Effector-selective modulation of the effective connectivity within frontoparietal circuits during visuomotor tasks

The collection of research on the human homologues of macaque parietal areas involved in finalized movements led to a lack of consensus on the topic, mainly due to issues in the activation studies performed with functional magnetic resonance imaging (fMRI). Indeed, a wide set of studies using fMRI detected overlapping activations in the parietal cortex during both saccades and reaching or pointing movements (for a review, see Vesia and Crawford, 2012). Here, we attempted to shed more light on this topic by applying a combined approach of individual surface-based and connectivity analyses. We reanalyzed previously collected BOLD data in our laboratory on pointing movements executed with either hand, foot or saccades (Pitzalis et al., 2019) with a threefold aim: a) segregating regions in the parietal cortex that underlie different visuomotor tasks through an individual surface-based analysis (SBA); b) exploring the parieto-frontal functional connectivity during resting state; c) employing an effective connectivity analysis (Dynamic Causal Modelling; DCM) to assess the dynamic fronto-parietal interactions that subserve the execution of visuomotor tasks. First, we found evidence of segregated areas in the posterior intraparietal sulcus, namely a medial (mpIPS) and a lateral (lpIPS) region. These areas were differently engaged during both pointing movements (regardless of the effector) and saccades. Beyond that, from a connectivity perspective we found evidence of preferred signal routes linking parietal and frontal areas at rest. Similarly, the DCM analysis revealed feedforward-feedback loops linking lpIPS and the frontal eye fields (FEF) during saccades and mpIPS and the premotor cortex (PMd) during pointing in an effector-specific fashion. As a matter of fact, in the present study the activation analysis depicted only a partial view of the subtle functional differences occurring between adjacent but distinct subregions. For instance, mpIPS and the human PEc (hPEc) appeared to be recruited to the same extent during hand and foot pointing, but when looking at effector-specific connectivity profiles crucial differences emerged. This finding does not point toward an incongruence between the two types of analyses, but rather emphasizes their different ability in unveiling on the one hand, if some areas are recruited across conditions, on the other hand, how they are recruited across conditions. Overall, our study suggests the existence of a variety of fronto-parietal networks that dynamically recruit common areas depending on the contextual requirements. References Pitzalis, S., Serra, C., Sulpizio, V., Di Marco, S., Fattori, P., Galati, G., Galletti, C., 2019. A putative human homologue of the macaque area PEc. NeuroImage 202, 116092. https://doi.org/10.1016/j.neuroimage.2019.116092 Vesia, M., Crawford, J.D., 2012. Specialization of reach function in human posterior parietal cortex. Exp Brain Res 221, 1–18. https://doi.org/10.1007/s00221-012-3158-9