Cortical activation in language tasks depends on semantic categories: An fMRI study

NeuroImage

11, Number

5, 2000, Part 2 of 2 Parts ID

E C;L@

LANGUAGE

Cortical Activation

in Language Tasks depends on Semantic Categories: An fMR1 Study

Gunther Fed*, Joe Ilmbergert, *Dept.of Neuroradiology,

Tarek A. Yousry*

Ludwig-Maximilians-University,

Munich, Germany

?Dept.of Physic& Medicine, Ludwig-Maximilians-University,

Munich, Germany

Introduction The occurrence of anomias restricted to specific semantic categories in brain-injured patients (i.e. selective difficulty in naming fruits and vegetables) indicates a differential involvement of cortical areas in the naming process that depends on semantic houndaries. Imaging data from normal subjects seem to confirm this hypothesis. For example, Martin et al. [ I] in a PET study used tool and animal items that had to be named. If the two conditions were contrasted directly in a group analysis, naming animals resulted in selective activation of the left medial occipital lobe, whereas naming tools led to activations in a left premotor and a left middle temporal gyms area. In our study we used fMRJ to identify cortical sites involved in the processing of these categories in two language tasks, naming and semantic fluency. Methods MRI Acquisition: We examined 16 healthy right-handed volunteers, FMRI was performed using EPI sequences (128*128 matix size, 26 slices/scan, 6 set interscan interval) on a Siemens Vision 1.5T. Stimuli were presented in the scanner through goggles which were connected to a computer outside the magnet. An examination consisted of 2 runs with 6 active and 6 baseline phases. In the active phase (60 set) 10 drawings of animals and 10 drawings of tools were presented in a row. In the baseline phase (30 set) a random dot image was presented. During the first run the volunteers had to name aloud the drawings of animals and tools presented (confrontation naming). During the second run the volunteers again named the drawings of animals and tools and in addition had to find and to pronounce the name of another animal or tool (confrontation naming plus semantic generation). During the baseline phase the volunteers just had to look at the random dot image in both mns. Postprocessing: For postprocessing SPM’99 (Wellcome Dept. Of Cognitive Neurology, London) was used. Group analysis (second level analysis: one sample t-test) was performed, defining an activation above T=7.66 (p-values corrected for the entire volume) as significant. Results When contrasting the two semantic categories (animals/tools), group analysis showed the following corrected significant activations: naming tools: left cingulate gyms; naming animals: inferior temporal gyms bilateral; semantic generation tools: left inferior parietal lobule; semantic generation animals: inferior temporal gyms bilateral. When subtracting the naming condition from the semantic condition, left sided activation was found in the medial frontal gyrus and in the inferior parietal gyms for both animals and tools. Discussion Our results confirm that the topographical pattern of knowledge representation seen in functional imaging depends on the semantic categories that are being processed in the respective tasks. When in a simple naming task knowledge about animals, as contrasted with tools, is processed. a temporo-occipital activation is found in both hemispheres. The activation is stronger in the right hemisphere possibly indicating that non-linguistic component5 such as knowledge about visual features of animals are involved in this specific task. A similar pattern of activation i\ seen for animal items when contrasting the two semantic categories in a generation task where another member of the same category has to be produced in addition to naming. For tools items, however. there is left-sided activation only. demonstrating a strong verbal encoding of knowledge about these items. If the aspect of ;ener-sting an dddittonal re,ponsr ts highhghted by contrastmg the nammg task wtth the generation task, there is strong left-Tided frontal activation irrespective of arm&c category possibly indicating selection processes that are involved in any generation task. Reference 1. Martin,

A., Wiggs.

C.L.,

Ungerleider,

L.C.

and Haxby,

J.V. Nature

S336

379, 649.652;

1996.