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Reduced competition between tool action neighbors in left hemisphere stroke
Frank E Garcea1, Harrison Stoll2, Laurel J Buxbaum3
1Moss Rehabilitation Research Institute, Elkins Park, PA, USA; University of Pennsylvania, Philadelphia, PA, USA.
Summary
Patients with limb apraxia after stroke struggle with tool use pantomime, especially with complex tools. This study shows their difficulty stems from weakened action activation, impacting competition for task selection.
Area of Science:
- Neuroscience
- Cognitive Psychology
- Rehabilitation Medicine
Background:
- Individuals with left hemisphere stroke-induced limb apraxia (LCVA) exhibit difficulties pantomiming tool use.
- Performance deficits are more pronounced with tools requiring distinct grasp and use actions (e.g., corkscrew) compared to those with unified actions (e.g., hammer).
- Two hypotheses exist: weakened automaticity of use-action activation or impaired competition of appropriate actions against inappropriate ones.
Purpose of the Study:
- To investigate the underlying mechanisms of impaired tool pantomime in LCVA using a Stroop-like paradigm.
- To differentiate between weakened automaticity and impaired action selection as causes of performance deficits.
- To identify neuroanatomical correlates of these deficits.
Main Methods:
- A Stroop-like experiment involving pantomiming tool use actions was conducted with 21 LCVA patients and 8 neurotypical controls.
- Participants performed actions in blocks with similar ('neighbor') or unrelated tools, under congruent and incongruent conditions.
- Lesion-symptom mapping using support vector regression was employed to identify affected brain regions.
Main Results:
- LCVA participants showed reduced hand action errors in incongruent trials compared to congruent trials, indicating a reduced incongruence effect.
- The magnitude of this reduction correlated with susceptibility to grasp-on-use conflict in a separate task.
- Lesion-symptom mapping implicated the left inferior frontal gyrus, supramarginal gyrus, and superior longitudinal fasciculus.
Conclusions:
- Weakened activation of tool use actions in LCVA leads to impaired competition for task-appropriate selection.
- This deficit affects competition both within single tools (grasp-on-use conflict) and between multiple tools (neighborhood effects).
- The findings highlight the role of specific left hemisphere structures in action selection and tool use.
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