The local field potential (LFP) is the low-frequency component of the extracellular voltage detected in the cortex, and changes in the LFP have been linked to many important processes, such as memory and motor function. Several recent reports have suggested that the LFP arises from neural activity within a few hundred micrometres of the recording electrode, but older studies had indicated that the LFP spreads further afield. Kajikawa and Schroeder looked at the extent ('spatial reach') of the LFP and found that the LFP undergoes passive spread that extends well beyond the area of contributing neuronal ensemble activity. The authors concluded that LFPs arise from a combination of local circuit activity and 'volume-conducted' electrical activity that spreads to more distal areas. In a related study, Lindén et al. provided potential insight into the nature of the LFP and how this influences its spatial reach. They created a detailed biophysical model of populations of cortical neurons, recreating the circuits and conditions that give rise to the LFP in the cortex. They found that the LFP detected by a single electrode arises from the neurons that surround the electrode up to a certain radius (spatial reach). This radius depended on neuronal morphology, the spatial arrangement of synapses and, importantly, on the degree of correlation between contributing populations of neurons.