Related Experiment Video
Updated: May 13, 2026
Translational Brain Mapping at the University of Rochester Medical Center: Preserving the Mind Through Personalized Brain Mapping
Published on: August 12, 2019
Reaching a moveable visual target: dissociations in brain tumour patients
Tania Buiatti1, Miran Skrap, Tim Shallice
1Cognitive Neuroscience Sector, SISSA, via Bonomea 265, Trieste, Italy; Human Science Department, University of Udine, via Margreth 3, Udine, Italy. buiatti@sissa.it
Abstract:
Damage to the posterior parietal cortex (PPC) can lead to Optic Ataxia (OA), in which patients misreach to peripheral targets. Recent research suggested that the PPC might be involved not only in simple reaching tasks toward peripheral targets, but also in changing the hand movement trajectory in real time if the target moves. The present study investigated whether patients with a lesion arising from operation for prefrontal, premotor or parietal tumours are selectively impaired in three experimental pointing conditions: (i) pointing to peripheral targets, (ii) pointing to fixatable targets, and (iii) pointing to moved targets (on-line movement corrections). The study confirmed the selective importance of the parietal cortex in all three tasks. Surprisingly, given clinical claims about OA, the degree of peripheral reaching errors correlated strongly in parietal patients with that to fixatable targets. However, there was no relation between peripheral reaching errors and the 'shift cost' of making on-line correction to moved targets, and classical double dissociations between the two skills were observed. The findings suggest that deficits in pointing to peripheral and to moved targets reflect two at least partly independent processes.
Insights
Damage to the posterior parietal cortex (PPC) impairs reaching. Patients with PPC damage struggle with peripheral and fixatable targets, but online movement corrections are independent. This suggests distinct processes for reaching and target adjustment.
Area of Science:
- Neuroscience
- Cognitive Psychology
- Neuro-ophthalmology
Background:
- Damage to the posterior parietal cortex (PPC) is linked to Optic Ataxia (OA), characterized by reaching errors to peripheral targets.
- Emerging evidence suggests the PPC's role extends beyond simple reaching to include real-time trajectory adjustments when targets move.
Purpose of the Study:
- To investigate selective impairments in patients with prefrontal, premotor, or parietal lesions across three pointing tasks: peripheral targets, fixatable targets, and moved targets (online corrections).
- To determine if deficits in reaching to peripheral targets and correcting movements to moved targets are independent processes.
Main Methods:
- Experimental study involving patients with lesions from tumor operations (prefrontal, premotor, parietal).
- Assessment of pointing accuracy in three conditions: peripheral targets, fixatable targets, and targets that moved mid-movement.
- Correlation analysis of reaching errors and 'shift cost' for online corrections.
Main Results:
- Parietal cortex lesions selectively impaired performance in all three pointing tasks.
- Peripheral reaching errors strongly correlated with errors to fixatable targets in parietal patients.
- No correlation was found between peripheral reaching errors and the 'shift cost' for online movement corrections, indicating double dissociations.
Conclusions:
- The parietal cortex is crucial for reaching to peripheral and fixatable targets, as well as for online movement corrections.
- Deficits in reaching to peripheral targets and correcting movements to shifted targets appear to involve at least partly independent processes.
- Clinical understanding of Optic Ataxia may need refinement regarding the distinct neural underpinnings of reaching errors and online movement adjustments.
