Warm Water Control Research Articles

Non-instrumental information seeking is resistant to acute stress

Previous research has shown that people intrinsically value non-instrumental information, which cannot be used to change the outcome of events, but only provides an early resolution of uncertainty. This is true even for information about rather inconsequential events, such as the outcomes of small lotteries. Here we investigated whether participants’ willingness to pay for non-instrumental information about the outcome of simple coin-flip lotteries with guaranteed winnings was modulated by acute stress. Stress was induced using the Socially Evaluated Cold Pressor Test (SECPT), and information-seeking choices were compared to a warm water control group. Our results neither support the hypothesis that stress decreases information-seeking by directing cognitive resources away from the relevance of the lotteries, nor the opposite hypothesis that stress increases information-seeking by driving anxiety levels up. Instead, we found that despite successful stress induction, as evidenced by increased saliva cortisol levels in the SECPT group, information valuation was remarkably stable. This finding is in line with recent findings that experimentally increased state anxiety did not modulate non-instrumental information seeking. Together, these results suggest that the aversiveness of “not knowing” is a stable cognitive state and not easily modulated by situational context, such as acute stress.

When stress enhances memory encoding: The beneficial effects of changing context

The effects of acute stress on memory encoding are complex, and we do not yet know all of the conditions that can determine whether stress at encoding improves or impairs memory. Recent work has found that changing contexts between encoding and stress can abolish the effects of post-encoding stress on memory, suggesting that context may play an important role in the effects of stress on memory. However, the role of context in the effects of stress on memory encoding is not yet known. We addressed this gap by examining the effects of context on the influence of acute stress on memory encoding. In a 2 × 2 experimental design, participants (N = 103) completed either a stressor (i.e., Socially Evaluated Cold Presser Test) or control task (i.e., warm water control) before completing a memory encoding task, which occurred in either in the same room as or a different room from the stressor or control task. Memory retrieval was tested for each participant within the context that they completed the encoding task. We found that, relative to nonstressed (i.e., control) participants, stressed participants who switched contexts prior to encoding showed better memory for both negative and neutral images. In contrast, when the stressor or control task occurred in the same room as memory encoding, stress had no beneficial effect on memory. These results highlight the importance of the ongoing context as a determinant of the effects of stress on memory encoding and present a challenge to current theoretical accounts of stress and memory.

Habituation of the stress response multiplex to repeated cold pressor exposure.

Humans show remarkable habituation to aversive events as reflected by changes of both subjective report and objective measures of stress. Although much experimental human research focuses on the effects of stress, relatively little is known about the cascade of physiological and neural responses that contribute to stress habituation. The cold pressor test (CPT) is a common method for inducing acute stress in human participants in the laboratory; however, there are gaps in our understanding of the global state changes resulting from this stress-induction technique and how these responses change over multiple exposures. Here, we measure the stress response to repeated CPT exposures using an extensive suite of physiologic measures and state-of-the-art analysis techniques. In two separate sessions on different days, participants underwent five 90 s CPT exposures of both feet and five warm water control exposures, while electrocardiography (ECG), impedance cardiography, continuous blood pressure, pupillometry, scalp electroencephalography (EEG), salivary cortisol and self-reported pain assessments were recorded. A diverse array of adaptive responses are reported that vary in their temporal dynamics within each exposure as well as habituation across repeated exposures. During cold-water exposure there was a cascade of changes across several cardiovascular measures (elevated heart rate (HR), cardiac output (CO) and Mean Arterial Pressure (MAP) and reduced left ventricular ejection time (LVET), stroke volume (SV) and high-frequency heart rate variability (HF)). Increased pupil dilation was observed, as was increased power in low-frequency bands (delta and theta) across frontal EEG electrode sites. Several cardiovascular measures also habituated over repeated cold-water exposures (HR, MAP, CO, SV, LVET) as did pupil dilation and alpha frequency activity across the scalp. Anticipation of cold water induced stress effects in the time-period immediately prior to exposure, indexed by increased pupil size and cortical disinhibition in the alpha and beta frequency bands across central scalp sites. These results provide comprehensive insight into the evolution of a diverse array of stress responses to an acute noxious stressor, and how these responses adaptively contribute to stress habituation.

