Domain-specific reorganization of semantic processing after extensive damage to the left temporal lobe.

We investigated with fMRI the cortical correlates of recovery of semantic processing in a patient (DL) with left temporal damage. Names of animals, plant, and artifacts (semantic conditions) and reversed words (baseline condition) were auditorily presented to the patient and nine control subjects in a category monitoring task. Data analyses showed large differences between the patterns of domain-specific semantic activation observed in DL and the control subjects, which could be attributed to a cortical reorganization compensating for the damaged part of the semantic processing system in DL. Such reorganization relied on three main mechanisms, first, upholding of a subset of the structurally intact domain-specific regions, second, functional changes (both decreases and increases) of the domain specificity in several structurally intact regions that are normally engaged in the domain-specific network and, third, recruitment of supplementary domain-specific areas. Thus, in DL, animal-specific processing engaged supplementary areas in the left lingual gyrus and right cuneus, which correspond to animal-specific regions usually engaged in more demanding semantic tasks whereas the supplementary areas recruited for artifact-specific processing within the left superior/middle occipital lobe and right angular gyrus probably are endowed with a related but not domain-specific, semantic function. In contrast, no supplementary area contributed to plant-specific processing in DL. These findings suggest that the pattern of cortical reorganization consecutive to damage to the semantic processing network depends on the particular domain-specific function sustained by the damaged areas and the capacity of the remaining areas to assume this function.

Targeted Ds-tagging strategy generates high allelic diversity at the Arabidopsis HY2 locus.

The targeted (or directed) tagging is a strategy aimed to mobilize a tranposon into a specific gene (target). Only a very few Arabidopsis genes have been tagged by this way, thus the efficiency of the strategy, as well as the diversity of the alleles obtained are not well documented. We have used a maize Ds element in a directed tagging of HY2. The starting Ds element, located 22 kb proximal to HY2, has been remobilized in a cross with an Ac transposase source line. From the F2 progeny of 4800 F1 we phenotypically isolated seven hy2 mutants. Molecular analysis of these alleles revealed that two contained a Ds element in HY2 and were instable, three have a large deletion that partially or completely removed HY2, one has a footprint in a HY2 exon and one leaky allele consisted of a 22 kb inversion upstream the HY2 coding sequence. Thus, the transposon-based directed tagging strategy generates a wide diversity of tagged and non-tagged alleles that can be used to generate allelic series or deletion of clustered genes.