The roles of human lateral temporal cortical neuronal activity in recent verbal memory encoding

Activity of 98 single neurons in human lateral temporal cortex was measured during memory encoding for auditory words, text, or pictures and compared with identification of material of the same modality in extracellular recordings during awake neurosurgery for epilepsy. Frequency of activity was divided into early or late epochs or activity sustained throughout both; 44 neurons had significant changes in one or more categories. Polymodal and sustained changes lateralized to dominant hemisphere and late changes to nondominant. The majority of polymodal neurons shifted categories for different modalities. In dominant hemisphere, the timing and nature of changes in activity provide the basis for a model of the roles of temporal cortex in encoding. Superior temporal gyrus excitatory activity was related to the early epoch, when perception and processing occur, and middle gyrus to the late epoch, when semantic labeling occurs. The superior two-thirds of middle gyrus also demonstrated sustained inhibition. In a subset of lateral temporal neurons, memory-encoding activity reflected simultaneous convergence of sustained attentional and early perceptual inputs.