Brain Electrical Potentials Research Articles

Investigating the impact of early deafness on learned action-effect contingency for action linked to peripheral sensory effects

Investigating peripheral visual processing in individuals with early auditory deprivation is a critical research area in the field of neuroscience, since it helps understanding the phenomenon of sensory adaptation and brain plasticity after sensory loss. Prior research has already demonstrated that the absence of auditory input, which is crucial to detect events occurring out of the central egocentric visual space, leads to an improved processing of visual and tactile stimuli occurring in peripheral regions of the sensory space. Nevertheless, no prior studies have explored whether such enhanced processing also takes place within the domain of action, particularly when individuals are required to perform actions that produce peripheral sensory outcomes. To test this hypothesis, we recruited 15 hearing (31 ± 3.3 years) and 15 early deaf adults (42 ± 2.6 years) for a neuro-behavioral experiment involving: 1) a behavioral task where participants executed a simple motor action (i.e., a button press) and received a visual feedback either in the center or in a peripheral region of the visual field, and 2) the electrophysiological recording of brain electrical potentials (EEG). We measured and compared neural activity preceding the motor action (the readiness potentials) and visual evoked responses (the N1 and P2 ERP components) and found that deaf individuals did not exhibit more pronounced modulation of neural responses when their motor actions resulted in peripheral visual stimuli compared to their hearing counterparts. Instead they showed a reduced modulation when visual stimuli were presented in the center. Our results suggest a redistribution of attentional resources from center to periphery in deaf individuals during sensorimotor coupling.

Low-frequency sounds combined with motor imagery elicits a transient disruption of force performance: A path to neuromotor reprogramming?

The effectiveness of motor imagery (MI) training on sports performance is now well-documented. Recently, it has been proposed that a single session of MI combined with low frequency sound (LFS) might enhance muscle activation. However, the neural mechanisms underlying this effect remain unknown. We set up a test-retest intervention over the course of 2 consecutive days to evaluate the effect of (i) MI training (MI, n = 20), (ii) MI combined with LFS (MI + LFS, n = 20), and (iii) a control condition (CTRL, n = 20) on force torque produced across repeated maximal voluntary contractions of the quadriceps before (Pretest), after (Posttest) and at +12 h (Retention) post-intervention. We collected the integrated electromyograms of the quadriceps muscles, as well as brain electrical potentials during each experimental intervention. In the CTRL group, total force torque decreased from Pretest to Retention and from Posttest to Retention. By contrast, there was an increase between Posttest and Retention in both MI + LFS and MI groups (both ηP2 = 0.03, p < 0.05). Regression analyses further revealed a negative relationship between force performance and EEG activity in the MI + LFS group only. The data support a transient interference of LFS on cortical activity underlying the priming effects of MI practice on force performance. Findings are discussed in relation to the potential for motor reprogramming through MI combined with LFS.

Nuances of knowing: Brain potentials reveal implicit effects of domain knowledge on word processing in the absence of sentence-level knowledge.

In previous work investigating the relationship between domain knowledge (of the fictional world of Harry Potter) and sentence comprehension, domain knowledge had a greater impact on electrical brain potentials to words which completed sentences about fictional "facts" participants reported they did not know compared to facts they did. This suggests that individuals use domain knowledge continuously to activate relevant/related concepts as they process sentences, even with only partial knowledge. As that study relied on subjective reports, it may have resulted in response bias related to an individual's overall domain knowledge. In the present study, we therefore asked participants with varying degrees of domain knowledge to complete sentences describing fictional "facts" as an objective measure of sentence-level knowledge. We then recorded EEG as the same individuals (re-)read the same sentences, including their appropriate final words, and sorted these according to their objective knowledge scores. Replicating and extending Troyer et al., domain knowledge immediately facilitated access to meaning for unknown words; greater domain knowledge was associated with reduced N400 amplitudes for unknown words. These findings constitute novel evidence for graded preactivation of conceptual knowledge (e.g., at the level of semantic features and/or relations) in the absence of lexical prediction. Knowledge also influenced post-N400 memory/integration processes for these same unknown words; greater domain knowledge was associated with enhanced late positive components (LPCs), suggesting that deeper encoding during language processing may be engendered when knowledgeable individuals encounter an apparent gap in their knowledge.

