Distinct contributions of human posterior parietal and dorsal premotor cortex to reach trajectory planning

Artur Pilacinski,Axel Lindner

doi:10.1038/s41598-019-39188-0

Abstract

Goal-directed hand movements are usually directed straight at the target, e.g. when swatting a fly. Their paths can also become quite complex, when drawing or avoiding obstacles. Studies on movement planning have largely neglected the latter movement type and the question of whether it is the same neural machinery that is planning such complex hand trajectories as well as straight, vector-like movements. Using time-resolved fMRI during delayed response tasks we examined planning activity in human superior parietal lobule (SPL) and dorsal premotor cortex (PMd). We show that the recruitment of both areas in trajectory planning differs significantly: PMd represented both straight and complex hand trajectories while SPL only those that led straight to the target. This suggests that while posterior parietal cortex only provides representations for simple, straight reaches, the complex and computationally demanding reach planning necessarily involves dorsal premotor cortex. Our findings yield new insights into the organization of cerebro-cortical strategies of forming reach trajectory plans.

Highlights

Goal-directed eye saccades and hand reaches share many commonalities
We conducted two human functional magnetic resonance imaging experiments where subjects had to plan and execute finger reaches towards visually cued targets
In Experiment 1 we showed that different reach trajectories for targets kept at the same visual locations produce differential planning responses in dorsal premotor cortex but not in superior parietal lobule (SPL), where responses were indistinguishable

Summary

Introduction

Goal-directed eye saccades and hand reaches share many commonalities. Both movement types are prepared based on target and effector representations in a visual (retinal) reference frame and even the neural correlates responsible for their programming do partially overlap[1]. A notable exception is the study of Torres and colleagues[15], who utilized a simplified obstacle avoidance task They demonstrated that single cells in monkey PRR modulated their activity prior to the reach whenever a barrier blocked the direct reach path. Previous research on reach planning in monkey posterior parietal cortex has highlighted its role in the vector-like coding of reach movements It is unclear, whether it contributes to the planning of complex trajectories. We tried to reveal how trajectory information is represented prior to movement execution in reach-related areas of the human brain, namely areas SPL and PMd. We intended to examine how trajectory representations change when a movement plan could theoretically be constructed by just defining a vector between the initial hand position and a target as compared to situations when these difference vectors are identical but the movement paths vary. We hypothesized that while PMd should contribute to the preparation of complex trajectories, SPL would be exclusively engaged in planning straight and direct paths

Methods

Results

Conclusion