Effects of visual stimuli and a stressor on head pain

Learning headache triggers through experience: A laboratory study

OBJECTIVE

To examine how individuals may learn headache trigger beliefs through sequential symbolic pairings of trigger candidates and headache attacks.

BACKGROUND

Learning from experience may be a major source of information about headache triggers. Little is known about learning-based influences on the establishment of trigger beliefs.

METHODS

This cross-sectional, observational study included N = 300 adults with headache who participated in a laboratory computer task. First, participants rated the chances (0%-100%) that encountering specific triggers would lead to experiencing a headache. Then, 30 sequential images with the presence or absence of a common headache trigger were presented alongside images representing the presence or absence of a headache attack. The primary outcome measure was the cumulative association strength rating (0 = no relationship to 10 = perfect relationship) between the trigger and headache using all previous trials.

RESULTS

A total of N = 296 individuals completed 30 trials for each of three triggers, yielding 26,640 total trials for analysis. The median [25th, 75th] association strength ratings for each of the randomly presented headache triggers were 2.2 [0, 3] for the Color Green, 2.7 [0, 5] for Nuts, and 3.9 [0, 8] for Weather Changes. There was a strong association between the "true" cumulative association strength and corresponding ratings. A 1-point increase on the phi scale (i.e., no relationship to perfect relationship) was associated with a 1.20 (95% CI: 0.81 to 1.49, p < 0.0001) point increase in association strength rating. A participant's prior belief about the potency of a trigger affected their perceived rating of the accumulating evidence, accounting for 17% of the total variation.

CONCLUSION

In this laboratory task, individuals appeared to learn trigger-headache associations through repeated exposures to accumulating symbolic evidence. Prior beliefs about the triggers appeared to influence ratings of the strength of relationships between triggers and headache attacks.

Forty-hertz light stimulation does not entrain native gamma oscillations in Alzheimer's disease model mice

There is a demand for noninvasive methods to ameliorate disease. We investigated whether 40-Hz flickering light entrains gamma oscillations and suppresses amyloid-β in the brains of APP/PS1 and 5xFAD mouse models of Alzheimer's disease. We used multisite silicon probe recording in the visual cortex, entorhinal cortex or the hippocampus and found that 40-Hz flickering simulation did not engage native gamma oscillations in these regions. Additionally, spike responses in the hippocampus were weak, suggesting 40-Hz light does not effectively entrain deep structures. Mice avoided 40-Hz flickering light, associated with elevated cholinergic activity in the hippocampus. We found no reliable changes in plaque count or microglia morphology by either immunohistochemistry or in vivo two-photon imaging following 40-Hz stimulation, nor reduced levels of amyloid-β 40/42. Thus, visual flicker stimulation may not be a viable mechanism for modulating activity in deep structures.

An observational study of self-reported migraine triggers and prospective evaluation of the relationships with occurrence of attacks enabled by a smartphone application (App)

OBJECTIVE

To investigate the relationship between self-reported triggers and the occurrence of migraine attacks using a smartphone application.

BACKGROUND

One of several issues around the study of migraine attack triggers is that limited available evidence supports whether self-reported triggers can induce a headache on a particular subject.

METHODS

This is an observational longitudinal cohort study of individuals with migraine registered to track their headaches prospectively using a smartphone application. For 90 days, participants entered daily data about triggers (potential triggers and premonitory symptoms) that may be associated with attack risk, as well as migraine symptoms. The statistical significance of univariate associations between each trigger and migraine recurrent events was determined for each individual. Statistically identified triggers were then compared to self-reported triggers.

RESULTS

In 328 individuals (290/328 [88.4%] female; mean [standard deviation] 4.2 [1.5] migraine attacks/month) the mean (standard deviation) number of triggers moderately or highly endorsed per individual was 28.0 (7.7) in individuals presented with up to 38 possible triggers. Of these, an average (standard deviation) of 2.2 (2.1) triggers per individual were statistically associated with increased risk of attacks. Even the most commonly endorsed triggers (sleep quality, stress, tiredness/fatigue, sleep duration, dehydration, neck pain, missed meals, eyestrain, mean barometric pressure, and anxiety) were statistically associated in fewer than one third of individuals suspecting each, with the exception of neck pain (117/302 [38.7%]).

