Motion Processing Deficits in Migraine

Balance disorders and migraine

BACKGROUND

Migraine is associated with motion sensitivity symptoms such as kinetosis, vestibular symptoms and balance alterations. While focus is given to headache management, addressing these symptoms is often neglected, although they are related to additional migraine burden and increased disability.

PURPOSE

Our aim is to disseminate the current understanding of the motion sensitivity symptoms among patients with migraine, with focus on balance impairments. We discuss the susceptibility of migraine to motion sensitivity, its suggested mechanisms, the balance alterations during quiet standing, mobility tasks and reactions to external perturbations. The role of migraine subdiagnosis, implications for clinical practice and future perspectives are also acknowledged.

IMPLICATIONS

Balance disorders are one of the signs reflecting a broader and complex spectrum of motion sensitivity, which are present even between attacks. Migraineurs are especially inherent to these symptoms probably due to brain hyperexcitability and to shared pathophysiological mechanisms. Patients, especially with aura and chronic migraine, exhibit balance instability during quiet standing under different surface and visual input conditions. Migraineurs demonstrated reduced limits of stability and lower performance on walk, transposing obstacles and sit to stand tasks. Only patients with aura present impairment of motor control reactions following external perturbations. Balance alterations are associated with falls and are influenced by aura, migraine frequency and psychosocial aspects, but not by vestibular symptoms or vestibular migraine diagnosis. There is a high demand for high quality of evidence regarding the assessment and care of motion sensitivity symptoms in migraineurs, considering approaches to manage not just the pain, but its associated symptoms.

Visual Motion and Decision-Making in Dyslexia: Reduced Accumulation of Sensory Evidence and Related Neural Dynamics

Children with and without dyslexia differ in their behavioral responses to visual information, particularly when required to pool dynamic signals over space and time. Importantly, multiple processes contribute to behavioral responses. Here we investigated which processing stages are affected in children with dyslexia when performing visual motion processing tasks, by combining two methods that are sensitive to the dynamic processes leading to responses. We used a diffusion model which decomposes response time and accuracy into distinct cognitive constructs, and high-density EEG. Fifty children with dyslexia (24 male) and 50 typically developing children (28 male) 6-14 years of age judged the direction of motion as quickly and accurately as possible in two global motion tasks (motion coherence and direction integration), which varied in their requirements for noise exclusion. Following our preregistered analyses, we fitted hierarchical Bayesian diffusion models to the data, blinded to group membership. Unblinding revealed reduced evidence accumulation in children with dyslexia compared with typical children for both tasks. Additionally, we identified a response-locked EEG component which was maximal over centro-parietal electrodes which indicated a neural correlate of reduced drift rate in dyslexia in the motion coherence task, thereby linking brain and behavior. We suggest that children with dyslexia tend to be slower to extract sensory evidence from global motion displays, regardless of whether noise exclusion is required, thus furthering our understanding of atypical perceptual decision-making processes in dyslexia.SIGNIFICANCE STATEMENT Reduced sensitivity to visual information has been reported in dyslexia, with a lively debate about whether these differences causally contribute to reading difficulties. In this large preregistered study with a blind modeling approach, we combine state-of-the art methods in both computational modeling and EEG analysis to pinpoint the stages of processing that are atypical in children with dyslexia in two visual motion tasks that vary in their requirement for noise exclusion. We find reduced evidence accumulation in children with dyslexia across both tasks, and identify a neural marker, allowing us to link brain and behavior. We show that children with dyslexia exhibit general difficulties with extracting sensory evidence from global motion displays, not just in tasks that require noise exclusion.

Visual stress responses to static images are associated with symptoms of Persistent Postural Perceptual Dizziness (PPPD)

BACKGROUND

Images that deviate from natural scene statistics in terms of spatial frequency and orientation content can produce visual stress (also known as visual discomfort), especially for migraine sufferers. These images appear to over-activate the visual cortex.

OBJECTIVE

To connect the literature on visual discomfort with a common chronic condition presenting in neuro-otology clinics known as persistent postural perceptual dizziness (PPPD). Patients experience dizziness when walking through highly cluttered environments or when watching moving stimuli. This is thought to arise from maladaptive interaction between vestibular and visual signals for balance.

METHODS

We measured visual discomfort to stationary images in patients with PPPD (N = 30) and symptoms of PPPD in a large general population cohort (N = 1858) using the Visual Vertigo Analogue Scale (VVAS) and the Situational Characteristics Questionnaire (SCQ).

RESULTS

We found that patients with PPPD, and individuals in the general population with more PPPD symptoms, report heightened visual discomfort to stationary images that deviate from natural spectra (patient comparison, F (1, 1865) = 29, p < 0.001; general population correlations, VVAS, rs (1387) = 0.46, p < 0.001; SCQ, rs (1387) = 0.39, p < 0.001). These findings were not explained by co-morbid migraine. Indeed, PPPD symptoms showed a significantly stronger relationship with visual discomfort than did migraine (VVAS, zH = 8.81, p < 0.001; SCQ, zH = 6.29, p < 0.001).

CONCLUSIONS

We speculate that atypical visual processing -perhaps due to a visual cortex more prone to over-activation -may predispose individuals to PPPD, possibly helping to explain why some patients with vestibular conditions develop PPPD and some do not.

Improvement in visual perception after high-frequency transcranial random noise stimulation (hf-tRNS) in those with migraine: An equivalent noise approach

Migraine is a common neurological disorder with strong links to vision. Interictal migraine is thought to be characterised by internal noise in the brain, possibly due to increased variability in neural firing, which can be estimated using equivalent noise tasks. High-frequency transcranial random noise stimulation (hf-tRNS) can be used to modulate levels of internal noise in the brain, and so presents a possible therapy to redress noise levels in the migraine brain. This is a case-control study using a 2-alternative forced choice (2AFC) design. Hf-tRNS and Sham control stimulation were used alongside a global motion direction discrimination task and visually based equivalent noise tasks. The migraine group demonstrated increased baseline internal noise levels compared to the control group. Internal noise levels, and sampling, were reduced using hf-tRNS but not Sham stimulation. However, there were no differences in terms of coherence thresholds, slopes, and lapse rate for global motion discrimination between the two groups. This is the first demonstration of the possibility of decreasing internal noise levels in migraine using hf-tRNS. Future work could explore the possibility of neurostimulation as a therapy for migraine.

Brain Processing of Visual Self-Motion Stimuli in Patients With Migraine: An fMRI Study

OBJECTIVE

To investigate the behavioral and neuronal responses of patients with migraine to a visual simulation of self-motion through a virtual roller coaster ride in comparison to controls.

METHODS

Twenty consecutive patients with migraine from a university-based hospital headache clinic and 20 controls were included. Participants underwent an experiment where a visually displayed self-motion paradigm was presented based on customized roller coaster videos during fMRI. Within each video, blocks of motion stimulation were interleaved with low-speed upward motion in a random order. In the scanning intervals and after the experiment, participants rated their perceived level of vestibular symptoms and motion sickness during the videos. We hypothesized that patients with migraine will perceive more motion sickness and that it correlates with different central processing and brain responses.

