Schweregrad und Rückbildung von Aphasien: Darstellung mittels funktioneller Bildgebung[1]

Zusammenfassung

Die Lokalisation sowie das Ausmaß einer fokalen Hirnläsion bestimmen das funktionelle Defizit. Die Wiederherstellung der betroffenen Funktion hingegen hängt in 1. Linie von der Plastizität der intakten Hirnrindenanteile ab. Die Bedeutung bestimmter Regionen im funktionellen Sprachnetzwerk kann mittels funktioneller bildgebender Verfahren dargestellt werden. Darüber hinaus kann der Effekt von Schädigungen spezifischer Kortexareale aufgezeigt werden. Im Rahmen solcher Untersuchungen bei Aphasikern wurden verschiedene Veränderungen des funktionellen Aktivierungsmusters bestimmten Sprachstörungen zugeordnet. Bei Patienten mit Aphasie durch einen ischämischen Hirninfarkt oder andere umschriebene Läsionen (z. B. Hirntumore) ist der Erhalt oder die funktionelle Reintegration des Gyrus temporalis superior (STG) entscheidend für eine zufriedenstellende klinische Erholung. Die Reaktivierung anderer ipsilateraler Sprachzentren oder kontralateraler Regionen fand sich bei Patienten mit geringerer Besserung ohne zufriedenstellende Sprachproduktion.

Abstract

Activation patterns in functional networks of the central nervous system can be studied with functional imaging modalities, e. g., positron emission tomography (PET) and functional magnetic resonance imaging (fMRI). If disturbances of neurologic function occur, these activation patterns are altered. Language is based on the interplay of a distributed network in which partial functions are executed in various centers, the primary language areas. The organization of these areas is hierarchical, lateralized to the dominant (usually left) hemisphere and adapts to the complexity of the specific language tasks. The specialization of different centers and the lateralization of functions are achieved by collateral and transcallosal inhibition of secondary language areas that are, under normal circumstances, not used for language performance. The interaction between primary and secondary language areas is of particular importance for the recovery from post-stroke aphasia. Functional imaging studies have demonstrated that aphasic patients with a favorable recovery predominantly activate areas in the dominant hemisphere during speech tasks. On the contrary, activation within the non-dominant (usually right) hemisphere might be a marker of failed or faulty recovery attempts or the breakdown of a balanced interhemispheric inhibition. Studies utilizing a combination of repetitive transcranial magnetic stimulation (rTMS) with functional imaging suggest a less effective compensatory potential of non-dominant network areas. Therefore, (over-)activation of non-dominant language areas may represent a maladaptive strategy by paradoxical functional facilitation as a result of decreased interhemispheric inhibition. Suppression of this paradoxical activation, e. g. with rTMS, might therefore be useful as a complementary therapy of aphasia.

Aktivierungsstudien - Aphasie - funktionelle Bildgebung - transkranielle Magnetstimulation - Schlaganfall

activation studies - aphasia - functional neuroimaging - language recovery - transcranial magnetic stimulation - stroke

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1 WSO Leadership in Stroke Medicine Award Lecture, Wien, 26.9.2008.

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