Laura Petrini

Attentional processes and cognitive performance during expectancy of painful galvanic stimulations: a high-resolution EEG study

In the present high-resolution electroencephalographic (EEG) study, an omitted-stimulus paradigm induced a strong expectancy for a predictable painful stimulation (nonpainful in the control condition). During the expectancy of pain, concurrent cognitive demands were superimposed. The aim was to investigate the effects on primary sensorimotor and central midline areas of the competition among concurrent attentional processes related to cognition and pain expectancy, as indexed by behavioral performance and EEG data. A main issue was whether cognitive performance decreases, due to a re-allocation of attentional resources on primary sensorimotor and midline areas for the anticipation of pain. Behavioral results showed no differences in the cognitive (working memory) performance during the expectancy of nonpainful versus painful stimulations. In parallel, anticipatory event-related potentials (ERPs) were negligible in line with a low emotional reactivity/alertness as revealed by heart rate deceleration (HRD), skin conductance response (SCR), and low-band (6-10Hz) alpha EEG oscillations. In contrast, high-band alpha EEG oscillations (10-12Hz) over the contralateral primary sensorimotor cortex decreased more during the expectancy of painful compared to nonpainful stimuli, in line with an increased anticipatory preparation of the somatosensory channel. These findings provide further evidence on the fact that attentional processes at the basis of cognition can be defended by the anticipation of pain, at least when the incoming painful stimuli are repetitive and predictable. This happens even if the brain increases preparatory processes of the specific sensory channel to be targeted by the painful stimulus.

Experimental pain processing in individuals with cognitive impairment: current state of the science

Abstract Cognitive impairment (CI) can develop during the course of ageing and is a feature of many neurological and neurodegenerative diseases. Many individuals with CI have substantial, sustained, and complex health care needs, which frequently include pain. However, individuals with CI can have difficulty communicating the features of their pain to others, which in turn presents a significant challenge for effective diagnosis and treatment of their pain. Herein, we review the literature on responsivity of individuals with CI to experimental pain stimuli. We discuss pain responding across a large number of neurological and neurodegenerative disorders in which CI is typically present. Overall, the existing data suggest that pain processing is altered in most individuals with CI compared with cognitively intact matched controls. The precise nature of these alterations varies with the type of CI (or associated clinical condition) and may also depend on the type of pain stimulation used and the type of pain responses assessed. Nevertheless, it is clear that regardless of the etiology of CI, patients do feel noxious stimuli, with more evidence for hypersensitivity than hyposensitivity to these stimuli compared with cognitively unimpaired individuals. Our current understanding of the neurobiological mechanisms underpinning these alterations is limited but may be enhanced through the use of animal models of CI, which also exhibit alterations in nociceptive responding. Further research using additional behavioural indices of pain is warranted. Increased understanding of altered experimental pain processing in CI will facilitate the development of improved diagnostic and therapeutic approaches for pain in individuals with CI.

The Role of Pain Catastrophizing in Experimental Pain Perception

Pain is a subjective experience influenced by multiple factors, and tremendous variety within individuals is present. To evaluate emotional state of pain, catastrophizing score can be used. This study investigated pain catastrophizing ratings in association with experimental pain perception.

High resolution topographical mapping of warm and cold sensitivities.

OBJECTIVE This study aims to explore the thermal sensitivity distribution (topographical mapping) over the glabrous skin of the hand in males and females. METHODS Warm (WT) and cold (CT) thresholds were measured in 25 healthy volunteers (12 females), applying a multi-site test of 23 locations on the volar part of the hand. RESULTS The palm area was more sensitive than the fingers to both warm (P<0.001) and cold (P<0.001) stimuli. On the palm itself, the proximal part was the most sensitive (P<0.05). Heterogeneity was also found to both warm and cold sensibilities within dermatomes (P<0.05) as well as to cold sensitivity across dermatomes (P<0.001). Females were more sensitive than males to both warm (P<0.001) and cold sensations (P<0.001). In addition, painful components were frequently reported as accompanying warm/cold sensations during mild warming/cooling. CONCLUSIONS The thermal sensitivity distribution over the glabrous skin of the hand is highly heterogeneous. SIGNIFICANCE It is appropriate to precisely define testing locations when conducting thermal examinations on the hand.

The importance of stimulus parameters for the experience of the thermal grill illusion.

AIMS This study aimed to investigate the quality of the thermal grill illusion (TGI) and the importance of stimulus parameters (distance between, and number of stimulation bars). MATERIAL AND METHODS Twenty-one different stimuli were applied to a group of 19 healthy subjects on the glabrous skin over the palm and fingers. RESULTS The TGI was found to be painful (19.42% on the palm; 17.98% on the fingers), mechanical (25.24% on the palm; 5.62% on the fingers), emotional (13.59% on the palm; 14.61% on the fingers) or unusual (42.72% on the palm; 61.8% on the fingers) sensations. A total of 89.5% (palm) and 94.4% (fingers) of the subjects reported TGI. Between 45% (fingers) and 50% (palm) of the stimuli elicited TGI. Neither the distance (2 approximately 10 mm) between adjacent warm (40 +/- 1 degrees C) and cold (20 +/- 1 degrees C) bars nor the number of the stimulation bars (2 approximately 6) significantly affected the occurrence of the TGI (N.S.). The average reaction time was 2.4 +/- 0.1 seconds to the TGI sensation. Females showed longer reaction time than males (P <or= 0.001). CONCLUSION The distance and number of stimulation bars were not important to the sensation of TGI, of which the responses varied. These results are useful for future TGI studies with respect to experimental design. The variability of the TGI needs to be considered in future experimental and clinical studies.

