Search

Summary Parietofrontal (PF) networks link the posterior parietal cortex to premotor and prefrontal areas, and are involved in the control of many motor and cognitive behaviors in healthy humans. In recent years, electrophysiological experiments have provided a better understanding of the functional specificity and temporal involvement of the PF networks' different components during the planning of visually guided upper limb movements. In particular, transcranial magnetic stimulation has been used to temporarily inactivate a cortical area (virtual lesions) or to assess connectivity using paired-pulse protocols)). This approach has shed new light on the neural mechanisms that underlie the planning stages of the reaching and grasping phases of transitive movements. Reaching and grasping were often presented as two distinct processes; in fact, the respective involvement of dorsolateral and dorsomedial networks may depend on the movement's complexity and the need for precise coordination between the two phases. The dorsolateral parietofrontal network (linking the anterior part of the intraparietal sulcus to the ventral premotor cortex) is involved in the grasping phase (i.e. hand shape and grip force scaling), whereas the dorsomedial part (from the posterior part of the intraparietal sulcus and the superior parieto-occipital cortex to the dorsal premotor cortex) appears to be involved not only in the reaching phase but also in more complex visually guided grasping movements. Changes in parietofrontal connectivity following brain injury might explain the impairments in visually guided upper limb movements observed in patients (such as optic ataxia and the motor component of spatial neglect). Lastly, parietofrontal changes may reflect neuronal plasticity in motor function recovery. [ABSTRACT FROM AUTHOR]

Abstract: Objective: We sought to determine temporal patterns of functional connectivity between the parietal, premotor, and motor cortices during preparation and execution of praxis hand movements. Methods: Normal subjects were instructed to perform six transitive (tool use) and intransitive (communicative gesture) self-paced pantomimes with the right hand while recording 64-channel electroencephalography (EEG) and electromyography (EMG) from right thumb and forearm flexors. Focusing on corticocortical coherence, we explored the time-course of synchronously active parietal and premotor circuits involved in these motor tasks. Trials were marked for EMG onset and averaged across subjects to determine changes in coherence relative to baseline between parietal, premotor, and motor areas. Results: Coherence of homologous electrode pairs was similar when comparing transitive and intransitive movements. During preparation, beta band (18–22Hz) coherence was maximal between electrodes over the left parietal lobe and left premotor electrodes. Additionally during preparation, the premotor area showed high coherence to the motor hand area and the parietal cortex. Electrodes over the supplementary motor area also showed coherence to the motor and parietal, but not the premotor area. Before and during execution, a second peak of high coherence increase was present in each area that demonstrated coherence increases during preparation. There was no coherence increase between parietal and motor areas. Coherence rapidly diminished 1.5–2.0s after movement onset. Conclusions: Patterns of increased corticocortical coupling within a parietal, premotor, and motor network are present during preparation and execution of praxis movements. Significance: This study adds to evidence that parietofrontal networks may be critical for integrating preparatory and motor-related activity for praxis movements. [Copyright &y& Elsevier]