Parietomotor Connectivity in the Contralesional Hemisphere after Stroke: A Paired-Pulse TMS Study

To assess the contralesional connectivity between the posterior parietal cortex (PPC) and the motor cortex (M1) in stroke patients, and to probe putative relationships with spatial neglect and motor impairment. In 12 right-side stroke patients and 12 age-matched healthy controls, we used paired-pulse transcranial magnetic stimulation to assess the contralesional connectivity between three left-side PPC sites (the anterior intraparietal sulcus (aIPS), the posterior intraparietal sulcus and the superior parieto-occipital cortex (SPOC)) and M1. The interstimulus interval (ISI) was set to 4 or 6 ms. Although there were no differences between the stroke patient group and the controls, a subgroup analysis showed that stimulation over the SPOC with an ISI of 6 ms facilitated motor-evoked potential responses in patients with neglect (and especially those with severe peripersonal neglect), relative to non-neglect patients. With an ISI of 4 ms, the aIPS exerted an inhibitory influence on M1 in all subjects. The severity of motor impairment was not associated with PPC-M1 connectivity. aIPS-M1 connectivity seems to be unaffected in stroke patients, whereas connectivity from the most posterior parts of the parietal cortex depends on the patient’s neglect status. These results provide insight into post-stroke changes in contralesional PPC-M1 connectivity.