Interaction between local blood flow and tolerance to prolonged pain in the elderly.

PURPOSE: We aimed to explore the link between local vasodilation and pain perception in elderly subjects, testing the hypothesis that altered local cutaneous blood flow participates in the decrease in pain tolerance with age. METHOD: Sixty-eight young and 83 older participants performed a pain tolerance test in which they hold their hand in an airtight box in which air temperature was regulated at 65 °C until the pain became unbearable. Participants continuously estimated pain intensity. Skin temperature and local blood flow in the box-exposed hand were continuously monitored. RESULTS: In the young group, 97% of subjects resisted pain until the end of the test, whereas only 53% in the elderly group managed to do so, indicating that pain tolerance is impaired in the elderly. Among all participants, the skin temperature associated with the first pain sensation was below the threshold for nociceptor activation (43 °C). Interestingly, blood flow in the elderly group was correlated with pain judgment, whereas no such correlation was observed in the young. CONCLUSION: Our results suggest that the local vasodilator response induced by local heating may be involved in pain perception and may influence thermal pain tolerance with aging. These results could contribute to a better understanding of vascular deficits and the development of chronic pain in vascular pathologies.

Virtual reality hypnosis diminishes experimental cold pain and alters autonomic responses.

Immersive virtual reality (VR) is a promising tool to reduce pain in clinical setting. Digital scripts displayed by VR disposals can be enriched by several analgesic interventions, which are widely used to reduce pain. One of these techniques is hypnosis induced through the VR script (VRH) which is facilitated by immersive environment and particularly efficient even for low hypnotizable patients. The aim of this study is to assess the efficacy of a VRH script on experimentally induced cold pain perception (intensity and unpleasantness) and physiological expression. 41 healthy volunteers had been recruited in this within-subjects study. They received 9 stimulations of 20 s (3 non-nociceptive cold; 3 low nociceptive cold and 3 highly nociceptive cold) during a VRH session of 20 min (VRH condition) or without VRH (noVRH condition). Physiological monitoring during the cold pain stimulation protocol consisted of recording heart rate, heart rate variability and respiratory frequency. Maximum cold pain intensity perception, measured through the visual analog scale (VAS) on 10, was of 3.66 ± 1.84 (VAS score/10) in noVRH condition and 2.46 ± 1.54 in VRH (Wilcoxon, p < 0.0001). Considering pain unpleasantness perception, 3.68 ± 2.06 in noVRH and 2.21 ± 1.63 in VRH (Wilcoxon, p < 0.0001). Hypnotizability negatively correlated with the decrease in VAS intensity from noVRH to VRH (Spearman r = -0.45; p = 0.0038). In our sample, we found that 31/41 volunteers (75.6%) displayed a reduction of more than 10% of their VAS pain intensity and unpleasantness scores. Trait anxiety was the best predictor of the VRH responders, as well as heart rate variability. In addition, respiratory rate was diminished under VRH in every subgroup. VRH is an effective tool to reduced pain intensity and unpleasantness in a vast majority of healthy subjects. We further indicate in this study that heart rate variability parameter RMSSD (root mean square of successive differences) is a good predictor of this effect, as well as anxiety as a personality trait (but not state anxiety). Further studies are expected to determine more precisely to whom it will be the most useful to offer tailored, non-pharmacological pain management solutions to patients.

An electronical stimulator for quantitative sensory testing and evoked potential analysis of tactile Aß nerve fibers.

OBJECTIVE: We aimed to determine the ability of an innovative device, the Cutaneous Mechanical Stimulator (CMS), to evaluate touch sensory pathways in Human. METHODS: Two experiments were conducted in 23 healthy volunteers aged 20-30 years. In the first, mechanical detection thresholds (MDTs) were assessed using Semmes-Weinstein monofilaments and the CMS. In the second experiment, touch-evoked potentials (TEPs) elicited by tactile stimulation of the CMS on the left hand dorsum and left foot dorsum were recorded. Electroencephalographic (EEG) data were recorded at each cutaneous stimulation site in blocks of 20 tactile stimulations delivered by the CMS. The data were segmented into 1000-ms epochs. RESULTS: MDTs measured by monofilaments and by the CMS were equivalent. Analyses of TEPs showed N2 and P2 components. The latencies of the N2 components on the hand dorsum and foot dorsum resulted in an estimated average conduction velocity of about 40 m.s-1, within the range of Aß fibers. CONCLUSIONS: These findings showed that the CMS could assess touch sensory pathways in young adults. SIGNIFICANCE: The CMS can offer new research perspectives, as this device allows easy assessment of the MDT and enables estimation of fiber conduction velocities after tactile stimulation by the device synchronized with EEG recordings.