The effect of various breath-hold techniques on the cardiorespiratory response to facial immersion in humans.

What is the central question of this study? What is the effect of three repeated breath-hold techniques routinely used by freedivers, thought to manipulate arterial partial pressures of O2 and CO2 , on the cardiorespiratory and haematological response to breath-holding during facial immersion? What is the main finding and its importance? All three techniques increased breath-hold by a similar duration, probably owing to the similar marked increase in end-tidal O2 and decrease in end-tidal CO2 observed in all three trials before facial immersion. These were the only cardiorespiratory changes that were consistently manipulated before the maximal breath-hold. This would suggest that pronounced bradycardia and vasoconstriction of selective vascular beds are probably not obligatory for prolonging breath-hold duration. Repeated maximal breath-holds have been demonstrated to induce bradycardia, increase haematocrit and haemoglobin and prolong subsequent breath-hold duration by 20%. Freedivers use non-maximal breath-hold techniques (BHTs) to improve breath-hold duration. The aim of this study was to investigate the cardiorespiratory and haematological responses to various BHTs. Ten healthy men (34.5±1.9 years) attended five randomized experimental trials and performed a 40min period of quiet rest or one of three BHTs followed by a maximal breath-hold challenge during facial immersion in water at 30 or 10°C. Cardiovascular and respiratory parameters were measured continuously using finger plethysmography and breath-by-breath gas analysis, respectively, and venous blood samples were collected throughout. Facial immersion in cold water caused marked bradycardia (74.1 vs. 50.2beats/min after 40 s) but did not increase breath-hold duration compared with warm water control conditions. Facial immersion breath-hold duration was 30.8-43.3% greater than the control duration when preceded by BHTs that involved repeated breath-holds of constant duration (P=0.021), increasing duration (P<0.001) or increasing frequency (P<0.001), with no difference observed between BHTs. The increased duration of apnoea across all three BHT protocols was associated with a 6.8% increase in end-tidal O2 and a 13.1% decrease in end-tidal CO2 immediately before facial immersion. There were no differences in blood pressure, cardiac output, heart rate, haematocrit or haemoglobin between each BHT and control conditions (P>0.05). In conclusion, the duration of apnoea can be extended by manipulating blood gases through repeated prior breath-holds, but changes in cardiac output and red blood cell mass do not appear essential.

SOLAR PV SYSTEM WITH MULTI-LEVEL INVERTER USING PI AND FUZZY LOGIC CONTROLLER

This paper presents a single-phase multi-string Nine-level PV inverter topology for grid-connected photovoltaic (PV) systems with a novel PWM control and fuzzy logic scheme. The Multilevel inverters are extensively used due to their increased power rating reduced EMI, improving harmonic performance. Multilevel inverters are switched at low switching frequency when compared to two level inverters, a single-phase multi-string nine-level PV inverter topology for grid-connected photovoltaic (PV) systems using novel PWM control Technology. A photovoltaic (PV) system generates electricity by direct conversion. The PV strings are cascaded together in parallel configuration and connected to a Nine-level inverter to generate output voltage. Two reference sinusoidal signals are identical to each other with an offset equivalent to the amplitude of the triangular carrier signal were used to generate gate signals for the nine level inverter switches and it is to implement this PWM using PI current control algorithm. The proposed nine level inverter offers much less THD and can operate at near unity power factor. the frequency of it will be 50Hz and from the result we minimizes the number of components and devices as well as switching losses are reduced when compared to the conventional multilevel inverter topology and its interconnects for grid utilization. Fuzzy Logic Control (FLC), originating from control theory focused on mathematical representations of the open-loop mechanism to be controlled, is an integral aspect of fuzzy reasoning. Fuzzy Logic Control has been successfully extended to a wide range of practical issues, including warm water control, robot control, heat exchange, traffic junction control, cement kiln control, vehicle speed control, automotive engineering, and mcar parking and turning, power system and nuclear reactor, on-line shopping, washing machines, etc. The validity of the proposed inverter is verified through simulation andcompared with other technique. The output voltage will be in the form of stepped waveform. The proposed system produces less THD and reduction of steady state time KEYWORDS –Maximum Power Point Tracking(MPPT) algorithm, Boost Converter, FLC contreoller, PWM technique.

