Investigating the spatiotemporal characteristics of the deoxyhemoglobin-related and deoxyhemoglobin-unrelated functional hemodynamic response across cortical layers in awake marmosets
Introduction
The blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) has proven to be a valuable tool to non-invasively probe various brain areas at a macroscopic scale (Fukuda et al., 2016, Goense et al., 2016). With continued improvement in both spatial and temporal resolution of MRI, BOLD fMRI has recently been applied to study the temporal dynamics of the laminar hemodynamic response and its underlying neural activity in both animal models and humans (Hirano et al., 2011, Jin and Kim, 2008, Siero et al., 2011, Silva and Koretsky, 2002). The distinct function of the six cortical layers is the foundation of interlaminar connections, which form a larger and more complex intracortical network at macroscopic scale (Thomson and Bannister, 2003). However, an in-depth understanding of the spatiotemporal characteristics of the laminar BOLD response is essential to interpret the laminar BOLD response as a function of its underlying neural activity, to optimize the BOLD fMRI protocol, and to realize the spatiotemporal limitations of the BOLD fMRI technique.
Several studies have been conducted that characterize the temporal aspects of laminar BOLD contrast in various brain areas and species. Faster laminar BOLD onset times were reported in cortical layer 4 or 5, followed by layer 6, and then layers 1–3 of somatosensory cortex in anesthetized rats (Silva and Koretsky, 2002, Tian et al., 2010, Yu et al., 2014). Cerebral blood volume or flow is reported to have onset time monotonically increasing by cortical depth in anesthetized rats or cats (Hirano et al., 2011, Jin and Kim, 2008, Norup Nielsen and Lauritzen, 2001). However, the aforementioned animal studies suffered from confounds of general anesthesia, which is known to alter hemodynamic regulation and neuronal response (Liu et al., 2013, Masamoto and Kanno, 2012). On the other hand, BOLD fMRI in humans shows promising results concerning faster BOLD onset times in layers 5–6 of the visual cortex (Siero et al., 2013). Nevertheless, insufficient spatiotemporal resolution causes laminar onset times to be contaminated by partial volume of white matter or pial vessels/cerebrospinal fluid (CSF). Consequently, conscious, awake marmosets were adopted in the current study as a nonhuman primate model to bridge the gap between high-resolution fMRI in small animals and low-resolution fMRI in humans (Hung et al., 2015c, Silva et al., 2011). Marmosets are phylogenetically closer to humans, compared to other small animals (Marmoset Genome and Analysis, 2014), and have one of the highest cortical thickness to brain mass ratios among primates (Sun and Hevner, 2014).
Another issue that commonly appears in high temporal resolution BOLD fMRI experiments is the large inflow contribution in BOLD contrast (Duyn et al., 1994). Inflow might account for more than half of the BOLD contrast when there is not enough time for the MR signal to recover (Glover et al., 1996). To separate the inflow contribution from the real BOLD contrast, a dual gradient-recalled echo planar imaging (GR-EPI) sequence was utilized to isolate spin-spin relaxation time (T2*) change from non-T2* change, which contained the inflow effect manifested as change in spin-lattice relaxation time (T1) (Speck and Hennig, 1998). The difference in T2* is presumably proportional to change in the amount of deoxyhemoglobin in the blood and directly related to BOLD contrast (Kim and Ogawa, 2012). In addition, inflow contribution was suppressed by saturating the incoming blood below the circle of Willis in marmosets. Therefore, any remaining non-T2* signal would be either from outside of the vasculature and/or exceptions in modeling T2* by dual echoes.
