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This study examined whether the memory encoding and short term maintenance of olfactory stimuli is associated with neurophysiological activation patterns which parallel those described for sensory modalities such as vision and auditory. We examined olfactory event-related potentials in an olfactory change detection task in twenty-four healthy adults and compared the measured activation to that found during passive olfactory stimulation. During the early olfactory post-processing phase, we found a sustained negativity over bilateral frontotemporal areas in the passive perception condition which was enhanced in the active memory task. There was no significant lateralization in either experimental condition. During the maintenance interval at the end of the delay period, we still found sustained activation over bilateral frontotemporal areas which was more negative in trials with correct - as compared to incorrect - behavioural responses. This was complemented by a general significantly stronger frontocentral activation. Summarizing, we were able to show that olfactory short term memory involves a parallel sequence of activation as found in other sensory modalities. In addition to olfactory-specific frontotemporal activations in the memory encoding phase, we found slow cortical potentials over frontocentral areas during the memory maintenance phase indicating the activation of a supramodal memory maintenance system. These findings could represent the neurophysiological underpinning of the 'olfactory flacon', the olfactory counter-part to the visual sketchpad and phonological loop embedded in Baddeley's working memory model.

The present study compared the temporal and spatial aspects of human olfactory and trigeminal processing. A relatively selective trigeminal stimulus, CO2, and a relatively selective olfactory stimulus, H2S, were delivered with an olfactometer to young, healthy volunteers. The analysis was performed in a classical (5-electrode, main ERPs peaks) and modern approach (high topographical resolution, inverse solution, source localization). Results of microstate segmentation highlighted 5 maps that generally described the two processes at cerebral level. The trigeminal response differed from the olfactory response up to 300 ms after stimulus onset. In this time range, source analysis pointed out that the olfactory stimulation involved olfactory related areas, while trigeminal stimulation involved noxious/somatosensory specific brain areas. Moreover, from 300 ms on our data showed a similarity between the two processes. Statistical parametrical mapping of the differences between conditions suggested greater activation in a specific motor/sniffing network for the CO2 stimulation (probably related to a regulation of the potential noxious stimulus) and a greater activation of the ipsilateral primary olfactory cortex for H2S.

Aim of the present study was to investigate laterality of the gustatory system in the human brain for the taste qualities elicited by MSG (monosodium glutamate) and NaCl (sodium chloride). A total of 23 subjects participated in a block-design functional magnetic resonance imaging (fMRI) study. Liquid stimuli were presented at supra-threshold concentrations and delivered by means of a computer controlled gustometer. Left and right sides of the mouth were stimulated separately in order to correlate statistical parametrical maps to both the site of the stimulus and the specific taste quality. Following the effects of the site of stimulation through primary and secondary gustatory cortices an effort was made to explore the laterality of the gustatory pathways. Our results showed for both tastants a predominance of ipsilateral connections at the thalamus level. Insula left and right regions were both involved for both tastants. In these regions we found a high proportion of ipsilateral connection again for both the tastants. Considering orbitofrontal/prefrontal cortex, left-sided stimulation with NaCl or MSG produced left-sided activation of the orbito-frontal cortex clearly indicating the presence of an ipsilateral path. Finally, the hypothesis of frontal operculum as primary gustatory cortex and lateral prefrontal cortex as secondary was also supported by the results from dynamic causal modeling.