Layer I is the molecular layer, and contains few scattered neurons, including GABAergic rosehip neurons. Layer I consists largely of extensions of apical dendritic tufts of pyramidal neurons and horizontally oriented axons, as well as glial cells. During development, Cajal-Retzius cells and subpial granular layer cells are present in this layer. Also, some spiny stellate cells can be found here. Inputs to the apical tufts are thought to be crucial for the "feedback" interactions in the cerebral cortex involved in associative learning and attention. While it was once thought that the input to layer I came from the cortex itself, it is now realized that layer I across the cerebral cortex mantle receives substantial input from "matrix" or M-type thalamus cells (in contrast to "core" or C-type that go to layer IV).