Preserved distraction analgesia but greater impact of pain on task performance in older adults compared with younger subjects.

OBJECTIVE: In this study, we compared two working memory conditions to study the analgesic effect of a distraction in elderly vs young people and the effect of pain on performance on the distracting task. METHODS: Younger (n=27) and older (n= 34) subjects performed 1- and 2-Back working memory tasks, representing low and high cognitive loads, respectively. Infrequent, brief hot nociceptive and cold non-nociceptive stimulations were delivered 100 ms before visual N-Back stimuli. Contact heat-evoked and cold-evoked potentials (N2P2 component) were analyzed in the absence of cognitive tasks and during the N-Back tasks. We compared the pain and cold intensity ratings and reaction times in trials preceded by nociceptive and cold stimulations and in trials not preceded by thermal stimulations between groups and between N-Back conditions. RESULTS: In both groups, performing the 1- and 2-Back working memory tasks reduced the perceived intensity of nociceptive and cold stimuli. In elderly subjects performing 2-Back memory tasks, response times to trials after nociceptive stimulation were longer than those to trials after cold or non-stimulation. By contrast, thermal stimulations had no effect on reaction times in young subjects. The amplitude of the N2P2 component was lower in the older than in the younger group in the absence of a cognitive task. In the older group, N-Back tasks had no effect on the N2P2 amplitude, whereas they reduced N2P2 amplitude in the young. CONCLUSION: Distraction analgesia is preserved in elderly subjects. However, this successful pain modulation seems to be accompanied by performance costs in the distracting tasks.

Effect of Virtual Reality Hypnosis on Pain Threshold and Neurophysiological and Autonomic Biomarkers in Healthy Volunteers: Prospective Randomized Crossover Study.

BACKGROUND: Virtual reality hypnosis (VRH) is a promising tool to reduce pain. However, the benefits of VRH on pain perception and on the physiological expression of pain require further investigation. OBJECTIVE: In this study, we characterized the effects of VRH on the heat pain threshold among adult healthy volunteers while monitoring several physiological and autonomic functions. METHODS: Sixty healthy volunteers were prospectively included to receive nociceptive stimulations. The first set of thermal stimuli consisted of 20 stimulations at 60°C (duration 500 milliseconds) to trigger contact heat evoked potentials (CHEPs). The second set of thermal stimuli consisted of ramps (1°C/second) to determine the heat pain threshold of the participants. Electrocardiogram, skin conductance responses, respiration rate, as well as the analgesia nociception index were also recorded throughout the experiment. RESULTS: Data from 58 participants were analyzed. There was a small but significant increase in pain threshold in VRH (50.19°C, SD 1.98°C) compared to that in the control condition (mean 49.45°C, SD 1.87; P<.001, Wilcoxon matched-pairs signed-rank test; Cohen d=0.38). No significant effect of VRH on CHEPs and heart rate variability parameters was observed (all P>0.5; n=22 and n=52, respectively). During VRH, participants exhibited a clear reduction in their autonomic sympathetic tone, as shown by the lower number of nonspecific skin conductance peak responses (P<.001, two-way analysis of variance; n=39) and by an increase in the analgesia nociception index (P<.001, paired t-test; n=40). CONCLUSIONS: The results obtained in this study support the idea that VRH administration is effective at increasing heat pain thresholds and impacts autonomic functions among healthy volunteers. As a nonpharmacological intervention, VRH has beneficial action on acute experimental heat pain. This beneficial action will need to be evaluated for the treatment of other types of pain, including chronic pain.

Investigating cold Aδ fibers in the 0-40 °C temperature range: A quantitative sensory testing and evoked potentials study.

