the relative increase (TPP-effect) has been used in a majority of studies, and its use seems to prevail without consideration of the proportion (latency) as a better alternative. In this letter, the statistical properties of the two measures are compared in the context of a thiamine-dependent enzyme. Proportion is a more bal-anced and sensitive measure than relative increase, and simulation shows that proportion is associated with equal or high-er statistical power than relative increase. The power difference can be as high as 0.12.

Representational Dynamics of Facial Viewpoint Encoding

2017 ◽  
Vol 29 (4) ◽  
pp. 637-651 ◽  
Author(s):  
Tim C. Kietzmann ◽  
Anna L. Gert ◽  
Frank Tong ◽  
Peter König
Keyword(s):  
Face Processing ◽  
Attentional Focus ◽  
Stimulus Onset ◽  
High Temporal Resolution ◽  
Response Patterns ◽  
Information Encoding ◽  
Cortical Responses ◽  
Temporal Aspects ◽  
Distinct Sequence ◽  
Visual Onset

Faces provide a wealth of information, including the identity of the seen person and social cues, such as the direction of gaze. Crucially, different aspects of face processing require distinct forms of information encoding. Another person's attentional focus can be derived based on a view-dependent code. In contrast, identification benefits from invariance across all viewpoints. Different cortical areas have been suggested to subserve these distinct functions. However, little is known about the temporal aspects of differential viewpoint encoding in the human brain. Here, we combine EEG with multivariate data analyses to resolve the dynamics of face processing with high temporal resolution. This revealed a distinct sequence of viewpoint encoding. Head orientations were encoded first, starting after around 60 msec of processing. Shortly afterward, peaking around 115 msec after stimulus onset, a different encoding scheme emerged. At this latency, mirror-symmetric viewing angles elicited highly similar cortical responses. Finally, about 280 msec after visual onset, EEG response patterns demonstrated a considerable degree of viewpoint invariance across all viewpoints tested, with the noteworthy exception of the front-facing view. Taken together, our results indicate that the processing of facial viewpoints follows a temporal sequence of encoding schemes, potentially mirroring different levels of computational complexity.

scholarly journals Gating Patterns to Proprioceptive Stimulation in Various Cortical Areas: An MEG Study in Children and Adults using Spatial ICA

2020 ◽  
Author(s):  
Jaakko Vallinoja ◽  
Julia Jaatela ◽  
Timo Nurmi ◽  
Harri Piitulainen
Keyword(s):  
Index Finger ◽  
Primary Response ◽  
Paired Stimulus ◽  
Response Patterns ◽  
Current Dipole ◽  
Cortical Responses ◽  
Cortical Regions ◽  
Parietal Cortices ◽  
Consistent Response ◽  
Processing Network

Abstract Proprioceptive paired-stimulus paradigm was used for 30 children (10–17 years) and 21 adult (25–45 years) volunteers in magnetoencephalography (MEG). Their right index finger was moved twice with 500-ms interval every 4 ± 25 s (repeated 100 times) using a pneumatic-movement actuator. Spatial-independent component analysis (ICA) was applied to identify stimulus-related components from MEG cortical responses. Clustering was used to identify spatiotemporally consistent components across subjects. We found a consistent primary response in the primary somatosensory (SI) cortex with similar gating ratios of 0.72 and 0.69 for the children and adults, respectively. Secondary responses with similar transient gating behavior were centered bilaterally in proximity of the lateral sulcus. Delayed and prolonged responses with strong gating were found in the frontal and parietal cortices possibly corresponding to larger processing network of somatosensory afference. No significant correlation between age and gating ratio was found. We confirmed that cortical gating to proprioceptive stimuli is comparable to other somatosensory and auditory domains, and between children and adults. Gating occurred broadly beyond SI cortex. Spatial ICA revealed several consistent response patterns in various cortical regions which would have been challenging to detect with more commonly applied equivalent current dipole or distributed source estimates.

Multiple Testing and Statistical Power With Modified Bonferroni Procedures

1997 ◽  
Vol 22 (4) ◽  
pp. 389-406 ◽  
Author(s):  
Stephen Olejnik ◽  
Jianmin Li ◽  
Suchada Supattathum ◽  
Carl J. Huberty
Keyword(s):  
Multiple Testing ◽  
Statistical Power ◽  
Type I Error ◽  
Average Power ◽  
Simulated Data ◽  
Type I ◽  
Correlation Matrices ◽  
Bonferroni Procedure ◽  
Power Difference ◽  
The Difference

The difference in statistical power between the original Bonferroni and five modified Bonferroni procedures that control the overall Type I error rate is examined in the context of a correlation matrix where multiple null hypotheses, H0 : ρ ij = 0 for all i ≠ j, are tested. Using 50 real correlation matrices reported in educational and psychological journals, a difference in the number of hypotheses rejected of less than 4% was observed among the procedures. When simulated data were used, very small differences were found among the six procedures in detecting at least one true relationship, but in detecting all true relationships the power of the modified Bonferroni procedures exceeded that of the original Bonferroni procedure by at least .18 and by as much as .55 when all null hypotheses were false. The power difference decreased as the number of true relationships decreased. Power differences obtained for the average power were of a much smaller magnitude but still favored the modified Bonferroni procedures. For the five modified Bonferroni procedures, power differences less than .05 were typically observed; the Holm procedure had the lowest power, and the Rom procedure had the highest.

Identification of Asbestos Fibres in a Water Sample by X-Ray Microanalysis

1975 ◽  
Vol 33 ◽  
pp. 274-275
Author(s):  
K. A. Brookes ◽  
D. Finbow ◽  
Madeleine Samuel
Keyword(s):  
Water Sample ◽  
Background Radiation ◽  
X Ray ◽  
Left Hand ◽  
Transmission Imaging ◽  
Different Types ◽  
Normal Specimen ◽  
Liquid Nitrogen Cooling ◽  
Normal Transmission ◽  
Additional Port

Investigation of the particulate matter contained in the water sample, revealed the presence of a number of different types and certain of these were selected for analysis.An A.E.I. Corinth electron microscope was modified to accept a Kevex Si (Li) detector. To allow for existing instruments to be readily modified, this was kept to a minimum. An additional port is machined in the specimen region to accept the detector, with the liquid nitrogen cooling dewar conveniently housed in the left hand cupboard adjacent to the microscope column. Since background radiation leads to loss in the sensitivity of the instrument, great care has been taken to reduce this effect by screening and manufacturing components that are near the specimen from material of low atomic number. To change from normal transmission imaging to X-ray analysis, the special 4-position specimen rod is inserted through the normal specimen airlock.

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