Neural Bases of Predictions During Natural Reading of Known Statements: An Electroencephalography and Eye Movements Co-registration Study

Predictions of incoming words performed during reading have an impact on how the reader moves their eyes and on the electrical brain potentials. Eye tracking (ET) experiments show that less predictable words are fixated for longer periods of times. Electroencephalography (EEG) experiments show that these words elicit a more negative potential around 400 ms (N400) after the word onset when reading one word at a time (foveated reading). Nevertheless, there was no N400 potential during the foveated reading of previously known sentences (memory-encoded), which suggests that the prediction of words from memory-encoded sentences is based on different mechanisms than predictions performed on common sentences. Here, we performed an ET-EEG co-registration experiment where participants read common and memory-encoded sentences. Our results show that the N400 potential disappear when the reader recognises the sentence. Furthermore, time–frequency analyses show a larger alpha lateralisation and a beta power increase for memory-encoded sentences. This suggests a more distributed attention and an active maintenance of the cognitive set, in concordance to the predictive coding framework.

Neural dynamics of pride and shame in social context: an approach with event-related brain electrical potentials.

The neural underpinnings of social emotions such as pride and shame are largely unknown. The present study aims to add evidence by exploiting the advantage of event-related brain electrical potentials (ERP) to examine the neural processes as they unfold over time. For this purpose, a dot-estimation task was adapted to explore these emotions as elicited in a simulated social context. Pride prompted an early negativity seemingly originated in medial parietal regions (precuneus) and possibly reflecting social comparison processes in successful trials. This was followed by a late positivity originated in medial frontal regions, probably reflecting the verification of singularly successful trials. Shame, in turn, elicited an early negativity apparently originated in the cuneus, probably related to mental imagery of the social situation. It was followed by a late positivity mainly originated in the same regions as the early negativity for pride, then conceivably reflecting social comparison processes, in this occasion in unsuccessful trials. None of these fluctuations correlated with self-reported feelings of either emotion, suggesting that they instead relate to social cognitive computations necessary to achieve them. The present results provide a dynamic depiction of neural mechanisms underlying these social emotions, probing the necessity to study them using an integrated approach with different techniques.

Lumos!: Electrophysiological tracking of (wizarding) world knowledge use during reading.

In Troyer and Kutas (2018), individual differences in knowledge of the world of Harry Potter (HP) rapidly modulated individuals' average electrical brain potentials to contextually supported words in sentence endings. Using advances in single-trial electroencephalogram analysis, we examined whether this relationship is strictly a result of domain knowledge mediating the proportion of facts each participant knew; we find it is not. Participants read sentences ending in a contextually supported word, reporting online whether they had known each fact. Participants' reports correlated with HP domain knowledge and reliably modulated event-related brain potentials to sentence-final words within 250 ms. Critically, domain knowledge had a dissociable influence in the same time window for endings that participants reported not having known and/or were less likely to be known/remembered across participants. We hypothesize that knowledge impacts written word processing primarily by affecting the neural processes of (implicit) retrieval from long-term memory (LTM): Greater knowledge eases otherwise difficult retrieval processes. (PsycINFO Database Record (c) 2020 APA, all rights reserved).

Brain Responses to Emotional Faces in Natural Settings: A Wireless Mobile EEG Recording Study.

The detection of a human face in a visual field and correct reading of emotional expression of faces are important elements in everyday social interactions, decision making and emotional responses. Although brain correlates of face processing have been established in previous fMRI and electroencephalography (EEG)/MEG studies, little is known about how the brain representation of faces and emotional expressions of faces in freely moving humans. The present study aimed to detect brain electrical potentials that occur during the viewing of human faces in natural settings. 64-channel wireless EEG and eye-tracking data were recorded in 19 participants while they moved in a mock art gallery and stopped at times to evaluate pictures hung on the walls. Positive, negative and neutral valence pictures of objects and human faces were displayed. The time instants in which pictures first occurred in the visual field were identified in eye-tracking data and used to reconstruct the triggers in continuous EEG data after synchronizing the time axes of the EEG and eye-tracking device. EEG data showed a clear face-related event-related potential (ERP) in the latency interval ranging from 165 to 210 ms (N170); this component was not seen whilst participants were viewing non-living objects. The face ERP component was stronger during viewing disgusted compared to neutral faces. Source dipole analysis revealed an equivalent current dipole in the right fusiform gyrus (BA37) accounting for N170 potential. Our study demonstrates for the first time the possibility of recording brain responses to human faces and emotional expressions in natural settings. This finding opens new possibilities for clinical, developmental, social, forensic, or marketing research in which information about face processing is of importance.