OBJECTIVE: To evaluate the activity of cold Aδ-type fibers to thermal stimuli above human skin temperature (i.e., >32 °C). METHODS: Twenty young adults aged 20-24 years participated in this study. The cold-detection threshold was measured from a basal temperature of 40 °C using an adaptive staircase method with high-speed cooling ramps (170 °C/s). A total of 150 stimulations at 36 °C, 32 °C, 28 °C, 24 °C, 20 °C, 16 °C, 12 °C, 8 °C, 4 °C and 0 °C (15 each) were performed. After each stimulation, subjects estimated the intensity of cold sensation using a visual analog scale, and evoked potentials were recorded. RESULTS: The average cold-detection threshold was 35 °C (SD = 1.8). Regardless of the stimulation temperature, subjects reported a cooling sensation. Interestingly, reported increments in sensation were prominent for stimulation temperatures between 32 °C and 20 °C, but below this latter temperature sensations varied only very slightly. Evoked potential recordings revealed that decreasing temperature stimuli from a baseline of 40 °C induced a previously unreported N2P2 component with a mean N2 peak latency of 275 ms (SD = 13.1). The peak-to-peak amplitude of the N2P2 complex increased as the intensity of the cooling stimulation increased, exhibiting a profile comparable to subject-perceived intensity, namely, a major increase up to 20 °C, followed by a plateau to 0 °C. CONCLUSIONS: The cool sensations reported by subjects were likely conveyed by Aδ fibers rather than by slow-conducting C fibers. Moreover, our rapid stimulation technique starting from a high temperature (40 °C) was capable of a) generating cold sensations at stimulation temperatures between 36 °C and 32 °C, and b) revealing the optimal activation range of Aδ fibers (20 °C-28 °C). Any decrease in temperature below this range did not result in a significant increase in sensation and thus probably did not evoke a significant increase in Aδ fiber activity. SIGNIFICANCE: The regular assessment of cold sensation in peripheral neuropathies (i.e., with temperatures below 32 °C), could be completed by investigating cold-detection thresholds at temperatures ranging from 40 °C to 32 °C. Indeed, the absolute threshold of cold perception appears to start at 35 °C. Changes in the activation threshold of cold fibers were more easily detectable at this level.

Spinal integration of hot and cold nociceptive stimuli by wide-dynamic-range neurons in anesthetized adult rats.

INTRODUCTION: Early neuronal processing of thermal noxious information relies mostly on molecular detectors of the transient receptor potential family expressed by specific subpopulation of sensory neurons. This information may converge to second-order wide-dynamic-range (WDR) neurons located in the deep layer of the dorsal horn of the spinal cord. METHOD: Using a micro-Peltier thermode thermal contact stimulator II delivering various cold and hot noxious stimulations, we have characterized the extracellular electrophysiological responses of mechanosensitive WDR neurons in anesthetized adult male and female Wistar rats. RESULTS: Most of the WDR neurons were activated after hot and cold noxious stimulations, at mean temperature thresholds corresponding to 43 and 20°C, respectively. If the production of action potential was not different in frequency between the 2 thermal modalities, the latency to observe the first action potential was significantly different (cold: 212 ms; hot: 490 ms, unpaired Student t-test: t = 8.041; df = 32; P < 0.0001), suggesting that different fiber types and circuits were involved. The temporal summation was also different because no facilitation was seen for cold noxious stimulations contrary to hot noxious ones. CONCLUSION: Altogether, this study helps better understand how short-lasting and long-lasting hot or cold noxious stimuli are integrated by mechanosensitive WDR neurons. In our experimental conditions, we found WDR neurons to be nociceptive specific for C-fiber-mediated hot stimuli. We also found that cold nonnoxious and noxious information, triggered at glabrous skin areas, are likely taken in charge by A-type sensory neurons. This study will be helpful to establish working hypothesis explaining the thermal pain symptoms displayed by animal models and patients in a translational extent.

Pain Behavioural Response to Acoustic and Light Environmental Changes in Very Preterm Infants.