RESULTS

Compared to controls, patients with migraine reported more dizziness (65% vs 30%; p = 0.03) and motion sickness (Simulator Sickness Questionnaire score 47.3 [95% confidence interval (CI), 37.1, 57.5] vs 24.3 [95% CI, 18.2, 30.4]) as well as longer symptom duration (01:19 minutes [95% CI, 00:51, 01:48] vs 00:27 minutes [95% CI, 00:03, 00:51]) and intensity (visual analogue scale score 0-100, 22.0 [95% CI, 14.8, 29.2] vs 9.9 [95% CI, 4.9, 14.7]) during the virtual roller coaster ride. Neuronal activity in patients with migraine was more pronounced in clusters within the superior (contrast estimate 3.005 [90% CI, 1.817, 4.194]) and inferior occipital gyrus (contrast estimate 1.759 [90% CI, 1.062, 2.456]), pontine nuclei (contrast estimate 0.665 [90% CI, 0.383, 0.946]), and within the cerebellar lobules V/VI (contrast estimate 0.672 [90% CI, 0.380, 0.964]), while decreased activity was seen in the cerebellar lobule VIIb (contrast estimate 0.787 [90% CI, 0.444, 1.130]) and in the middle frontal gyrus (contrast estimate 0.962 [90% CI, 0.557, 1.367]). These activations correlated with migraine disability (r = -0.46, p = 0.04) and motion sickness scores (r = 0.32, p = 0.04). We found enhanced connectivity between the pontine nuclei, cerebellar areas V/VI, and interior and superior occipital gyrus with numerous cortical areas in patients with migraine but not in controls.

CONCLUSIONS

Migraine is related to abnormal modulation of visual motion stimuli within superior and inferior occipital gyrus, middle frontal gyrus, pontine nuclei, and cerebellar lobules V, VI, and VIIb. These abnormalities relate to migraine disability and motion sickness susceptibility.

No Evidence of Reduced Contrast Sensitivity in Migraine-with-Aura for Large, Narrowband, Centrally Presented Noise-Masked Stimuli

Individuals with migraine aura show differences in visual perception compared to control groups. Measures of contrast sensitivity have suggested that people with migraine aura are less able to exclude external visual noise, and that this relates to higher variability in neural processing. The current study compared contrast sensitivity in migraine with aura and control groups for narrow-band grating stimuli at 2 and 8 cycles/degree, masked by Gaussian white noise. We predicted that contrast sensitivity would be lower in the migraine with aura group at high noise levels. Contrast sensitivity was higher for the low spatial frequency stimuli, and decreased with the strength of the masking noise. We did not, however, find any evidence of reduced contrast sensitivity associated with migraine with aura. We propose alternative methods as a more targeted assessment of the role of neural noise and excitability as contributing factors to migraine aura.

Investigating the Interaction Between Form and Motion Processing: A Review of Basic Research and Clinical Evidence

A widely held view of the visual system supported the perspective that the primate brain is organized in two main specialized streams, called the ventral and dorsal streams. The ventral stream is known to be involved in object recognition (e.g., form and orientation). In contrast, the dorsal stream is thought to be more involved in spatial recognition (e.g., the spatial relationship between objects and motion direction). Recent evidence suggests that these two streams are not segregated but interact with each other. A class of visual stimuli known as Glass patterns has been developed to shed light on this process. Glass patterns are visual stimuli made of pairs of dots, called dipoles, that give the percept of a specific form or apparent motion, depending on the spatial and temporal arrangement of the dipoles. In this review, we show an update of the neurophysiological, brain imaging, psychophysical, clinical, and brain stimulation studies which have assessed form and motion integration mechanisms, and the level at which this occurs in the human and non-human primate brain. We also discuss several studies based on non-invasive brain stimulation techniques that used different types of visual stimuli to assess the cortico-cortical interactions in the visual cortex for the processing of form and motion information. Additionally, we discuss the timing of specific visual processing in the ventral and dorsal streams. Finally, we report some parallels between healthy participants and neurologically impaired patients in the conscious processing of form and motion.

Illusory Motion Perception Is Associated with Contrast Discrimination but Not Motion Sensitivity, Self-Reported Visual Discomfort, or Migraine Status

Purpose

Altered visual processing of motion and contrast has been previously reported in people with migraine. One possible manifestation of this altered visual processing is increased self-reported susceptibility to visual illusions of contrast and motion. Here, we use the Fraser–Wilcox illusion to explore individual differences in motion illusion strength in people with and without migraine. The motion-inducing mechanisms of the Fraser–Wilcox illusion are purported to be contrast dependent. To better understand the mechanisms of the illusion, as well as visual processing anomalies in migraine, we explored whether migraine status, susceptibility to visual discomfort, contrast discrimination, or motion sensitivity are related to quantified motion illusion strength.

Methods

Thirty-six (16 with aura, 20 without aura) people with migraine and 20 headache-free controls participated. Outcome measures were motion illusion strength (the physical motion speed that counterbalanced the illusory motion), motion sensitivity, and contrast discrimination thresholds (measured for each contrast pair that formed part of the illusory motion stimulus). Typical daily visual discomfort was self-reported via questionnaire.

Results

Motion illusion strength was negatively correlated with contrast discrimination threshold (r = –0.271, P = 0.04) but was not associated with motion sensitivity or migraine status. People with migraine with aura reported experiencing visual discomfort more frequently than the control group (P = 0.001). Self-reported visual discomfort did not relate to quantified perceptual motion illusion strength.

Conclusions

Individuals with better contrast discrimination tend to perceive faster illusory motion regardless of migraine status.

Exploration of anomalous perceptual experiences in migraine between attacks using the Cardiff Anomalous Perceptions Scale

Distortions in sensory experiences that precede a migraine attack have been extensively documented, the most well-known being the visual aura. Distortions in the experience of other senses are also reported as part of an aura, albeit less frequently, together with changes in the perception or ownership of the body or body parts. There are many examples of differences in aspects of visual perception between migraine and control groups, between attacks, but not as much on unusual experiences involving other senses, the sense of the body or the experience of the environment. Seventy-seven migraine (33 with aura) and 74 control participants took part. Anomalous perceptions were experienced by both migraine and control groups, but more with migraine experienced them and rated them as more distressing, intrusive and frequent. Associations with reports of visual triggers of migraine and visual discomfort are presented. This study is the first to show relationships between these factors.

Tracking the Migraine Cycle Using Visual Tasks

There are a number of reports that perceptual, electrophysiological and imaging measures can track migraine periodicity. As the electrophysiological and imaging research requires specialist equipment, it has few practical applications. This study sought to track changes in performance on four visual tasks over the migraine cycle. Coherence thresholds were measured for two motion and two orientation tasks. The first part of the study confirmed that the data obtained from an online study produced comparable results to those obtained under controlled laboratory conditions. Thirteen migraine with aura, 12 without aura, and 12 healthy controls participated. The second part of the study showed that thresholds for discriminating vertical coherent motion varied with the migraine cycle for a majority of the participants who tested themselves multiple times (four with aura, seven without). Performance improved two days prior to a migraine attack and remained improved for two days afterwards. This outcome is as expected from an extrapolation of earlier electrophysiological research. This research points to the possibility of developing sensitive visual tests that patients can use at home to predict an impending migraine attack and so take steps to try to abort it or, if it is inevitable, to plan their lives around it.

