Clinvest would propose a pilot study of chronic migraine patients randomized 1:1 to onabotulinumtoxinA and daily topiramate or onabotulinumtoxinA and placebo. This pilot study will examine the degree to which subjects are able to tolerate and are satisfied with a migraine preventive medication in addition to onabotulinumtoxinA over an extended period of time and the effect of the subjects' quality of life compared with onabotulinumtoxinA as a single therapy. It will also assess short and long term effects of these two treatments on cognition. Cognitive performance will be measured by the Mental Efficiency Workload Test (MEWT), a repeated measures handheld neuropsychological test battery that measures mental efficiency via 4 sub-tests (Simple Reaction Time, Running Memory, Continuous Performance Task, Matching to Sample, and Mathematical Processing) to demonstrate short and long term changes in mental status compared to their baseline. The Controlled Oral Word Association Test (COWAT) will be used to test verbal fluency and screen for anomic aphasia, a known side effect of several migraine prophylactic medications including topiramate.