CONCLUSIONS

Individuals with episodic migraine believe that many triggers contribute to their attacks; however, few of these withstand statistical testing at the individual level. Improved personal knowledge of potential triggers and premonitory symptoms may help individuals adopt behavioral changes to mitigate attack risk.

Pattern-Induced Visual Discomfort and Anxiety in Migraineurs: Their Relationship and the Effect of Colour

In migraineurs, coloured lenses were found to reduce the visual stress caused by an aversive pattern known to trigger migraines by 70%, but do such patterns also produce a low-level anxiety/fear response? Is this response lessened by colour? We sought to investigate this in a study comprising a broad screening component followed by a dot-probe experiment to elicit attentional biases (AB) to aversive patterns. Undergraduate psychology students completed headache and visual discomfort (VD) questionnaires (N = 358), thereby forming a subject pool from which 13 migraineurs with high visual discomfort and 13 no-headache controls with low visual discomfort, matched on age and sex, completed a dot-probe experiment. Paired stimuli were presented for 500 ms: aversive achromatic 3 cpd square wave gratings vs control, scrambled patterns. These conditions were repeated using the colour that was most comfortable for each participant. VD was greater in the more severe headache groups. On all measures, the migraineurs were more anxious than the controls, and a positive relationship was found between VD and trait anxiety. The 3 cpd gratings elicited an aversive AB in the migraine group which was somewhat reduced by the use of colour, and this was not seen in the controls. The results suggest a new role for colour in reducing visual stress via anxiety/fear reduction.

Triggers of Primary Headaches: Issues and Pathways Forward

The triggers of primary headaches have considerable significance for our understanding and management of headache and migraine. Triggers explain the variance in headaches - why they occur when they do. Trigger management is generally viewed as an important component of a comprehensive treatment approach for headaches. Historically, however, triggers have not had a prominent place in the headache literature. This situation began to change 20 to 30 years ago, and the pace of change has increased exponentially in recent times. Nevertheless, the field is beset with issues that have held it back from achieving more. This review will focus on elaborating those issues with the goal of suggesting ways forward. The first issue considered will be the definition of a trigger, and how specific triggers are labeled. Consideration will then be given to a classification system for triggers. The review will discuss next the evidence relating to whether self-reported triggers can, indeed, precipitate headaches, and how the capacity to elicit headaches may be acquired or extinguished. Attention will be given to the very important clinical issue of trigger management. Finally, the pathways forward will be proposed. Perhaps the most useful thing to accomplish at this point in time would be agreement on a definition of headache triggers, a list of triggers, and a classification system for triggers. This would greatly assist in comparing research on triggers from different research groups as well as eliminating some of the issues identified in this review. An authoritative body such as the American Headache Society or the International Headache Society, could establish a multidisciplinary committee that would complete these tasks. Consideration should also be given to incorporating triggers into the International Classification of Headache Disorders as an axis or via the use of codes, as this would raise the profile of triggers in assessment and management.

Characterization and predictive mechanisms of experimentally induced tension-type headache

Objective

Studies have shown it is possible to elicit a tension-type headache episode in 15 to 30% of healthy individuals following a tooth-clenching or stress-inducing task. Despite this, no studies have attempted to understand why some healthy individuals develop a headache episode while others do not.

Methods

The present randomized, single-blind, controlled study recruited 60 healthy participants who participated in a 30-minute tooth-clenching task and 10 participants who participated in a control task. Before the tasks, participants had their pericranial tenderness and pain modulation profiles (wind-up ratio and conditioned pain modulation) assessed. Two hours later, pericranial tenderness and pressure pain thresholds were assessed as well as any developing temporomandibular disorders. Pain diaries were kept for 24 hours to register any developing pain or headache.