Physical therapy and migraine: musculoskeletal and balance dysfunctions and their relevance for clinical practice

BACKGROUND

Migraine is a primary headache with high levels of associated disability that can be related to a variety of symptoms and comorbidities. The role of physical therapy in the management of migraine is largely unknown. Therefore, the aim of this review is to highlight and critically discuss the current literature and evidence for physical therapy interventions in individuals with migraines.

METHODS

A narrative review of the literature was performed.

RESULTS

Physical therapists assessing and treating patients with migraine should focus on two primary aspects: (1) musculoskeletal dysfunctions, and (2) vestibular symptoms/postural control impairment. Signs and symptoms of musculoskeletal and/or vestibular dysfunctions are prevalent among individuals with migraines and different disability levels can be observed depending on the presence of aura or increment of the migraine attacks.

CONCLUSION

A proper physical examination and interview of the patients will lead to a tailored treatment plan. The primary aim regarding musculoskeletal dysfunctions is to reduce pain and sensitization, and physical therapy interventions may include a combination of manual therapy, exercise therapy, and education. The aim regarding postural control impairment is to optimize function and reduce vestibular symptoms, and interventions should include balance exercises and vestibular rehabilitation. However, consistent evidence of benefits is still lacking due to the lack of and therefore need for tailored and pragmatic clinical trials with high methodological quality.

A Review of Motion and Orientation Processing in Migraine

Visual tests can be used as noninvasive tools to test models of the pathophysiology underlying neurological conditions, such as migraine. They may also be used to track changes in performance that vary with the migraine cycle or can track the efficacy of prophylactic treatments. This article reviews the literature on performance differences on two visual tasks, global motion discrimination and orientation, which, of the many visual tasks that have been used to compare differences between migraine and control groups, have yielded the most consistent patterns of group differences. The implications for understanding the underlying pathophysiology in migraine are discussed, but the main focus is on bringing together disparate areas of research and suggesting those that can reveal practical uses of visual tests to treat and manage migraine.

Temporal Integration of Motion Streaks in Migraine

Migraine is associated with differences in visual perception, specifically, deficits in the perception of motion. Migraine groups commonly show poorer performance (higher thresholds) on global motion tasks compared to control groups. Successful performance on a global motion task depends on several factors, including integrating signals over time. A "motion streak" task was used to investigate specifically integration over time in migraine and control groups. The motion streak effect depends on the integration of a moving point over time to create the illusion of a line, or "streak". There was evidence of a slower optimum speed for eliciting the motion streak effect in migraine compared to control groups, suggesting temporal integration is different in migraine. In addition, performance on the motion streak task showed a relationship with headache frequency.

Perception of facial expressions of emotion in migraine

Both lower-level perceptual changes and especially higher-level cognitive alterations in individuals with migraine are poorly understood. Here, we behaviorally and electrophysiologically investigated the perception of emotional facial expressions in migraine. Young female individuals with migraine and healthy controls watching neutral faces gradually shifting to either happy, fearful, or angry expressions were asked to classify the facial expressions as quickly and accurately as possible by pressing a corresponding button, and to keep looking at the face until the last frame disappeared. Migraine individuals, compared to healthy controls, had a reduced habituation in the N170 time interval towards a gradually emerging emotional expression. The early P1, the early posterior negativity (EPN), and the late positive potential (LPP) amplitudes were not statistically different between groups and among expressions. The mean reaction time for recognizing an expression did not differ between groups and it was not at a cost of more incorrect responses. Interestingly, the amplitude of the early posterior negativity correlated negatively with the time interval since the last attack. It is concluded that young female individuals with migraine, compared to healthy controls, do not show a biased emotional facial processing toward positive or negative expressions.

Practice makes the deficiency of global motion detection in people with pattern-related visual stress more apparent

Aims

Pattern-related visual stress (PRVS) refers to the perceptual difficulties experienced by some individuals when exposed to high contrast striped patterns. People with PRVS were reported to have reduced sensitivity to global motion at baseline testing and the difference disappears at a second estimate. The present study was to investigate the effect of practice on global motion threshold in adults with and without PRVS.

Methods

A total of 101 subjects were recruited and the Wilkins & Evans Pattern Glare Test was used to determine if a subject had PRVS. The threshold to detect global motion was measured with a random dot kinematogram. Each subject was measured 5 times at the first visit and again a month later. Receiver operating characteristic (ROC) curve analysis was applied to show the agreement between the two tests.

Results

Twenty-nine subjects were classified as having PRVS and 72 were classified as normal. At baseline, the threshold to detect global motion was significantly higher in subjects with PRVS (0.832 ± 0.098 vs. 0.618 ± 0.228, p < 0.001). After 5 sessions, the difference between the normal and subjects with PRVS increased (0.767 ± 0.170 vs. 0.291 ± 0.149, p < 0.001). In ROC analysis, the area under the curve (AUC) improved from 0.792 at baseline to 0.964 at the fifth session. After a one-month break, the difference between normal and subjects with PRVS was still significant (0.843 ± 0.169 vs. 0.407 ± 0.216, p < 0.001) and the AUC was 0.875.

Conclusion

The ability to detect global motion is impaired in persons with PRVS and the difference increased after additional sessions of practice.

Volumetric brain changes in migraineurs from the general population

OBJECTIVE

To assess volumetric brain changes in migraineurs from the general population compared with controls.

METHODS

Structural brain changes in migraineurs from the general population-based MRI Cerebral Abnormalities in Migraine, an Epidemiologic Risk Analysis (CAMERA)-2 observational cohort study were assessed by state-of-the-art voxel-based morphometry. T1-weighted MRIs of 84 migraineurs (52 with aura, 32 without aura) and 35 headache-free controls were evaluated. Regional volumes were compared voxelwise, corrected for age, sex, and total intracranial volume, with region-of-interest and whole-brain analyses.

RESULTS

In region-of-interest analyses, migraineurs showed decreased gray matter volume in the visual areas V3 and V5 of the right occipital cortex compared to controls (p < 0.05, familywise error correction). Post hoc analyses revealed that similar changes were present regardless of migraine aura status, disease activity (>1 year attack-free [inactive] vs ≥1 attack within the last year [active] and attack frequency [≤1 (low) vs ≥1 attack per month [high]). In exploratory whole-brain analyses (p < 0.001, uncorrected for multiple comparisons), we identified additional structural differences in migraineurs in other cortical and subcortical areas, including white matter tracts, that are particularly involved in visual processing.

CONCLUSIONS

Migraineurs from the general population showed small volumetric brain changes, mainly in cortical areas involved in visual motion processing, compared to controls. The presence of morphologic changes regardless of the presence of migraine aura or disease activity suggests that migraines with and without aura share common pathophysiologic pathways and suggests that these changes are (partially) irreversible or might have been present throughout life.

