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Hemisphere differences in language processing: A neuroimaging study in men and in women, taking into account changes in progesterone level during the menstrual cycle

Unterschiede der Hemisphäre in Sprachverarbeitung: Ein Neurobildgebungsstudie in Männer und Frauen, hinsichtlich Fluktuierungen in Progesteron Konzentration während der Menstruationszyklus

  • The human brain is characterised by two apparently symmetrical cerebral hemispheres. However, the functions attributed to each half of the brain are very distinct with a relative specialisation of the left hemisphere for language processing. Most laterality research has been performed on a behavioural level, using techniques such as visual half-field presentation. The visual half-field technique involves the presentation of stimuli in the left or right visual field for a very short time (about 200 ms). During the presentation of lateralized stimuli, the gaze of the participants is fixated on a centrally presented fixation cross. This technique takes advantage of the anatomy of the visual pathway as the temporal hemiretinae project ipsilateral, while the nasal hemiretinae project contralateral. Thus, stimuli presented in the left or right visual field are initially processed in the contralateral hemisphere. Language organisation can also be directly investigated using functional magnetic resonance imaging (fMRI). Both behavioural and neuroimaging studies showed that about 95% of right-handed men have a left hemispheric specialisation for language. In contrast, data on language organisation in women are ambiguous. It is supposed that this ambivalent picture might be associated with changes in gonadal steroid levels in blood during the menstrual cycle. However, gonadal steroid effects are complex and their role in functional cerebral lateralization is still open to discussion. The aim of this PhD project was to investigate, using fMRI: (1) the processing of linguistic information initially received in the specialised, non-specialised or both hemispheres; (2) linking the associated brain activation pattern with progesterone levels during the menstrual cycle. Firstly, brain activation was measured in 16 right-handed, healthy males during processing of different components of language (orthography, phonology and semantics) after reception in the left, right or both hemispheres. Secondly, to investigate changes in language organisation during the menstrual cycle, we conducted an event-related fMRI study during semantic and phonological processing also using visual half-field and central presentation of linguistic stimuli. Our results revealed higher BOLD signal intensity change in the visual cortex contralateral to the visual field of stimulus presentation compared to the ipsilateral visual cortex reflecting the crossing of visual pathways. We also found support for the hypothesis that the superiority of word recognition in the left VWFA is the result of a reduced activity in the right VWFA under left hemispheric control. Further, linguistic information received in the subdominant RH, is interhemispheric transferred to the left hemisphere for phonological processing. Semantic processing in contrast occurs in the specialised and in the non-specialised hemisphere. For the group of women, data analysis revealed that during semantic processing, salivary progesterone levels correlated positively with brain activity of the left superior frontal gyrus, left middle and inferior occipital gyri and bilateral fusiform gyrus. In contrast, the brain activation pattern for phonological processing did not change significantly across the menstrual cycle. In conclusion, the effect of serum progesterone levels on brain activity is task and region specific.
  • Ungefähr 95% der männlichen Rechtshänder haben eine linkshemisphärische Spezialisierung für Sprache. Im Gegensatz hierzu sind Ergebnisse der sprachlichen Organisation bei Frauen nicht eindeutig. Es wird angenommen dass diese Vielfalt mit Konzentrationsveränderungen der gonadalen Steroidhormone während des Menstruationszyklus assoziiert sei. In der vorliegenden Arbeit wurde bei männlichen Probanden mittels lateralisierte Darbietung von linguistischen Stimuli während einer funktioneller Magnet Resonanz Tomographie Aufnahme wurde die Organisation und Kapazität der Sprachverarbeitung in der einzelnen Hemisphären erfasst in Männer. In einem weiteren Schritt wurde die gleiche Untersuchung an weiblichen Probanden an zwei Zeitpunkten des Zyklus durchgeführt.

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Metadaten
Author:Gwendy Steendam
URN:urn:nbn:de:hbz:385-4904
Title Additional (English):Hemisphere differences in language processing: A neuroimaging study in men and in women, taking into account changes in progesterone level during the menstrual cycle
Advisor:Gwendy Steendam
Document Type:Doctoral Thesis
Language:English
Date of completion:2008/09/15
Publishing institution:Universität Trier
Granting institution:Universität Trier, Fachbereich 1
Date of final exam:2008/07/09
Release Date:2008/09/15
Tag:fMRI; functional specialisation of hemispheres; language processing; menstrual cycle
GND Keyword:Funktionelle NMR-Tomographie; Hemisphärendominanz; Menstruationszyklus; Sprachverarbeitung
Institutes:Fachbereich 1 / Psychologie
Dewey Decimal Classification:1 Philosophie und Psychologie / 15 Psychologie / 150 Psychologie

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