Stress effects on the top-down control of visuospatial attention: Evidence from cue-dependent alpha oscillations

Stress is assumed to inhibit the top-down control of attention and to facilitate bottom-up processing. Evidence from human experiments, however, remains scarce. Previous studies have addressed how stress affects the interplay of bottom-up and top-down mechanisms of attention. A key open question is in how far such effects can actually be attributed to a stress-induced modulation of top-down attention control. We sought to isolate top-down from bottom-up effects by assessing stress effects on anticipatory changes in alpha oscillations that precede stimulus processing. Participants performed in a cued target detection task in which a cue prompted them to covertly shift their attention to left or right screen positions, 20 min after being exposed to the bilateral feet cold pressor test or a warm water control procedure. The stressor led to a substantial increase in cortisol, peaking 20 min post stressor, along with rises in heart rate, blood pressure, and subjective ratings of stress and arousal. As expected, cued attention deployment led to higher alpha power over posterior electrodes contralateral versus ipsilateral to the attended hemifield during the cue-target interval. Importantly, this purely endogenous effect was potentiated by stress, however, significant differences were restricted to the middle of the cue-target interval and thus temporally separated from the appearance of the target. These results indicate that stress does not impair top-down attentional control per se but may introduce a qualitative change modulating the way attention is deployed to meet action goals.

Stress-Induced Increase in Cortisol Negatively Affects the Consolidation of Contextual Elements of Episodic Memories.

Stress can modulate episodic memory in various ways. The present study asks how post-encoding stress affects visual context memory. Participants encoded object images centrally positioned on background scenes. After encoding, they were either exposed to cold pressure stress (CPS) or a warm water control procedure. Forty-right hours later, participants were cued with object images, and for each image, they were asked to select the background scene with which it was paired during study among three highly similar options. Only male but not female participants reacted with a significant increase in salivary cortisol to CPS, and the stress and control group did not differ in recognition performance. Comparing recognition performance between stress responders and non-responders, however, revealed a significant impairment in context memory in responders. Additionally, proportional increase in cortisol was negatively correlated with the number of correctly recognized scenes in responders. Due to the small number of responders, these findings need to be interpreted with caution but provide preliminary evidence that stress-induced cortisol increase negatively affects the consolidation of contextual elements of episodic memories.

Emotional stress regulation: The role of relative frontal alpha asymmetry in shaping the stress response

Frontal EEG asymmetry has been proposed as an index of emotional regulation, reflecting both state and trait components, and there is evidence that these factors influence the cortisol response to stress. Here, we asked whether cold pressor stress modulates frontal asymmetry and whether this is predictive of the neuroendocrine stress response. Twenty-four male participants underwent an automatized bilateral feet cold pressor test (bfCPT) and a warm water control procedure in counterbalanced order on two separate days, one week apart. EEG, heart rate and blood pressure were assessed at baseline as well as during and after the bfCPT. Salivary cortisol and subjective ratings of stress and arousal were assessed before and after the bfCPT. The bfCPT led to a significant increase in cortisol, cardiovascular parameters and in subjective ratings of stress and arousal that was absent in the control condition. Furthermore, analysis of relative frontal alpha-band asymmetry revealed a stronger relative right frontal activation during the bfCPT compared to the control condition at electrode pairs F7/8 but not F3/4. However, frontal asymmetry scores during the bfCPT were not predictive for neither physiological responses nor subjective ratings. Moreover, an association between physiological responses and frontal asymmetry assessed during rest at baseline could be observed at electrode pairs F3/F4, with stronger responses being associated with stronger relative right frontal activation. Our results show that cold pressor stress leads to an alteration of emotional processes as reflected in frontal EEG asymmetry at F7/F8. Moreover, physiological responses to the CPT seem to be differentially moderated by trait and state components present in frontal asymmetry.