Assessment of gray and white matter structural alterations in migraineurs without aura

Background

Migraine constitute a disorder characterized by recurrent headaches, and have a high prevalence, a high socio-economic burden and severe effects on quality of life. Our previous fMRI study demonstrated that some brain regions are functional alterations in migraineurs. As the function of the human brain is related to its structure, we further investigated white and gray matter structural alterations in migraineurs.

Methods

In current study, we used surface-based morphometry, voxel-based morphometry and diffusion tensor imaging analyses to detect structural alterations of the white matter and gray matter in 32 migraineurs without aura compared with 32 age- and gender-matched healthy controls.

Results

We found that migraineurs without aura exhibited significantly increased gray matter volume in the bilateral cerebellar culmen, increased cortical thickness in the lateral occipital-temporal cortex, decreased cortical thickness in the right insula, increased gyrification index in left postcentral gyrus, superior parietal lobule and right lateral occipital cortex, and decreased gyrification index in the left rostral middle frontal gyrus compared with controls. No significant change in white matter microstructure was found in DTI analyses.

Conclusion

The significantly altered gray matter brain regions were known to be associated with sensory discrimination of pain, multi-sensory integration and nociceptive information processing and were consistent with our previous fMRI study, and may be involved in the pathological mechanism of migraine without aura.

Increased intrinsic brain connectivity between pons and somatosensory cortex during attacks of migraine with aura

The neurological disturbances of migraine aura are caused by transient cortical dysfunction due to waves of spreading depolarization that disrupt neuronal signaling. The effects of these cortical events on intrinsic brain connectivity during attacks of migraine aura have not previously been investigated. Studies of spontaneous migraine attacks are notoriously challenging due to their unpredictable nature and patient discomfort. We investigated 16 migraine patients with visual aura during attacks and in the attack-free state using resting state fMRI. We applied a hypothesis-driven seed-based approach focusing on cortical visual areas and areas involved in migraine pain, and a data-driven independent component analysis approach to detect changes in intrinsic brain signaling during attacks. In addition, we performed the analyses after mirroring the MRI data according to the side of perceived aura symptoms. We found a marked increase in connectivity during attacks between the left pons and the left primary somatosensory cortex including the head and face somatotopic areas (peak voxel: P = 0.0096, (x, y, z) = (-54, -32, 32), corresponding well with the majority of patients reporting right-sided pain. For aura-side normalized data, we found increased connectivity during attacks between visual area V5 and the lower middle frontal gyrus in the symptomatic hemisphere (peak voxel: P = 0.0194, (x, y, z) = (40, 40, 12). The present study provides evidence of altered intrinsic brain connectivity during attacks of migraine with aura, which may reflect consequences of cortical spreading depression, suggesting a link between aura and headache mechanisms. Hum Brain Mapp 38:2635-2642, 2017. © 2017 Wiley Periodicals, Inc.

Visual processing in migraine

Background

Migraine is a common neurological condition that often involves differences in visual processing. These sensory processing differences provide important information about the underlying causes of the condition, and for the development of treatments.

Review of psychophysical literature

Psychophysical experiments have shown consistent impairments in contrast sensitivity, orientation acuity, and the perception of global form and motion. They have also established that the addition of task-irrelevant visual noise has a greater effect, and that surround suppression, masking and adaptation are all stronger in migraine.

Theoretical signal processing model

We propose utilising an established model of visual processing, based on signal processing theory, to account for the behavioural differences seen in migraine. This has the advantage of precision and clarity, and generating clear, falsifiable predictions.

Conclusion

Increased effects of noise and differences in excitation and inhibition can account for the differences in migraine visual perception. Consolidating existing research and creating a unified, defined theoretical account is needed to better understand the disorder.

Motion Perception in Migraineurs: Abnormalities are Not Related to Attention

Migraine groups have impaired ability to identify global motion direction in noisy random dot stimuli, an observation that has been used as evidence for cortical hyperexcitability. Several studies have also suggested abnormalities in cognitive processing, particularly in the domains of attention, visuo-spatial processing and memory. This study aimed to determine whether poor performance by migraineurs in motion coherence tasks could be explained by non-visual cognitive factors such as attention. Twenty-nine migraineurs and 27 non-headache controls participated. Global motion coherence thresholds were measured along with measures of neuropsychological function, using the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS). The migraine group had significantly higher motion coherence thresholds than controls. No significant difference in attention or any other RBANS index score was found between groups. Index scores did not correlate with motion perception thresholds. This study does not support inattention or other cognitive abnormality as an explanation for motion perception anomalies in migraine.

Visual motion processing in migraine: Enhanced motion after-effects are related to display contrast, visual symptoms, visual triggers and attack frequency

Background Visual after-effects are illusions that occur after prolonged viewing of visual displays. The motion after-effect (MAE), for example, is an illusory impression of motion after viewing moving displays: subsequently, stationary displays appear to drift in the opposite direction. After-effects have been used extensively in basic vision research and in clinical settings, and are enhanced in migraine. Objective The objective of this article is to assess associations between ( 1 ) MAE duration and visual symptoms experienced during/between migraine/headache attacks, and ( 2 ) visual stimuli reported as migraine/headache triggers. Methods The MAE was elicited after viewing motion for 45 seconds. MAE duration was tested for three test contrast displays (high, medium, low). Participants also completed a headache questionnaire that included migraine/headache triggers. Results For each test contrast, the MAE was prolonged in migraine. MAE duration was associated with photophobia; visual triggers (flicker, striped patterns); and migraine or headache frequency. Conclusions Group differences on various visual tasks have been attributed to abnormal cortical processing in migraine, such as hyperexcitability, heightened responsiveness and/or a lack of intra-cortical inhibition. The results are not consistent with hyperexcitability simply from a general lack of inhibition. Alternative multi-stage models are discussed and suggestions for further research are recommended, including visual tests in clinical assessments/clinical trials.

No difference in cross-modal attention or sensory discrimination thresholds in autism and matched controls

Autism has been associated with abnormalities in sensory and attentional processing. Here, we assessed these processes independently in the visual and auditory domains using a visual contrast-discrimination task and an auditory modulation-depth discrimination task. To evaluate changes in sensory function by attention, we measured behavioral performance (discrimination accuracy) when subjects were cued to attend and respond to the same stimulus (frequent valid cue) or cued to attend to one stimulus and respond to the non-cued stimulus (infrequent invalid cue). The stimuli were presented at threshold to ensure equal difficulty across participants and groups. Results from fifteen high-functioning adult individuals with autism and fifteen matched controls revealed no significant differences in visual or auditory discrimination thresholds across groups. Furthermore, attention robustly modulated performance accuracy (performance was better for valid than invalid cues) in both sensory modalities and to an equivalent extent in both groups. In conclusion, when using this well-controlled method, we found no evidence of atypical sensory function or atypical attentional modulation in a group of high functioning individuals with clear autism symptomatology.