Noise and high light illumination in the neonatal intensive care unit (NICU) are recognized as stressors that could alter the well-being and development of vulnerable preterm infants. This prospective observational study evaluated the pain behaviours of very preterm infants (VPIs) to sound peaks (SPs) and light levels variations (LLVs) in the NICU. We measured spontaneously occurring SPs and LLVs in the incubators of 26 VPIs over 10 h. Their behavioural responses were analysed through video recordings using the "Douleur Aigue du Nouveau-né" (DAN) scale. We compared the maximum DAN scores before and after environmental stimuli and the percentage of VPIs with a score ≥ 3 according to the type of stimuli. A total of 591 SPs and 278 LLVs were analysed. SPs of 5 to 15 dBA and LLVs significantly increased the maximum DAN scores compared to baseline. The occurrence of DAN scores ≥ 3 increased with both stressors, with a total of 16% of SPs and 8% of LLVs leading to quantifiable pain behaviour. Altogether, this study shows that VPIs are sensitive to SPs and LLVs, with a slighter higher sensitivity to SPs. The mechanisms leading to pain behaviours induced by noise and light changes should be evaluated further in the context of VPIs brain development. Our results provide further arguments to optimize the NICU sensory environment of neonatal units and to adapt it to the expectations and sensory abilities of VPIs.

Volatility of subliminal haptic feedback alters the feeling of control in schizophrenia.

It has been proposed that agency disorders found in schizophrenia rely on aberrant processing of prediction error. Overreactivity to nonpertinent prediction errors may lead to the attribution of one's own actions to an external source. When applied to perception, this could explain hallucinations. However, experiments in motor control or perception have mainly suggested deficient prediction errors. Using a novel approach based on the manipulation of temporal delays, 23 patients with schizophrenia, 18 patients with bipolar disorder, and 22 healthy participants performed a pointing task with a haptic device that provided haptic feedback without or with delays, which were processed consciously (65 ms) or unconsciously (15 ms). The processing of prediction errors was measured via the adaptation of the hand trajectory, that is, the deceleration in anticipation of the surface, and its modulation as a function of recent history (stable or unstable sensory feedback). Agency was evaluated by measuring the participants' feeling of controlling the device. Only patients with schizophrenia reported a decrease in the feeling of control following subliminally delayed haptic feedback and adapted deceleration durations following subliminally delayed haptic feedback. This effect was correlated with positive symptoms. The overreactivity to subliminal delays was present only when delays occurred repeatedly in an unpredictable way, that is, with a volatile distribution. The results suggest that small temporal uncertainties that should be held as negligible, trigger an aberrant overreactivity which could account for hallucinations and alterations of the patients' conscious feeling of control. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Accurate Determination of the Cold Detection Threshold with High-Speed Cooling of the Skin.

OBJECTIVE: This study used high-speed cooling of the skin and exact control of stimulus duration to measure the cold detection threshold in healthy participants. The objective was to compare the method of limits, in which the temperature is slowly and gradually increased/decreased until the subject perceives the stimulation, and the method of levels, in which the subject must detect brief thermal stimulations close to the threshold of perception. METHODS: Twenty healthy volunteers (nine women, 11 men) aged 20-30 years participated in the study. The method of limits and method of levels were performed in all subjects in a counterbalanced order. Four cold detection thresholds were measured with the method of levels, with a temperature ramp of 300°C/sec and stimulus durations of 50 ms, 100 ms, 300 ms, and 500 ms. Three thresholds were measured with the method of limits, with temperature ramps of 1°C/sec, 2°C/sec, and 4°C/sec. RESULTS: On average, the cold detection thresholds were -0.47°C below skin temperature with the method of levels and -1.67°C the method of limits. Interindividual variability was significantly lower with the method of levels than with the method of limits. CONCLUSIONS: These results suggest that the method of levels is more accurate than the method of limits for measuring cold detection threshold. The improvement of cold detection threshold measurement may provide new perspectives to more precisely assess the function of A-delta fibers and the spino-thalamic pathway.

Driving Skills Tested on Simulator After Strabismus Surgery: A Prospective Study.

