Does obstetric brachial plexus injury influence speech dominance?

Area of Science:

• Neuroscience
• Cognitive Science
• Human Physiology

Background:

• The relationship between right-handedness and left-hemisphere language dominance is a long-standing neurological question.
• Current theories propose that language lateralization is a primary brain asymmetry, with handedness being a secondary consequence.

Purpose of the Study:

• To investigate the potential causal influence of asymmetric hand usage on language lateralization.
• To explore if damage to one upper limb (UL) can alter established language processing in the brain.

Main Methods:

• Functional magnetic resonance imaging (fMRI) was used to assess language lateralization in 15 participants.
• Participants had experienced unilateral brachial plexus injury at birth, resulting in impaired use of one upper limb (UL).

Main Results:

• A correlation was observed between the severity of right-sided upper limb (UL) injury and hand dysfunction, and a shift in language lateralization from left to right.
• The observed shift in language lateralization was not a complete reversal of dominance.

Conclusions:

• Right-sided upper limb (UL) injury can induce a left-to-right shift in language lateralization, indicating that hand usage can influence brain lateralization.
• These findings challenge the conventional view that language lateralization dictates handedness.
• The study suggests a potential role for gestures in language evolution and contemporary language processing, while acknowledging the unresolved cause-effect relationship.