PT  - JOURNAL ARTICLE
AU  - Ali Danish Zaidi
AU  - Niels Birbaumer
AU  - Eberhard Fetz
AU  - Nikos Logothetis
AU  - Ranganatha Sitaram
TI  - The timing of hemodynamic changes reliably reflects spiking activity
AID  - 10.1101/269696
DP  - 2018 Jan 01
TA  - bioRxiv
PG  - 269696
4099  - http://biorxiv.org/content/early/2018/02/22/269696.short
4100  - http://biorxiv.org/content/early/2018/02/22/269696.full
AB  - Functional neuroimaging is a powerful non-invasive tool for studying brain function, using changes in blood-oxygenation as a proxy for underlying neuronal activity. The neuroimaging signal correlates with both spiking, and various bands of the local field potential (LFP), making the inability to discriminate between them a serious limitation for interpreting hemodynamic changes. Here, we record activity from the striate cortex in two anesthetized monkeys (Macaca mulatta), using simultaneous functional near-infrared spectroscopy (fNIRS) and intra-cortical electrophysiology. We find that low-frequency LFPs correlate with hemodynamic signal’s peak amplitude, whereas spiking correlates with its peak-time and initial-dip. We also find spiking to be more spatially localized than low-frequency LFPs. Our results suggest that differences in spread of spiking and low-frequency LFPs across cortical surface influence different parameters of the hemodynamic response. Together, these results demonstrate that the hemodynamic response-amplitude is a poor correlate of spiking activity. Instead, we demonstrate that the timing of the initial-dip and the hemodynamic response are much more reliable correlates of spiking, reflecting bursts in spike-rate and total spike-counts respectively.[HbO]: concentration of oxy-hemoglobin (mol·cm−3)[HbR]: concentration of deoxy-hemoglobin (mol·cm−3)BOLD: blood-oxygen level dependent signalFNIRS: functional near-infrared spectroscopyLFP: local field potentialMUA: multi-unit activityHbO peak-amplitude: peak amplitude of the HbO responseHbO peak-time: time from stimulus onset until peak of HbO responseSDU: Standard-deviation units