Cortico-cortical connectivity between the superior and inferior parietal lobules and the motor cortex assessed by intraoperative dual cortical stimulation

• Published in: Brain stimulation Vol. 13; no. 3; pp. 819 - 831
• Main Authors: Cattaneo, Luigi, Giampiccolo, Davide, Meneghelli, Pietro, Tramontano, Vincenzo, Sala, Francesco
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.05.2020; Elsevier
• ISSN: 1935-861X; 1876-4754
• DOI: 10.1016/j.brs.2020.02.023

The function of the primate’s posterior parietal cortex (PPC) in sensorimotor transformations is well-established, though in humans its complexity is still challenging. Well-established models indicate that the posterior parietal cortex influences motor output indirectly, by means of connections to the premotor cortex, which in turn is directly connected to the motor cortex. The possibility that the PPC could be at the origin of direct afferents to M1 has been suggested in humans but has never been confirmed directly. We aim to do so in the present study by using the novel technique of paired intraoperative cortical stimulation. In the present cross-sectional study, we assessed during intraoperative monitoring of the corticospinal tract in brain tumour patients the existence of short-latency effects of parietal stimulation on corticospinal excitability to the upper limb. MEPs were evoked by test stimuli over the motor cortex, which were preceded in some trials by conditioning stimuli on the PPC. We identified two active cortical loci. One in the inferior parietal lobule exerted short-latency excitatory effects and one in the superior parietal lobule that drove short-latency inhibitory effects on cortical motor output. All active foci were distributed in the rostral portion of the PPC and on the postcentral sulcus. For the first time in humans, the present data show direct evidence in favour of a distributed system of connections from the posterior parietal cortex to the ipsilateral primary motor cortex. In addition, we show that dual cortical stimulation is a novel and efficient technique to investigate intraoperative brain connectivity in the anaesthetized patient. •The parietal cortex controls goal-directed movement by unclear neural pathways.•We performed intraoperative monitoring of the corticospinal tract for brain tumours.•Motor cortex stimulation was conditioned by preceding electrical stimuli of the parietal cortex.•We show that the parietal cortex is functionally connected with the motor cortex.•Dual cortical stimulation is a tool for assessing connectivity intraoperatively.