Validation of an automated bilateral feet cold pressor test

The Cold Pressor Test (CPT) is often used in psychobiological research. However, the classical CPT version (unilateral hand immersion into ice-water) involves some disadvantages: hands may be needed for further applications, attentional drift towards the affected sensory hemi-field and/or physiological activation of the contralateral hemisphere may produce a laterality bias. Furthermore, instruction-induced motor activity may bias physiologic reactivity. To avoid these problems, a fully automated bilateral feet CPT was developed and tested for validity and feasibility. The test procedure is based on computerized control of water influx and efflux. This allows for maximal standardization and precise timing. Furthermore, water is kept in permanent flow to prohibit formation of stable temperature layers in skin proximity. Laterality bias, instructions effects and motor responses (e.g. lifting feet out of a water basin) are avoided.In a counterbalanced within-subject design, 28 healthy male students were exposed to the CPT and to a warm water control (CNT) condition twice, one week apart. Cardiovascular parameters, salivary cortisol and subjective ratings (stress, arousal and pain) were assessed before, during, and after interventions.The CPT profoundly affected physiology as well as subjective ratings. Expectation effects (immediately before testing) were small. Furthermore, post-CPT (presumably compensatory/counter-regulatory) effects on heart rate and stroke volume were found.In conclusion, the automated bilateral feet CPT is a valid and feasible stress test modification. Hemodynamic, subjective and endocrine stress responses are substantial, suggesting that this test version represents an advanced and suitable tool in human stress research.

The effects of experimental pain and induced optimism on working memory task performance

Background/aimsPain can interrupt and deteriorate executive task performance. We have previously shown that experimentally induced optimism can diminish the deteriorating effect of cold pressor pain on a subsequent working memory task (i.e., operation span task). In two successive experiments we sought further evidence for the protective role of optimism on pain-induced working memory impairments. We used another working memory task (i.e., 2-back task) that was performed either after or during pain induction. MethodsStudy 1 employed a 2 (optimism vs. no-optimism)×2 (pain vs. no-pain)×2 (pre-score vs. post-score) mixed factorial design. In half of the participants optimism was induced by the Best Possible Self (BPS) manipulation, which required them to write and visualize about a life in the future where everything turned out for the best. In the control condition, participants wrote and visualized a typical day in their life (TD). Next, participants completed either the cold pressor task (CPT) or a warm water control task (WWCT). Before (baseline) and after the CPT or WWCT participants working memory performance was measured with the 2-back task. The 2-back task measures the ability to monitor and update working memory representation by asking participants to indicate whether the current stimulus corresponds to the stimulus that was presented 2 stimuli ago. Study 2 had a 2 (optimism vs. no-optimism)×2 (pain vs. no-pain) mixed factorial design. After receiving the BPS or control manipulation, participants completed the 2-back task twice: once with painful heat stimulation, and once without any stimulation (counter-balanced order). Continuous heat stimulation was used with temperatures oscillating around 1°C above and 1°C below the individual pain threshold. ResultsIn study 1, the results did not show an effect of cold pressor pain on subsequent 2-back task performance. Results of study 2 indicated that heat pain impaired concurrent 2-back task performance. However, no evidence was found that optimism protected against this pain-induced performance deterioration. ConclusionsExperimentally induced pain impairs concurrent but not subsequent working memory task performance. Manipulated optimism did not counteract pain-induced deterioration of 2-back performance. ImplicationsIt is important to explore factors that may diminish the negative impact of pain on the ability to function in daily life, as pain itself often cannot be remediated. We are planning to conduct future studies that should shed further light on the conditions, contexts and executive operations for which optimism can act as a protective factor.

"Moderate Stress Enhances Immediate and Delayed Retrieval of Educationally Relevant Material in Healthy Young Men": Correction to Hupbach and Fieman (2012).

