# What is the actual interpretation of the "correlation of a connection between neurons"?

I am student of Mathematics who is currently studying the utility of Algebraic Topology in the field of Neuroscience. In the paper I am reading (Reimann et al 2017) the authors explain that for several pairs of neurons they calculated the correlation of their spiking activity. Sometimes they also use the expression "correlation of connection", which I think refers to the correlation of spiking activity between two neurons (as the prior references). I am interested in understanding the following:

1. How does one measure the correlation of a connection?
2. I know the mathematical definition of correlation and have an intuitive understanding of it as a measurement of dependence. But in the case of neurons what is the actual interpretation for the correlation of a connection? Is it in the sense of synchronicity? Or something else?

Any insight will be appreciated. This is not my area of studies, so the most elementary observation might help. Thank you in advance.

Reimann, M. W., Nolte, M., Scolamiero, M., Turner, K., Perin, R., Chindemi, G., ... & Markram, H. (2017). Cliques of neurons bound into cavities provide a missing link between structure and function. Frontiers in computational neuroscience, 11, 48.

• Can you provide a full citation? Titles aren't citations. Correlation of connection might refer to correlating the rows of a connectivity matrix for two nodes. Could also be anything else owing to non-native English speakers writing papers in English. Commented Jul 6, 2021 at 2:45
• Yes, of course. This is the first time "correlation" is mentioned in the paper: "(...) we observed that pairwise correlations in neuronal activity increased with the number and dimension of the directed cliques to which a pair of neurons belongs (...)" Second reference: "We then calculated for each connected pair of neurons the correlation of their spiking activity and found a broad distribution of correlation coefficients (...)" Commented Jul 6, 2021 at 10:28
• Those are now quotes, but still not a citation :) Commented Jul 6, 2021 at 14:06
• I edited to add what I meant by a citation. Hope it is now clear from my answer. Commented Jul 6, 2021 at 19:42