Purpose: The sense of vision is responsible for 90% of the information obtained by the motorist. Improvement in binocular visual acuity (VA) and visual field (VF) achieved after strabismus surgery could have beneficial effects on driving. Our study sought to identify functional improvements (VA and VF) and improvements in driving ability following strabismus surgery. Methods: In a prospective cohort study, the following parameters are analyzed before and 3 months after strabismus surgery: simulated driving performance (including eye movements and actions on vehicle control), binocular VA, binocular VF, and self-confidence during driving. Results: Twenty patients participated in the study. The mean preoperative logMAR binocular VA and stereopsis do not significantly differ from the postoperative. The mean Esterman VF score increases from 91.3 (±17.2) preoperatively to 96.9 (±13.9) postoperatively (P = 0.045). The mean self-confidence directed at driving scores decreases from 20.5 (±10.3) points before surgery to 11.0 (±6.0) points after surgery (P < 0.001). The distance at which the road signs are identified is significantly higher after surgery. The average speed of the vehicle and the speed near the targets (30 m) increase significantly after strabismus surgery. A significant decrease in ocular movements near targets is also observed. The number of brake pedal depressions and the rate of brake pedal depressions slightly decrease after surgery. Conclusions: This study demonstrates the potential beneficial effects of strabismus surgery on driving ability, with significant improvements in self-confidence during driving, VF, and driving on a simulator. Translational Relevance: This was the first study to use a driving simulator in strabismus.

Involvement of Frontal Functions in Pain Tolerance in Aging: Evidence From Neuropsychological Assessments and Gamma-Band Oscillations.

Reduced pain tolerance may be one of the possible explanations for high prevalence of chronic pain among older people. We hypothesized that age-related alterations in pain tolerance are associated with functioning deterioration of the frontal cortex during normal aging. Twenty-one young and 41 elderly healthy participants underwent a tonic heat pain test, during which cerebral activity was recorded using electroencephalography (EEG). Elderly participants were divided into two subgroups according to their scores on executive tests, high performers (HPs; n = 21) and low performers (LPs; n = 20). Pain measures [exposure times (ETs) and perceived pain ratings] and cerebral activity were compared among the three groups. ETs were significantly lower in elderly LPs than in young participants and elderly HPs. Electroencephalographic analyses showed that gamma-band oscillations (GBOs) were significantly increased in pain state for all subjects, especially in the frontal sites. Source analysis showed that GBO increase in elderly LPs was contributed not only by frontal but also by central, parietal, and occipital regions. These findings suggest that better preservation of frontal functions may result in better pain tolerance by elderly subjects.

Thermal sensitivity in humans at the depth of thermal receptor endings beneath the skin: validation of a heat transfer model of the skin using high-temporal resolution stimuli.

PURPOSE: The bioheat transfer equation predicts temperature distribution in living tissues such as the skin. This study aimed at psychophysically validating this model in humans. METHODS: Three experiments were performed. In the first, participants were asked to judge the thermal intensity of stimuli with combinations of intensity and duration that yielded, according to the model, identical temperatures at the thermoreceptor's depth. In experiment 2, participants' thermal detection thresholds for stimuli of different durations were measured to verify whether these thresholds correspond, according to the model, to equivalent temperatures at the thermoreceptor's location. In experiment 3, an alternative forced choice method was used, in which subjects indicated which of the two consecutive thermal stimulations was more intense. RESULTS: The model predicted results that agreed with subjects' perceptions. Participants judged stimuli of different combinations of intensities and durations yielding identical temperature at the receptor level as having equivalent intensity. Moreover, although cold detection thresholds for stimuli of different durations differed for temperatures of the stimulating probe, stimulations using the model's parameters showed equivalence at the depth of the thermal receptors. Furthermore, stimuli with temperature/duration combinations for which the model predicts temperature equivalence at the depth of the receptors corresponded to subjective equalization. CONCLUSION: These findings indicate that heat transfer models provide good estimates of temperatures at the thermal receptors. Use of these models may facilitate comparisons among studies using different stimulation devices and may facilitate the establishment of standards involving all stimulation parameters.

Effects of thermosensory aging well demonstrated by cold stimulations with high temporal resolution.