Attentional Network Differences Between Migraineurs and Non-migraine Controls: fMRI Evidence

Migraine is a headache disorder characterized by sensitivity to light and sound. Recent research has revealed abnormal visual-spatial attention in migraineurs in between headache attacks. Here, we ask whether these attentional abnormalities can be attributed to specific regions of the known attentional network to help characterize the abnormalities in migraine. Specifically, the ventral frontoparietal network of attention is involved with assessing the behavioural relevance of unattended stimuli. Given the decreased suppression of unattended stimuli reported in migraineurs, we hypothesized that migraineurs would have abnormal processing in the ventral portion of the frontoparietal network of attention. To address this, we used functional magnetic resonance imaging to assess the attentional control networks during visual spatial-orienting tasks in migraineurs (N = 16) as compared to non-migraine controls (N = 16). We employed two visual orienting paradigms with target discrimination tasks: (1) voluntary orienting to central arrow cues, and (2) reflexive orienting to peripheral flash cues. While both groups showed activation in the key areas of attentional processing networks, migraineurs showed less activation than non-migraine controls in a key area of the ventral frontoparietal network of attention, the right temporal parietal junction (rTPJ), during both voluntary and reflexive visual spatial orienting. Given the role of rTPJ is to assess the visual environment for behaviorally relevant sensory stimuli outside the focus of attention and signal other attentional areas to reorient attention to behaviorally salient stimuli, our findings fit with previous research showing that migraineurs lack suppression of unattended events and have heightened orienting to sudden onset stimuli in peripheral locations.

Clinical impact of migraine for the management of glaucoma patients

Migraine is a common and debilitating primary headache disorder that affects 10-15% of the general population, particularly people of working age. Migraine is relevant to providers of clinical eye-care because migraine attacks are associated with a range of visual sensory symptoms, and because of growing evidence that the results of standard tests of visual function necessary for the diagnosis and monitoring of glaucoma (visual fields, electrophysiology, ocular imaging) can be abnormal due to migraine. These abnormalities are measureable in-between migraine events (the interictal period), despite patients being asymptomatic and otherwise healthy. This picture is further complicated by epidemiological data that suggests an increased prevalence of migraine in patients with glaucoma, particularly in patients with normal tension glaucoma. We discuss how migraine, as a co-morbidity, can confound the results and interpretation of clinical tests that form part of contemporary glaucoma evaluation, and provide practical evidence-based recommendations for the clinical testing and management of patients with migraine who attend eye-care settings.

Reduced functional connectivity between salience and visual networks in migraine with aura

BACKGROUND

Migraine with visual aura (MA) is associated with distinct visual disturbances preceding migraine attacks, but shares other visual deficits in between attacks with migraine without aura (MO). Here, we seek to determine if abnormalities specific to interictal MA patients exist in functional brain connectivity of intrinsic cognitive networks. In particular, these networks are involved in top-down modulation of visual processing.

METHODS

Using resting-state functional magnetic resonance imaging, whole-brain functional connectivity maps were derived from seeds placed in the anterior insula and the middle frontal gyrus, key nodes of the salience and dorsal attention networks, respectively. Twenty-six interictal MA patients were compared with 26 matched MO patients and 26 healthy matched controls.

RESULTS

The major findings were: connectivity between the anterior insula and occipital areas, including area V3A, was reduced in MA but not in MO. Connectivity changes between the anterior insula and occipital areas further correlated with the headache severity in MA only.

CONCLUSIONS

The unique pattern of connectivity changes found in interictal MA patients involved area V3A, an area previously implicated in aura generation. Hypoconnectivity to this and other occipital regions may either represent a compensatory response to occipital dysfunctions or predispose MA patients to the development of aura.

Abnormal inhibition-excitation imbalance in migraine

Background

People with migraine show increased surround suppression of perceived contrast, a perceptual analogue of centre-surround antagonistic interactions in visual cortex. A proposed mechanism is that cortical ‘hyperexcitability’ or ‘hyperresponsivity’, a prominent theory in the migraine literature, drives abnormal excitatory-inhibitory balance to give increased local inhibition. The purpose of this cross-sectional study was to determine whether cortical hyperresponsivity and excitatory-inhibitory imbalance manifests in the visual cortical response of migraine sufferers.

Methods

Interictal steady-state visual evoked potentials (VEPs) in response to 0 to 97% contrast were recorded in 30 migraine participants (15 without aura, 15 with aura) and 21 non-headache controls. Monotonicity indices were calculated to determine response saturation or supersaturation. Contrast gain was modelled with a modified saturating hyperbolic function to allow for variation in excitation and inhibition.

Results

A greater proportion of migraine participants (43%) than controls (14%) exhibited significant VEP supersaturation at high contrast, based on monotonicity index (chi-square, p = 0.028). Supersaturation was also evident by the trend for greater suppressive exponent values in migraine compared to control individuals (Mann-Whitney rank sum, p = 0.075).

Conclusions

Supersaturation in migraine is consistent with excess excitation (hyperresponsivity) driving increased network inhibition and provides support for excitatory-inhibitory imbalance as a pathophysiological disturbance in migraine.

Deficient local biological motion perception in migraineurs: results from a duration discrimination paradigm

Migraine ranks as the third most common disease in the world and has caused significant losses of daily life abilities. Previously, people gave more attention to the pain of migraines and usually ignored the impairments of cognitive function in migraineurs. In the present study, a duration discrimination paradigm was used to assess the global and local biological motion perception in migraineurs and healthy controls. In the experiment, biological motion sequences and inanimate motion sequences (the inverted biological motion sequences) were sequentially presented on a screen. Observers were instructed to make a two-alternative forced choice to accurately indicate which interval (the first or the second) appeared longer. The stimuli involved global biological motion sequences and local biological motion sequences. The statistical analyses were conducted on the points of subjective equality that were obtained by fitting a psychometric function to each individual observer's data. In migraineurs, global biological motion signals lengthened the perceived temporal duration (as occurs in normal people), whereas local biological motion signals did not have this temporal dilation effect. The results indicated that patients with migraine showed a deficit in local biological motion perception, whereas their global biological motion perception was comparable to that of healthy subjects.

An inability to exclude visual noise in migraine

PURPOSE

People with migraine are relatively poor at judging the direction of motion of coherently moving signal dots when interspersed with noise dots drifting in random directions, a task known as motion coherence. Although this has been taken as evidence of impoverished global pooling of motion signals, it could also arise from unreliable coding of local direction (of each dot), or an inability to segment signal from noise (noise-exclusion). The aim of this study was to determine how these putative limits contribute to impoverished motion processing in migraine.

METHODS

Twenty-two participants with migraine (mean age, 34.7 ± 8.3 years; 16 female) and 22 age- and sex-matched controls (mean age, 34.4 ± 6.2 years) performed a motion-coherence task and a motion-equivalent noise task, the latter quantifying local and global limits on motion processing. In addition, participants were tested on analogous equivalent noise paradigms involving judgments of orientation and size, so that the specificity of any findings (to visual dimension) could be ascertained.

RESULTS

Participants with migraine exhibited higher motion-coherence thresholds than controls (P = 0.01, independent t-test). However, this difference could not be attributed to deficits in either local or global processing since they performed normally on all equivalent noise tasks (P > 0.05, multivariate ANOVA).

