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Right-lateralized neural activity during inner speech repeated by cues.
Norio Fujimaki1, Tomoe Hayakawa, Ayumu Matani
1Brain Information Group, National Institute of Information and Communications Technology, 588-2 Iwaoka, Iwaoka-cho, Nishi-ku, Kobe 651-2492, Japan. fujimaki@po.nict.go.jp
Neuroreport
|January 11, 2005
Summary
This study on inner speech reveals right-hemisphere brain activity, suggesting a focus on prosody (pitch and rhythm) over phonemes. This finding offers new insights into how the brain processes spoken language elements.
Area of Science:
- Neuroscience
- Cognitive Science
- Psycholinguistics
Background:
- Inner speech, the internal monologue, is crucial for cognitive functions.
- Understanding the neural basis of inner speech, particularly its hemispheric lateralization, remains an active area of research.
- Previous studies often focused on phonemic processing, potentially overlooking other linguistic features.
Purpose of the Study:
- To investigate the neural activity during the inner speech of meaningless syllable sequences.
- To determine the hemispheric lateralization of brain regions involved in this task.
- To explore whether prosodic or phonemic features are more dominant in right-hemisphere activation during inner speech.
Main Methods:
- Magnetoencephalography (MEG) and functional Magnetic Resonance Imaging (fMRI) were employed to measure neural activity.
- An fMRI-constrained MEG multi-dipole analysis was performed.
- Eight right-handed subjects completed a delayed-response task involving inner speech of meaningless syllables.
Main Results:
- Active neural sources were detected approximately 200-300 ms after cue presentation.
- These sources were located near the posterior superior temporal sulcus.
- Significantly more active neural sources were observed in the right hemisphere compared to the left hemisphere.
Conclusions:
- The observed right-hemisphere dominance suggests a greater involvement of prosodic processing (e.g., pitch, rhythm) than phonemic processing during the inner speech of meaningless sequences.
- This challenges traditional views of language lateralization, highlighting the role of the non-dominant hemisphere in certain aspects of speech processing.
- Findings contribute to a more nuanced understanding of the neural networks supporting verbal working memory and speech production.