Elodie Lerens

Right occipital cortex activation correlates with superior odor processing performance in the early blind.

Using functional magnetic resonance imaging (fMRI) in ten early blind humans, we found robust occipital activation during two odor-processing tasks (discrimination or categorization of fruit and flower odors), as well as during control auditory-verbal conditions (discrimination or categorization of fruit and flower names). We also found evidence for reorganization and specialization of the ventral part of the occipital cortex, with dissociation according to stimulus modality: the right fusiform gyrus was most activated during olfactory conditions while part of the left ventral lateral occipital complex showed a preference for auditory-verbal processing. Only little occipital activation was found in sighted subjects, but the same right-olfactory/left-auditory-verbal hemispheric lateralization was found overall in their brain. This difference between the groups was mirrored by superior performance of the blind in various odor-processing tasks. Moreover, the level of right fusiform gyrus activation during the olfactory conditions was highly correlated with individual scores in a variety of odor recognition tests, indicating that the additional occipital activation may play a functional role in odor processing.

Does visual experience influence the spatial distribution of auditory attention

Sighted individuals are less accurate and slower to localize sounds coming from the peripheral space than sounds coming from the frontal space. This specific bias in favour of the frontal auditory space seems reduced in early blind individuals, who are particularly better than sighted individuals at localizing sounds coming from the peripheral space. Currently, it is not clear to what extent this bias in the auditory space is a general phenomenon or if it applies only to spatial processing (i.e. sound localization). In our approach we compared the performance of early blind participants with that of sighted subjects during a frequency discrimination task with sounds originating either from frontal or peripheral locations. Results showed that early blind participants discriminated faster than sighted subjects both peripheral and frontal sounds. In addition, sighted subjects were faster at discriminating frontal sounds than peripheral ones, whereas early blind participants showed equal discrimination speed for frontal and peripheral sounds. We conclude that the spatial bias observed in sighted subjects reflects an unbalance in the spatial distribution of auditory attention resources that is induced by visual experience.

Development of a fully automated system for delivering odors in an MRI environment.

We describe the development and evaluation of a computer-controlled system for delivering odors in a magnetic resonance imaging (MRI) environment. The system allows a timely presentation of different odors in synchrony with MRI sequences and participant’s inspiration phase. The rise/fall time of odor deliverance has been optimized to generate prompt and strong stimulations. Equipped with a user-friendly programming interface, the system can be used reliably in a wide range of experimental paradigms. We have paid particular attention to developing a portable system that is relatively easy, rapid, and inexpensive to replicate. The equipment has been tested in a 3-Tesla MRI in a boxcar paradigm, in which stimulation conditions alternated with rest periods (no stimulation). The experiment demonstrated the good functioning of the device and its efficiency in producing the expected activation in the olfactory cortex; it also revealed some methodological and technical aspects to be improved.

Improved Beat Asynchrony Detection in Early Blind Individuals

Although early blind (EB) individuals are thought to have a better musical sense than sighted subjects, no study has investigated the musical rhythm and beat processing abilities in EB individuals. Using an adaptive ‘up and down’ procedure, we measured the beat asynchrony detection threshold and the duration discrimination threshold, in the auditory and vibrotactile modalities in both EB and sighted control (SC) subjects matched for age, gender, and musical experience. We observed that EB subjects were better than SC in the beat asynchrony detection task; that is, they showed lower thresholds than SC, both in the auditory and in the vibrotactile modalities. In addition, EB subjects had a lower threshold than SC for duration discrimination in the vibrotactile modality only. These improved beat asynchrony detection abilities may contribute to the known excellent musical abilities often observed in many blind subjects.

Perception of rhythm through auditory, vibro-tactile and visual stimulations: an fMRI study

Recent studies reported an involvement of motor/premotor brain areas during the perception of rhythm and beat in audition. However, little is known about the neural network of beat perception through non-auditory modalities. Here we used functional magnetic resonance imaging with auditory, vibro-tactile and visual rhythmic sequences in order to highlight the modality-specific areas involved in beat perception. We contrasted the brain activity changes in 20 healthy volunteers exposed to rhythmic sequences with a beat and control sequences without a beat. Results showed a recruitment of premotor cortex, supplementary motor area (SMA) and basal ganglia during beat sequences compared to rest in all three modalities. Beat sequences compared to no-beat sequences elicited the selective recruitment of the putamen and the SMA in the three sensory modalities, although to a lesser extent in vision. We conclude that the putamen and the SMA play a role in the prediction ability of a regular temporal pattern, although this seems less pronounced in vision compared to audition and to the vibro-tactile sensory modality.

The spatial distribution of auditory attention in early blindness

Early blind people compensate for their lack of vision by developing superior abilities in the remaining senses such as audition (Collignon et al., 2006; Gougoux et al., 2004; Wan et al., 2010). Previous studies reported supra-normal abilities in auditory spatial attention, particularly for the localization of peripheral stimuli in comparison with frontal stimuli (Lessard et al., 1998; Roder et al., 1999). However, it is unknown whether this specific supra-normal ability extends to the non-spatial attention domain. Here we compared the performance of early blind subjects and sighted controls, who were blindfolded, during an auditory non-spatial attention task: target detection among distractors according to tone frequency. We paid a special attention to the potential effect of the sound source location, comparing the accuracy and speed in target detection in the peripheral and frontal space. Blind subjects displayed shorter reaction times than sighted controls for both peripheral and frontal stimuli. Moreover, in the two groups of subjects, we observed an interaction effect between the target location and the distractors location: the target was detected faster when its location was different from the location of the distractors. However, this effect was attenuated in early blind subjects and even cancelled in the condition with frontal targets and peripheral distractors. We conclude that early blind people compensate for the lack of vision by enhancing their ability to process auditory information but also by changing the spatial distribution of their auditory attention resources.

Dissociation between Olfactory and Auditory-Verbal Processing in the Occipital Cortex of Early Blind Subjects

Despite numerous studies on cross-modal brain plasticity, it is still unclear to what extent distinct (nonvisual) sensory modalities are segregated in the reorganized occipital cortex (OC) of blind subjects. In addition, little is known about the potential role of the OC in olfactory processing that is enhanced in these subjects. Using fMRI, we monitored the brain activity in ten early blind (EB) subjects while they were discriminating or categorizing olfactory (fruit and flower odors) versus auditory-verbal stimuli (fruit and flower names). Both modalities selectively activated the ventral part of the OC and were segregated in this cortex; the right fusiform gyrus was most activated during olfactory conditions while part of the left ventral lateral occipital complex showed a preference for auditory-verbal processing. No such occipital activation was observed in sighted controls, but the same right-olfactory/left-auditory hemispheric lateralization was found overall in their brain. These findings constitute the first evidences (1) that the OC is involved in the processing of odors in EB subjects and (2) that sensory modalities are (to some extent) segregated in the OC of EB subjects. Furthermore, the ventral stream seems to develop its designated functional role in processing stimulus identity independently of visual experience.