CONCLUSIONS

These findings indicate that motion perception in the participants with migraine was limited by an inability to exclude visual noise. We suggest that this is a defining characteristic of visual dysfunction in migraine, a theory that has the potential to integrate a wide range of findings in the literature.

Thickening of the somatosensory cortex in migraine without aura

OBJECTIVE

We aimed to explore cortical thickness abnormalities in a homogeneous group of patients with migraine without aura and to delineate possible relationships between cortical thickness changes and clinical variables.

METHODS

Fifty-six female migraine patients without aura and T2-visible white matter hyperintensities and 34 female controls were scanned on a 3T magnetic resonance imager. Cortical thickness was estimated and compared between patients and controls using a whole-brain vertex-by-vertex analysis. Correlation analysis was conducted between cortical thickness of significant clusters and clinical variables.

RESULTS

Compared to controls, migraine patients had cortical thickening in left rostral middle frontal gyrus and bilateral post-central gyri. Region-of-interest analysis revealed cortical thickening of bilateral post-central gyri in migraine patients relative to controls. The average thickness of bilateral post-central gyri positively correlated with disease duration as well as estimated lifetime headache frequency.

CONCLUSIONS

We have provided evidence for interictal cortical abnormalities of thickened prefrontal cortex and somatosensory cortex in female migraine patients without aura. Our findings of greater thickening of the somatosensory cortex in relation to increasing disease duration and increasing headache frequency suggest that repeated migraine attacks over time may lead to structural changes of the somatosensory cortex through increased noxious afferent input within the trigemino-thalamo-cortical pathway in migraine.

Modulation of visual evoked potentials by high-frequency repetitive transcranial magnetic stimulation in migraineurs

OBJECTIVE

High-frequency repetitive transcranial magnetic stimulation (rTMS) modulates cortical excitability. We investigated its effect on visual evoked potentials (VEPs) in migraine.

METHODS

Thirty-two headache-free controls (CO), 25 interictal (MINT) and 7 preictal migraineurs (MPRE) remained after exclusions. VEPs to 8' and 65' checks were averaged in six blocks of 100 single responses. VEPs were recorded before, directly after and 25min after 10Hz rTMS. The study was blinded for diagnosis during recording and for diagnosis and block number during analysis. First block amplitudes and habituation (linear amplitude change over blocks) were analysed with repeated measures ANOVA.

RESULTS

With 65' checks, N70-P100 habituation was reduced in MINT compared to CO after rTMS (p=0.013). With 8' checks, habituation was reduced in MPRE compared to MINT and CO after rTMS (p<0.016). No effects of rTMS on first block amplitudes were found.

CONCLUSION

RTMS reduced habituation only in migraineurs, indicating increased responsivity to rTMS. The magnocellular visual subsystem may be affected interictally, while the parvocellular system may only be affected preictally.

SIGNIFICANCE

Migraineurs may have increased responsiveness to rTMS because of a cortical dysfunction that changes before a migraine attack.

Interictal neurocognitive processing of visual stimuli in migraine: evidence from event-related potentials

Research has established decreased sensory habituation as a defining feature in migraine, while decreased cognitive habituation has only been found with regard to cognitive assessment of the relative probability of the occurrence of a stimulus event. Our study extended the investigation of interictal habituation in migraine to include cognitive processing when viewing of a series of visually-complex images, similar to those we encounter on the internet everyday. We examined interictal neurocognitive function in migraine from a habituation perspective, using a novel paradigm designed to assess how the response to a series of images changes over time. Two groups of participants--migraineurs (N = 25) and non-migraine controls (N = 25)--were asked to view a set of 232 unfamiliar logos in the context of a target identification task as their brain electrical responses were recorded via event-related potentials (ERPs). The set of logos was viewed serially in each of 10 separate trial blocks, with data analysis focusing on how the ERP responses to the logos in frontal electrodes from 200-600 ms changed across time within each group. For the controls, we found that the amplitude of the late positive potential (LPP) ERP component elicited by the logos had no significant change across trial blocks. In contrast, in migraineurs we found that the LPP significantly increased in amplitude across trial blocks, an effect consistent with a lack of habituation to visual stimuli seen in previous research. Our findings provide empirical support abnormal cognitive processing of complex visual images across time in migraineurs that goes beyond the sensory-level habituation found in previous research.

The effect of duration post-migraine on visual electrophysiology and visual field performance in people with migraine

Purpose:

In between migraine attacks, some people show visual field defects that are worse when measured closer to the end of a migraine event. In this cohort study, we consider whether electrophysiological responses correlate with visual field performance at different times post-migraine, and explore evidence for cortical versus retinal origin.

Methods:

Twenty-six non-headache controls and 17 people with migraine performed three types of perimetry (static, flicker and blue-on-yellow) to assess different aspects of visual function at two visits conducted at different durations post-migraine. On the same days, the pattern electroretinogram (PERG) and visual evoked response (PVER) were recorded.

Results:

Migraine participants showed persistent, interictal, localised visual field loss, with greater deficits at the visit nearer to migraine offset. Spatial patterns of visual field defect consistent with retinal and cortical dysfunction were identified. The PERG was normal, whereas the PVER abnormality found did not change with time post-migraine and did not correlate with abnormal visual field performance.

Conclusions:

Dysfunction on clinical tests of vision is common in between migraine attacks; however, the nature of the defect varies between individuals and can change with time. People with migraine show markers of both retinal and/or cortical dysfunction. Abnormal visual field sensitivity does not predict abnormality on electrophysiological testing.

Cortical abnormalities in patients with migraine: a surface-based analysis

PURPOSE

To explore the patterns of cortical thickness and cortical surface area abnormalities in patients with migraine (with the expectation of seeing reduced cortical thickness and surface area in regions subserving nociception and increased cortical thickness and surface area in regions involved in migraine pathogenesis) and to assess their correlation with clinical and radiologic manifestations of the disease.

MATERIALS AND METHODS

Approval of the local ethical committee was obtained, as well as written informed consent from each participant. T2-weighted and three-dimensional T1-weighted magnetic resonance images of the brain were acquired in 63 migraineurs and 18 matched healthy control subjects. Cortical thickness and cortical surface area were estimated. By using a general linear model approach, a vertex-by-vertex statistical analysis (P < .01) was used to assess between-group comparisons (migraineurs vs control subjects, the aura effect, the effect of white matter hyperintensities [WMHs]) and the correlations between cortical thickness and surface area measurements and patients' clinical and radiologic characteristics.

RESULTS

Compared with control subjects, patients with migraine showed reduced cortical thickness and surface area in regions subserving pain processing (P < .01). These two metrics were increased in regions involved in executive functions and visual motion processing (P < .01). The anatomic overlap of cortical thickness and cortical surface area abnormalities was only minimal, with cortical surface area abnormalities being more pronounced and more widely distributed than cortical thickness abnormalities. Cortical thickness and surface area abnormalities were related to aura and WMHs (P < .01) but not to disease duration and attack frequency.