Reports an error in "Moderate stress enhances immediate and delayed retrieval of educationally relevant material in healthy young men" by Almut Hupbach and Rachel Fieman (Behavioral Neuroscience, 2012[Dec], Vol 126[6], 819-825). In the article there are computational errors in the last sentence of the Memory Performance section. "(M = .30, SD = .11 for CPS, and M = .13, SD = 17 for the warm water control)." should read instead: "(M = .03, SD = .11 for CPS, and M = .13, SD = .17 for the warm water control)." (The following abstract of the original article appeared in record 2012-27908-001.) Retrieval practice is a powerful memory enhancer. However, in educational settings, test taking is often experienced as a stressful event. While it is known that stress can impair retrieval processes, little is known about the delayed consequences of testing memory for educationally relevant material under stressful conditions, which is the focus of the present study. Participants (38 women, 37 men) memorized a scientific text passage on Day 1. On Day 2, they were either exposed to a stressor (cold pressor test; CPS) or a warm water control, and immediately afterward, they were asked to recall the text passage (i.e., retrieval under stress vs. control). Salivary cortisol was measured as an index of the stress response before, and 20 min after the CPS versus control treatment. The delayed effects of testing under stress were assessed with a final recall test on Day 3. In comparison to the control condition, CPS caused significant increases in salivary cortisol, and, surprisingly resulted in enhanced memory in men. Importantly, this enhancement was not only observed in the test that immediately followed the stressor, but also in the delayed test. In women, CPS caused only marginal increases in cortisol concentrations, and retrieval remained unaffected. Our study suggests that moderate stress can improve memory performance for educationally relevant material in a long-lasting manner in healthy young men. (PsycINFO Database Record

Stress selectively affects the reactivated components of a declarative memory.

When long-term memories are reactivated, they can reenter a transient plastic state in which they are vulnerable to interference or physiological manipulations. The present study attempted to directly affect reactivated memories through a stress manipulation, and compared the effects of stress on reactivated and nonreactivated components of a declarative memory in a within-subject design. We presented image pairs that consisted of an image of an animal and an image of an unrelated object. Participants were instructed to memorize the object images. Forty-eight hours later, we presented half of the animal images again in an unrelated task to indirectly reactivate the associated object images. Immediately after reactivation, participants were exposed to cold pressor stress or a warm water control condition. Forty-eight hours later, we assessed memory for the object images with a free recall test. Reactivation boosted memory performance in the control condition, such that reactivated items were better recalled than nonreactivated items. This memory-enhancing effect of reactivation was completely abolished by cold pressor stress. Importantly, stress selectively impacted only the reactivated items while leaving memory for the nonreactivated items unaffected. The present study shows that it is possible to selectively reactivate and modulate specific parts of a declarative memory.

Effects of Pre-Encoding Stress on Brain Correlates Associated with the Long-Term Memory for Emotional Scenes

Recent animal and human research indicates that stress around the time of encoding enhances long-term memory for emotionally arousing events but neural evidence remains unclear. In the present study we used the ERP old/new effect to investigate brain dynamics underlying the long-term effects of acute pre-encoding stress on memory for emotional and neutral scenes. Participants were exposed either to the Socially Evaluated Cold Pressure Test (SECPT) or a warm water control procedure before viewing 30 unpleasant, 30 neutral and 30 pleasant pictures. Two weeks after encoding, recognition memory was tested using 90 old and 90 new pictures. Emotional pictures were better recognized than neutral pictures in both groups and related to an enhanced centro-parietal ERP old/new difference (400–800 ms) during recognition, which suggests better recollection. Most interestingly, pre-encoding stress exposure specifically increased the ERP old/new-effect for emotional (unpleasant) pictures, but not for neutral pictures. These enhanced ERP/old new differences for emotional (unpleasant) scenes were particularly pronounced for those participants who reported high levels of stress during the SECPT. The results suggest that acute pre-encoding stress specifically strengthens brain signals of emotional memories, substantiating a facilitating role of stress on memory for emotional scenes.

Stress Sensitizes the Brain: Increased Processing of Unpleasant Pictures after Exposure to Acute Stress

A key component of acute stress is a surge in vigilance that enables a prioritized processing of highly salient information to promote the organism's survival. In this study, we investigated the neural effects of acute stress on emotional picture processing. ERPs were measured during a deep encoding task, in which 40 male participants categorized 50 unpleasant and 50 neutral pictures according to arousal and valence. Before picture encoding, participants were subjected either to the Socially Evaluated Cold Pressor Test (SECPT) or to a warm water control procedure. The exposure to the SECPT resulted in increased subjective and autonomic (heart rate and blood pressure) stress responses relative to the control condition. Viewing of unpleasant relative to neutral pictures evoked enhanced late positive potentials (LPPs) over centro-parietal scalp sites around 400 msec after picture onset. Prior exposure to acute stress selectively increased the LPPs for unpleasant pictures. Moreover, the LPP magnitude for unpleasant pictures following the SECPT was positively associated with incidental free recall performance 24 hr later. The present results suggest that acute stress sensitizes the brain for increased processing of cues in the environment, particularly priming the processing of unpleasant cues. This increased processing is related to later long-term memory performance.

