Visual attention and working memory are two different cognitive functions. However, because of their close relationship and interactions, it is often claimed that they share the same underlying neuronal mechanisms. Here, I will first describe results from experiments using multi-area neuronal recordings and large-scale optogenetic inactivation of the lateral prefrontal cortex in macaque monkeys to characterize the neuronal mechanisms of feature attention and working memory across multiple visual processing stages of the cortex. I will present evidence that feature attention and working memory have dissociable neuronal substrates. Lastly, as part of an effort to characterize the roles of specific cortical layers in feature attention and working memory, I will present the discovery of the first ubiquitous laminar motif of neuronal activity that is preserved across the cortex, characterized by opposite gradients of local field potential power in the alpha-beta and gamma frequency bands. Based on this finding, I will propose a Spectrolaminar Framework for the electrophysiological study of the cortex, and I will present FLIP, a fully-automated Frequency-based Layer Identification Procedure we developed.