Transcranial Magnetic Stimulation (TMS) of the Supramarginal Gyrus: A Window to Perception of Upright

Abstract

Although the pull of gravity, primarily detected by the labyrinth, is the fundamental input for our sense of upright, vision and proprioception must also be integrated with vestibular information into a coherent perception of spatial orientation. Here, we used transcranial magnetic stimulation (TMS) to probe the role of the cortex at the temporal parietal junction (TPJ) of the right cerebral hemisphere in the perception of upright. We measured the perceived vertical orientation of a visual line; that is, the subjective visual vertical (SVV), after a short period of continuous theta burst stimulation (cTBS) with the head upright. cTBS over the posterior aspect of the supramarginal gyrus (SMGp) in 8 right-handed subjects consistently tilted the perception of upright when tested with the head tilted 20° to either shoulder (right: 3.6°, left: 2.7°). The tilt of SVV was always in the direction opposite to the head tilt. On the other hand, there was no significant tilt after sham stimulation or after cTBS of nearby areas. These findings suggest that a small area of cerebral cortex--SMGp--has a role in processing information from different sensory modalities into an accurate perception of upright.

Differential effect of visual motion adaption upon visual cortical excitability

“…This lack of relationship suggests that the neural mechanisms underlying visual dependency are likely to not be dependent on these visual cortical areas. It may be that visual dependency is not a function of the visual cortex per se, but rather involves higher order frontoparietal areas that are implicated for vestibular cortical and attentional processing (Arshad et al 2013(Arshad et al , 2014 Van Elk and Blanke 2012; Kheradmand et al 2015). Another recent study utilizing continuous theta burst stimulation (cTBS) showed that the early visual cortices (V1-V2) did not play any role in verticality estimation; however, their study showed that the right temporoparietal junction (rTPJ) is crucial for maintaining an internal representation of verticality (Fiori et al 2015), similar to what was recently found by Kheradmand et al (2015).…”

Can we simulate an action that we temporarily cannot perform?

“…This finding is in line with Desmurget et al [21,22] proposition that the posterior parietal cortex (i.e., angular and supramarginal gyri; BA39, BA40) is involved in the generation of conscious motor intentions in which processing may be related to sensory predictions. Involvement of the parietal cortex is also suggested in encoding the kinematics and orientation of movements within the body space [17,43,57,67] and storing kinesthetic representations to map them onto the premotor and motor areas [76]. The present activation lies in area PF [90], which probably corresponds to area 7b in the macaque monkey [58].…”

Anatomía, fisiología y rol clínico de la corteza vestibular

“…Eickhofft y cols el año 2006, utilizando estimulación vestibular galvánica, describieron mediante resonancia magnética funcional (fMRI) la activación bilateral del opérculo parietal el cual homologan con el área PIVC descrita en primates 30 . Kheradmand y cols en el año 2013 han reportado que la estimulación magnética transcraneana en la unión témporo-parietal de la corteza derecha de sujetos sanos, provocó una desviación de casi 20 grados en la prueba vertical visual subjetiva (el promedio de desviación sin estimulación en los sujetos fue de 3,6° a derecha y 2,7° a izquierda) siendo esta desviación opuesta a la dirección de la inclinación cefálica 32 (Figura 2).…”