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Redgrave P, Mayhew JE. Fine detail of neurovascular coupling revealed by spatiotemporal analysis of the hemodynamic response to single whisker stimulation in rat barrel cortex.

Summary: This article investigates the relation between stimulus-evoked neural activity and cerebral hemodynamics. Specifically, the hypothesis is tested that hemodynamic responses can be modeled as a linear convolution of experimentally obtained measures of neural activity with a suitable hemodynamic impulse response function. To obtain a range of neural and hemodynamic responses, rat whisker pad was stimulated using brief (Յ2 seconds) electrical stimuli consisting of single pulses (0.3 millisecond, 1.2 mA) combined both at different frequencies and in a paired-pulse design. Hemodynamic responses were measured using concurrent optical imaging spectroscopy and laser Doppler flowmetry, whereas neural responses were assessed through current source density analysis of multielectrode recordings from a single barrel. General linear modeling was used to deconvolve the hemodynamic impulse response to a single "neural event" from the hemodynamic and neural responses to stimulation. The model provided an excellent fit to the empirical data. The implications of these results for modeling schemes and for physiologic systems coupling neural and hemodynamic activity are discussed.

Optical imaging spectroscopy was used to measure the hemodynamic response of somatosensory cortex to stimulation of the whiskers. Responses to brief puffs of air were compared in anesthetized and unanesthetized rats. The hemodynamic response was approximately four times larger in the unanesthetized animal than the corresponding anesthetized animal. In unanesthetized animals, a short-latency (approximately 400 milliseconds) short-duration (approximately 300 milliseconds) hemodynamic startle response was observed. General linear model analysis was used to extract this component from the time series, and revealed an underlying short-latency increase in deoxygenated hemoglobin in response to somatosensory stimulation. It is proposed that anesthesia can have a marked affect on the relation between changes in blood volume and blood flow. This work represents a step in the development of an experimental model that can be used to investigate fundamental neurologic processes in the awake-behaving rodent.

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