In humans, corticospinal excitability is reduced when preparing for an action; i.e. motor preparatory inhibition. Functional relevance of this inhibition has been proposed, however, the site where the actual inhibition occurs, either at the primary motor cortex (M1) or at the downstream spinal-circuit, is still unclear. By measuring vascular space occupancy (VASO) with 7T fMRI, we investigated the direct signature of preparatory inhibition of neural activity across M1 cortical layers. Our preliminary analysis showed that preparation was associated with a reduced activity of the superficial layers of M1. Motor preparatory inhibition likely takes place in M1 in a layer-dependent manner.