Electrical low-frequency stimulation induces central neuroplastic changes of pain processing in man

Electrical low‐frequency stimulation (LFS) inhibits pain perception and nociceptive processing as shown by psychophysical and electrophysiological means (long‐term depression, LTD). Information regarding central mechanisms involved in LTD induction and maintenance are still missing. This study hypothesizes that electrical LFS induces changes in activation pattern of pain‐related brain areas.

Spatiotemporal analysis of RGB-D-T facial images for multimodal pain level recognition

Pain is a vital sign of human health and its automatic detection can be of crucial importance in many different contexts, including medical scenarios. While most available computer vision techniques are based on RGB, in this paper, we investigate the effect of combining RGB, depth, and thermal facial images for pain intensity level recognition. For this purpose, we extract energies released by facial pixels using a spatiotemporal filter. Experiments on a group of 12 elderly people applying the multimodal approach show that the proposed method successfully detects pain and recognizes between three intensity levels in 82% of the analyzed frames, improving by more than 6% the results that only consider RGB data.

Influence of attention alternation on movement-related cortical potentials in healthy individuals and stroke patients

OBJECTIVE In this study, we analyzed the influence of artificially imposed attention variations using the auditory oddball paradigm on the cortical activity associated to motor preparation/execution. METHODS EEG signals from Cz and its surrounding channels were recorded during three sets of ankle dorsiflexion movements. Each set was interspersed with either a complex or a simple auditory oddball task for healthy participants and a complex auditory oddball task for stroke patients. RESULTS The amplitude of the movement-related cortical potentials (MRCPs) decreased with the complex oddball paradigm, while MRCP variability increased. Both oddball paradigms increased the detection latency significantly (p<0.05) and the complex paradigm decreased the true positive rate (TPR) (p=0.04). In patients, the negativity of the MRCP decreased while pre-phase variability increased, and the detection latency and accuracy deteriorated with attention diversion. CONCLUSION Attention diversion has a significant influence on MRCP features and detection parameters, although these changes were counteracted by the application of the laplacian method. SIGNIFICANCE Brain-computer interfaces for neuromodulation that use the MRCP as the control signal are robust to changes in attention. However, attention must be monitored since it plays a key role in plasticity induction. Here we demonstrate that this can be achieved using the single channel Cz.

Robustness of movement detection techniques from motor execution: Single trial movement related cortical potential

Alterations in attention are known to modify excitability of underlying cortical structures and thus the activity recorded during non-invasive electroencephalography (EEG). Brain-Computer-Interface systems for neuromodulation are based on reliable detection of intended movements from continuous EEG signals, thereby generating real time feedback to induce neuroplasticity. We have shown in past studies that the movement related cortical potential (MRCP), a slow negative potential commencing 1-2 s prior to movement, can be reliably detected in real time within a single session and used to drive an external device that reproduces the intended movement. In the present study, our main objective was to characterize movement detection performance of two algorithms, when the subjects attention is altered. In nine healthy participants the auditory oddball paradigm was used to modulate attention. All subjects completed a set of movement executions prior to and following the oddball paradigm. The locality preserving projection followed by the linear discriminant analysis (LPP-LDA) and the matched-filter (MF) technique were applied offline for detection of movement. Results show that LPP-LDA significantly outperformed MF. The robustness of the LPP-LDA method was demonstrated by a higher true positive rate (TPR), lower false positive rate (FPR) and a shorter detection latency when attention levels were altered.

An automated method for micro-state segmentation of evoked potentials

We present a method for segmenting evoked potentials into functional micro-states. The method is based on measuring the similarity between all the topographic maps in the evoked potential and grouping them into functional micro-states based on minimizing an error function. The similarity is measured as the normalized cross-correlation coefficient. The method was validated on simulated data and tested on its ability to segment a visual evoked potential. On simulated data the method missed from 1% to 8.5% of the micro-state boundaries for evoked potentials with a signal-to-noise ratio of 20-1dB, respectively. The proposed segmentation method was compared with segmentation based on K-mean clustering. It was found that the proposed method was better at detecting the correct number of micro-states and was computationally more efficient. The automatic segmentation of the visual evoked potential was compared to the manual segmentation performed by eleven EEG specialists. No significant difference in the deviation of micro-state boundaries was observed between two random EEG specialists and between a random EEG specialist and the automatic method. Thus it was found that the method could reliably segment evoked potentials into their functional micro-states.