Moderate stress enhances immediate and delayed retrieval of educationally relevant material in healthy young men.

Retrieval practice is a powerful memory enhancer. However, in educational settings, test taking is often experienced as a stressful event. While it is known that stress can impair retrieval processes, little is known about the delayed consequences of testing memory for educationally relevant material under stressful conditions, which is the focus of the present study. Participants (38 women, 37 men) memorized a scientific text passage on Day 1. On Day 2, they were either exposed to a stressor (cold pressor test; CPS) or a warm water control, and immediately afterward, they were asked to recall the text passage (i.e., retrieval under stress vs. control). Salivary cortisol was measured as an index of the stress response before, and 20 min after the CPS versus control treatment. The delayed effects of testing under stress were assessed with a final recall test on Day 3. In comparison to the control condition, CPS caused significant increases in salivary cortisol, and, surprisingly resulted in enhanced memory in men. Importantly, this enhancement was not only observed in the test that immediately followed the stressor, but also in the delayed test. In women, CPS caused only marginal increases in cortisol concentrations, and retrieval remained unaffected. Our study suggests that moderate stress can improve memory performance for educationally relevant material in a long-lasting manner in healthy young men.

Effects of cold pressor pain on the abuse liability of intranasal oxycodone in male and female prescription opioid abusers

BackgroundApproximately 1.9 million persons in the U.S. have prescription opioid use disorders often with concomitant bodily pain, but systematic data on the impact of pain on abuse liability of opioids is lacking. The purpose of this study was to determine whether pain alters the intranasal abuse liability of oxycodone, a commonly prescribed and abused analgesic, in males and females. MethodsSporadic prescription opioid abusers (10 females, 10 males) participated in this mixed (between and within-subject), randomized inpatient study. Experimental sessions (n=6) tested intranasal placebo, oxycodone 15 or 30mg/70kg during cold pressor testing (CPT) and a warm water control. Observer- and subject-rated drug effect measures, analgesia, physiologic and cognitive effects were assessed. ResultsThe CPT significantly increased blood pressure, heart rate, pain, stress, and “opiate desire” compared to the no-pain control but did not alter opioid liking, high or street value. Intranasal oxycodone produced effects within 10min, significantly decreasing pain and significantly increasing subjective measures of abuse liability (e.g., high). Females had higher ratings of street value, high, and liking for one or both active doses. ConclusionsThe CPT was a reliably painful and stressful stimulus that did not diminish the abuse liability of intranasal oxycodone. Females were more sensitive to oxycodone on several abuse liability measures that warrant further follow-up. Snorting oxycodone rapidly produced psychoactive effects indicative of substantial abuse liability.

Action of centrally mediated autonomic stimulation on human upper gastrointestinal transit: a comparative study of two stimuli.

Two well established experimental stressors, hand immersion in cold water, and mental stimulation with dichotomous listening, were applied to 37 normal subjects after the ingestion of a standard meal. Orocaecal transit was measured by serial exhaled breath hydrogen sampling. Cold water significantly delayed transit compared with warm water control (warm water 71.8 +/- 3.6 mins v cold water 93.2 +/- 5.7 mins p less than 0.01), with significant rises in blood pressure pulse rate perceived discomfort and plasma catecholamines. In contrast mental stimulation was unaccompanied by any change in transit (control; 67.4 +/- 4.7 v test 64.3 +/- 5.3 mins p greater than 0.1) despite a significant rise in pulse rate, skin conductance and plasma catecholamines. Repeated cold water immersion studies in eight individuals produced consistent orocaecal transit and autonomic responses, whereas mental stimulation showed reduced autonomic responses on repeat testing, suggesting that tolerance to the stimulus had occurred. The results of these studies show stimulus specific gastrointestinal response patterns to autonomic stimuli, and appear to have important implications for the design of future studies of human gastrointestinal autonomic physiology and for the investigation of patients with stress related gut dysfunction.