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  1. 1. Journal of Cerebral Blood Flow & Metabolism (2010), 1–8 & 2010 ISCBFM All rights reserved 0271-678X/10 $32.00 www.jcbfm.comFeature ArticleFunctional white-laser imaging to study brainoxygen uncoupling/recoupling in songbirdsStephane Mottin1, Bruno Montcel2, Hugues Guillet de Chatellus3 and Stephane Ramstein1 ´ ´1 CNRS; Universite de Lyon; Universite de St-Etienne, UMR5516, Saint-Etienne, France; 2Universite de Lyon; ´ ´ ´CREATIS-LRMN; CNRS UMR5220; INSERM U630; Universite Lyon 1; INSA Lyon, Villeurbanne, France; 3CNRS; ´ ´Universite Joseph Fourier; Laboratoire de Spectrome´trie Physique, UMR5588, St Martin d’He `res, France Contrary to the intense debate about brain oxygen dynamics and its uncoupling in mammals, very little is known in birds. In zebra finches, picosecond optical tomography with a white laser and a streak camera can measure in vivo oxyhemoglobin (HbO2) and deoxyhemoglobin (Hb) concentration changes following physiologic stimulation (familiar calls and songs). Picosecond optical tomography showed sufficient submicromolar sensitivity to resolve the fast changes in the hippocampus and auditory forebrain areas with 250 lm resolution. The time course is composed of (1) an early 2-second- long event with a significant decrease in Hb and HbO2 levels of À0.7 and À0.9 lmol/L, respectively, (2) a subsequent increase in blood oxygen availability with a plateau of HbO2 ( + 0.3 lmol/L), and (3) pronounced vasodilatation events immediately after the end of the stimulus. One of the findings of our study is the direct link between blood oxygen level-dependent signals previously published in birds and our results. Furthermore, the early vasoconstriction event and poststimulus ringing seem to be more pronounced in birds than in mammals. These results in birds, tachymetabolic vertebrates with a long lifespan, can potentially yield new insights, e.g., into brain aging. Journal of Cerebral Blood Flow & Metabolism advance online publication, 20 October 2010; doi:10.1038/jcbfm.2010.189 Keywords: brain activation; cerebral hemodynamics; near-infrared spectroscopy; neurovascular coupling; optical imaging; songbirdsIntroduction suppressed by hypercapnia (Steinmeier et al, 1996; Biswal et al, 1997; Fox and Raichle, 2007). WhenUnlike other organs, the brain of mammals and birds activation occurs, step responses are complexis a constant energy sink, consuming energy irre- (Kasischke et al, 2004; Niven and Laughlin, 2008;spective of whether it is at rest or active, but on the Petzold et al, 2008; Vanzetta and Grinvald, 2008)other side of the coin is its low tolerance to a long list and induce changes in blood flow and oxygenof ‘perturbations’, such as hypoglycemia, hypoxia, transport (Ress et al, 2009). The coupling of perfu-hypercapnia, hyperthermia, and mitochondrial dis- sion and oxidative metabolism in the resting braineases (Siesjo, 1978; Mottin et al, 2003). The coupling ¨ has been shown to be disrupted in the first minutebetween transport and metabolism allows the bal- after the onset of a sudden functional challengeance between the storage and the production of (Kasischke et al, 2004; Niven and Laughlin, 2008;adenosine triphosphate, despite the very high rate Petzold et al, 2008; Vanzetta and Grinvald, 2008).of combustion of glucose with B5.5 dioxygen mole- This uncoupling has also been a major problem forcules per glucose molecule (Siesjo, 1978; Sokoloff, ¨ the interpretation of brain imaging (Vanzetta and2001). This steady state is an oscillatory regime that Grinvald, 2008). To better understand the linkis poorly understood, and low frequencies have been between tachymetabolism and this uncoupling, weobserved in various cerebral parameters reversibly developed a method for measuring the full time course of oxygen transport in the higher-order auditory region of the telencephalon in the zebra ´Correspondence: Dr B Montcel, Universite Lyon 1, CREATIS-LRMN, finch, Taeniopygia guttata. The need for an im-4 Rue V, Grignard, Villeurbanne 69616, France. proved understanding of the mechanisms underlyingE-mail: brain activation, especially in songbirds, has becomeThese experiments were supported by the Program ‘Emergence’ ´ ˆ obvious (Voss et al, 2007; Boumans et al, 2007).of the Region Rhone-Alpes and the Agence Nationale de laRecherche. Following the growing evidence of mammalian-likeReceived 21 June 2010; revised 13 September 2010; accepted 14 cognitive abilities in songbirds (Vignal et al, 2004), ofSeptember 2010 the neocortex-like functions of the avian pallium
