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Disordered sensorimotor transformations for reaching following posterior cortical lesions
W G Darling1, M Rizzo, A J Butler
1Department of Exercise Science, The University of Iowa, Iowa City, IA 52241, USA. warren.darling@uiowa.edu
Abstract:
Preparation for reaches to visual targets depends on sensorimotor transformations (SMT) between target and limb coordinate systems. To examine neural substrates for SMT, we studied 19 individuals with focal lesions of the visual association cortices and white matter and 11 control subjects without brain lesions. SMT were assessed by measuring accuracy of reaches to remembered locations of visually presented targets. Results showed abnormally large SMT errors in all individuals with inferior parietal lobule (IPL) lesions and some subjects with lesions of the temporo-occipital regions and in occipital area 19. Types of abnormal errors (direction or distance) varied between subjects with similar lesions, e.g. IPL. Patterns of abnormality included dissociations of distance and direction errors and of constant and variable errors. These findings are compatible with the hypothesis of different systems for guiding distance and direction of reaches distributed among structures in superior and inferior visual association cortex.
Insights
Sensorimotor transformations (SMT) for reaching visual targets involve brain areas like the inferior parietal lobule (IPL). Lesions in these visual association cortices disrupt SMT, causing significant reaching errors in distance and direction.
Area of Science:
- Neuroscience
- Cognitive Neuroscience
- Visuomotor Control
Background:
- Accurate visually guided reaching relies on sensorimotor transformations (SMT) to convert target coordinates into limb movements.
- Understanding the neural basis of SMT is crucial for explaining visuomotor deficits after brain injury.
Purpose of the Study:
- To investigate the neural substrates supporting sensorimotor transformations (SMT) for reaching.
- To determine the impact of visual association cortex lesions on the accuracy of reaches to remembered visual targets.
Main Methods:
- Studied 19 individuals with focal lesions in visual association cortices and white matter.
- Included 11 control subjects without brain lesions for comparison.
- Assessed SMT by measuring the accuracy of reaching to remembered visual target locations.
Main Results:
- All individuals with inferior parietal lobule (IPL) lesions exhibited significant SMT errors.
- Subjects with temporo-occipital or occipital area 19 lesions also showed abnormal SMT.
- Error patterns (direction vs. distance, constant vs. variable) varied even among subjects with similar lesions.
Conclusions:
- Inferior parietal lobule (IPL) and other visual association areas are critical for sensorimotor transformations (SMT).
- Distinct neural systems within the visual association cortex may underlie the guidance of reach direction and distance.