Allocentric coding in ventral and dorsal routes during real-time reaching: Evidence from imaging-guided multi-site brain stimulation.

Recent evidence has revealed an advantage for movements to last target positions in a structured visual display, suggesting a mediating role of allocentric, in addition to egocentric, information in goal-directed reaching. This notion is accommodated by the recently updated perception-action model (Milner and Goodale, 2008), which postulates functional roles of ventral and dorsal neural areas in allocentric coding. In the present study, we used imaging-guided multi-site continuous theta burst stimulation (cTBS) over regions of the ventral and dorsal processing streams to unravel their functional contribution on visually guided reaching in two display conditions: the "egocentric" condition where the target appeared in an empty display and the "allocentric" condition where the target appeared in a structured display with placeholders marking possible target locations. Cortical sites for cTBS were identified individually for each participant via coregistration with magnetic resonance scans. Results indicated that cTBS in the egocentric condition did not affect movement time, but cTBS in the allocentric condition modulated movement time contingent on stimulation site and target position. In particular, cTBS over the lateral occipital cortex (part of the ventral stream) and over the angular gyrus (part of the dorsal stream) eliminated the last-target advantage by slowing down reaching to the salient last target position. cTBS over the superior parietal occipital cortex did not affect the last-target advantage. These outcomes provide the first causal evidence for allocentric coding in ventral and dorsal routes during real-time reaching, thereby supporting the updated perception-action model.

Evaluation of the Modified Jebsen Test of Hand Function and the University of Maryland Arm Questionnaire for Stroke.

OBJECTIVE: To examine the concurrent validity and test-retest reliability of the Modified Jebsen Test of Hand Function (MJT) and the University of Maryland Arm Questionnaire for Stroke (UMAQS). DESIGN: Individuals with acquired neurological disorders were retested within an average of 9.6 days after the first assessment. SETTING: Individuals were recruited from two specialist rehabilitation units, members of the Multiple Sclerosis Society and Headway Group. SUBJECTS: Twenty-six individuals with acquired neurological disorders; stroke (12), MS (7), head injury (4), tumour (3) with moderate to high functioning upper limbs were recruited for this study. MAIN OUTCOME MEASURES: Arm function was assessed using the MJT, the UMAQS, the Nine Hole Peg Test (NHPT) and grip strength, calculating the ratio between affected and unaffected arm. RESULTS: The MJT showed good concurrent validity. Pearson's correlation with the NHPT was 0.86 and 0.88, on T1 and T2 respectively. The UMAQS showed no significant correlation with grip strength, the NHPT and the MJT. Test-retest reliability of the MJT was high with a correlation of 0.95, and 95% limits of agreement of 0.02 +/- 0.14. Correlations over time of the dominant hand/nondominant hand of the UMAQS were 0.72 and 0.83, with limits of agreement of -2.92 +/- 13.28 and 1.73 +/- 11.53. CONCLUSIONS: The present study supports the use of the MJT as a measure of gross functional dexterity. More information is needed to evaluate the UMAQS.