Results

Participants with a decrease in pericranial tenderness after the tooth-clenching task were less likely to develop headache when compared to participants without. Pain modulation profiles could not predict who developed headache and who did not. Finally, no difference was found between groups for developing temporomandibular disorders. No difference in frequency of participants who developed headache was found between the tooth-clenching and the control task.

Conclusions

In conclusion, it was shown that increased pericranial tenderness was not required to trigger an episode of tension-type headache in healthy participants. Furthermore, pain modulation profiles could not predict who developed headache and who did not. Finally, activation of descending inhibitory pathways, as assessed by decreases in pericranial tenderness, was protective against the development of headache. These findings provide new insights into the pathophysiology of experimentally-induced tension-type headache.

Migraine Triggers and Oxidative Stress: A Narrative Review and Synthesis

BACKGROUND

Blau theorized that migraine triggers are exposures that in higher amounts would damage the brain. The recent discovery that the TRPA1 ion channel transduces oxidative stress and triggers neurogenic inflammation suggests that oxidative stress may be the common denominator underlying migraine triggers.

OBJECTIVE

The aim of this review is to present and discuss the available literature on the capacity of common migraine triggers to generate oxidative stress in the brain.

METHODS

A Medline search was conducted crossing the terms "oxidative stress" and "brain" with "alcohol," "dehydration," "water deprivation," "monosodium glutamate," "aspartame," "tyramine," "phenylethylamine," "dietary nitrates," "nitrosamines," "noise," "weather," "air pollutants," "hypoglycemia," "hypoxia," "infection," "estrogen," "circadian," "sleep deprivation," "information processing," "psychosocial stress," or "nitroglycerin and tolerance." "Flavonoids" was crossed with "prooxidant." The reference lists of the resulting articles were examined for further relevant studies. The focus was on empirical studies, in vitro and of animals, of individual triggers, indicating whether and/or by what mechanism they can generate oxidative stress.

RESULTS

In all cases except pericranial pain, common migraine triggers are capable of generating oxidative stress. Depending on the trigger, mechanisms include a high rate of energy production by the mitochondria, toxicity or altered membrane properties of the mitochondria, calcium overload and excitotoxicity, neuroinflammation and activation of microglia, and activation of neuronal nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. For some triggers, oxidants also arise as a byproduct of monoamine oxidase or cytochrome P450 processing, or from uncoupling of nitric oxide synthase.

CONCLUSIONS

Oxidative stress is a plausible unifying principle behind the types of migraine triggers encountered in clinical practice. The possible implications for prevention and for understanding the nature of the migraine attack are discussed.

Enhancing cognitive-behavioural therapy for recurrent headache: design of a randomised controlled trial

Background

We have argued against the traditional approach of counselling avoidance of all triggers of headaches and migraine. Problems with this approach include the impossibility of avoiding all triggers and the high costs associated with trying to do so, and that avoidance could lead to reduced tolerance for the triggers. We have developed an alternative approach called Learning to Cope with Triggers (LCT) that encourages avoidance of triggers that are detrimental to health and wellbeing, but uses exposure to other triggers to desensitise headache sufferers to the triggers. This approach has been shown to be more effective than advising avoidance of all triggers. Trigger management is only one component of a comprehensive treatment program and the current study is designed to evaluate a new approach to treating headaches in which LCT has been integrated into an established cognitive-behavioural therapy (CBT) package (LCT/CBT).

Methods/Design

A target sample of 120 adult participants who suffer from migraine or tension-type headache, at least six days per month, and have done so for at least 12 months will be recruited. Participants will be randomly assigned to one of three groups: LCT/CBT; Avoid/CBT (CBT combined with instructions to avoid all triggers); and waiting-list control. Measures will include: daily diaries for recording headaches, triggers and medication consumption; headache disability and quality of life; trigger avoidance; locus of control and self-efficacy; and coping strategies. Treatment will involve 12 60-minute sessions scheduled weekly. Assessment will be completed before and after treatment, and at 4 and 12 month follow-up. The data will be analysed to determine which approach is most effective, and predictors of response to treatment.

Discussion

Migraine and tension-type headache are common and can be disabling. CBT has been demonstrated to be an efficacious treatment for both disorders. However, there is room for improvement. This study aims to increase the efficacy of behavioural approaches and identify factors predictive of a positive response.

