Context Matters
Using fMRI scans, researchers observed the brain activity of people trying to remember images they had first viewed in the presence of a specific scent (Gottfried et al., 2004). When recalling images they had linked to smells, odor-processing areas of the brain became noticeably excited, even in the absence of any odors. The scan shows the activity in the brain (see yellow on scan) of a person recalling an odor-linked image.

(Gottfried, J. A., Smith, A. P. R., Rugg, M. D., & Dolan, R. J. (2004). Remembrance of odors past: Human olfactory cortex in cross-modal recognition memory. neuron, 42, 687-895.)