Information-Theoretical Analysis of EEG Microstate Sequences in Python.

We present an open-source Python package to compute information-theoretical quantities for electroencephalographic data. Electroencephalography (EEG) measures the electrical potential generated by the cerebral cortex and the set of spatial patterns projected by the brain's electrical potential on the scalp surface can be clustered into a set of representative maps called EEG microstates. Microstate time series are obtained by competitively fitting the microstate maps back into the EEG data set, i.e., by substituting the EEG data at a given time with the label of the microstate that has the highest similarity with the actual EEG topography. As microstate sequences consist of non-metric random variables, e.g., the letters A–D, we recently introduced information-theoretical measures to quantify these time series. In wakeful resting state EEG recordings, we found new characteristics of microstate sequences such as periodicities related to EEG frequency bands. The algorithms used are here provided as an open-source package and their use is explained in a tutorial style. The package is self-contained and the programming style is procedural, focusing on code intelligibility and easy portability. Using a sample EEG file, we demonstrate how to perform EEG microstate segmentation using the modified K-means approach, and how to compute and visualize the recently introduced information-theoretical tests and quantities. The time-lagged mutual information function is derived as a discrete symbolic alternative to the autocorrelation function for metric time series and confidence intervals are computed from Markov chain surrogate data. The software package provides an open-source extension to the existing implementations of the microstate transform and is specifically designed to analyze resting state EEG recordings.

Large-scale replication study reveals a limit on probabilistic prediction in language comprehension.

Do people routinely pre-activate the meaning and even the phonological form of upcoming words? The most acclaimed evidence for phonological prediction comes from a 2005 Nature Neuroscience publication by DeLong, Urbach and Kutas, who observed a graded modulation of electrical brain potentials (N400) to nouns and preceding articles by the probability that people use a word to continue the sentence fragment ('cloze'). In our direct replication study spanning 9 laboratories (N=334), pre-registered replication-analyses and exploratory Bayes factor analyses successfully replicated the noun-results but, crucially, not the article-results. Pre-registered single-trial analyses also yielded a statistically significant effect for the nouns but not the articles. Exploratory Bayesian single-trial analyses showed that the article-effect may be non-zero but is likely far smaller than originally reported and too small to observe without very large sample sizes. Our results do not support the view that readers routinely pre-activate the phonological form of predictable words.

Random Recurrent Networks Near Criticality Capture the Broadband Power Distribution of Human ECoG Dynamics.

Brain electric field potentials are dominated by an arrhythmic broadband signal, but the underlying mechanism is poorly understood. Here we propose that broadband power spectra characterize recurrent neural networks of nodes (neurons or clusters of neurons), endowed with an effective balance between excitation and inhibition tuned to keep the network on the edge of dynamical instability. These networks show a fast mode reflecting local dynamics and a slow mode emerging from distributed recurrent connections. Together, the 2 modes produce power spectra similar to those observed in human intracranial EEG (i.e., electrocorticography, ECoG) recordings. Moreover, such networks convert spatial input correlations across nodes into temporal autocorrelation of network activity. Consequently, increased independence between nodes reduces low-frequency power, which may explain changes observed during behavioral tasks. Lastly, varying network coupling causes activity changes that resemble those observed in human ECoG across different arousal states. The model links macroscopic features of empirical ECoG power to a parsimonious underlying network structure, and suggests mechanisms for changes observed across behavioral and arousal states. This work provides a computational framework to generate and test hypotheses about cellular and network mechanisms underlying whole brain electrical dynamics, their variations across states, and potential alterations in brain diseases.

Do emotion-induced blindness and the attentional blink share underlying mechanisms? An event-related potential study of emotionally-arousing words.

