The term cluster describes the typical chronological pattern of these headaches. The tend to occur regularly for days or weeks and are then separated by periods of remission lasting months or years.
Attacks typically last between 15 minutes and 3 hours. This type of pattern makes cluster headache a good candidate for imaging studies conducted during and between attacks.
Qui and colleagues from the People's Republic of China conducted a brain conductivity study in a series of male subjects. The key elements of the design of the study included:
Subjects: 12 male right-handed men between the ages of 19 and 46 off medication with a control group of 12 right-handed men without a history of cluster headaches
Imaging sequence: Case subjects completed two fMRI scans. One was done during an acute attack and a second scan was completed at least four hours after an attack but during the cluster period.
Imaging protocol: Resting-state functional connectivity with focus on the hypothalamus, a brain region linked to cluster headache in previous studies.
The key findings from this study were:
- Statistically significant increased right hypothalamus connectivity occurred during the cluster attack phase compared to between attacks in the cluster subjects
- This increased hypothalamic connectivity could be linked to three regions/circuits
- First region: Anterior cingulate cortex (ACC), several frontal cortex regions, the parahippocampal region and the amygdala
- Second region: precuneus, supramarginal gyrus and the supratemporal gyrus
- Third region: precuneus, parietal lobe, posterior cingulate cortex (PCC)
- Case subjects between cluster attacks continued to show connectivity patterns distinct from controls in the right hypothalamus and circuits connected to regions of the temporal lobe, the insular cortex, the occipital lobe and the uncus
The authors note their findings confirm that the ipsilateral hypothalamus (hemi-hypothalamus on the same side as the headache) appears to be a key area of involvement in cluster headache. The brain image on the left highlights the right hypothalamus in the green color.
The authors also note (acronym clarifications in parentheses added by me): "Our findings in the acute spontaneous CH (cluster headache) attack showed that the altered rs-FC (resting state functional connectivity) of the hypothalamus is involved in the processing and modulation of pain referred to as the pain matrix, and/or is involved in cognitive and emotional modulation of pain".
The findings of a connection between the hypothalamus and the occipital (or vision lobe) is interesting as this occipital lobe is typically not involved in brain pain circuitry. However, the authors note that many cluster headache sufferers have light sensitivity (photophobia) and symptom may reflect some changes in the occipital lobe connectivity.
The typical pattern of cluster headaches makes it a promising model to study not only headaches but pain processing in general. This is an informative and important study and interested readers can access the free full-text article by clicking on the reference below.
Photo of sandhill crane taken at Venice, Florida rookery is from the author's files. Brain hypothalamus figure is an iPad screenshot from the 3D Brain app.
Qiu E, Wang Y, Ma L, Tian L, Liu R, Dong Z, Xu X, Zou Z, & Yu S (2013). Abnormal brain functional connectivity of the hypothalamus in cluster headaches. PloS one, 8 (2) PMID: 23460913