Integration of multiple motion vectors over space: an fMRI study of transparent motion perception

Visual scenes are frequently composed of objects that move in different directions. To segment such scenes into distinct objects or image planes, local motion cues have to be evaluated and integrated according to criteria of global coherence. When several populations of coherently moving random dots penetrate each other, the visual system tends to assign them to different planes-perceived as transparent motion. This process of integration was studied by changing the angle of motion trajectories with which groups of dots penetrate each other or by varying the spatial constellation of dots moving in opponent directions. Psychophysical testing revealed that stimuli providing almost identical local motion cues could be perceived in three very different ways: (1) as a matrix of stationary flickering dots, (2) as a single surface of coherently moving dots, and (3) as two transparent dot matrices moving in different directions. Behaviorally controlled functional magnetic resonance imaging (fMRI) was used to identify brain regions that contribute to the integration of local motion cues into coherently moving surfaces. Activation of the human motion complex (hMT+/V5) and of areas in the fusiform gyrus (FG) as well as in the intraparietal sulcus (IPS-occ) was correlated with the perception of coherent motion and especially hMT+/V5 took a central role in differentiating transparent motion from single-surface coherent motion.     

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.     

Consecutive transcranial magnetic stimulation: phosphene thresholds in migraineurs and controls

OBJECTIVE: To characterize the temporal course of transcranial magnetic stimulation-induced phosphene thresholds in subjects with migraine and in controls. METHODS: Eleven subjects with migraine with aura, 10 subjects with migraine without aura, 9 subjects with menstrual migraine, and 15 controls (no history of migraine and without migraine during the study) were studied. Subjects were not on preventive medication. Transcranial magnetic stimulation was performed, and a phosphene threshold was measured 3 times a week over 3 weeks in a manner timed to incorporate the menstrual period in females. A headache calendar was kept during the study. RESULTS: Mean transcranial magnetic stimulation thresholds were lower for each migraine group compared with controls (P <.001) for each comparison. There was a trend for lower thresholds among subjects with migraine with aura compared with subjects with migraine without aura (P <.10), but not subjects with menstrual migraine. There was consistent lowering of thresholds from the first to the last stimulation in all migraine groups and in the controls. Maximum and minimum thresholds did not predict headache occurrence, nor did the occurrence of headache predict an ensuing maximum or minimum phosphene threshold. CONCLUSIONS: Transcranial magnetic stimulation thresholds are lower in subjects with migraine compared with controls. The reported phosphene threshold is lowered with repeated measurement. Neither high nor low phosphene thresholds predict a subsequent headache, nor do migraines predict a subsequent high or low threshold.     

Cortical hyperexcitability is cortical under-inhibition: evidence from a novel functional test of migraine patients

Recent studies of the visual cortex in patients with migraine have generally concluded that migraine (particularly migraine with aura) is associated with a state of functional cortical hyperexcitability. The mechanisms giving rise to this hyperexcitability have hitherto been unclear. This paper reports two studies that used a novel investigative technique, derived from basic research in vision science, to examine specific deficits of inhibitory processing in primary visual cortex. The technique is termed the metacontrast test, and it examines visual masking under highly specified conditions. In Study 1, 12 migraine with aura patients (MA), 12 age-matched migraine without aura patients (MO) and 12 age- and sex-matched headache-free control subjects (C) were compared using the metacontrast test. MA patients were significantly less susceptible to visual masking in the metacontrast test than both MO and C groups: this result is highly consistent with a deficit in cortical inhibitory processing in MA patients. Study 2 examined MA patients taking a variety of migraine prophylactics, again using the metacontrast test. Test results normalized in those MA patients taking sodium valproate, but not in those taking other prophylactics. Sodium valproate is a GABA-A agonist that is known to cross the blood-brain barrier: GABA-ergic networks act as the primary inhibitory mechanism in visual cortex. Taken together, the results of these studies argue that cortical hyperexcitability, at least in MA patients, is likely to be a result of deficient intracortical inhibitory processes.     

Exteroceptive suppression of masseter muscle activity in juvenile migraineurs

The second exteroceptive suppression period (ES2) of masseter or temporalis muscle activity may be reduced in adults with chronic tension-type headache. In adults with migraine, ES2 was found normal or tended to be protracted. To date, no studies on exteroceptive suppression in children and adolescents with headaches have been published. We investigated the exteroceptive suppression of masseter muscle activity in 14 migraineurs and 19 controls between 6 and 18 years of age. It was elicited by electrical stimulation at the labial commissure. No differences were found regarding the first suppression period, but ES2 was significantly longer in the migraine group than in controls. The results of the migraine group suggest overactivity of the interneurons of the reflex loop due to impaired inhibitory control from superior antinociceptive systems already at the beginning of this headache disorder.     

