John O'Keefe FRS is Professor of Cognitive Neuroscience at the Sainsbury Wellcome Centre, University College London and a Principal Research Fellow of the Wellcome Trust. In 2014, he was awarded both the Kavli Prize for Neuroscience and the Nobel Prize for Physiology or Medicine. He is interested in the role of the hippocampal formation in spatial and episodic memory, and navigation. He discovered that hippocampal pyramidal cells in the rat respond selectively to an animal's spatial location. The discovery of 'place cells' suggested that this part of the brain might function as a cognitive map, a notion developed extensively by himself and Nadel (www.cognitive.map.net) and now the dominant theory of hippocampal function. Numerous subsequent behavioral and neurophysiological experiments have contributed to our understanding of the place cells including their development prior to spatial experience. In 1993, he discovered phase precession, the coding of location by spike times relative to the hippocampal theta rythm, a phenomenon which he suggested could be due to interference wawelengths from the summation of 2 theta-like oscillators of differing frequencies. Extension of this model to 2 spatial dimensions can account for the symmetrical entorhinal grid cell pattern. Recent experiments show these grid patters are modified by alterations of the enclosure geometry and cannot therefore be entirely generated autochthonously by brain wiring.