Bimanual non-congruent actions in motor neglect syndrome: a combined behavioral/fMRI study.

F Garbarini,A Piedimonte,M Rabuffetti,L Turella,A Berti,L Fadiga,E Fainardi,A Cantagallo

doi:10.3389/fnhum.2015.00541

Abstract

In Motor Neglect (MN) syndrome, a specific impairment in non-congruent bimanual movements has been described. In the present case-control study, we investigated the neuro-functional correlates of this behavioral deficit. Two right-brain-damaged (RBD) patients, one with (MN+) and one without (MN−) MN, were evaluated by means of functional Magnetic Resonance Imaging (fMRI) in a bimanual Circles-Lines (CL) paradigm. Patients were requested to perform right-hand movements (lines-drawing) and, simultaneously, congruent (lines-drawing) or non-congruent (circles-drawing) left-hand movements. In the behavioral task, MN− patient showed a bimanual-coupling-effect, while MN+ patient did not. The fMRI study showed that in MN−, a fronto-parietal network, mainly involving the pre-supplementary motor area (pre-SMA) and the posterior parietal cortex (PPC), was significantly more active in non-congruent than in congruent conditions, as previously shown in healthy subjects. On the contrary, MN+ patient showed an opposite pattern of activation both in pre-SMA and in PPC. Within this fronto-parietal network, the pre-SMA is supposed to exert an inhibitory influence on the default coupling of homologous muscles, thus allowing the execution of non-congruent movements. In MN syndrome, the described abnormal pre-SMA activity supports the hypothesis that a failure to inhibit ipsilesional motor programs might determine a specific impairment of non-congruent movements.

Highlights

Motor Neglect (MN) is a neuropsychological syndrome, which occurs as a result of stroke and is characterized by the underutilization of the contralesional limbs, in presence of normal strength, reflexes and sensibility and preserved potential for actual movement on the affected side
Whole-brain analysis was performed by applying the General Linear Model (GLM) for analysis of functional Magnetic Resonance Imaging (fMRI) time series
Regressors were defined based on the timing of presentation for each of the conditions and were modeled using a box-car function convolved with the hemodynamic response function (HRF) with duration equal to the experimental block

Summary

Introduction

Motor Neglect (MN) is a neuropsychological syndrome, which occurs as a result of stroke and is characterized by the underutilization of the contralesional limbs, in presence of normal strength, reflexes and sensibility and preserved potential for actual movement on the affected side. MN, especially in its pure form (without motor deficits), is a rare disorder—Laplane and Degos (1983) collected 20 patients over more than 10 years—and its frequency depends on the phase of the illness. Crucial to the present study, when MN patients are asked to perform bimanual movements, they only perform ipsilesional hand movements, even though they are capable of moving the contralesional hand. A behavioral dissociation has been found in MN patients, showing that the underutilization of the affected hand is greater when non-congruent In the present case-control study, we investigated the neuro-functional correlates of this behavioral dissociation

Methods

Results

Conclusion