Habituation and migraine

The most reproducible and ubiquitous interictal abnormality of the migraineurs’ brain is lack of habituation in neuronal information processing. The underlying mechanisms are uncertain. Increased neuronal excitability, decreased inhibition or decreased pre-activation levels have all been proposed as possible culprits.The present review summarizes the available data on habituation in migraine patients obtained with different methodological approaches. We will discuss the change of habituation level over the migraine cycle and we will show that these data congruently indicate that the sensory cortices of migraineurs react excessively to repetitive, but not to a small series of stimuli.Although the precise cellular and molecular mechanisms of this hyper-responsivity must still be determined, we will describe experimental data suggesting that a dysrhythmic thalamo-cortical activity due to inadequate monoaminergic control might be a plausible explanation.     

Evidence for distinct clusters of diverse anomalous experiences and their selective association with signs of elevated cortical hyperexcitability

Visual cortical hyperexcitability is now known to be an underlying factor for aberrant visual experience, including hallucinations, and pattern or light induced visual discomfort. Such factors have also been observed in neurological and non-clinical groups (albeit in attenuated form) – consistent with the notion of a continuum of anomalous experiences. Utilizing an exploratory factor analysis (EFA) approach (n = 300), Study 1 developed a revised proxy screening measure for visual cortical hyperexcitability – the Cortical Hyperexcitability index – II(CHi-II). The EFA revealed a stable 3-factor solution which can be characterised as; (i) Heightened Visual Sensitivity and Discomfort (HVSD); (ii) Aura-like Hallucinatory Experience (AHE); and, (iii) Distorted Visual Perception (DVP). Study 2 tested both a self-reported migraine group and a control group on the CHi-II in conjunction with a computerised pattern-glare task that is known to reflect visual cortical hyperexcitability. The migraine group produced significantly elevated scores on both the AHE and HVSD factors of the CHi-II, relative to controls. Among the non-migraine group, subjects who scored higher in the pattern-glare task also produced significantly elevated scores on the AHE factor compared to those with low pattern-glare task scores. Collectively, these findings support the utility of the CHi-II as an indirect proxy measure for signs of cortical hyperexcitability and reveal new categorical distinctions for the nature of the anomalous perceptions. These perceptions may well reflect diverse neurocognitive underpinnings leading to advancements in our understanding of aberrations in conscious experience.     

Headache triggers: To avoid or not to avoid,that is the question

Abstract

Traditional clinical advice in the management of headaches is to avoid trigger factors. There is a danger, however, that avoidance of triggers results in a sensitisation process whereby tolerance for the triggers decreases, in a manner analogous to increments in anxiety arising from avoidance of anxiety-eliciting stimuli. Reported here are six single-case experiments in which the aim was to desensitise headache sufferers to an experimentally validated trigger, namely “visual disturbance”. The results demonstrated that repeated, prolonged exposure to a headache trigger led to desensitisation with participants experiencing less visual disturbance, less negative affect and less head pain in response to the trigger. These findings have theoretical significance as they speak to the issue of the aetiology of chronic headache, and practical significance as they suggest that a key aspect of current management may contribute to the disorder becoming worse rather than better.     

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.