Behavioral/Systems/Cognitive Neuronal Synchronization in Human Posterior Parietal Cortex during Reach Planning

Althoughsingle-unit studies inmonkeyshave identified effector-related regions in theposteriorparietal cortex (PPC)during saccadeand reach planning, the degree of effector specificity of corresponding human regions, as established by recordings of the blood oxygen level-dependent signal, is still under debate. Here, we addressed this issue from a different perspective, by studying the neuronal synchronization of the human PPC during both reach and saccade planning. Using magnetoencephalography (MEG), we recorded ongoing brain activity while subjects performed randomly alternating trials of memory-guided reaches or saccades. Additionally, sub-jects performed a dissociation task requiring them to plan both a memory-guided saccade and reach to locations in opposing visual hemifields.Weexaminedchanges in spectralpowerof theMEGsignalduringa1.5 smemoryperiod in relation to target location (left/right) and effector type (eye/hand). The results show direction-selective synchronization in the 70–90 Hz gamma frequency band, originating from the medial aspect of the PPC,whenplanning a reachingmovement. In contrast, activity in amore central portion of the PPCwas synchronized in a lower gammaband (50–60Hz)when planning the direction of a saccade. Both observationswere corroborated in the dissociation task. In the lower frequency bands, we observed sustained alpha-band (8–12 Hz) desynchronization in occipitoparietal regions, but in an effector-unspecific manner. These results suggest that distinct modules in the posterior parietal cortex encode movement goals of different effectors by selective gamma-band activity, compatible with the functional organization of monkey PPC