CONCLUSION

Cortical abnormalities occur in migraineurs and may represent the results of a balance between an intrinsic predisposition, as suggested by cortical surface area abnormalities, and disease-related processes, as indicated by cortical thickness abnormalities.

Long-range inhibitory mechanisms in the visual system are impaired in migraine sufferers

Background: After viewing dynamic noise surrounding a homogeneous grey patch (artificial scotoma), observers perceive a prolonged twinkling-noise after-image within the unstimulated area. It has been suggested that noise-stimulated neurons induce a long-range inhibition in neurons within the artificial scotoma, which generates a rebound signal perceived as twinkling noise following noise termination. We used this paradigm to test whether migraineurs have enhanced excitability or weakened inhibition.

Methods: Twinkling-noise duration was measured in 13 headache-free volunteers, 13 migraineurs with aura and 13 migraineurs without aura.

Results: The durations of the after-image were significantly shorter for both migraine groups compared to controls.

Discussion: Enhanced excitation of noise-activated neurons in migraineurs would produce stronger rebound activity and longer after-image durations, while weakened inhibitory mechanisms would diminish the rebound activity and shorten the after-image durations compared to control subjects. The results suggest that cortical inhibitory mechanisms might be impaired in migraineurs with and without aura.

Simultaneous retinal and cortical visually evoked electrophysiological responses in between migraine attacks

PURPOSE

People with migraine often report aversion to flickering lights and show abnormal results on behavioural tasks that require the processing of temporal visual information. Studies have reported that the cortically evoked electrophysiological response to a flickering visual stimulus is abnormal; however, none have considered whether there is an underlying pre-cortical abnormality. In this cross-sectional study, we consider whether people with migraine have retinal and cortical electrophysiological abnormalities to flickering stimuli.

METHODS

Monocular transient (1 Hz) and steady-state (8.3 Hz) pattern reversal electroretinograms (PERGs) and pattern visual evoked responses (PVERs) were measured simultaneously in 45 people with migraine (26 without aura, 19 with aura) and 30 non-headache controls at a time between migraine attacks.

RESULTS

PERG amplitude and timing did not differ significantly between groups. Transient PVER amplitude was significantly reduced (28%) in the migraine with aura group compared to the controls F(2,72) = 3.6, p = 0.03). Both migraine groups showed significant reductions (32%, 39%) in steady-state PVER amplitude relative to controls (F(2,70) = 4.3, p = 0.02).

CONCLUSIONS

This study finds normal retinal processing of flickering stimuli in the presence of abnormal cortical function between migraine attacks.

Motion processing deficits in migraine are related to contrast sensitivity

Background: There are conflicting reports concerning the ability of people with migraine to detect and discriminate visual motion. Previous studies used different displays and none adequately assessed other parameters that could affect performance, such as those that could indicate precortical dysfunction.

Methods: Motion-direction detection, discrimination and relative motion thresholds were compared from participants with and without migraine. Potentially relevant visual covariates were included (contrast sensitivity; acuity; stereopsis; visual discomfort, stress, triggers; dyslexia).

Results: For each task, migraine participants were less accurate than a control group and had impaired contrast sensitivity, greater visual discomfort, visual stress and visual triggers. Only contrast sensitivity correlated with performance on each motion task; it also mediated performance.

Conclusions: Impaired performance on certain motion tasks can be attributed to impaired contrast sensitivity early in the visual system rather than a deficit in cortical motion processing per se. There were, however, additional differences for global and relative motion thresholds embedded in noise, suggesting changes in extrastriate cortex in migraine. Tasks to study the effects of noise on performance at different levels of the visual system and across modalities are recommended. A battery of standard visual tests should be included in any future work on the visual system and migraine.

Delayed development of visual motion processing in childhood migraine

Introduction: Altered visual processing has been observed in adult migraineurs. But because visual processing has not been studied in paediatric cases, it is not known whether such visual system alterations are already present in early development. We therefore used a dynamic visual task to investigate motion detection threshold in paediatric migraine.

Methods: Fourteen migraineurs and 21 controls participated in the study (age range: 8–17 years). The minimal percentage of coherently moving dot stimuli at which subjects were still able to detect coherent movement (absolute threshold) was determined using a random dot kinematogram paradigm.

Results: Motion coherence detection threshold was higher in migraineurs ( p < 0.05). This difference between groups was more pronounced at younger ages, but migraineurs seem to catch up with healthy controls over the years.

Conclusions: Children with migraine exhibit a delayed development of visual motion processing. This might be a useful supplementary biomarker in paediatric migraine.

Sequential changes in neuronal activity in single neocortical neurons after spreading depression

BACKGROUND

Cortical spreading depression (CSD) has an important role in migraine with aura. Prolonged neuronal depression is followed by a late excitatory synaptic plasticity after CSD.

METHOD

Intra- and extracellular recordings were performed to investigate the effect of CSD on intracellular properties of mouse neocortical tissues in the late excitatory period.

RESULTS

During CSD, changes in the membrane potentials usually began with a relatively short hyperpolarization followed by an abrupt depolarization. These changes occurred roughly at the same time point after CSD as the beginning of the negative extracellular deflection. Forty-five minutes after CSD, neurons showed significantly smaller amplitude of afterhyperpolarization and a reduced input resistance. Depolarization and hyperpolarization of the cells by constant intracellular current injections in this period significantly changed the frequency of the action potentials.

CONCLUSION

These data indicate higher excitability of the neocortical neurons after CSD, which can be assumed to contribute to hyperexcitability of neocortical tissues in patients suffering from migraine.

Evidence for increased internal noise in migraineurs for contrast and shape processing

Aim: Increased contrast-level dependent internal noise has been reported in migraine. This study aimed to investigate whether a general increase in internal noise impacted on other tasks thought to assess functioning in cortical area V1 and was evident in global contour coding (V4).

Methods: Eleven migraineurs (six with aura) and 12 headache-free controls completed three psychophysical tasks: (i) contrast detection, (ii) discrimination of the angle of a spiral path and (iii) detection of deformation from circularity. Internal noise estimates were obtained using an N-pass method that compared responses to repeated presentations of identical stimuli. Internal noise results in inconsistent responses across different runs.

Results: Migraineurs had significantly higher contrast thresholds when there was high external luminance noise. There were no other significant group differences in thresholds. Increased multiplicative noise associated with contrast processing was replicated and increased additive noise, which is independent of the visual input, was found for the global form task.

Conclusions: This study provides further evidence for increased multiplicative internal noise associated with contrast processing in migraineurs. However there is no generalised increase in internal noise in V1 as noise estimates for angular discrimination were normal. Increased additive internal noise was associated with the global shape task, co-occurring with increased efficiency.

Absence of changes in cortical thickness in patients with migraine

OBJECTIVE

Previous studies have reported gray matter alterations in patients with migraine, particularly thinning of the cingulate gyrus, and thickening of the somatosensory cortex (SSC) and visual motion processing areas (V3A/MT+). We attempted to replicate these findings in a larger patient population.

METHODS

Brain anatomy was collected with 3T MRI. Surface-based morphometry was used to segment each brain volume, reconstruct and inflate the cortical sheet, and estimate gray matter thickness.

