Transcranial Magnetic Stimulation Over the Human Medial Posterior Parietal Cortex Disrupts Depth Encoding During Reach Planning

Abstract

Accumulating evidence supports the view that the medial part of the posterior parietal cortex (mPPC) is involved in the planning of reaching, but while plenty of studies investigated reaching performed toward different directions, only a few studied different depths. Here, we investigated the causal role of mPPC (putatively, human area V6A–hV6A) in encoding depth and direction of reaching. Specifically, we applied single-pulse transcranial magnetic stimulation (TMS) over the left hV6A at different time points while 15 participants were planning immediate, visually guided reaching by using different eye-hand configurations. We found that TMS delivered over hV6A 200 ms after the Go signal affected the encoding of the depth of reaching by decreasing the accuracy of movements toward targets located farther with respect to the gazed position, but only when they were also far from the body. The effectiveness of both retinotopic (farther with respect to the gaze) and spatial position (far from the body) is in agreement with the presence in the monkey V6A of neurons employing either retinotopic, spatial, or mixed reference frames during reach plan. This work provides the first causal evidence of the critical role of hV6A in the planning of visually guided reaching movements in depth.

Complementary contribution of the medial and lateral human parietal cortex to grasping: a repetitive TMS study

“…Fifteen healthy volunteers (6 males; age range 19–33 years; mean age 21.93 ± 4.27 years) participated in this study. The number of participants was determined based on a power analysis that indicated that a sample size of 15 participants is an appropriate sample size to achieve statistical power (1−β) of 0.95 (2-tailed α = 0.05; effect size f = 0.20, Breveglieri et al. 2021 ), analysis performed using G*Power software ( Faul et al.…”

“…The coordinates of hV6A are the same as those used in previous TMS studies on this brain region ( Ciavarro et al. 2013 ; Breveglieri et al. 2021 ) and are similar to those used for studying the SPOC ( Vesia et al.…”

Mild-to-Moderate Traumatic Brain Injury: A Review with Focus on the Visual System

“…The parietal lobes integrate visual data from rapid eye movements (saccadic movements) to direct the mechanistic reaching movements of the hand, allowing the individual to place an object in space and reach out to grasp it [88,92]. However, when the parietal cortex is impaired, depth perception cannot function properly, causing loss of the ability to perceive the spatial layout of the objects surrounding them [93]. Another consequence of parietal lobe dysfunction occurs in patients who lose the ability to shift their spatial attention or distinguish things on their left or their right side, leading to difficulty navigating even simple tasks such as walking across a room [90,94].…”

Functional Connectivity at Rest between the Human Medial Posterior Parietal Cortex and the Primary Motor Cortex Detected by Paired-Pulse Transcranial Magnetic Stimulation

“…The Talairach coordinates of hV6A we used were x = −10, y = −78, and z = 40 [49]. These coordinates are the same as those used in two previous TMS studies on hV6A [50,51], and are similar to those used for studying area SPOC [12,52], a region also investigated in imaging studies [8,10,53] that likely includes hV6A [54]. Then, the neuronavigation system was used to estimate the projections of scalp sites on the brain surface.…”