Stimulation of the left parietal lobe improves spatial and temporal attention in right parietal lobe patients: tipping the inter-hemispheric balance with TMS

Abstract

It is widely accepted that the right parietal lobe has an advantage over the left in visual attentional tasks. However, such asymmetry is poorly understood. For example, while patients affected by right parietal lesion show severe deficits in attentional tasks in the contralesional space, other studies have demonstrated that the deficits can be equally severe in the ipsilesional space (Battelli et al., 2007). fMRI studies on patients have shown that areas in the healthy hemisphere are hyperactive along with attentional deficits in the contralesional field. One hypothesis is that these deficits are a consequence of an increased inhibition exerted on the damaged hemisphere by the hyperactive unaffected hemisphere (Kinsbourne, 1977). Here we used TMS on the healthy hemisphere in right parietal patients to tip the balance between hemispheres to relieve patients’ symptoms in spatial and temporal attention tasks. Patients completed a I) a multiple object tracking task, in which they were asked to track 2 or 4 moving discs amidst moving distracters (8 total discs, four in each hemifield) in the left and/or right hemifield and, II) a simultaneity judgment task in which they were asked to judge whether two of four flickering disks (two in each hemifield) were in or out-of-phase. For each task patients underwent two counterbalanced sessions: 1Hz TMS over the left (healthy) parietal lobe and sham control stimulation. Their performance was compared before and after stimulation. At baseline patients were impaired in the contralesional field on multiple objects tracking while they showed a bilateral deficit in the simultaneity task. However, after 10min-TMS patients’ performance selectively improved on the side contralateral to the lesion in both tasks. The results show that TMS might have beneficial effects on rehabilitation of spatial and temporal attention deficits by re-balancing the activity of the two parietal lobes.

Meeting abstract presented at VSS 2013