  2. 2. Brain oxygen uncoupling/recoupling S Mottin et al2 (Jarvis et al, 2005; Reiner, 2005), and that of some neuroscience results and to measure for the first time peculiarities of the avian metabolism (Barja and the full time course of coupling/uncoupling in small Herrero, 1998; Turner et al, 2005; Moe et al, 2009), songbirds. birds have become an important focus of interest for comparative neuroscience (Vignal et al, 2004; Clayton, 2007). Materials and methods The reliability of optical measurements of changes Animals and Stimulation Protocols in the concentration of hemoglobin in tissues has been a challenge for several years (Vanzetta and Adult male zebra finches (T. guttata) served as subjects Grinvald, 2008; Calderon-Arnulphi et al, 2009). for the experiments. Bred in the aviary of the University Owing to its noninvasive nature, transcranial optical of Saint-Etienne in a 12-light/12-dark photoperiod, they cerebral oximetry (near infrared spectroscopy, dif- received normal tutoring by adult males. Four and five fuse optical tomography, etc.) has become a source of birds were used for spectral-POT and spatial-POT, respec- quantitative or semiquantitative information about tively. Birds were anesthetized with 2% isoflurane under brain oxygenation, cerebral blood flow, and volume. spontaneous breathing conditions (Vignal et al, 2008). However, continuing technical controversies about Animal preparation and the spectral-POT setup have signal derivation, accuracy, precision, and quantita- been described previously (Vignal et al, 2008). Anesthe- tive ability have limited the application of transcra- tized zebra finches with the head previously plucked nial optical cerebral oximetry. Clearly, transcranial (3 days before experiments) were fixed in a stereotaxic optical cerebral oximetry still needs developments. frame (Stoelting Co., Wood Dale, IL, USA, adaptations for Recent ultrafast technological advancements have birds). Body temperature was kept within a narrow range opened up a new promising avenue in neuroscience (391C to 401C) using a feedback-controlled heating pad. (Gibson et al, 2006; Vignal et al, 2008; Montcel et al, Optical fibers were fixed into stereotaxic manipulators 2005, 2006; Pifferi et al, 2008; Liebert et al, 2004; (Stoelting Co.) and placed directly on the skin. Positions of Selb et al, 2006). the input optical fiber F1 providing illumination and those As part of our broader effort to develop a of the optical fiber F2 collecting transmitted light were noninvasive neuro-method and to improve quantita- chosen to probe the auditory regions of the telencephalon tive measurement of absorbing chromophores into (field L, NCM (caudomedial nidopallium), and CMM scattering brain tissues, we worked on a time (caudomedial mesopallium)). The precise anatomic locali- domain-based device. Using a white-light super- zation of the optical fiber (Figure 1 in Ramstein et al, 2005) continuum or ‘white laser’ (Chin et al, 1999), we and probed region (Figure 1 in Vignal et al, 2008) has been combined picosecond optical tomography (POT) with described in previous studies. The head of the bird was near-infrared spectroscopy (spectral-POT) (Vignal turned until the beak (rostral extremity) was perpendicular et al, 2008) and a new POT with contact-free spatial to the body plane. This position allowed us to define a imaging (spatial-POT). In the near-infrared spectral stereotaxic origin point (0, 0, 0) defined by the intersection window of 650 to 850 nm, the nonmonotonic of the vertical plane passing through the interaural line and behavior of the absorption spectrum of deoxyhemo- the sagittal suture (the vena cerebralis dorsocaudalis). The globin (Hb) provides reliable ‘molecular fingerprints’ stereotaxic axes were chosen according to this origin point. (Vignal et al, 2008). Furthermore, optical signals are F1 was placed more rostrally on the right hemisphere than integrated into a selected picosecond time-of-flight