Trial registration

Australian and New Zealand Clinical Trials Registry ACTRN12614000435684.

Emotional reactions to pain predict psychological distress in adult patients with Sickle Cell Disease (SCD)

Differentiating somatic from emotional influences on the experience of chronic pain has been of interest to clinicians and researchers for many years. Although prior research has not well specified these pathways at the anatomical level, some evidence, both theoretical and empirical, suggest that emotional reactions influence the experience of disease and non-disease-related pains. Other studies suggest that treatments directed at negative emotional responses reduce suffering associated with pain. The current study was conducted to explore the influence of emotional reactions to pain as a predictor of psychological distress in a sample of adult Blacks with Sickle Cell Disease (SCD). Using cross-sectional survey data, we evaluated whether negative emotional reactions to the experience of pain were predictive of psychological distress after controlling for the somatic dimension of pain and age in n = 67 Black patients with Sickle Cell Disease (SCD). Results showed that greater negative emotion associated with pain predicted Somatization (p < .01), Anxiety (p < .05), Phobic Anxiety (p < .05), and Psychoticism (p < .05). Increased negative emotion associated with pain was also predictive of the General Symptoms Index (p < .05) and the Positive Symptoms Total from the SCL-90-R (p < .01). We believe the current study demonstrates that negative emotional reactions to the experience of pain in adults with SCD are predictive of psychological distress above and beyond the influences of age and the direct nociceptive experience. We also believe these data to be valuable in conceptualizing the allocation of treatment resources toward a proactive approach with early identification of patients who are responding poorly for the purpose of potentially reducing later psychopathology. A deeper understanding of the ways that subpopulations cope with chronic disease-related pain may produce models that can be ultimately generalized to the consumers of the majority of healthcare resources.

Pain, mindfulness, and spirituality: A randomized controlled trial comparing effects of mindfulness and relaxation on pain-related outcomes in migraineurs

In order to examine mindfulness as an intervention for pain, 107 migraineurs, predominantly college students, were randomly assigned to brief training in standardized mindfulness, spiritualized mindfulness, and simple relaxation instructions. After 2 weeks of daily practice, participants completed the cold-pressor task while practicing their assigned technique, and their experience of the task was assessed. Among the 74 study-completers, standardized mindfulness led to significantly reduced pain-related stress relative to simple relaxation, providing modest support for the utility of mindfulness in pain management. Pain-related outcomes in the spiritualized mindfulness condition were similar to those of standardized mindfulness, though spirituality did appear to enhance mindful awareness.

Behavioral management of migraine headache triggers: learning to cope with triggers

The literature on migraine triggers is reviewed, including the most common triggers, interactions between triggers, the research evidence related to the capacity of self-reported triggers to precipitate headaches, and the neurobiologic pathways by which triggers induce migraine attacks. An argument is developed against the standard advice to avoid migraine triggers as the best way of preventing attacks, based on conceptual and practical criticisms, and consideration of cognate literatures on chronic pain, stress, and anxiety. A small number of studies suggest that exposure to headache triggers has the same effect as exposure to anxiety-eliciting stimuli, with short exposure associated with increased pain response and prolonged exposure associated with decreased pain response. On the basis of this literature, "learning to cope with triggers" is advocated, where controlled exposure and approach/confront strategies are used to manage migraine triggers, except in cases where such an approach would probably be inappropriate.

Noxious inhibition of temporal summation is impaired in chronic tension-type headache

OBJECTIVE

To examine effects of stress on noxious inhibition and temporal summation (TS) in tension-type headache.

BACKGROUND

Stress is the most commonly reported trigger of a chronic tension-type headache (CTH) episode; however, the mechanisms underlying this are unclear. Stress affects pain processing throughout the central nervous system, including, potentially, mechanisms of TS and diffuse noxious inhibitory controls (DNIC), both of which may be abnormal in CTH sufferers (CTH-S). No studies have examined TS of pressure pain or DNIC of TS in CTH-S to date. Similarly, effects of stress on TS or DNIC of TS have not been reported in healthy subjects or CTH-S to date.

