The researchers found the biggest differences in activity in the posterior cingulate cortex.

BBC: NEWS | Health | Alzheimer's linked to daydreams

Another suggests hypnotherapy may have an impact on a part of the brain which processes pain called the anterior cingulate cortex (ACC).

BBC: Hypnotherapy session

When they were faced with tossing or keeping their own items, the hoarders' brain responses also differed from that of the other participants: they showed excessive activation in the anterior cingulate cortex, a brain region involved with decision-making, particularly in situations involving conflicting information or uncertainty.

CNN: STORY HIGHLIGHTS

Areas of the brain thought to be included in this network include medial frontal, the lateral parietal and the posterior cingulate regions of the cortex.

BBC: NEWS | Health | Alzheimer's linked to daydreams