F2. The distance between F1 and F2 was 5 mm (Figure 1). window specifically defined so as to probe only the The chosen coordinates in millimeters were: F1 (2.0, 5.4, targeted deep brain structures (Vignal et al, 2008). À2.7) and F2 (2.0, 0.4, À0.3). This system allows us to monitor in vivo and Animals were kept in a custom-made sound-attenuated quantify an evoked brain hemodynamic response box (48 Â 53 Â 70 cm3) equipped with 2 fixed high-fidelity with submicromolar sensitivity and submillimeter speakers (Triangle Comete 202, Triangle SAS, Villeneuve spatial resolution. The spatial-POT is different from Saint Germain, France). After a 1-minute baseline period, the classic strategy of several discrete detectors each bird was subjected to a 20-second stimulus, followed (Gibson et al, 2006). This configuration is without by 1 minute for recovery of baseline. The original auditory contact between the skin and detectors. The position signal was a random sequence of songs and calls recorded of this imaged segment on the head of the bird can be in the zebra finch aviary, normalized to the same intensity. controlled by eye by shining the intermediate slit Among the 20 seconds of stimulus recorded, 94% repre- using a He-Ne laser and by checking and adjusting sented songs and calls, whereas 6% represented silence. the position of its image on the skin. In the case of For each animal, 15 stimuli were used, with 9 random such small animals, this imaging system allows the white-noise stimuli. After experiments, all animals were analysis of the resolution limits of POT. kept in the recording room for 24 hours for physiologic Having developed a spectral-POT, we have pre- and behavioral verifications. All experimental proce- viously been able to measure oxyhemoglobin (HbO2) dures were approved by the University’s animal care and Hb changes following hypercapnia (Vignal et al, committee. Statistical methods have been described previ- 2008). We now address the task of mapping the ously (Vignal et al, 2008) (multiple comparison procedure, acoustic field with the best possible spatial resolu- one-way ANOVAs (analyses of variance) for repeated tion to show that POT is able to reproduce classic measures, Tukey–Kramer test, Statistics toolbox, Matlab,Journal of Cerebral Blood Flow & Metabolism (2010), 1–8
  3. 3. Brain oxygen uncoupling/recoupling S Mottin et al 3Figure 1 The imaging setup based on two lenses (L4 and L1) conjugates the surface of the skull with the plane of the slit of thestreak camera. An afocal system made of two lenses (L2 and L3) is placed between the two imaging lenses. The slit (F) is placed atthe focal point of the afocal system. The position of the 5-mm-long segment on the head of the bird can be controlled by eye, byshining a He-Ne laser through the intermediate slit and adjusting the position of its image on the skull (with mirror M). A narrowbandwidth filter (IF) is placed just before the streak camera. The 5-mm-long segment is located 5 mm away from the white-laserinput optical fiber (F1).The Mathworks, Natick, MA, USA). The variation of the long segment located 5 mm apart from the fiber (Figure 1).time-resolved transmittance spectrum was also fitted to We put a narrow bandwidth filter (IF) (10 nm full-widththe spectra of HbO2 and Hb known in mammals by classic half-maximum) centered at 700 nm, at which the differencelinear least-squares procedure. The same procedure was of absorption between the two hemoglobin species wasapplied to calculate variations in the concentration of maximal. The position of the imaged segment on the headHbO2 and Hb. These concentration variations could be of the bird could be controlled by eye by shining theexpressed using an absolute scale (mmol) because our time- intermediate slit with a He-Ne laser and by checking andresolved detection system could measure the mean optical adjusting the position of its image on the surface of thepath through the bird’s head owing to the mean arrival time head (mirror M). The spatial resolution along the slit wasof photons (Vignal et al, 2008). determined by imaging a white sheet of paper half covered with black ink. The image consisted in the response of the system to a Heaviside step and characterized the spatialExperimental Setup of Spatial-Picosecond