Cerebral blood flow and CO2 reactivity in interictal migraineurs: a transcranial Doppler study

There is still some controversy about alterations in velocity of blood flow and in cerebral vasomotor reactivity of intracranial arteries in migraineurs during the interictal phase. By means of simultaneous bilateral transcranial Doppler ultrasonography we, therefore, assessed intracranial blood flow velocities and cerebrovascular reactivity to carbon dioxide of all three basal brain arteries in 20 migraineurs during the interictal phase and 30 nonheadache-prone control subjects. Mean blood flow velocities were higher in migraineurs than in controls in all three arteries on both sides, with a significant difference (P < 0.05) for the right anterior cerebral artery and middle cerebral artery under basal conditions and for the right posterior cerebral artery during hypercapnia. Similarly, the cerebrovascular reactivity to carbon dioxide was always higher in patients than in controls, with a significant difference for the left anterior and the right middle cerebral arteries (P < 0.05) and the right posterior cerebral artery (P < 0.01). The broad overlap of cerebrovascular blood flow velocities and CO2 reactivities in patients and controls precluded identification of values diagnostic of migraine. Nevertheless, transcranial Doppler ultrasonography offers the opportunity to noninvasively monitor cerebral blood flow parameters and, therefore, represents a valuable tool for vascular research in migraine.     

Interictal pattern-induced visual discomfort and ictal photophobia in episodic migraineurs: an association of interictal and ictal photophobia

Background.— Pattern‐induced visual discomfort and photophobia are frequently observed symptoms in migraineurs. The presumed pathophysiologic mechanisms of pattern glare and photophobia seem to overlap anatomically within the central nervous system. Objective.— To assess the relationship between interictal pattern‐induced visual discomfort and ictal photophobia in episodic migraineurs. Methods.— We compared pattern‐induced visual discomfort among 3 groups: controls, migraineurs without ictal photophobia (MwoP), and migraineurs with ictal photophobia (MwP). Photophobia was assessed with a validated photophobia questionnaire. Visual discomfort tests were performed using 3 striped patterns with different spatial frequencies. After viewing the patterns for 10 seconds, subjects were asked to report the severity of visual discomfort using 4 scales (none, mild, moderate, and severe) and using a 0‐10 visual analog scale (VAS). We compared the proportion of subjects choosing moderate‐to‐severe discomfort and the median values of VAS scores for each pattern among the 3 groups. Results.— We enrolled 35 controls, 18 MwoP, and 44 MwP, and there were no significant differences in clinical features among the 3 groups. MwP reported a significantly higher proportion of moderate‐to‐severe discomfort and higher median VAS scores than the controls and MwoP did. The intensity of discomfort increased with higher frequency of visual stimuli. Conclusions.— We conclude that MwP experienced more severe pattern‐induced visual discomfort as compared with the controls and MwoP.     

Visual cortical inhibitory function in migraine is not generally impaired: evidence from a combined psychophysical test with an fMRI study

A robust, visual masking test that was developed to be feasible with functional magnetic resonance imaging (fMRI) was used to examine the visual cortical inhibitory function in migraine patients with visual aura at both psychophysical and cortical levels. The study showed that the decreased visibility of a visual target was associated with a reduction in cortical activation in the primary visual cortex. The suppression of the transient on-response and after-discharge of neurons to the target was most likely to be responsible for reducing cortical activation, rendering the target less visible or invisible. The migraine patients were equally susceptible to visual masking and showed no difference in cortical activation when compared with age- and sex-matched non-headache controls, demonstrating that visual cortical inhibitory function was not impaired under the experimental conditions. Although these results are not in conflict with the general cortical hyperexcitability theory in migraine, they provide evidence to show the limitation to the theory.     

