Functional increases in cerebral blood volume over somatosensory cortex

Area of Science:

• Neuroscience
• Cerebrovascular Physiology
• Electrophysiology

Background:

• Understanding the relationship between brain activity and blood flow is crucial for interpreting functional neuroimaging signals.
• Cerebral blood volume (CBV) is a key indicator of vascular response, but its precise spatial and temporal correlation with neuronal activity requires further investigation.
• Previous studies have suggested a link between electrophysiological activity and hemodynamic responses, but detailed comparisons are limited.

Purpose of the Study:

• To investigate the relationship between cerebral blood volume (CBV) and electrophysiology in the rat primary somatosensory cortex (S-I).
• To compare the spatial characteristics and temporal dynamics of activity-related changes in plasma fluorescence, intrinsic optical reflectance, and single-unit electrophysiology.
• To determine if CBV changes accurately reflect the spatial extent of neuronal activation.

Main Methods:

• Experiments were conducted on urethane-anesthetized male Sprague-Dawley rats with exposed S-I cortex.
• Fluorescent Texas Red dextran dye was administered intravenously to measure CBV changes via plasma fluorescence.
• Stimuli included foredigit electroshock and vibrissal deflection, with simultaneous recording of fluorescence, intrinsic optical reflectance, and single-unit electrophysiology.

Main Results:

• Activity-related fluorescence increases, indicative of CBV changes, were observed over the contralateral forelimb or posteromedial barrel subfield cortex.
• CBV increases were delayed (1-1.5 s) and prolonged (peaking at 2-2.5 s) after stimulus onset.
• The spatial extent of the smallest detectable fluorescence changes consistently exceeded the boundaries of the electrophysiologic center receptive fields, and intrinsic optical reflectance changes showed similar spatial and temporal characteristics.

Conclusions:

• Delayed increases in cerebral blood volume (CBV) are observed over activated cortex in the rat somatosensory cortex.
• The spatial spread of CBV changes, as measured by fluorescence, is broader than the core area of neuronal firing.
• Intrinsic optical reflectance changes are strongly related to CBV changes, suggesting vascular contributions to optical signals.