The main goal of the current study was to investigate the spatiotemporal characteristics of the laminar BOLD hemodynamic response function in the primary somatosensory (S1) cortex of awake marmosets. To accomplish our goal, the present study implemented several strategies to avoid shortcomings in prior studies, such as confounding effects of anesthesia, insufficient spatiotemporal resolution, and inflow contribution. Our results show early onset times of laminar BOLD and deoxyHb component in layers 3–4 of S1, whereas the non-deoxyHb component, which was insensitive to T2* changes, was significant only in layers 1 and 2. The non-deoxyHb component in layers 1 and 2 exhibited a significantly faster onset time when compared to the deoxyHb component. Since inflow contribution was suppressed by saturation of arterial spins below the circle of Willis, this could only be explained by the shrinkage of the cerebrospinal fluid (CSF) compartment due to expansion of the arterial blood compartment. However, CSF partial volume could not fully explain the peak amplitude of the deoxyHb component in layers 1 and 2. The gap could be filled by the contribution of the slower intravenous signal that was not properly modeled by the dual-echo fitting.
Section snippets
Methods
All procedures were approved by the Animal Care and Use Committee of the National Institute of Neurological Disorders and Stroke. Four male adult common marmosets (Callithrix jacchus) weighting 350–500 g and aged 4–5 years old were housed in pairs in dedicated cages and maintained on a diurnal 12-hour light cycle. Their diet consisted of ad libitum Zupreem canned marmoset food, Purina 5040 biscuits, unfiltered water, and P.R.A.N.G. rehydrator. In addition, the animals were fed daily with
Results
During fMRI experiments, marmosets were constantly monitored by an MR-compatible camera inside the magnet. The individualized 3D-printed helmet/chin pieces were very effective in providing comfortable yet effect head restraint, and for the vast majority of their time inside the magnet, the marmosets were resting with their eyes closed. Occasionally, they would open their eyes to check their surroundings or momentarily adjust their body position. Supplementary Fig. S1 shows an example session
Sources of the non-deoxyHb component in superficial layers
In the present work, we show that the BOLD fMRI response to somatosensory stimulation has distinct and heterogeneous spatiotemporal characteristics across the layers of somatosensory cortex in awake marmosets. The largest and fastest BOLD signal changes were found in L1+2–L4, whereas the smallest and slowest responses were found in L5–L6 of the somatosensory cortex. The heterogeneous laminar distribution of the BOLD fMRI response was largely associated with changes in the deoxyHb component (T2
Conclusions
A heterogeneous spatiotemporal distribution of relative BOLD signal changes in response to functional stimulation was observed across the layers of the primary somatosensory cortex in awake marmosets. The mid-upper cortical layers tended to have stronger relative BOLD signal changes and faster onset times than the lower ones. When the laminar BOLD signal changes were decomposed into their deoxyhemoglobin-related (absolute ΔT2*) and deoxyhemoglobin-unrelated (relative S0 changes) components, the
Acknowledgments
We thank Xianfeng (Lisa) Zhang, and Jennifer Lynn Ciuchta for their technical support in animal preparation. Also, many thanks go to the Scientific and Statistical Computing Core for their technical support in using AFNI to process the data. This research was supported by the Intramural Research Program of the NIH, NINDS (Alan P. Koretsky, Scientific Director).
References (80)
- et al.
Dual-echo EPI for non-equilibrium fMRI - implications of different echo combinations and masking procedures
Neuroimage
(2010) - et al.
Visualizing the entire cortical myelination pattern in marmosets with magnetic resonance imaging
J. Neurosci. Methods
(2009) - et al.
Identification of cortical lamination in awake monkeys by high resolution magnetic resonance imaging
Neuroimage
(2012) - et al.
Layer-specific BOLD activation in awake monkey V1 revealed by ultra-high spatial resolution functional magnetic resonance imaging
Neuroimage
(2013) - et al.
Submillimeter-resolution fMRI: toward understanding local neural processing
Prog. Brain Res.
(2016) - et al.
Functional MRI of visual responses in the awake, behaving marmoset
Neuroimage
(2015) - et al.
Comparative analysis of cortical layering and supragranular layer enlargement in rodent carnivore and primate species
Brain Res.
(2005) - et al.
Improved cortical-layer specificity of vascular space occupancy fMRI with slab inversion relative to spin-echo BOLD at 9.4 T
Neuroimage
(2008) - et al.