INTRODUCTION: The method of limits (MLi) is the most commonly used paradigm to measure the threshold of thermal stimuli. However, the threshold measured by MLi is dependent on reaction time (RT). Because RT in adults increases with age, the inclusion of RT in the MLi paradigm may result in an overestimation of thermal threshold in the older individuals. METHODS: A device with a very rapid cooling rate (300°C/s) was employed to measure cool thresholds by using the method of levels (MLe), a method independent of RT, in 11 older patients and 14 younger adults. RESULTS: Compared with the MLi, the MLe resulted in a greater than 2°C gain in threshold measurement accuracy in older patients. DISCUSSION: The MLe confirmed that cool perception threshold is dependent on age. The use of MLe provides new opportunities for the study of mechanisms underlying age-associated alterations in thermal perception. Muscle Nerve 60: 141-146, 2019.

Cooling the skin for assessing small-fibre function.

In this clinical and neurophysiological study using a novel cold stimulator, we aim at investigating whether cold-evoked potentials (CEPs) may prove to be a reliable diagnostic tool to assess trigeminal small-fibre function. Using a novel device consisting of micro-Peltier elements, we recorded CEPs after stimulating the supraorbital and perioral regions and the hand dorsum in 15 healthy participants and in 2 patients with exemplary facial neuropathic pain conditions. We measured peripheral conduction velocity at the upper arm and studied the brain generators using source analysis. In healthy participants and patients, we also compared CEPs with laser-evoked potentials. In the healthy participants, cold stimulation evoked reproducible scalp potentials, similar to those elicited by laser pulses, although with a latency of about 30 ms longer. The mean peripheral conduction velocity, estimated at the upper arm, was 12.7 m/seconds. The main waves of the scalp potentials originated from the anterior cingulate gyrus and were preceded by activity in the bilateral opercular regions and bilateral dorsolateral frontal regions. Unlike laser stimulation, cold stimulation evoked scalp potential of similar amplitude across perioral, supraorbital, and hand dorsum stimulation. In patients with facial neuropathic pain, CEP recording showed the selective damage of cold pathways providing complementary information to laser-evoked potential recording. Our clinical and neurophysiological study shows that this new device provides reliable information on trigeminal small fibres mediating cold sensation and might be useful for investigating patients with facial neuropathic pain associated with a distinct damage of cold-mediating fibres.

Modification of Descending Analgesia in Aging: Critical Role of the Prefrontal Cortex.

OBJECTIVE: Aging has been associated with increases in pain threshold and reductions in tolerance threshold, as well as a deficiency in endogenous pain inhibition. Top-down pain modulation mainly involves the frontal cortex network, which is also one of the most vulnerable brain regions in aging. As the frontal cortex also sustains executive functions, we aimed to determine whether reductions in executive functions subtended by the frontal network are associated with the lack of descending inhibitor control in pain-free elderly participants. METHODS: Executive functions were assessed in pain-free elderly participants using neuropsychological tests. Endogenous inhibition of pain was investigated using the paradigm of conditioned pain modulation. We compared pain thresholds before and after the conditioned pain modulation procedure in older and younger participants and in seniors with poor and good performances on executive tests. RESULTS: Younger participants showed a significant inhibitory effect of phasic pain during prolonged pain stimulation. Older participants with good performance on executive tests showed an absence of inhibiting effect, whereas older participants with poor performance showed a facilitating effect, indicating a significant link between cognitive functions and mechanisms of endogenous inhibition of pain. DISCUSSION: These results highlight a significant link between cognitive functions and mechanisms of endogenous inhibition of pain and open new perspectives in investigations of chronic pain in aging.

Event-related brain potentials elicited by high-speed cooling of the skin: A robust and non-painful method to assess the spinothalamic system in humans.

