Pooling with different orders of operations can have a large effect on measured brain signals.
(A) The approach to directly correlate local field potential (LFP) and blood-oxygen-level dependent (BOLD) data. (B) The current approach to relate the LFP and BOLD from the same neuronal population activity. (C) In this illustration, the currents of two neurons (x1 and x2) has the shape of a sinusoid with noise, and the sinusoid is in phase between the two neurons. In the simulated electrode measurement, the signals are summed and the power is calculated (POWER[SUM] = 2.00). In the simulated measurement of metabolic demand, the power of each of these neurons is first calculated and then summed across the neurons (SUM[POWER] = 1.01). Here, the LFP and BOLD are both large. (D) In this illustration, the membrane currents of two neurons (x1 and x2) are the same as in panel (C) except that the two time series are in counterphase. Here, unlike (C), the LFP is nearly 0 and the BOLD signal is large (code to reproduce this figure can be found on https://github.com/dorahermes/Paper_Hermes_2017_PLOSBiology function ns_script01_Fig1.m).