When two targets are presented within approximately 500ms of each other in the context of rapid serial visual presentation (RSVP), participants' ability to report the second target is reduced compared to when the targets are presented further apart in time. This phenomenon is known as the attentional blink (AB). The AB is increased in magnitude when the first target is emotionally arousing. Emotionally arousing stimuli can also capture attention and create an AB-like effect even when these stimuli are presented as to-be-ignored distractor items in a single-target RSVP task. This phenomenon is known as emotion-induced blindness (EIB). The phenomenological similarity in the behavioral results associated with the AB with an emotional T1 and EIB suggest that these effects may result from similar underlying mechanisms - a hypothesis that we tested using event-related electrical brain potentials (ERPs). Behavioral results replicated those reported previously, demonstrating an enhanced AB following an emotionally arousing target and a clear EIB effect. In both paradigms highly arousing taboo/sexual words resulted in an increased early posterior negativity (EPN) component that has been suggested to represent early semantic activation and selection for further processing in working memory. In both paradigms taboo/sexual words also produced an increased late positive potential (LPP) component that has been suggested to represent consolidation of a stimulus in working memory. Therefore, ERP results provide evidence that the EIB and emotion-enhanced AB effects share a common underlying mechanism.

Event related speech readiness potentials to spoken words and CV’s

This study investigated the temporal and dynamics of brain activity to speech and motor preparation. Previous EEG studies have identified a slow negativity wave that occurs previous to the onset of speech. Brain electrical potentials were obtained in subjects prior to initiation of speech in a using a single vertex electrode. Both a repeated single syllable word and CV’s were used. The sample rate permitted an analysis of both slow negative waves and faster neurogenic signals. The purpose of this research was to establish a real-time event related brain electrical potential system. This research uses a vocal signal as the marking point, and displays in real time the event-related potential. Each time epoch was sampled at 25600 samples/sec. One second of these signals were averaged for 100 trials just prior to initiation of the word “pool” or a randomly presented CV. The inter-trial interval was approximately 25 seconds. For the 100 trials, each trial was saved. Separate odd and even event potentials were ...

The Importance of Reading Naturally: Evidence From Combined Recordings of Eye Movements and Electric Brain Potentials.

How important is the ability to freely control eye movements for reading comprehension? And how does the parser make use of this freedom? We investigated these questions using coregistration of eye movements and event-related brain potentials (ERPs) while participants read either freely or in a computer-controlled word-by-word format (also known as RSVP). Word-by-word presentation and natural reading both elicited qualitatively similar ERP effects in response to syntactic and semantic violations (N400 and P600 effects). Comprehension was better in free reading but only in trials in which the eyes regressed to previous material upon encountering the anomaly. A more fine-grained ERP analysis revealed that these regressions were strongly associated with the well-known P600 effect. In trials without regressions, we instead found sustained centro-parietal negativities starting at around 320ms post-onset; however, these negativities were only found when the violation occurred in sentence-final position. Taken together, these results suggest that the sentence processing system engages in strategic choices: In response to words that don't match built-up expectations, it can either explore alternative interpretations (reflected by regressions, P600 effects, and good comprehension) or pursue a "good-enough" processing strategy that tolerates a deficient interpretation (reflected by progressive saccades, sustained negativities, and relatively poor comprehension).

Event-related cortical potentials occurring prior to speech initiation

Real time brain electrical potentials were obtained in subjects prior to the initiation of speech in a potential clinical paradigm using a single vertex electrode. The purpose of this research was to establish a real-time event related brain electrical potential system. Research in this area in the past has used a great number of facial and lip EMG electrodes. The marking point for determining the pre-event time epoch has been an EMG source. The data are typically acquired off-line and later averaged. This research uses a vocal signal as the marking point and displays in real time the event-related potential. The sample rate (25, 600 samples/s) permitted an analysis of both slow negative waves and faster neurogenic signals. Results indicated reliable waveform morphology within and between subjects.

Electrophysiological alterations in a complex rat model of schizophrenia

BackgroundPsychiatric disorders are frequently accompanied by changes in brain electrical oscillations and abnormal auditory event related potentials. The goal of this study was to characterize these parameters of a new rat substrain showing several alterations related to schizophrenia. MethodsMale rats of the new substrain, developed by selective breeding after combined subchronic ketamine treatment and postweaning social isolation, and naive Wistar ones group-housed without any interventions were involved in the present study. At the age of 3 months, animals were implanted with cortical electroencephalography electrodes. Auditory evoked potentials during paired-click stimuli and power of oscillation in different frequency bands were determined with and without acute ketamine (20mg/kg) treatment. ResultsRegarding the auditory evoked potentials, the latency of P2 was delayed and the amplitude of N1 peak was lower in the new substrain. The new substrain showed increased power of oscillations in the theta, alpha and beta bands, while decreased power was detected in delta and gamma2 bands (52–70Hz) compared with control animals. Acute ketamine treatment increased the gamma1 band (30–48Hz) power in both groups, while it elicited significant changes only in the new substrain in the total power and in alpha, beta and gamma2 bands. ConclusionsThe validation of the translational utility of this new rat substrain by electrophysiological investigations revealed that these rats show abnormalities that may model a part of the neurophysiological deficits observed in schizophrenia.