METHODS

The present study measured TS and DNIC of TS in CTH-S and healthy controls (CNT) exposed to an hour-long stressful mental task, and in CTH-S exposed to an hour-long neutral condition. TS was elicited at finger and shoulder via 10 pulses from a pressure algometer, applied before and during stimulation from an occlusion cuff at painful intensity.

RESULTS

Algometer pain ratings increased more in the CTH compared with the CNT group, and were inhibited during occlusion cuff more in the CNT compared with CTH groups. Task effects on TS or DNIC were not significant.

CONCLUSIONS

The results indicate increased TS to pressure pain and impaired DNIC of TS in CTH-S. Stress does not appear to aggravate abnormal TS or DNIC mechanisms in CTH-S.

Central mechanisms of stress-induced headache

Stress is the most commonly reported trigger of an episode of chronic tension-type headache (CTTH); however, the causal significance has not been experimentally demonstrated to date. Stress may trigger CTTH through hyperalgesic effects on already sensitized pain pathways in CTTH sufferers. This hypothesis could be partially tested by examining pain sensitivity in an experimental model of stress-induced headache in CTTH sufferers. Such examinations have not been reported to date. We measured pericranial muscle tenderness and pain thresholds at the finger, head and shoulder in 23 CTTH sufferers (CTH-S) and 25 healthy control subjects (CNT) exposed to an hour-long stressful mental task, and in 23 CTTH sufferers exposed to an hour-long neutral condition (CTH-N). Headache developed in 91% of CTH-S, 4% of CNT, and 17% of CTH-N subjects. Headache sufferers had increased muscle tenderness and reduced pain thresholds compared with healthy controls. During the task, muscle tenderness increased and pain thresholds decreased in the CTH-S group compared with CTH-N and CNT groups. Pre-task muscle tenderness and reduction in pain threshold during task were predictive of the development and intensity of headache following task. The main findings are that stress induced a headache in CTTH sufferers, and this was associated with pre-task muscle tenderness and stress-induced reduction in pain thresholds. The results support the hypothesis that stress triggers CTTH through hyperalgesic effects on already increased pain sensitivity in CTTH sufferers, reducing the threshold to noxious input from pericranial structures.

Cognitive-behavioral therapy versus temporal pulse amplitude biofeedback training for recurrent headache

Sixty-four headache sufferers were allocated randomly to cognitive-behavioral therapy (CBT), temporal pulse amplitude (TPA) biofeedback training, or waiting-list control. Fifty-one participants (14M/37F) completed the study, 30 with migraine and 21 with tension-type headache. Treatment consisted of 8, 1-hour sessions. CBT was highly effective, with an average reduction in headaches from pre- to posttreatment of 68%, compared with 56% for biofeedback, and 20% for the control condition. Headaches continued to decrease to 12 month follow-up for CBT. Improvement with CBT was associated with baseline coping skills, social support, and physiological measures at rest and in response to stress, particularly TPA. Changes on some of these measures were correlated with changes in headaches. No significant predictors of response to biofeedback emerged.

Noise as a Trigger for Headaches: Relationship Between Exposure and Sensitivity

OBJECTIVE

This study investigated how triggers acquire the capacity to precipitate headaches.

BACKGROUND

Traditional clinical advice is that the best way to prevent headache/migraine is to avoid the triggers. Avoidance of anxiety-eliciting stimuli, however, results in sensitization to the stimuli, so is there a danger that avoidance of migraine/headache triggers results in decreased tolerance for the triggers?

DESIGN

One hundred and fifty subjects, 60 of whom suffered from regular headaches, were randomly assigned to 5 experimental conditions, defined by length of exposure to the headache trigger of noise.

METHODS

Subjects attended a laboratory session divided into 3 phases: preintervention test, intervention (1 of 5 levels of exposure to the trigger), and postintervention test. Response to the intervention was measured in terms of noise tolerance, sensitivity to noise, and nociceptive response to noise.

