Biomedical subjects

Cyril Pernet

Publications and source records attributed to Cyril Pernet.

3 recordsLinked to original sources

PubMed2005

Selective response to letter categorization within the left fusiform gyrus.

Neuroimaging studies that look at reading processes using words, pseudowords, nonwords and letters frequently report specific left fusiform gyrus (BA37) activations. In the present study, we examined fMRI signal variations within the left and right BA37 for paired Latin letters, Korean letters and geometrical figures in discrimination and categorization tasks. Data of Pernet et al. (Pernet, C., Franceries, X., Basan, S., Cassol, E., Démonet, J.F., Celsis, P., 2004. Anatomy and time course of discrimination and categorization processes in vision: an fMRI study. NeuroImage 22, 1563-1577) were re-analyzed using a ROI methodology that highlights the selective response of the left BA37 to Latin letter categorization. First, differences according to stimulus type were observed for the categorization task only. Second, we found weaker activation for Latin letter categorization than for both geometrical figure and Korean letter categorization. Third, only Latin letter categorization elicited as left-sided activation, although the direct comparison between regions did not demonstrate a significant difference. These data suggest that the left fusiform gyrus sustains access to letter representations in memory; and results are discussed with reference to the relationship between letter categorization and word recognition and to selective vs. specific (i.e. task-independent) neural response.

Adult↗

PubMed2004

Verb and noun generation tasks in Huntington's disease.

We compared noun- and verb-generation tasks in a demented group (n = 9, Dementia Rating Scale < or = 129) and in a non-demented group (n = 17, Dementia Rating Scale > 129) of Huntington's disease (HD) patients compared to 26 matched normal subjects. We did not find a specific deficit for verb production in non-demented patients who had a performance similar to but weaker than that of the controls across the four tasks. The profile of results was different in the demented group because, apart from a global deficit whatever the task in comparison with both non-demented and control groups, the demented patients exhibited increased difficulties in the two tasks implying verb production. The deficit of verb production observed in demented HD patients is discussed in relation to the damage to the motor loop in HD patients at later stages of disease.

Aphasia, Broca↗

PubMed2003

Neural timing of visual implicit categorization.

Most of the neuroimaging studies that have shown visual category-specific activations or categorization effects have been based on a subtractive approach. In the present study, we investigated, by means of EEG, not only the net result of the categorization but also the dynamics of the process. Subjects had to perform a target detection task throughout an image set of distractors belonging to six categories: letters, geometrical figures, faces, tools, structured textures and Asiatic characters. Multivariate analyses were performed on the responses to the non-target stimuli according to their category. Categorical neural responses were only obtained on P2 latencies and N2 amplitudes. This result suggests that there are no differences in the first stage of the implicit categorization of the distractors (visual analysis and proximal stimulus representation elaboration from 100 to 220 ms) and that differences appear between 220 and 280 ms (matching to structural representations). Over-learned stimuli (e.g. letters) elicited the shortest P2 latency, contrasting with unknown categories (e.g. Asiatic characters) that revealed the longest P2 latencies and flattened N2 waves. Categorical differences indicate that the more a subject knows about an object, the less cognitive resources are used. In conclusion, our results suggest that a reduction in neural activity could reflect an improved accuracy in cognitive and cortical processing.

Adult↗