In the last decade, brain connectomics has evolved into a widely used concept in neuroscience. The idea is that cognitive functions rely on interactions of distributed brain regions operating in large-scale networks. Given that chemical synapses represent the predominant mode of signal transduction in the human brain, targeting the molecular level of neural communication represents a necessary step for advancing brain connectomics. At the macroscale, this can be achieved by means of molecular imaging. In particular, positron emission tomography (PET) has become an established method for measuring glucose metabolism, neurotransmitter systems, and proteinopathies. Preliminary evidence indicates that molecular imaging can provide reasonable estimates of brain connectivity, so called molecular connectivity.

In a broad sense, the term molecular connectivity refers to a statistical dependence between regional measures of molecular imaging. Molecular connectivity is now a rapidly growing field of neuroscientific research and analytics outside the scope of traditional fMRI imaging, offering applications and opportunities for basic and methodological research advancement. We, the “Molecular Connectivity Working Group”, are an interdisciplinary group of scientists, who share a vision to establish molecular imaging as a tool to study brain connectivity. 

This long-term mission will be realized in three major steps:

1. Validation: e.g., definition of best methodological practices, including rigorous testing of accuracy, reproducibility, and replicability; definition of a consensus nomenclature to designate molecular connectivity results;
2. Methods development: e.g., development of new model-based and data-driven analytic approaches focused on the molecular connectome;
3. Application: e.g., development of an atlas of molecular imaging maps of the connectome; integration of molecular connectivity into the framework of causal models; derivation and validation of molecular connectivity indices at the individual level for clinical purposes. 

To this end, we will design and conduct research studies, disseminate methods and results, raise mutual funding, and share resources (e.g. datasets, tools) with the scientific community to enhance research in the field of molecular connectivity.

Ultimately, we encourage the neuroscientific community to take an integrative perspective on the brain connectome, where various methods including MRI-based techniques, electrophysiological tools, and molecular imaging contribute to the characterization of the human brain connectome, advancing our understanding of organization of the brain.