Evaluating fMRI methods for assessing hemispheric language dominance in healthy subjects

Area of Science:

• Neuroscience
• Cognitive Science
• Psycholinguistics

Background:

• Quantifying hemispheric language dominance is crucial for understanding brain function.
• Existing methods for assessing language lateralization have varying degrees of statistical rigor.
• The impact of preprocessing steps on lateralization measures requires further investigation.

Purpose of the Study:

• To evaluate two distinct methods, the flip method (FM) and lateralization indices method (LIM), for quantifying hemispheric language dominance.
• To assess the robustness of FM and LIM by comparing their results with manual lateralization indices (MLI).
• To investigate the effect of neuroimaging preprocessing steps (spatial normalization, smoothing, clustering - NSC) on lateralization measures.

Main Methods:

• Utilized rhyme detection and word fluency tasks in healthy subjects.
• FM involved direct statistical comparison of hemispheric activity.
• LIM calculated lateralization indices based on activated pixel counts.

Main Results:

• Both FM and LIM showed significant correlations with MLI, indicating robustness.
• NSC preprocessing did not alter hemispheric specialization.
• NSC preprocessing led to an increased inter-hemispheric difference value.

Conclusions:

• FM and LIM are robust and reliable methods for quantifying language dominance in healthy individuals.
• The choice of preprocessing steps can influence the magnitude of inter-hemispheric differences.
• Further research can refine these methods for clinical and research applications.