Optical resolution of the setup. Its resolution along the slit wasTomography nearly 250 mm. The single shot streak camera measured the propagationWe used the same setup and the same laser fiber position as time of the photons through tissues. All measurementsdescribed previously (Vignal et al, 2008), with the omis- were carefully corrected from shading effects. Eachsion of the polychromator and with an imaging system measurement consisted in a frame integrating 33 laserbetween the head of the animal and the streak camera pulses. The 5-mm-long segment (of 150 mm thickness) was(Hamamatsu Streakscope C4334, Hamamatsu, Bridgewater, imaged onto the slit of the streak camera and at the end,NJ, USA). The imaging setup based on two lenses (L4 and transformed to 640 pixels. The 2.1-nanosecond deflectionL1) (100 mm focal length) optically conjugated the surface time was converted to 480 pixels. The temporal resolutionof the skull with the plane of the entrance slit of the streak of the system was set by the temporal width of the tracecamera (Figure 1). An afocal system composed of two on the CCD camera of a femtosecond pulse. Instrumentlenses (L2 and L3) (100 mm focal) was placed between the response function was obtained by directly sending atwo imaging lenses, and a slit (F) was put at the focal point leaking of a femtosecond laser pulse. Owing to the jitterof the afocal system. This slit was optically conjugated (with 33 laser pulses), the resolution was 25 picosecondswith the entrance slit of the streak camera, resulting in a (6 pixels).great simplification of the alignment procedure and in the An advantage of this setup comes from the possibility ofpossibility of controlling the intensity of the light by contact-free measurements. The versatility of the opticalnarrowing the slit as well. The magnification of the setup design we implemented has another interesting advantagewas 1. Intrinsic filtering properties of the imaging setup in terms of imaging. In the near future, by simply tiltingenabled to collect only the photons emerging from a 5 mm- the M mirror, we will sweep the imaging segment. This Journal of Cerebral Blood Flow & Metabolism (2010), 1–8
  4. 4. Brain oxygen uncoupling/recoupling S Mottin et al4 possibility is way more flexible than fiber bundles and transmittance were equivalent for spatial-POT and leads to a narrower spatial resolution, not limited by the spectral-POT. The maximum change in transmit- diameter of the optical fibers, but only by the numerical tance induced by the auditory stimulus was 1.03. To aperture and the properties of the optical setup. establish a calibrated functional technique, acoustic response experiments were carried out under the same conditions as the 7% normoxic hypercapnic Results experiments (Vignal et al, 2008). The functional signal under these conditions was found to be Figure 2 shows the full time courses of picosecond equivalent to 10% of the hypercapnic changes time-resolved transmittance measured by spectral- (Vignal et al, 2008). Our results showed that the POT (Figure 2A) and by spatial-POT (Figure 2B). The dynamics of these physiologic changes required at shape of the time courses and the level of variation of least a 2-second time resolution (Figures 2 and 3). Significant Hb and HbO2 changes were obtained by linear unmixing (Vignal et al, 2008) and were 840 analyzed with a 0.667-second time resolution. Dur- ing the 2 seconds following the onset of acoustic stimuli, Hb and HbO2 levels significantly decreased to À0.7 and À0.9 mmol/L, respectively (Figure 3). The HbO2 level then increased significantly (during Wavelength (nm) Transmittance 12.4 seconds, 100 concentration measurements) to reach a plateau of 0.3 mmol/L (P = 0.015 when compared with the 100 concentrations preceding the stimulus). Immediately after the end of the stimulus, Hb and HbO2 pulses reached + 0.7 mmol/L. Changes were significantly localized (Figures 2B and 4A) above the auditory forebrain areas (such as the NCM, field L, CMM). A small contribution could have derived from the hippocampus (dorsal and 672 0 silence 20 stimulus 40 silence 60 Time (s) * 1 ** ** * ** * * * * Hb (microMole/L) Left -1 0 Transmittance Length (mm) 0 *** -1 Silence Stimulus Silence 1 0 20 40 60 Time (s) 2 ** * Right