阻断对视运动启动方向知觉影响的行为学研究

目的：记录正常青年人在对视运动启动知觉实验中方向判断的反应时与准确率。方法：24名被试者参与本实验。实验一在单步骤运动的两图片中加入空白阻断；实验二在启动运动的两个步骤中加入空白阻断。结果：发现由某一特定方向的视觉运动引导一个方向二义的运动，二义的运动方向知觉受前者启动，偏向前者同一个方向。当两个步骤之间加入一个空白的阻断时，其运动方向启动效应会呈现如下变化：短时间隔时二义运动受特定方向的启动效应明显；时间间隔延长时，启动性减弱或消失；当时间间隔进一步延长时，出现相反方向的启动效应。结论：该结果间接地提供了运动知觉启动效应为神经元细胞在空间与时间上整合观点的证据，支持基于计算模型的运动知觉方向加工的神经机制。     

不同相干水平视觉运动刺激皮层反应特征的fMRI研究

目的探讨随机点动态运动图作为刺激源是否能够对参与视觉运动觉处理的大脑皮层区域进行准确的功能定位,并在此基础上进一步观测在不同运动相干水平情况下,相关大脑皮层的血氧水平依赖反应特点。方法12名受试者在功能磁共振扫描过程中接受三种不同相干水平的视觉运动刺激(5%,20%,80%),刺激呈现采用组块设计模式。数据经预处理和统计分析得到激活图,并进一步进行兴趣区分析。结果随机点动态运动图作为刺激源能够有效的激活视觉运动觉处理相关视觉皮层区域;以hMT 作兴趣区分析得到三种不同相干水平运动刺激下该区域的激活体积。结论随机点动态运动图刺激能对参与视觉运动觉处理的大脑皮层区域进行准确的功能定位;hMT 的激活体积随着相干水平的提高而减小。     

Effects of L-5HTP with and without carbidopa on plasma β-endorphin and pain perception: possible implications in migraine prophylaxis

L-Tryptophan (L-TP) has been used in migraine and other pain conditions. The mechanism underlying the analgesic effect is still partly undefined. In this study the effects of subchronic administration of L-5-hydroxytryptophan (L-5HTP) (with and without carbidopa) on plasma beta-endorphin (beta-EP) levels and subjective pain threshold and tolerance were investigated in seven healthy volunteers. To measure also an objective indicator of pain, the nociceptive flexion reflex threshold was studied. L-5HTP treatment with and without carbidopa administration increased beta-EP levels significantly (p less than 0.05). L-5HTP plus carbidopa induced an increase in beta-EP significantly (p less than 0.05) greater than that induced by L-5HTP alone. Neither the subjective pain threshold and tolerance nor the RIII threshold was modified by either treatment. Our data seem to point to the existence of a complex linkage between plasma opioid levels and pain perception.     

Frequent analgesics consumption in migraineurs: comparison between chronic and episodic migraineurs

Abstract To assess the frequent consumption of symptomatic medications in migraineurs, we consecutively recruited 536 migraineurs from a headache clinic. Among them, 194 (36.2%) had chronic migraine and 342 had episodic migraine. When grouped according to duration of headache, the proportion of patients with chronic migraine increased from 25.5% to 50.9% as headache history increased from <1 to >20 years. The percentage of patients with frequent analgesics consumption also increased with the duration of headache, in patients with both chronic migraine (from 25.0% to 85.7%) and episodic migraine (from 20.0% to 59.3%). Nonetheless, patients with chronic migraine had a higher prevalence of frequent consumption of abortive medications than patients with episodic migraine regardless of duration of headache history, and the common odds ratio across strata of headache duration was 2.8 (95% confidence interval, 1.9–4.1). However, we found that a long headache history is an important risk factor for frequent consumption of symptomatic medications in migraineurs in patients with both episodic migraine and chronic migraine.     

Time perception in migraine sufferers: an experimental matched-pairs study

Despite occasional case reports, the influence of migraine on time perception has not been systematically investigated. We used an experimental technique to study the estimation of auditory duration in 40 migraineurs at different tone intervals in the ms and in the 1-s range and compared their performance with 40 matched normal subjects. With a time awareness questionnaire we also evaluated the subjective experience of elapsing time for long durations involving long-term memory processes. Migraine did not influence temporal judgements in either of the tests, suggesting that migraineurs do not generally over- or underestimate temporal events. The subgroup of migraineurs with a depressive disorder, however, showed a marked speeding up of their internal timekeeping mechanisms, pointing to depression as an important covariable in time perception.     

