Competition between tool and hand motion impairs movement planning in limb apraxia

Area of Science:

• Neuroscience
• Cognitive Psychology
• Motor Control

Background:

• Tool use relies on complex motor planning, involving resolving action representation competition.
• Incongruent tool-hand motions may exacerbate this competition.
• Limb apraxia following left-hemisphere stroke (LCVA) is linked to abnormal action competition.

Purpose of the Study:

• To investigate if tool-hand incongruence increases planning deficits in individuals with LCVA.
• To determine the relationship between apraxia severity and planning difficulties with incongruent tools.
• To identify brain regions associated with impaired planning for incongruent tools.

Main Methods:

• 34 individuals with chronic LCVA and 16 controls used novel congruent and incongruent tools.
• Apraxia severity was assessed.
• Lesion-symptom mapping was performed.
• A second experiment assessed gesturing of conventional tools.

Main Results:

• Individuals with LCVA showed increased planning time for incongruent tools, correlated with apraxia severity.
• Impairments were most prominent early in task introduction.
• Lesions in posterior temporal and inferior parietal areas were linked to planning deficits for incongruent tools.
• Gesture impairment for conventional tools increased with tool incongruence.

Conclusions:

• Tool-hand incongruence triggers action competition, worsening planning deficits in LCVA.
• This competition contributes to the tool-use difficulties observed in apraxia.
• Specific brain regions are critical for planning tool use, particularly when hand-tool motions are incongruent.