When Broca experiences the Janus syndrome: an ER-fMRI study comparing sentence comprehension and cognitive sequence processing.

The determining of brain regions that exhibit specific activity during sentence comprehension compared to other non-linguistic cognitive tasks constitutes one of the important challenges in the domain of functional neuroimaging of the faculty of language. In the current paper we report an event-related functional magnetic resonance imaging (ER-fMRI) experiment, in which we directly compared the cerebral basis of sentence comprehension on the one hand, and of abstract sequence processing on the other hand. Previous experimental work done in our group, as well as different observations from recent behavioural, neurophysiological and functional neuroimaging experiments led us to propose the hypothesis that both of these tasks would share certain computational properties. Thus, this experiment was designed to show which brain regions would be implicated in both tasks and compare them to brain regions that would be specifically engaged in sentence comprehension. Results from this experiment suggest that distinct sub-regions in the left prefrontal cortex, potentially including Broca's area show distinct activation patterns during both of these tasks. Results are discussed in the context of a construction-based model of sentence processing (see Dominey and Hoen, 2006, this issue) that is based on a dual-path processing mechanism separating function and content information processing. We propose and discuss the hypothesis that subparts of Broca's area BA 44 and BA 45 would respectively be implicated in two different aspects of sentence comprehension: i) a general structure mapping capability and ii) the online integration of semantic representations onto structural constraints.

Global integration of local color differences in transparency perception: An fMRI study.

In normal viewing, the visual system effortlessly assigns approximately constant attributes of color and shape to perceived objects. A fundamental component of this process is the compensation for illuminant variations and intervening media to recover reflectance properties of natural surfaces. We exploited the phenomenon of transparency perception to explore the cortical regions implicated in such processes, using fMRI. By manipulating the coherence of local color differences around a region in an image, we interfered with their global perceptual integration and thereby modified whether the region appeared transparent or not. We found the major cortical activation due to global integration of local color differences to be in the anterior part of the parahippocampal gyrus. Regions differentially activated by chromatic versus achromatic geometric patterns showed no significant differential response related to the coherence/incoherence of local color differences. The results link the integration of local color differences in the extraction of a transparent layer with sites activated by object-related properties of an image.

Involvement of right piriform cortex in olfactory familiarity judgments.

Previous studies have shown activation of right orbitofrontal cortex during judgments of odor familiarity. In the present study, we sought to extend our knowledge about the neural circuits involved in such a task by exploring the involvement of the right prefrontal areas and limbic/primary olfactory structures. Fourteen right-handed male subjects were tested using fMRI with a single functional run of two olfactory conditions (odor detection and familiarity judgments). Each condition included three epochs. During the familiarity condition, subjects rated whether odors were familiar or unfamiliar. During the detection condition, participants decided if odors were present. When contrasting the familiarity with the detection conditions, activated areas were found mainly in the right piriform cortex (PC) and hippocampus, the left inferior frontal gyrus and amygdala, and bilaterally in the mid-fusiform gyrus. Further analyses demonstrated that the right PC was more strongly activated than the left PC. This result supports the notion that the right PC is preferentially involved in judgments of odor familiarity.