Irritable bowel syndrome (IBS) is one of over 20 functional gastrointestinal disorders. There is considerable overlap of IBS with panic disorder as well as other anxiety disorders and depression. It has been proposed that the high prevalence of psychiatric disorders in clinical samples of IBS patients is a result of self-selection of individuals with anxiety and depression, which drives treatment-seeking behavior. Over the past several years, data from some community studies have shown that there is a high prevalence of psychiatric disorders in individuals with IBS who never sought treatment. This suggests that there may be a more fundamental linnk between IBS, anxiety and mood disorders, such as shared pathophysiology.

This month's issue of CNS Spectrums brings together reviews on the brain-gut axis, each of which provides a unique perspective, which is complementary to the other reviews.

Kirsten Tillisch, MD, and Emeran A. Mayer, MD, review the neurobiology of visceral sensation, focusing on visceral hyperalgesia in IBS. In their paper, the importance of expectancy, comorbidity, gender, and other issues on pain perception is discussed. One of the most fascinating points the authors make is that extra-intestinal functional disorders, such as fibromyalgia, which often coexists with IBS, may affect somatic perception and pain thresholds. The observation that these disorders not only co-exist, but can affect each other raises an important and often overlooked issue for researchers. Comorbid disorders should be assessed and taken into account when conducting studies in patients with IBS. The authors highlight advances in methodology and new conceptual frameworks for understanding the functional gastrointestinal disorders (FGIDs) as well as remaining gaps in our knowledge about visceral hyperalgesia.