Change of the cerebrospinal fluid volume during brain activation investigated by T(1rho)-weighted fMRI
Neuroimage
(2010) - et al.
Multi-echo fMRI of the cortical laminae in humans at 7 T
Neuroimage
(2011)
Differentiating BOLD and non-BOLD signals in fMRI time series from anesthetized rats using multi-echo EPI at 11.7 T
Neuroimage
Repeated fMRI using iron oxide contrast agent in awake, behaving macaques at 3 T
Neuroimage
Magnetic resonance imaging quantification of regional cerebral blood flow and cerebrovascular reactivity to carbon dioxide in normotensive and hypertensive rats
Neuroimage
Extensive heterogeneity in white matter intensity in high-resolution T2*-weighted MRI of the human brain at 7.0 T
Neuroimage
Dynamic resting state functional connectivity in awake and anesthetized rodents
Neuroimage
fMRI in the awake marmoset: somatosensory-evoked responses, functional connectivity, and comparison with propofol anesthesia
Neuroimage
Anesthesia and neuroimaging: investigating the neural correlates of unconsciousness
Trends Cogn. Sci.
Measurements of tissue T1 spin-lattice relaxation time and discrimination of large draining veins using transient EPI data sets in BOLD-weighted fMRI acquisitions
Neuroimage
Functional MR imaging in the awake monkey: effects of motion on dynamic off-resonance and processing strategies
Magn. Reson. Imaging
Methods to detect, characterize, and remove motion artifact in resting state fMRI
Neuroimage
BOLD responses to different temporal frequency stimuli in the lateral geniculate nucleus and visual cortex: insights into the neural basis of fMRI
Neuroimage
Quantification of cerebral blood flow in nonhuman primates using arterial spin labeling and a two-compartment model
Magn. Reson Imaging
Cortical layer-dependent BOLD and CBV responses measured by spin-echo and gradient-echo fMRI: insights into hemodynamic regulation
Neuroimage
S1 laminar specialization
Scholarpedia
Large-scale brain networks in the awake, truly resting marmoset monkey
J. Neurosci.
Evaluation of the contribution of signals originating from large blood vessels to signals of functionally specific brain areas
Biomed. Res. Int.
Distribution of temperature changes and neurovascular coupling in rat brain following 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy") exposure
NMR Biomed.
Software tools for analysis and visualization of fMRI data
NMR Biomed.
Real-time functional magnetic resonance imaging
Magn. Reson. Med.
Theoretical and experimental investigation of the VASO contrast mechanism
Magn. Reson. Med.
Inflow versus deoxyhemoglobin effects in BOLD functional MRI using gradient echoes at 1.5 T
NMR Biomed.
Functional magnetic resonance imaging in conscious animals: a new tool in behavioural neuroscience research
J. Neuroendocrinol.
Nonlinear event-related responses in fMRI
Magn. Reson. Med.
Auditory cortical neurons respond to somatosensory stimulation
J. Neurosci.
Effects of the alpha(2)-adrenergic receptor agonist dexmedetomidine on neural, vascular and BOLD fMRI responses in the somatosensory cortex
Eur. J. Neurosci.
Decomposition of inflow and blood oxygen level-dependent (BOLD) effects with dual-echo spiral gradient-recalled echo (GRE) fMRI
Magn. Reson. Med.
fMRI at High Spatial Resolution: implications for BOLD-Models
Front Comput. Neurosci.
Cerebral blood flow modeling in primate cortex
J. Cereb. Blood Flow Metab.
Stereotaxic and Chemoarchitectural Atlas of the Brain of the Common Marmoset (Callithrix jacchus)
Quantitative BOLD: mapping of human cerebral deoxygenated blood volume and oxygen extraction fraction: default state
Magn. Reson. Med.
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Present address: Department of Physics, Universidade Federal do ABC, Santo Andre, Sao Paulo, 09210, Brazil.