Timing of V1/V2 and V5+ activations during coherent motion of dots: an MEG study

In order to study the temporal activation course of visual areas V1 and V5 in response to a motion stimulus, a random dots kinematogram paradigm was applied to eight subjects while magnetic fields were recorded using magnetoencephalography (MEG). Sources generating the registered magnetic fields were localized with Magnetic Field Tomography (MFT). Anatomical identification of cytoarchitectonically defined areas V1/V2 and V5 was achieved by means of probabilistic cytoarchitectonic maps. We found that the areas V1/V2 and V5+ (V5 and other adjacent motion sensitive areas) exhibited two main activations peaks at 100-130 ms and at 140-200 ms after motion onset. The first peak found for V1/V2, which corresponds to the visual evoked field (VEF) M1, always preceded the peak found in V5+. Additionally, the V5+ peak was correlated significantly and positively with the second V1/V2 peak. This result supports the idea that the M1 component is generated not only by the visual area V1/V2 (as it is usually proposed), but also by V5+. It reflects a forward connection between both structures, and a feedback projection to V1/V2, which provokes a second activation in V1/V2 around 200 ms. This second V1/V2 activation (corresponding to motion VEF M2) appeared earlier than the second V5+ activation but both peaked simultaneously. This result supports the hypothesis that both areas also generate the M2 component, which reflects a feedback input from V5+ to V1/V2 and a crosstalk between both structures. Our study indicates that during visual motion analysis, V1/V2 and V5+ are activated repeatedly through forward and feedback connections and both contribute to m-VEFs M1 and M2.     

Effects of L-5HTP with and without carbidopa on plasma ß-endorphin and pain perception

L-Tryptophan (L-TP) has been used in migraine and other pain conditions. The mechanism underlying the analgesic effect is still partly undefined. In this study the effects of subchronic administration of L-5-hydroxy-tryptophan (L-5HTP) (with and without carbidopa) on plasma beta-endorphin (beta-EP) levels and subjective pain threshold and tolerance were investigated in seven healthy volunteers. To measure also an objective indicator for pain, the nociceptive flexion reflex threshold was studied. L-5HTP treatment with and without carbidopa administration increased beta-EP levels significantly (p less than 0.05). L-5HTP plus carbidopa induced an increase in beta-EP significantly (p less than 0.05) higher than that after L-5HTP alone. Neither subjective pain threshold and tolerance nor RIII threshold was modified by either treatment. Our data seem to point to the existence of a complex linkage between plasma opioid levels and pain perception.     

Interictal executive dysfunction in migraineurs without aura: relationship with duration and intensity of attacks

Subjects with migraine are at increased risk of subcortical white matter lesions (WML). Reports of cognitive testing in adults with migraine have yielded inconsistent results. We performed a cross-sectional study to assess whether migraine without aura (MwA) is associated with impairment in executive functioning, a typical cognitive correlate of subcortical WML. Forty-five subjects with MwA and 90 controls, matched for age and education, underwent a cognitive battery of tests evaluating executive functions. The following migraine characteristics were collected: age at onset and length of migraine history, and frequency, duration and intensity of attacks. Subjects with MwA performed significantly lower than controls in tests evaluating complex, multifactorial executive functions. After multiple adjustments, the duration and intensity of migraine attacks significantly predicted cognitive disturbances. In the interictal phase of MwA there is evidence of mild executive dysfunction. The cumulative effects of repeated migraine attacks on prefronto-cerebellar loop probably account for our results.     

Topiramate in migraine prevention: a double-blind, placebo-controlled study

OBJECTIVE: To evaluate the efficacy of topiramate in the preventative treatment of episodic migraine. BACKGROUND: Topiramate is a broad-spectrum antiepileptic drug effective for treatment of multiple seizure types in adults and children. Antiepileptic agents have demonstrated efficacy in migraine prevention, and open-label experience from our clinic has suggested that topiramate might be effective for this use. We consequently conducted a single-center, double-blind, placebo-controlled trial to evaluate the efficacy and safety of topiramate for the preventative treatment of migraine. METHODS: Forty patients, aged 19 to 62 years (mean, 38.2 years), were randomly assigned in a 1:1 ratio to receive topiramate (n = 19; all women) or placebo (n = 21; 20 women, 1 man). Following a prospective baseline phase of 4 weeks, the study drug dose was titrated weekly in 25-mg increments over 8 weeks to 200 mg per day or to the maximum tolerated dose. The titration phase was followed by an 8-week maintenance phase. RESULTS: During the entire double-blind phase, topiramate-treated patients experienced a significantly lower 28-day migraine frequency (3.31 +/- 1.7 versus 3.83 +/- 2.1; P =.002) compared to placebo, irrespective of use of concomitant migraine prevention medications. The mean 28-day migraine frequency was reduced by 36% in patients receiving topiramate as compared with 14% in patients receiving placebo (P =.004). Twenty-six percent of the patients on topiramate and 9.5% of the patients on placebo achieved a 50% reduction in migraine frequency (P >.05). The mean dose of topiramate was 125 mg per day (range, 25 to 200 mg per day). Topiramate was well tolerated; 2 of 19 topiramate-treated patients discontinued treatment due to adverse events. Adverse effects that occurred more frequently in topiramate-treated patients included paresthesia, weight loss, altered taste, anorexia, and memory impairment. CONCLUSIONS: Preventative therapy with topiramate significantly reduced migraine frequency. Larger multicenter clinical studies may further delineate the role of topiramate in migraine prevention.     

