Research in the field of cognitive neuroscience has provided extensive evidence in support of a strong relationship between time, space, and number in the human brain. In 1993, Dehaene et al. discovered the SNARC (spatial-numerical association of response codes) effect and suggested that numbers may be internally represented along a spatial dimension, with low numbers on the left of a mental number line, and high numbers on the right. The investigation of this effect has been studied through the use of different methodologies and recent insights have extent this effect also to decisional processes (Daar and Pratt, 2008; Loetscher et al., 2008; Vicario, 2012, 2013).

Similar relationships were also documented in research investigating link between space and time (DeLong, 1981; Vicario et al., 2007, 2009, 2011a,b; Ishihara et al., 2008; Vallesi et al., 2008; Fabbri et al., 2013) as well as between time and numbers (for instance see Dormal et al., 2006; Vicario et al., 2008; Lu et al., 2009; Vicario, 2011).

This literature corroborates the suggestion of common cortical metrics for space time and numbers (Walsh, 2003). However, despite the 10 years that have elapsed since Walsh (2003) published his theoretical work, the debate about “A theory of Magnitude” (ATOM) is still object of discussion.

This research topic entitled “On a generalized magnitude system in the brain: insights from experimental evidence” contains 10 state-of-the-art original research articles exploring the relationships between time, space and number. These research articles provide original contributions about the representation of magnitude in different research fields including childhood participants (Bottini and Casasanto, 2013; Lonnemann et al., 2013; Tokita and Ishiguchi, 2013), genetic polymorphism (Júlio-Costa et al., 2013), clinical populations such as schizophrenia (Martinez-Cascales et al., 2013) and right brain damaged patients (Ishihara et al., 2013), investigations on healthy adults (Baker et al., 2013; Blini et al., 2013; Crollen et al., 2013; Viarouge and de Hevia, 2013).

A lively contribute to this debate is also provided by the mini-review of Leibovich and Henik (2013) and six opinion articles (Agrillo and Miletto Petrazzini, 2013; Arzy et al., 2013; De Simone, 2013; Tzelgov et al., 2013; Van Opstal and Verguts, 2013; Vicario et al., 2013). These theoretical contributions address ATOM from different perspectives, revealing the strengths but also the weaknesses of this model.

Much more work needs to be done and many issues remain to be addressed before we fully understand the brain mechanisms underlying the existence of analogies (Vicario and Martino, 2010) between magnitudes.

It has been a great pleasure and honor to be involved in this Research Topic. I would like to thank all of the authors, reviewers, and Frontiers staff for helping to make this Research Topic possible and I look forward to further explorations of the brain mechanisms underlying ATOM.