Page 158 - Migraine, the heart and the brain

Chapter 8
information. To assess the impact of migraine on working memory ef ciency, we employed the well established N-back task (for an overview, see Kane et al. (19)), which requires participants to hold information and continuously update this information based on new incoming stimuli. In this study, however, no difference in N-back task was found between migraineurs and controls.
Several caveats are in order and some limitations apply. It is possible that migraine- speci c prophylaxis played a role in producing the observed elimination of the global- local effect in migraineurs. Various adverse effects of prophylaxis on cognition have been reported (22) and a direct effect of the prophylactic medication can be suggested. Migraine characteristics between prophylaxis users and non-users as age of migraine onset, total migraine years, current attack frequency, current attack duration, and current presence of photophobia or phonophopia did not differ. However this does not rule out that some clinical characteristics before the start of prophylaxis were in fact different (for example attack frequency) compared to the non-prophylaxis using group. The types of prophylaxes used by our participants were too heterogeneous to correct for their respective type-speci c potential effects.
The absence of a post-attack effect could be explained by the high percentage of triptan users in our study, 94% of the participants used triptan during the attack preceding the tests. Possibly the use of triptans prevented the development of cognitive complaints, and differences would probably be easier to detect after untreated attacks. However, participants willing to skip their attack treatment will probably lead to the inclusion of less severely affected migraineurs. Another explanation for the absence of a post-attack effect is the long time which passed between the end of the attack and actual testing. However, testing sooner would invite possible artefacts, such as side effects of headache, mood, medication, and exhaustion. A fatigue score in each participant before each session was not obtained, and therefore adjusting for this possible important factor was not possible.
Another caveat relates to testing procedures. With regard to the fact that we tested participants repeatedly, it is important to point out that there were pronounced session effects, i.e. learning improved performance considerably. This underscores the need for a control group in studies investigating post-attack changes, as this permits the correction for learning effects, which might be particularly strong if participants are relatively old and not used to computerized testing. Even though the examiners were not blinded for diagnosis, all the relevant tests were computerized and the sequence of trials was fully randomized which should have prevented systematic biases.
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