RESULTS

A curvilinear relationship was found between length of exposure to the trigger and pain response for individuals who do not suffer from regular headaches, that is, short exposure was associated with sensitization and prolonged exposure with desensitization. The relationship for headache patients was less clear.

CONCLUSIONS

The findings are consistent with the proposition that 1 etiological pathway to suffering from frequent headaches is via trying to avoid, or escape from, potential trigger factors. These results suggest that the traditional clinical advice to headache patients, that the best way to prevent migraine/headache is to avoid the triggers, runs the risk of establishing an insidious sensitization process thereby increasing headache frequency.

Effects of Noise and a Stressor on Head Pain

OBJECTIVE

Can causal relationships be established between negative affect (NA) and headaches, and noise (N) and headaches? Do NA and N interact to cause headaches? Do NA and N cause headaches by means of the same or different physiological mechanisms? Are the answers to these questions a function of diagnostic status?

BACKGROUND

A functional model of chronic headaches has been proposed that seeks to understand the variance in headaches by focusing on the controlling variables, that is, the antecedents and consequences. This study is one in a series investigating the immediate antecedents of headaches, namely the trigger factors.

DESIGN

Twenty-four subjects with migraine and 44 subjects with tension-type headache were randomly assigned to one of four experimental conditions defined by the presence or absence of two antecedent challenges, a stressor (S) designed to induce NA and N.

METHODS

The S challenge consisted of difficult-to-solve anagrams accompanied by failure feedback. The N challenge consisted of 50 dB of white N. Laboratory sessions were divided into adaptation, baseline, challenge, and recovery phases. Responses were measured in terms of headache intensity ratings, forehead electromyographic activity, heart rate, blood pressure, and temporal pulse amplitude (TPA).

RESULTS AND CONCLUSIONS

Both NA and N precipitated headaches. These two factors did not interact in triggering headaches. Headaches induced by N were associated with elevated TPA but headaches induced by NA were not associated with significant physiological changes. Diagnosis was not related to any of the outcomes.

The relationship between anger and pain

Anger is defined with reference to a cognitive-motivational perspective. This forms the basis for identifying the variety of reasons why pain sufferers are angry and the many ways in which they react when angry. Statistics are provided for the comorbidity of anger in chronic pain and headache. Going beyond such statistics, five dynamic interactions between anger and pain are emphasized and empirical evidence is provided for each of these interactions.

A brief review of the pathophysiology, associated pain, and psychosocial issues in sickle cell disease

Sickle cell disease (SCD) is the most common genetic disorder of the blood. The disease produces significantly abnormal hemoglobin (Hgb) molecules in red blood cells (RBCs). The sickling of RBCs occurs when partially or totally deoxygenated Hgb molecules distort their normal disk shape, producing stiff, sticky, sickle-shaped cells that obstruct small blood vessels and produce vasoocclusion as well as the disruption of oxygen to body tissues. Because tissue damage can occur at multiple foci, patients with SCD are at risk for other medical complications including, but not limited to, delayed growth and sexual maturation; acute and chronic pulmonary dysfunction; stroke; aseptic necrosis of the hip, shoulders, or both; sickle cell retinopathy; dermal ulcers; and severe chronic pain. The chronicity of the illness combined with frequent hospitalizations for pain and other medical management can contribute significantly to impaired psychosocial functioning, altered intra- and interpersonal relationships, and reduced quality of life. Unlike previous qualitative reviews of SCD, this article describes the relevant clinical and research data on the relation between psychosocial functioning and SCD in adult and child populations. The authors discuss the significant role of psychosocial issues in the trajectory and management of the disease and conclude that understanding the pathophysiology of SCD without thoroughly understanding the equally important psychosocial influences is misunderstanding SCD.