Investigation of the Music's Effect on Human Brain Activity Using Electrical Capacitance Volume Tomography Brain Scanner and Electroencephalo-Graphy

In this study, ECVT brain scanner is used to measure electrical signals generated by the activity of the human brain to the audio response. The basic principle of ECVT is the permittivity distribution mapping of objects based on data measured capacitance. Data capacitance is a response to changes in the permittivity distribution in the brain which are affected by brain electrical potential. ECVT system consists of shaped-helmet sensors, 32-channel data acquisition system, and a computer for image reconstruction process and display the results of scanning. Based on the experimental results, the electrical signals from the electrode capacitance shows a clear distinction, when subjects listened to classical, pop and rock music. Furthermore, it also showed that the brain electrical signal of right hemisphere is higher than the left hemisphere when listening to music. These results from ECVT are consistent with the results of measurement using EEG. Analysis of the reconstructed image show that there is an increase in brain activity in the temporal lobe when listening to rock music when compared to the classical music. ECVT brain scanners can be used to observe the electrical activity of the brain that includes auditory activity.

A neurolinguistic study of South Swedish word accents: Electrical brain potentials in nouns and verbs

The brain response to words with correct and incorrect word accent–suffix combinations in South Swedish was investigated using electroencephalography (EEG). Accent 1 yielded an increased brain response (‘preactivation negativity’) that has previously been interpreted as reflecting preactivation of suffixes. Preactivation is greater for accent 1 due to its association with a limited set of suffixes, whereas accent 2 is default for compound words. The tonal realization of the word accent opposition in South Swedish is practically the mirror image of that in Central Swedish, where a similar preactivation negativity has been found. Therefore, the brain response is unlikely to result from a difference in acoustic features between the word accents. Invalidly cued suffixes yielded brain response pattern showing increased processing load of the unexpected suffix (negative electric potential) followed by its reprocessing (positivity ‘P600’).

The impact of the stimulation method on differences in pain thresholds and brain responses between chronic pain patients and healthy controls.