MTHFR T677 homozygosis influences the presence of aura in migraineurs

It has been suggested that folate metabolism could be involved in migraine pathogenesis. We analysed the 5',10'-methylenetetrahydrofolate reductase (MTHFR) genotypic distribution in a large migraine sample. We genotyped 230 migraine patients (152 migraine without aura (MO) and 78 migraine with aura (MA)) and 204 nonheadache controls. The incidence of TT homozygosis for migraine in general (12%), MO (9%) and MA (18%) did not significantly differ from that found in healthy controls (13%). Differences were significant when the frequency of TT homozygosis between MA and MO (P = 0.03, OR = 2.34, 95% CI = 1.04-5.26) was compared. There was a tendency for a higher frequency of the MTHFR T allele in the MA group (42%) as compared to MO (29%) and controls (36%). These differences were significant only in the case of MA vs. MO (P = 0.006, OR = 1.75, 95% CI = 1.15-2.65). These results could indicate that the MTHFR C677T polymorphism, causing mild hyperhomocystinaemia, might be a genetic risk factor for experiencing aura among migraineurs. Overall, however, there was no association between migraine and the C677T MTHFR polymorphism.     

Triggers of motion sickness in migraine sufferers

OBJECTIVE: To determine whether susceptibility to motion sickness provoked by unexpected movement is associated with susceptibility to visually induced motion sickness in migraine sufferers. BACKGROUND: Migraine sufferers are unusually susceptible to motion sickness, but the mechanism of this susceptibility is not well understood. Possibilities include vestibular dysfunction secondary to vasomotor disturbances during migraine attacks, hyperexcitability of brainstem circuits that produce symptoms of motion sickness and migraine, and heightened susceptibility to visual illusions of movement. METHOD: A motion sickness susceptibility questionnaire that listed common triggers of motion sickness was filled out by 42 migraine sufferers and 39 headache-free controls of similar age and sex distribution to migraine sufferers. RESULTS: A greater proportion of migraine sufferers than controls reported that traveling in cars and buses, reading in the car, using playground equipment, watching wide-screen movies and movement simulators, induced motion sickness. However, visually induced motion sickness appeared to be independent of motion sickness to most movement-related stimuli in migraine sufferers. CONCLUSIONS: The lack of association between susceptibility to movement-induced and visually induced motion sickness implies that more than one mechanism increases susceptibility to motion sickness in migraine sufferers.     

Subclinical dysfunction of cochlea and cochlear efferents in migraine: an otoacoustic emission study

Otoacoustic emission (OAE) testing enables us to identify the cochlear component of a hearing disorder and to monitor objectively minute changes in cochlear status undetectable by other audiological methods. Contralateral sound-induced suppression is mediated by medial superior olivary complex efferents which induce hyperpolarization counteracting the amplifying effects of outer hair cell (OHC) activity. The aim of this study was to assess functions of cochlea and its efferents in migraine using OAE testing and contralateral suppression of transiently evoked OAEs (TEOAE). Fifty-three migraineurs (106 ears) and 41 healthy subjects (82 ears) were included and pure tone audiometry (PTA), speech discrimination scores (SDS), distortion product OAE (DPOAE), TEOAE and contralateral suppression of TEOAEs were tested. PTA and SDS of migraineurs and controls were not different ( P  > 0.05). DPOAEs were tested between 1 and 6 kHz and a significant difference was detected only at 5 kHz frequency, where DPOAE amplitudes in migraine with aura (MA) were lower than in controls ( P  < 0.03). The mean amplitudes of TEOAEs were statistically insignificant between controls and migraine groups. Contralateral sound stimulus induced significant decrease in amplitudes of TEOAE ( P  = 0.005) in controls. In patients with migraine without aura and MA, mean amplitudes of TEOAEs were not suppressed by contralateral sound stimulus ( P  > 0.05). As PTA, SDS and DPOAE tests demonstrate normal functioning of inner ear between 1 and 4 kHz, absence of suppression of the TEOAEs by contralateral sound stimulation indicates the presence of dysfunction either in the medial olivocochlear complex in the brainstem or at the synaptic transmission between olivocochlear efferents and OHCs in the cochlea. Disruption in the contralateral suppression may be one of the mechanisms predisposing to the phonophobia symptom associated with migraine headache.