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Bilateral thalamic activation occurs during lexical but not semantic processing
Neurolmage
11, Number
5, 2000, Part 2 of 2 Parts 1 D E al@
LANGUAGE
Bilateral Thalamic Activation Occurs During Lexical but Not Semantic Processing Mika Oki, Staci A. Gruber, William D. Scott Killgore, Deborah A. Yurgehm-Todd Cognitive Neuroimaging Luboratoty, McLean Hospital, Harvard Medical School Introduction The thalamus consists of a complex group of subcortical nuclei that function to transfer information among a distributed network of sensory, motor, motivational, and associative regions of the brain. Lesion studies suggest that the thalamus serves to activate higher order cortical networks necessary for lexical and semantic processing and that thalamic injury can severely disrupt oral reading performance (1) and lexical retrieval (2). Abnormal function within the thalamua has also been implicated in a number of psychopathological conditions involving language systems, such as the generation of auditory hallucinations in psychotic illness (3). With recent advances in functional magnetic resonance imaging (FMRI) technology, it is now possible to map the stream of information processing involved in lexical and semantic cognitive functions (4). To clarify the role of the thalamus in language processing. we examined the activation of the mediodorsal nuclei of the thalamus during the Stroop Color-Word Test, permitting a comparison of simple lexical processing (Word Reading), semantic processing (Color Naming), and inhibition of lexical processing in service of semantic processing (Interference). Method Ten healthy right-handed subjects (4 male; 23.5 years of age, 15.9 years of education), screened for psychopathology with the Structured Clinical Interview for DSM-IV (Patient edition) to rule out psychiatric disorder, participated in the study. Scanning was performed using a quadrature head coil on a 1.5 Tesla scanner retrofitted with a whole-body echoplanar coil. Images were acquired every three seconds using a gradient echo pulse sequence (TE = 40 msec., flip angle 75 degrees, slice thickness 6mm with lmm skip). Subjects were administered the three conditions of the Stroop Color-Word Test during three scanning epochs (150 seconds each). During Word Reading, subjects were presented with a series of color names (e.g., red, blue, green) printed in black ink and were required to read each printed word aloud. During Color Naming, subjects were presented with a series of colored rectangles and were required to state the ink color. The Color-Word Interference task presented subjects with a series of typed color names, printed in an incongruent ink color (e.g., “red” printed in blue ink) and subjects reported the color of the ink. During each epoch, the Stroop stimuli alternated in 30 second blocks with a resting fixation control task. Functional images were corrected for in plane and rotational motion (5). Statistical analyses were restricted to anatomically pre-defined regions of interest (ROIs) consisting of the left and right mediodorsal neclei of the thalamus. Signal intensity was normalized to baseline and the mean percent change in signal intensity was calculated for each ROI across all three conditions for every subject. Results A comparison of the normalized signal intensity within each thalamus was made between baseline and task-activated status. The Word-Reading task produced significant activation within the left (p = ,004) and right (p < .OOOl) mediodorsal nuclei, suggesting that both thalami participate in simple lexical processing. In contrast, the Color-Naming task produced significant activation only within the left thalamus (p = .006), while the right showed no significant change from baseline. Interestingly, there was no task-related activation in within either thalamus during the Stroop Color-Word Interference condition. Conclusions These findings support the role of the thalamus in lexical and semantic processing, suggesting that bilateral thalamic nuclei are mobilized during oral reading. Because the thalamus is a major information processing relay, its activation represents an initial stage of processing leading to increased activity among a distributed network of bilateral cortical regions involved in language processing (6J. Color nanung, ri task mvolving semantic retrieval, appears to activate the left thalamus preferentially. consistent with earlier positron emission tomography findings (4). Finally, suppression of lexical processing during the interference condition resulted in a failure to activate either thalamux above baseline. suggesting that inhibition of thalamic relays may play a role in modulating language processing. This modulatory role of the thalamus may provide a key element to further modeling the function and dysfunction of the language system. References 1. 2. 3. 4. 5. 6.
Crosson, B. (1999). Brain Raymer. A. M.. Moberg, Silbersweig, et al., (1995). Rumsey. J. M.. Horowitz, Maas, L. C., Fredrick, B. Faiz, J. A.. Balota. D. A..
