Abstract
Neurovascular coupling is the generic term for changes in cerebral metabolic rate of oxygen (CMRO 2), cerebral blood flow, and cerebral blood volume related to brain activity. The goal of this paper is to better understand the effects of neurovascular coupling in the visual and motor cortices using frequency-domain near-infrared spectroscopy. Maps of concentration changes in oxyhemoglobin [O 2Hb], deoxyhemoglobin [HHb], and total hemoglobin of the visual and motor cortices were generated during stimulation using a reversing checkerboard screen and palm-squeezing, respectively. Seven healthy volunteers of 18–37 years of age were included. In the visual cortex the patterns of [O 2Hb] and [HHb] were strongly linearly correlated ( r 2 > 0.8 in 13 of a total of 24 locations). In 20 locations the change in [O 2Hb] was larger than 0.25 μM. The mean slope of the linear regression between [O 2Hb] and [HHb] was −3.93 ± 0.31 (SE). The patterns of the [O 2Hb] and [HHb] traces over the motor cortex looked different. The [O 2Hb] reached its maximum change a few seconds before the [HHb] reached its minimum. This was confirmed by the linear regression analysis ( r 2 > 0.8 in none of 40 locations). In 20 locations the change in [O 2Hb] was larger than 0.25 μM. The mean slope of the regression line was −1.76 ± 0.20, which is significantly higher than that in the motor cortex ( P < 0.0000001). Patterns of [O 2Hb] and [HHb] differ among cortex areas. This implies that the regulation of perfusion in the visual cortex is different from that in the motor cortex. There is evidence that the CMRO 2 increases substantially in the visual cortex, while this is not the case for the motor cortex.
Highlights
Neurovascular coupling is the generic term for changes in cerebral metabolic rate of oxygen (CMRO2), cerebral blood flow (CBF), and cerebral blood volume (CBV) related to brain activity (Frostig et al, 1990; Maki et al, 1995; Villringer and Dirnagl, 1995)
The patterns of the [O2Hb] and [HHb] traces are quite different over the motor cortex compared to those over the visual cortex (Figs. 5–7)
For the visual cortex we find an increase in cerebral hemoglobin flow (CHbF), which is bigger than the one we find
Summary
Neurovascular coupling is the generic term for changes in cerebral metabolic rate of oxygen (CMRO2), cerebral blood flow (CBF), and cerebral blood volume (CBV) related to brain activity (Frostig et al, 1990; Maki et al, 1995; Villringer and Dirnagl, 1995). CMRO2 and CBF can be determined (Meltzer et al, 2000) While both techniques provide an excellent spatial resolution on the order of millimeters, continuous monitoring is not possible due to its relatively low time resolution (s) and the requirement of the application of a contrast agent. Near-infrared spectroscopy (NIRS), due to its high time resolution (ms) and good spatial resolution (cm) offers the option of continuously recording changes of physiological parameters during brain activation Due to this and its other advantageous features such as noninvasiveness, the capability to be performed at bedside, the absence of ionizing radiation, and the relatively low cost, it has been increasingly used in brain research (Hoshi et al, 1994; Villringer and Chance, 1997).
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