The current functional state of local neuronal circuits controls the magnitude of a BOLD response to incoming stimuli.
The purpose of this study was to determine how the history-dependent activation state of neuronal networks controls fMRI signals to incoming stimuli. Simultaneous electrophysiological and blood oxygen level-dependent (BOLD) responses were monitored during stimulation of the perforant pathway with low, high, and again low intensity but, otherwise identical pulse trains. Under three different anesthetics (alpha-chloralose, medetomidine, isoflurane) consecutive low intensity stimulation trains, set just below the threshold for population spike generation to single pulses, yielded a stable BOLD response, although at different magnitudes. The first high intensity train increased the BOLD response under all anesthetics and generated population spikes, with varying amplitudes and latencies (alpha-chloralose, metedomidine) or in a regular pattern (isoflurane). Concurrent to the second high intensity train, the BOLD response became minimal, then slowly increasing with subsequent trains (alpha-chloralose, metedomidine), or immediately rising to a stable level (isoflurane). Second train population spikes became regularized, but at low amplitudes and long latencies that were slowly reversed across trains (alpha-chloralose, medetomidine); while under isoflurane, amplitude and latencies became stabilized with the second train. In comparison to initial stimulation, the final low intensity stimulation trains failed to produce BOLD responses (alpha-chloralose, medetomidine), or left the response unchanged (isoflurane), only reaching stable potentiation of population spikes when under isoflurane. Therefore, the fate of BOLD responses depends on whether a new stable functional state of the intrinsic network can be reached after high intensity stimulation.
Angenstein
Frank
F
Leibniz Institute for Neurobiology, Special Lab Non-Invasive Brain Imaging, Brenneckestr. 6, 39118 Magdeburg, Germany. angenstein@ifn-magdeburg.de
Krautwald
Karla
K
Scheich
Henning
H
D000777:Anesthetics / Q000494:pharmacology; D000818:Animals; D002560:Cerebrovascular Circulation / Q000187:drug effects / Q000502:physiology*; D002698:Chloralose / Q000494:pharmacology; D018891:Dentate Gyrus / Q000098:blood supply / Q000187:drug effects / Q000502:physiology*; D004558:Electric Stimulation; D004567:Electrodes, Implanted; D007530:Isoflurane / Q000494:pharmacology; D008279:Magnetic Resonance Imaging; D008297:Male; D020926:Medetomidine / Q000494:pharmacology; D008839:Microelectrodes; D009474:Neurons / Q000502:physiology*; D010100:Oxygen / Q000097:blood*; D019580:Perforant Pathway / Q000098:blood supply / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D013997:Time Factors
D000777:Anesthetics; D002698:Chloralose; D007530:Isoflurane; D020926:Medetomidine; D010100:Oxygen