Human lateral geniculate nucleus and visual cortex respond to screen flicker

The first electrophysiological study of the human lateral geniculate nucleus (LGN), optic radiation, striate, and extrastriate visual areas is presented in the context of presurgical evaluation of three epileptic patients (Patients 1, 2, and 3). Visual-evoked potentials to pattern reversal and face presentation were recorded with depth intracranial electrodes implanted stereotactically. For Patient 1, electrode anatomical registration, structural magnetic resonance imaging, and electrophysiological responses confirmed the location of two contacts in the geniculate body and one in the optic radiation. The first responses peaked approximately 40 milliseconds in the LGN in Patient 1 and 60 milliseconds in the V1/V2 complex in Patients 2 and 3. Moreover, steady state visual-evoked potentials evoked by the unperceived but commonly experienced video-screen flicker were recorded in the LGN, optic radiation, and V1/V2 visual areas. This study provides topographic and temporal propagation characteristics of steady state visual-evoked potentials along human visual pathways. We discuss the possible relationship between the oscillating signal recorded in subcortical and cortical areas and the electroencephalogram abnormalities observed in patients suffering from photosensitive epilepsy, particularly video-game epilepsy. The consequences of high temporal frequency visual stimuli delivered by ubiquitous video screens on epilepsy, headaches, and eyestrain must be considered.

What is the evolutionary advantage of migraine?

Susceptibility to migraine is determined by genetic factors and is therefore subject to the forces of natural selection. Migraine is a common and ancient disorder whose prevalence may be increasing, suggesting that a migraine-prone nervous system may be associated with reproductive or survival advantages. Five evolutionary explanations are reviewed that might account for the persistence of migraine: (i). migraine as a defence mechanism; (ii). migraine as a result of conflict with other organisms; (iii). migraine as result of novel environmental factors; (iv). migraine as a trade-off between genetic harms and benefits; and (v). migraine as a design constraint. An evolutionary perspective on migraine allows the generation of important hypotheses about the disorder and suggests rewarding possibilities for further research.

Transient visual disturbances during migraine without aura attacks

OBJECTIVE

To evaluate the prevalence and clinical features of transient visual disturbances (TVDs) during migraine without aura (MO) attacks and to point out any similarities with the disturbances listed among the diagnostic criteria of the International Headache Society (IHS) classification for migraine with aura (MA).

METHODS

We studied a sample of 191 patients (145 women and 46 men) with MO and no other associated forms of primary headache who had been referred to the University of Parma Headache Centre between December 1, 1999 and December 1, 2000.

RESULTS

A total of 165 patients reported that they had never experienced TVDs during their MO attacks. In the remaining 26 patients (19 women and 7 men), MO attacks were at times accompanied by TVDs, which were present in over 30% of MO attacks in 65.4% of patients. In about 60% of cases, TVDs lasted less than half a minute. TVDs consisted of phosphenes in most patients, general blurring of vision in about one-fourth, and scintillating scotomas in 15%. In 73% of cases, TVDs occurred during the headache phase, whereas in the remainder they preceded it. Strict application of the IHS diagnostic criteria would have led to a diagnosis of MA in 12 cases, corresponding to 46% of our MO patients with TVDs and to 6.3% of all patients with an established clinical diagnosis of MO.

CONCLUSION

The results of our study suggest that current IHS diagnostic criteria for MA may lead to an overestimation of MA cases.

How do trigger factors acquire the capacity to precipitate headaches?

This study tested two contrasting theories of how trigger factors acquire the capacity to precipitate headaches. The sample consisted of 110 participants, of whom 48 suffered from regular headaches. Participants were exposed to a validated headache trigger factor for one of five exposure durations. The trigger used was "visual disturbance" (flicker, glare and eyestrain) induced by a very bright, stroboscopic light. Response to the stimulus was measured by participant ratings of the degree of visual disturbance and head pain caused by the stimulus. As expected, the headache sufferers experienced more visual disturbance and head pain in response to the stimulus than the non-headache individuals. Longer exposure to the stimulus was associated with a subsequent reduction in pain ratings in response to the stimulus. This desensitization effect supported an avoidance model of how trigger factors acquire the capacity to precipitate headaches. The findings of this study have implications for the etiology of headache disorders. Also, the findings imply that the traditional clinical advice that the best way to prevent migraine and headache is to avoid the factors that trigger them, may be counterproductive, as any short-term gains may be more than wiped out by decreased tolerance for the trigger factors.