Effector general representation of movement goals in human frontal and parietal cortex

The ability to execute precise movements depends on transforming visuospatial information about the goal of the movement into a movement plan. In the nonhuman primate, discrete parts of premotor frontal and parietal cortex appear to code for movements of different effectors. However, the evidence regarding homologous effector selectivity within the human brain remains inconclusive. Here, we aimed to ask how human brains code spatial information during the motor planning process for eye and hand movements and test whether spatial-specific planning is effector-dependent.

To overcome previous limitations, human participants planned and executed saccades and reaches with natural kinematics recorded by infrared MRI-compatible cameras. We isolated neural activities for the motor-planning process distinct from sensory-processing and motor-execution.

Task design, movement trajectories, and behavioral results

We used assumption-free multivariate searchlight analysis to identify brain regions that could decode the spatial goals of planned movements. Critically, we performed two types of decoding analyses to determine if the spatial information embedded in activation patterns was effector-specific or effector-general. For effector-specific spatial coding, we compared brain regions that could decode target locations within each effector. However, we did not identify areas that coded spatial information in one effector but not the other. For effector-general spatial coding, we performed spatial decoding using trials across effectors and conducted cross-effector decoding. Both analyses identified several areas in the frontal and parietal regions that encoded spatial information for both effectors, including precentral sulcus, superior parietal lobe, and intraparietal sulcus.

Within effector and across effector decoding of the spatial goals of motor planning

Next, we plotted the time series of BOLD signal change for clusters identified in the within-effector location decoding while ignoring effector and the cross-effector location decoding.

Trial-averaged BOLD time courses time-locked to the target and response onset

Finally, we identified brain regions that could differentiate which type of movement was being planned. Critically, this analysis ignored the spatial locations of the targets of the planned movements and therefore cannot identify areas that are planning the specific metrics of a movement. Instead, it can identify areas sensitive to the instruction to use one effector or the other.

Decoding the instructed effector type

In summary, We identified several regions in the dorsal parietal and frontal cortices that coded for target locations used for planning both eye saccades and hand reaches. Importantly, these regions were not anatomically segregated. Instead, we found multiple regions that encoded the spatial positions of targets; the patterns of activity that encoded these spatial goals were interchangeable and generalized across effectors. Overall, our results suggest that premotor frontal and parietal cortex codes for spatial goals rather than effector-specific metrics for motor instructions.

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