OBJECTIVE: To investigate whether cool-evoked potentials (CEP) elicited by brisk innocuous cooling of the skin could serve as an alternative to laser-evoked potentials (LEP), currently considered as the best available neurophysiological tool to assess the spinothalamic tract and diagnose neuropathic pain. METHODS: A novel device made of micro-Peltier elements and able to cool the skin at -300 °C/s was used to record CEPs elicited by stimulation of the hand dorsum in 40 healthy individuals, characterize the elicited responses, and assess their signal-to-noise ratio. Various stimulation surfaces (40 mm2 and 120 mm2), cooling ramps (-200 °C/s and -133 °C/s) and temperature steps (20 °C, 15 °C, 10 °C, 5 °C) were tested to identify optimal stimulation conditions. RESULTS: CEPs were observed in all conditions and subjects, characterized by a biphasic negative-positive complex maximal at the vertex (Cz), peaking 190-400 ms after stimulus onset, preceded by a negative wave over central-parietal areas contralateral to the stimulated hand. Their magnitude was modulated by stimulation surface, cooling ramp and temperature step. CONCLUSION: Rapid innocuous skin cooling elicits robust CEPs at latencies compatible with the conduction velocity of Aδ-fibers. SIGNIFICANCE: CEPs can be a complementary tool to the recording of LEPS for assessing the function of small-diameter Aδ-fibers and the spinothalamic tract.

Observational study found that even small variations in light can wake up very preterm infants in a neonatal intensive care unit.

AIM: This prospective observational study evaluated the behavioural responses of very preterm infants to spontaneous light variations. METHODS: We measured spontaneous light variations in the incubators of 27 very preterm infants, with a median gestational age of 28 weeks (range 26-31 weeks), over 10 hours. All of them had been admitted to the neonatal care unit of the Strasbourg University Hospital, France, between April 2008 and July 2009. Two independent raters examined changes in the infants' behavioural states using video recordings. The percentage of awakenings was recorded when there were light variations and during control periods with no changes. RESULTS: We analysed 275 periods following light variations and 275 control periods. The overall percentage of awakenings was greater during periods following a change in light than during control periods (16.3% vs 11%, p = 0.03). The extent of light protection affected the percentage of awakenings. In mild light protection, there were more awakenings following changes in light than in control periods (25.6% vs 6.7%, p = 0.01). This difference was not found in high light protection. CONCLUSION: Very preterm infants can be woken up by small variations in light, when the light protection in their incubator is insufficient.

Reduced parahippocampal theta activity during spatial navigation in low, but not in high elderly performers.

OBJECTIVE: Cognitive aging varies widely among individuals. Whereas optimal cognitive agers show highly preserved cognitive functions throughout life, other subjects experience cognitive deficits in various cognitive domains. Among them, elderly individuals frequently report difficulties in spatial navigation. In this study, we aimed to determine whether elderly participants with different cognitive profiles would perform differently at a navigation task, and explore underlying medial hippocampal activity. METHOD: Two groups of elderly subjects were selected, high- and low-performing (HP and LP, respectively), based on their performance on a detailed neuropsychological examination. A group of young adults was recruited as controls. Cerebral activity was recorded by electroencephalography (EEG) during a virtual navigation task in which participants had 3 trials to find their way in mazes. We analyzed theta activity during navigation in the mazes and performed source reconstruction analyses. RESULTS: The LP group was less accurate than the HP group during the navigation task. Theta activity during navigation was greater in HP subjects compared with controls, whereas that theta activity was reduced in LP subjects. Moreover, theta activity in the left parahippocampal gyrus increased across trials in HP, but not in LP, subjects. CONCLUSION: Elderly participants performed differently at a navigation task according to their cognitive profile: elderly with cognitive deficits seem to have greater difficulties in spatial navigation than HP elderly. Navigational difficulties in elderly with cognitive deficits might be related to functional alteration of the parahippocampal gyrus. (PsycINFO Database Record

Gamma oscillatory activity is impaired in episodic memory encoding with age.

The present study proposes to investigate age-related episodic memory impairment in encoding. We collected ERPs in young and old participants performing a word-encoding task. For subsequently remembered words, young adults had greater activity at the left and anterior electrode sites, whereas old adults had greater posterior activity. Performance correlated positively with central sites in young adults but with left parietal hemisphere activity in old adults. Plus, a large left frontoparietal network increased its activity during the successful encoding for the Beta (13-30 Hz) and Gamma (30-100 Hz) bands in young adults. Old adults had increased activity in the right posterior parietal region for forgotten words in the Gamma band. Using a source localization analysis, we found that age leads to a decrease in Gamma band cerebral activity during encoding of words in the left hemisphere and the bilateral parahippocampal regions. These findings indicate that encoding impairment with age may be associated with dysfunctional Gamma oscillatory activity across a widespread network of left cortical regions.