RESULTS

Eighty-four age and sex-matched participants (28 migraine with aura, 28 migraine without aura, and 28 controls) were studied. No significant differences in somatosensory, cingulate gyrus, or V3A/MT+ cortical thickness were found between the groups, including analysis of specific subregions previously reported to be affected. Whole brain analysis found no regions of differential gray matter thickness between groups. A highly significant inverse correlation between age and whole brain and regional cortical thickness was identified. Power analyses indicate that even a small difference (∼0.07 to 0.14 mm) in cortical thickness could have been detected between groups given the sample size.

INTERPRETATION

Using highly sensitive surface-based morphometry, no differences in cortical thickness between patients with migraine and controls could be identified.

Spatial frequency differentially affects habituation in migraineurs: a steady-state visual-evoked potential study

A lack of habituation in visual-evoked potentials (VEPs) is the main abnormality observed in migraineurs. However, no study of steady-state VEPs has yet evaluated pattern-reversal stimuli with respect to habituation behavior or spatial frequency. The aim of this study was to clarify habituation behavior in migraineurs between attacks and to establish characteristics of VEPs in these patients. Steady-state VEPs were sequentially recorded as checkerboard patterns in four consecutive blocks from 12 patients with migraine without aura (MO), 12 patients with migraine with aura (MA), and 12 healthy controls (HC) at four spatial frequencies of 0.5, 1.0, 2.0, and 4.0 cycles per degree (cpd) with a stimulus rate of 7.5 Hz (15 reversal/s). VEP amplitudes were consistently higher in migraineurs. However, habituation was not demonstrated in HCs, and migraineurs did not reveal a clear lack of habituation. MAs exhibited high-amplitude VEPs, depending on spatial frequency. In the MA patients, amplitude differences reached statistical significance at 2.0 cpd. The sequential amplitude changes at 0.5 cpd were significantly different in MAs compared with HCs. Migraine patients exhibited high-amplitude VEPs, which were dependent on spatial frequency, and may be related to altered excitability in pre-cortical and cortical visual processing.

Increased internal noise cannot account for motion coherence processing deficits in migraine

Aim: This study aimed to revisit previous findings of superior processing of motion direction in migraineurs with a more stringent direction discrimination task and to investigate whether increased internal noise can account for motion processing deficits in migraineurs.

Methods: Groups of 13 migraineurs (4 with aura, 9 without aura) and 15 headache-free controls completed three psychophysical tasks: one detecting coherence in a motion stimulus, one discriminating the spiral angle in a glass pattern and another discriminating the spiral angle in a global-motion task. Internal noise estimates were obtained for all tasks using an N-pass method.

Results: Consistent with previous research, migraineurs had higher motion coherence thresholds than controls. However, there were no significant performance differences on the spiral global-motion and global-form tasks. There was no significant group difference in internal noise estimates associated with any of the tasks.

Conclusions: The results from this study suggest that variation in internal noise levels is not the mechanism driving motion coherence threshold differences in migraine. Rather, we argue that motion processing deficits may result from cortical changes leading to less efficient extraction of global-motion signals from noise.

Visual and auditory perceptual rivalry in migraine

INTRODUCTION

Recent evidence demonstrates that perceptual rivalry rate can be modulated by perturbation of the serotonergic system. Specifically, pharmacologically lowering the availability of serotonin results in slower rivalry rates. As it has been suggested that brain serotonin is low during the interictal phase of migraine, we hypothesized that perceptual rivalry rates would be reduced in individuals with migraine.

METHODS

Visual and auditory perceptual rivalry measures were obtained for a group of 30 participants with migraine (15 migraine with aura, 15 migraine without aura) and 20 non-headache control individuals.

RESULTS

Our experiments reveal fewer perceptual rivalry switches within both visual and auditory domains for our migraine without aura group, while the with-aura group performed similarly to non-headache controls. Dividing the data by headache frequency rather than headache subtype classification revealed fewer perceptual switches in those with more frequent headaches.

CONCLUSIONS

Our data provides further support for interictal differences in brain sensory reactivity in migraine, with the observed effects being in the same direction as those caused by pharmacologically reducing brain availability of serotonin in normal observers.

Migraine increases centre-surround suppression for drifting visual stimuli

BACKGROUND

The pathophysiology of migraine is incompletely understood, but evidence points to hyper-responsivity of cortical neurons being a key feature. The basis of hyper-responsiveness is not clear, with an excitability imbalance potentially arising from either reduced inhibition or increased excitation. In this study, we measure centre-surround contrast suppression in people with migraine as a perceptual analogue of the interplay between inhibition and excitation in cortical areas responsible for vision. We predicted that reduced inhibitory function in migraine would reduce perceptual surround suppression. Recent models of neuronal surround suppression incorporate excitatory feedback that drives surround inhibition. Consequently, an increase in excitation predicts an increase in perceptual surround suppression.

METHODS AND FINDINGS

Twenty-six people with migraine and twenty approximately age- and gender-matched non-headache controls participated. The perceived contrast of a central sinusoidal grating patch (4 c/deg stationary grating, or 2 c/deg drifting at 2 deg/sec, 40% contrast) was measured in the presence and absence of a 95% contrast annular grating (same orientation, spatial frequency, and drift rate). For the static grating, similar surround suppression strength was present in control and migraine groups with the presence of the surround resulting in the central patch appearing to be 72% and 65% of its true contrast for control and migraine groups respectively (t(44) = 0.81, p = 0.42). For the drifting stimulus, the migraine group showed significantly increased surround suppression (t(44) = 2.86, p<0.01), with perceived contrast being on average 53% of actual contrast for the migraine group and 68% for non-headache controls.

CONCLUSIONS

In between migraines, when asymptomatic, visual surround suppression for drifting stimuli is greater in individuals with migraine than in controls. The data provides evidence for a behaviourally measurable imbalance in inhibitory and excitatory visual processes in migraine and is incompatible with a simple model of reduced cortical inhibitory function within the visual system.

Detection and discrimination of flicker contrast in migraine

AIMS

Flickering light is strongly aversive to many individuals with migraine. This study was designed to evaluate other abnormalities in the processing of temporally modulating visual stimulation.

METHODS

We measured psychophysical thresholds for detection of a flickering target and for the discrimination of suprathreshold flicker contrasts (increment thresholds) in 14 migraineurs and 14 healthy controls with and without prior adaptation to high-contrast flicker. Visual discomfort (aversion) thresholds were also assessed.

RESULTS

In the baseline (no adaptation) conditions, detection and discrimination thresholds did not differ significantly between groups. Following adaptation, flicker detection thresholds were elevated equivalently in both groups; however, discrimination thresholds were more strongly affected in migraineurs than in controls, showing greater elevation at moderate contrasts and greater threshold reduction (sensitisation) at high contrast (70%). Migraineurs also had significantly elevated discomfort scores, and these were significantly correlated with number of years with migraine.

DISCUSSION

We conclude that visual flicker not only causes discomfort but also exerts measurable effects on contrast processing in the visual pathways in migraine. The findings are discussed in the context of the existing literature on habituation, adaptation and contrast-gain control.