Linear superposition of sensory-evoked and ongoing cortical hemodynamics

Abstract

Modern non-invasive brain imaging techniques utilize changes in cerebral blood flow, volume and oxygenation that accompany brain activation. However, stimulus-evoked hemodynamic responses display considerable inter-trial variability even when identical stimuli are presented and the sources of this variability are poorly understood. One of the sources of this response variation could be ongoing spontaneous hemodynamic fluctuations. To investigate this issue, 2-dimensional optical imaging spectroscopy was used to measure cortical hemodynamics in response to sensory stimuli in anesthetized rodents. Pre-stimulus cortical hemodynamics displayed spontaneous periodic fluctuations and as such, data from individual stimulus presentation trials were assigned to one of four groups depending on the phase angle of pre-stimulus hemodynamic fluctuations and averaged. This analysis revealed that sensory evoked cortical hemodynamics displayed distinctive response characteristics and magnitudes depending on the phase angle of ongoing fluctuations at stimulus onset. To investigate the origin of this phenomenon, “null-trials” were collected without stimulus presentation. Subtraction of phase averaged “null trials” from their phase averaged stimulus-evoked counterparts resulted in four similar time series that resembled the mean stimulus-evoked response. These analyses suggest that linear superposition of evoked and ongoing cortical hemodynamic changes may be a property of the structure of inter-trial variability.

The resting‐state neurovascular coupling relationship: rapid changes in spontaneous neural activity in the somatosensory cortex are associated with haemodynamic fluctuations that resemble stimulus‐evoked haemodynamics

“…Fig. E) (Saka et al ., ) a peak at similar frequency (∼1.2 Hz in this case) could be seen in the Fourier transform of both the end‐tidal CO 2 trace and the cortical haemodynamics.…”

“…We have previously demonstrated that the haemodynamics contain low-frequency fluctuations with higher frequency 'noise' superimposed on the time series (Saka et al, 2010). These higher frequency fluctuations are orders of magnitude lower than the predominant fluctuations at $ 0.1 Hz (Saka et al, 2010). The haemodynamic data were smoothed using a low-pass zero-phase ninth-order butterworth filter to below 0.25 Hz.…”

Low-frequency calcium oscillations accompany deoxyhemoglobin oscillations in rat somatosensory cortex

“…There is growing interest in using optical imaging to study resting-state fluctuations in human (38,43) and rodent cortex (44)(45)(46)(47). For example, a recent study (10) demonstrated LFOs in HbO 2 , HbR, and cytochrome oxidase in human visual cortex using NIRS.…”

Direct, intraoperative observation of ~ 0.1 Hz hemodynamic oscillations in awake human cortex: Implications for fMRI

“…These large oscillations, with amplitudes comparable to the hemodynamic response to sensory stimulus, are sporadic, but have been shown to occur in the rat (Golanov et al, 1994; Grosberg et al, 2012; Majeed et al, 2009; Mayhew et al, 1996; Saka et al, 2010), cat (Spitzer et al, 2001), awake rabbit (Hundley et al, 1988) and non-invasively in humans using near-infrared spectroscopy (Elwell et al, 1999; Kolyva et al, 2013; Näsi et al, 2011; Obrig et al, 2000; Sassaroli et al, 2012; Schroeter et al, 2005), and fMRI BOLD (Mitra et al, 1997). In some cases the appearance of SSHOs in the brain has been linked to distinct physiological conditions or states of arousal (Näsi et al, 2011).…”