In this issue you will find a paper by Franz et al. (2014) titled ‘Laser heat hyperalgesia is not a feature of non-specific chronic low back pain’. In this study, 16 patients with chronic back pain and 16 healthy controls were stimulated with noxious laser heat. Laser heat pain thresholds and nociceptive laser-evoked electrical brain potentials following skin stimulation of the pain-affected back and the pain-free abdomen were assessed. The surprising results of this study are that there were no significant differences between the groups in the laser heat pain thresholds and the nociceptive laser-evoked electrical brain potentials. This is in contrast to a large number of studies in different chronic pain disorders (e.g. fibromyalgia or chronic back pain) which report altered or more specifically augmented brain responses to painful stimulation. These studies used pressure, heat and incision stimuli to evoke the experimental pain. One reason for these differing results might be that there is considerably more spatial summation when using a thermode compared with laser stimulation. However, there were also studies using a CO2 laser which reported differences in pain thresholds and brain activation (Gibson et al., 1994; de Tommaso et al., 2011) in pain patients. Gibson et al. (1994) reported a significant reduction in the heat pain threshold on the dorsal surface of the hand in patients with fibromyalgia. Comparing stimulation at the intensity of the pain threshold and 1.5 times the pain threshold, patients with fibromyalgia showed increased peak to peak amplitude of the N270-P370 laser-evoked potential complex compared with healthy controls. In a recent study, de Tommaso et al. (2011) replicated these findings. They reported increased subjective pain intensity ratings of the laser pain and increased amplitude of the vertex N2-P2 complex as well as a decreased habituation in fibromyalgia. What are the differences between these studies and the study by Franz et al. (2014)? Especially important is the distinction of different pain disorders with localized pain in chronic back pain and wide spread pain in fibromyalgia. Patients with fibromyalgia might have changes of the peripheral nervous system promoting sensitization using a stimulation method which induces less spatial summation. Since pain processing in both chronic back pain and fibromyalgia differ from healthy controls using other stimulation methods, a relevant factor could be the interstimulus interval of the experimental pain stimuli. For example, central sensitization could be prompted by the continuous nature of the stimulation in patients predisposed to acquire chronic pain. Patients and controls could process distinct stimuli similarly but at the same time process a series of fast successive stimuli or tonic stimulation different, due to plastic changes in chronic pain patients. A similar dissociation between phasic and tonic stimulation was previously reported in children who were exposed to pain around birth (Hermann et al., 2006). School-aged preterm and full-term children with repeated pain experiences during the neonatal period showed enhanced perceptual thermal sensitization to tonic painful heat stimulation and hypoalgesia to brief heat pain stimuli compared with full-term children without pain experiences during the neonatal period. This may reflect both normal descending inhibition and sensitized ascending pain pathways and parallels animal data (Ren et al., 2004) suggesting that there might be alterations in antinociceptive mechanisms while other pronociceptive mechanisms may have been maintained. It is still an open question which stimulation parameters for each experimental painful stimulation method are necessary to find differences between patients and controls. On the other hand, it would be interesting to have parameters which are known to be processed similarly in both patients and controls. With such stimulation, the influence of emotional and cognitive evaluative aspects of pain processing could be investigated more precisely. It seems that it is not the question if chronic pain patients and controls differ from each other but rather which parameters are needed to find the differences. From a physiological point of view, knowledge of the similarities and differences in pain processing could provide insights into the mechanisms underlying changes in the nervous system accompanied by the development of chronic pain. A study comparing the effects of different stimulation parameters for different methods is desperately needed. In conclusion, similarities in pain perception between patients and controls give as much insight into the mechanisms behind pain processing as differences between groups. None declared.

Waveform morphology of pre-speech brain electrical potentials

The inter- and intra-subject variations of the cortical responses before the initiation of speech were recorded. These evoked potentials were obtained at a sufficient sample rate that both slow negative waves as well as faster neurogenic signals were obtained. The marking point for determining the pre-event time epoch has been an EMG source. The data are typically acquired off-line and later averaged. This research uses a vocal signal as the marking point, and displays in real time the event-related potential. Subjects were 12 males and females. Electrodes were recorded with a silver–silver chloride electrodes positioned at Cz and using the earlobes as reference and ground. A biological preamplifier was used to amplify the weak bioelectric signals 100,000 times. Each time epoch was sampled at 20,000 samples/sec. The frequency response of these amplifiers had a high-pass of 0.1 Hz and a low-pass of 3 kHz. One second of these signals were averaged for 100 trials just prior to the subject initiation of the word “pool.” Electrical brain potentials have proven to be extremely useful for diagnosis, treatment, and research in the auditory system, and are expected to be of equal importance for the speech system.

Laser heat hyperalgesia is not a feature of non-specific chronic low back pain.

Based upon studies using mechanical pin-prick, pressure, electrical or heat stimuli applied to painful and/or pain-free parts of the body, chronic low back pain (CLBP) has been shown to be associated with generalized and enhanced pain sensitivity and altered brain responses to noxious stimuli. To date, no study examined the processing of noxious laser heat pulses, which are known to selectively excite thermal nociceptors located in the superficial skin layers, in CLBP. We studied laser heat pain thresholds (LHPTs) and nociceptive laser-evoked brain electrical potentials (LEPs) following skin stimulation of the pain-affected back and the pain-free abdomen using noxious laser heat stimulation in 16 CLBP patients and 16 age- and gender-matched healthy controls (HCs). We observed no statistically significant differences in LHPTs between CLBP patients and HCs, neither on the back nor on the abdomen. Furthermore, we found no evidence for altered brain responses between CLBP patients and HCs in response to stimulation of the back and abdomen in single-trial latencies and amplitudes of LEP components (N2, P2). The results are in contrast to previous studies showing hypersensitivity to different experimental noxious stimuli (e.g., contact heat). We argue that these discrepancies may be due to low spatial and temporal summation within the central nervous system following laser heat stimulation. Our results indicate important methodological differences between laser heat and thermode stimulation that should be taken into account when interpreting results, such as from thermal quantitative sensory testing.