Published online before print November 13, 2003, doi: 10.1161/01.STR.0000103833.70778.20
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(Stroke. 2003;34:2906.)
© 2003 American Heart Association, Inc.
Original Contributions |
Editorial Comment—Key Role of the Superior Temporal Gyrus for Language Performance and Recovery From Aphasia
Max-Planck-Institut für neurologische Forschung, Neurologische Universitätsklinik, Köln, Germany
The plasticity of functional networks is an intriguing phenomenon that plays a role in learning and is important for recovery after brain damage. Activation studies by PET and functional MRI (fMRI) can be used to study neuroplasticity noninvasively and have opened new ways to understand the interaction within neural networks in the performance of complex tasks and for achieving new skills, to detect changes in activation patterns induced by lesions, and to follow compensatory mechanisms in recovery. Cardebat et al1 have used this concept to study activation of regional cerebral blood flow by PET during a word generation task in 8 stroke victims and compared the changes in the activation patterns in the chronic course with changes over time in healthy subjects. Whereas their data in the patient cohort add to longitudinal studies in poststroke aphasia, especially by extending the observation period over 1 year, the changes in activation patterns observed in healthy volunteers in relation to improved performance in language tasks are important as a basis for longitudinal studies in patients and indicate the ability of functional networks to minimize the workload for repeated and familiar tasks: It is the main finding of this study that with improved performance the extent of activation in normals is reduced, and the pattern is "normalized" in patients.
This study contributes important pieces to the puzzle of language performance and recovery after stroke, but it is quite difficult to compare the results with previous findings: The small group of patients included is rather heterogeneous with infarcts in different locations involving variable subcortical and cortical regions. Therefore, a correlation between extent of improvement and (re)activation pattern could not be obtained, which was reported previously.2 The patients were also studied rather late in the course after the stroke (first PET session 
2 months, second PET session >12 months after the stroke) and some of the differences to other reports could well be due to this time factor as the observation period was in the subacute phase in other studies (8 patients, studied at 2 weeks and 6 months,3 23 patients, studied at 2 and 8 weeks2) when usually most of improvements of poststroke aphasia occur.4 It is important to note that the present study again stresses the eminent role of the superior temporal gyrus for performance in language tasks in normals5,6 and for recovery of relevant language function after stroke.2,7,8 It is, however, still a matter of controversy if lateralized or bilateral involvement of this area is important for performance and recovery of speech: the majority of authors stress the superior role of the dominant left hemisphere,9,10 whereas the data presented show bilateral activation in normals and patients and thereby stress the importance of a bihemispheric network, in which the 2 hemispheres act as a unit with the right hemisphere aiding and sustaining speech processing and inhibiting unrelated activity.11 However, one still must consider that the role of the 2 hemispheres is differentiated with the left dominant regions more involved in complex and difficult tasks and in recovery of function to a high level, both of which could not be tested in the small cohorts.
In addition to positive correlations between performance and flow activations in superior temporal regions, Cardebat et al1 observed negative correlations between performance and flow in various regions, among others, in the left superior frontal cortex in healthy subjects and in the right superior frontal cortex in aphasic patients. This pattern of activation shows some similarity to that observed in patients with tumors in the dominant hemisphere, where the degree of lateralization of frontal activation to the right—a reversed speech dominance—was inversely related to language performance.12 Whereas the reduced activation in various regions might be related to changes in the emotional state with attention focused on task performance,13 the deactivation in some regions within the functional network might also be related to collateral inhibition by increased activity of specialized areas.10,14 The impact of the various activation patterns on the estimation of prognosis and recovery of poststroke aphasia, however, needs to be established in larger studies. The imaging protocols could also help to evaluate the efficacy of various rehabilitative therapies including adjuvant drug treatment.15
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 Top References |
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1. Cardebat D, Demonet JF, de Boissezon X, Marie N, Marie RM, Lambert J, Baron JC, Puel M. Behavioral and neurofunctional changes over time in healthy and aphasic subjects: a PET language activation study. Stroke. 2003; 34: 2900–2907.
2. Heiss W-D, Kessler J, Thiel A, Ghaemi M, Karbe H. Differential capacity of left and right hemispheric areas for compensation of poststroke aphasia. Ann Neurol. 1999; 45: 430–438.[CrossRef][Medline] [Order article via Infotrieve]
3. Cappa SF, Perani D, Grassi F, Bressi S, Alberoni M, Franceschi M, Bettinardi V, Todde S, Fazio F. A PET follow-up study of recovery after stroke in acute aphasics. Brain Lang. 1997; 56: 55–67.[CrossRef][Medline] [Order article via Infotrieve]
4. Basso A. Prognostic factors in aphasia. Aphasiology. 1992; 6: 337–348.
5. Raichle ME, Fiez JA, Videen TO, Macleod AMK, Pardo JV, Fox PT, Petersen SE. Practice-related changes in human brain functional anatomy during nonmotor learning. Cerebral Cortex. 1994; 4: 8–26.
6. Indefrey P, Levelt WJ. The neural correlates of language production. In: Gazzaniga M, ed. The New Cognitive Neurosciences. Cambridge, UK: Bradford Book and the MIT Press; 2002: 845–865.
7. Warburton E, Price CJ, Swinburn K, Wise RJS. Mechanisms of recovery from aphasia: evidence from positron emission tomography studies. J Neurol Neurosurg Psychiatry. 1999; 66: 155–161.
8. Cao Y, Vikingstad EM, George KP, Johnson AF, Welch KMA. Cortical language activation in stroke patients recovering from aphasia with functional MRI. Stroke. 1999; 30: 2331–2340.
9. Benson DF. Language in the left hemisphere. In: Benson DF, Zaidel E, eds. The Dual Brain. New York, NY: Guilford; 1985: 193–203.
10. Selnes OA. The ontogeny of cerebral language dominance. Brain Lang. 2000; 71: 217–220.[CrossRef][Medline] [Order article via Infotrieve]
11. Sperry R. Consciousness, personal identity, and the divided brain. In: Leporé F, Ptito M, Jasper HH, eds. Two Hemispheres - One Brain. Functions of the Corpus Callosum. New York, NY: Alan R. Liss; 1986: 3–20.
12. Thiel A, Herholz K, Koyuncu A, Ghaemi M, Kracht L, Habedank B, Heiss W-D. Plasticity of language networks in patients with brain tumors: a PET activation study. Ann Neurol. 2001; 50: 620–629.[CrossRef][Medline] [Order article via Infotrieve]
13. Simpson JR Jr, Snyder AZ, Gusnard DA, Raichle ME. Emotion-induced changes in human medial prefrontal cortex, I: during cognitive task performance. Proc Natl Acad Sci U S A. 2001; 98: 683–687.
14. Karbe H, Herholz K, Halber M, Heiss W-D. Collateral inhibition of transcallosal activity facilitates functional brain asymmetry. J Cereb Blood Flow Metab. 1998; 18: 1157–1161.[CrossRef][Medline] [Order article via Infotrieve]
15. Kessler J, Thiel A, Karbe H, Heiss W-D. Piracetam improves activated blood flow and facilitates rehabilitation of poststroke aphasic patients. Stroke. 2000; 31: 2112–2116.
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