Suppressed neuronal activity and concurrent arteriolar vasoconstriction may explain negative blood oxygenation level-dependent signal.
Synaptic transmission initiates a cascade of signal transduction events that couple neuronal activity to local changes in blood flow and oxygenation. Although a number of vasoactive molecules and specific cell types have been implicated, the transformation of stimulus-induced activation of neuronal circuits to hemodynamic changes is still unclear. We use somatosensory stimulation and a suite of in vivo imaging tools to study neurovascular coupling in rat primary somatosensory cortex. Our stimulus evoked a central region of net neuronal depolarization surrounded by net hyperpolarization. Hemodynamic measurements revealed that predominant depolarization corresponded to an increase in oxygenation, whereas predominant hyperpolarization corresponded to a decrease in oxygenation. On the microscopic level of single surface arterioles, the response was composed of a combination of dilatory and constrictive phases. Critically, the relative strength of vasoconstriction covaried with the relative strength of oxygenation decrease and neuronal hyperpolarization. These results suggest that a neuronal inhibition and concurrent arteriolar vasoconstriction correspond to a decrease in blood oxygenation, which would be consistent with a negative blood oxygenation level-dependent functional magnetic resonance imaging signal.
Devor
Anna
A
Department of Neurosciences, University of California, San Diego, California 92093, USA. adevor@ucsd.edu
Tian
Peifang
P
Nishimura
Nozomi
N
Teng
Ivan C
IC
Hillman
Elizabeth M C
EM
Narayanan
S N
SN
Ulbert
Istvan
I
Boas
David A
DA
Kleinfeld
David
D
Dale
Anders M
AM
D000818:Animals; D001160:Arterioles / Q000502:physiology*; D001810:Blood Volume; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000502:physiology*; D006454:Hemoglobins / Q000378:metabolism; D009474:Neurons / Q000502:physiology*; D010100:Oxygen / Q000097:blood*; D010108:Oxyhemoglobins / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D009435:Synaptic Transmission / Q000502:physiology*; D014661:Vasoconstriction / Q000502:physiology*
D006454:Hemoglobins; D010108:Oxyhemoglobins; C100003:deoxyhemoglobin; D010100:Oxygen