& Cognition, 40, 414-438. P., Crosson, B., Nadeau, S. & Roghi. L. J. (1997). Neurop.sycholo,qirr, -1.5, 21 l-219. Nature, 378, 176. B., Donohue, B. C., Nate. K.. Maisog, J. M., & Andreason, P. (1997). Brrrin, 120, 739-759. D., & Renshaw, P. F. (1997). Magnetic Resonance in Medicine, 37, 131-139. Raichle, M. E., & Petersen, S. E. (1993). Society for Neuroscience [Abstract], 19, 1808.
s353
11, Number
5, 2000, Part 2 of 2 Parts 1 D E al@
LANGUAGE
Bilateral Thalamic Activation Occurs During Lexical but Not Semantic Processing Mika Oki, Staci A. Gruber, William D. Scott Killgore, Deborah A. Yurgehm-Todd Cognitive Neuroimaging Luboratoty, McLean Hospital, Harvard Medical School Introduction The thalamus consists of a complex group of subcortical nuclei that function to transfer information among a distributed network of sensory, motor, motivational, and associative regions of the brain. Lesion studies suggest that the thalamus serves to activate higher order cortical networks necessary for lexical and semantic processing and that thalamic injury can severely disrupt oral reading performance (1) and lexical retrieval (2). Abnormal function within the thalamua has also been implicated in a number of psychopathological conditions involving language systems, such as the generation of auditory hallucinations in psychotic illness (3). With recent advances in functional magnetic resonance imaging (FMRI) technology, it is now possible to map the stream of information processing involved in lexical and semantic cognitive functions (4). To clarify the role of the thalamus in language processing. we examined the activation of the mediodorsal nuclei of the thalamus during the Stroop Color-Word Test, permitting a comparison of simple lexical processing (Word Reading), semantic processing (Color Naming), and inhibition of lexical processing in service of semantic processing (Interference). Method Ten healthy right-handed subjects (4 male; 23.5 years of age, 15.9 years of education), screened for psychopathology with the Structured Clinical Interview for DSM-IV (Patient edition) to rule out psychiatric disorder, participated in the study. Scanning was performed using a quadrature head coil on a 1.5 Tesla scanner retrofitted with a whole-body echoplanar coil. Images were acquired every three seconds using a gradient echo pulse sequence (TE = 40 msec., flip angle 75 degrees, slice thickness 6mm with lmm skip). Subjects were administered the three conditions of the Stroop Color-Word Test during three scanning epochs (150 seconds each). During Word Reading, subjects were presented with a series of color names (e.g., red, blue, green) printed in black ink and were required to read each printed word aloud. During Color Naming, subjects were presented with a series of colored rectangles and were required to state the ink color. The Color-Word Interference task presented subjects with a series of typed color names, printed in an incongruent ink color (e.g., “red” printed in blue ink) and subjects reported the color of the ink. During each epoch, the Stroop stimuli alternated in 30 second blocks with a resting fixation control task. Functional images were corrected for in plane and rotational motion (5). Statistical analyses were restricted to anatomically pre-defined regions of interest (ROIs) consisting of the left and right mediodorsal neclei of the thalamus. Signal intensity was normalized to baseline and the mean percent change in signal intensity was calculated for each ROI across all three conditions for every subject. Results A comparison of the normalized signal intensity within each thalamus was made between baseline and task-activated status. The Word-Reading task produced significant activation within the left (p = ,004) and right (p < .OOOl) mediodorsal nuclei, suggesting that both thalami participate in simple lexical processing. In contrast, the Color-Naming task produced significant activation only within the left thalamus (p = .006), while the right showed no significant change from baseline. Interestingly, there was no task-related activation in within either thalamus during the Stroop Color-Word Interference condition. Conclusions These findings support the role of the thalamus in lexical and semantic processing, suggesting that bilateral thalamic nuclei are mobilized during oral reading. Because the thalamus is a major information processing relay, its activation represents an initial stage of processing leading to increased activity among a distributed network of bilateral cortical regions involved in language processing (6J. Color nanung, ri task mvolving semantic retrieval, appears to activate the left thalamus preferentially. consistent with earlier positron emission tomography findings (4). Finally, suppression of lexical processing during the interference condition resulted in a failure to activate either thalamux above baseline. suggesting that inhibition of thalamic relays may play a role in modulating language processing. This modulatory role of the thalamus may provide a key element to further modeling the function and dysfunction of the language system. References 1. 2. 3. 4. 5. 6.
Crosson, B. (1999). Brain Raymer. A. M.. Moberg, Silbersweig, et al., (1995). Rumsey. J. M.. Horowitz, Maas, L. C., Fredrick, B. Faiz, J. A.. Balota. D. A..
& Cognition, 40, 414-438. P., Crosson, B., Nadeau, S. & Roghi. L. J. (1997). Neurop.sycholo,qirr, -1.5, 21 l-219. Nature, 378, 176. B., Donohue, B. C., Nate. K.. Maisog, J. M., & Andreason, P. (1997). Brrrin, 120, 739-759. D., & Renshaw, P. F. (1997). Magnetic Resonance in Medicine, 37, 131-139. Raichle, M. E., & Petersen, S. E. (1993). Society for Neuroscience [Abstract], 19, 1808.
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