, 2013 and Zhang et al., 2014). A third topic that we consider fundamental for future studies is the relationship between space and memory. The observation that grid cells are organized as discrete modules is important not only because it provides a neural architecture for space, but also because of its putative consequences for the formation of representations JAK2 inhibitor drug in downstream brain areas, such as the hippocampus. Simultaneous recording from multiple grid modules has shown that when the local environment is geometrically deformed, some modules rescale in accordance with the deformation, whereas others do not (Stensola et al., 2012). If

individual modules respond independently to changes in the environment, the coactivity pattern among grid cells may be changed at all locations in the recording environment, and a different subset of place cells is likely to be recruited at each place (Fyhn et al., 2007, Stensola et al., 2012 and Buzsáki and Moser, 2013). Independent module responses might thus give rise SCH772984 datasheet to a very large number of coactivity patterns in the hippocampus in the same way that a combination lock with only five digits may give rise to a hundred thousand unique patterns with only ten response alternatives per module (Rowland and Moser, 2014). Computational

simulations have verified that extensive diversity can be generated with a number of modules that correspond closely to the experimental data (Monaco and Abbott, 2011). This expansion of neuronal patterns may have been the mechanism that during evolution allowed the hippocampus to take on an increasingly important role in high-capacity episodic memory formation (Buzsáki and Moser, 2013). The proposed link between grid modules and hippocampal memory capacity remains to be tested, however. We know that individual grid maps maintain their functional structure from one environment to the next (Fyhn et al., 2007 and Solstad et al., 2008), whereas hippocampal representations are diverse, showing

complete independence across pairs second of recording environments (Muller and Kubie, 1987 and Leutgeb et al., 2004). Whether this transformation from a small number of entorhinal maps to a large number of hippocampal maps is evoked by independent responses among grid modules remains to be tested. Similarly, the neural mechanisms that could enable such a transformation and the detailed consequences for memory formation remain elusive. The fundamental properties of the entorhinal-hippocampal space circuit seem to be preserved across mammalian evolution. While most studies of this system use rodents, grid cells have also been found in bats, which are phylogenetically distant from rodents (Yartsev et al., 2011).