HbO2 (microMole/L) 1 3 0 silence 20 stimulus 40 silence 60 0 Time (s) Figure 2 Time course of the picosecond time-resolved transmit- -1 * tance. (A) The full time course of the picosecond time-resolved * transmittance spectra was measured by spectral-POT. The near-infrared spectral window is 668 to 844.4 nm, with Figure 3 Hb and HbO2 concentration changes. (A) Hb and (B) 20 spectral windows of 8.83 nm. (B) The time course of the HbO2 concentration changes obtained by linear unmixing of the picosecond time-resolved transmittance for 20 spatial regions picosecond time-resolved transmittance spectra. Each point is of 0.25 mm was imaged by spatial-POT. The 695 to 705 nm an average of five concentrations along the time axis, allowing a spectral window was used for spatial-POT. Each point of time resolution of 0.667 seconds. Bars corresponds to P = 0.05 measurement corresponds to 33 milliseconds. For illustration for multiple comparisons (one-way ANOVAs for repeated purposes, these results were filtered to get rid of high-frequency measures) between periods. The limits of significance of Hb noise, using a Chebyshev window only along the time axis, and HbO2 are 0.42 and 0.75 mmol/L, respectively. The asterisk 1 second for spectral-POT and 2 seconds for spatial-POT. (*) indicates significant difference (P < 0.05) from the detection The 0-mm position corresponds to the sagittal midline. POT, limit. ANOVA, analysis of variance; Hb, deoxyhemoglobin; picosecond optical tomography. HbO2, oxyhemoglobin.Journal of Cerebral Blood Flow & Metabolism (2010), 1–8
  5. 5. Brain oxygen uncoupling/recoupling S Mottin et al 5 1.02 * § ** § § 1.01 1 ns 1.01 0.99 ns ns ns ns ns Transmittance ns * * 1 1.01 # # # # 1 Transmittance 0.99 0.99 * * * * * * * * * * 1.01 0.98 1 3 1.5 0 -1.5 0.99 Length (mm) * *Figure 4 Spatial-POT transmittance changes. Spatial-POTaveraged 20-second-long transmittance changes for (A) the 1.01stimulus (20 to 40 seconds) period and for (B) the poststimulus 1(40 to 60 seconds) period. The transmittance of the rest period 0.99(on 0 to 20 seconds) is normalized to 1 in all regions. Bars *corresponds to P = 0.01 for multiple comparisons (one-way * * * * * *ANOVAs for repeated measures) between the rest period and the Silence Stimulus Silencetwo respective periods. Points without the NS (nonsignificant) 0 20 40 60symbol indicate areas with significant changes when compared Time (s)with the rest period (P < 0.01). The symbols for stimulus period Figure 5 Time course of spatial-POT transmittance. Time courseand for the poststimulus period are y and # (P < 0.01) for the of transmittance measured by spatial-POT at four positionsleft hemisphere and right hemisphere, respectively, compared (A: left hemisphere, position À1.25 mm; B: sagittal midline,with more lateral positions (2.75 to 3 mm). The position 0 mm position 0 mm; C: right hemisphere, position + 1.25 mm; andcorresponds to the sagittal midline and positions (0.25 to D: right hemisphere position + 1.75 mm). Each bar (P = 0.01)1.25 mm and À0.25 to À1.25 mm) to the auditory-hippocam- allows multiple comparisons (one-way ANOVAs for repeatedpal areas. ANOVA, analysis of variance; POT, picosecond optical measures) between the prestimulus period and the two otherstomography. periods (the symbol * indicates P < 0.01). ANOVA, analysis of variance; POT, picosecond optical tomography.posterior areas) (Vignal et al, 2008). Furthermore, other methods (Clayton, 2007; Voss et al, 2007;there was a significant bilateral increase in transmit- Poirier et al, 2009). In addition to bilateral responsestance (Figure 4A) when compared with more lateral in these areas, lateralized activation has beenpositions (2.75 and 3 mm). During the poststimulus suggested to take place (Voss et al, 2007; Poirierperiod (Figure 4B), all areas showed significant et al, 2009). With our less specific stimulation para-decreases in transmittance when compared with digm, we obtained a bilateral response withoutthe rest period. These results show that recoupling lateralization (Figures 2B and 4). Unlike electrophy-was less localized than uncoupling. Compared with siology and immediate early gene expression, func-more lateral positions and within the stimulation tional magnetic resonance imaging and POT measureperiod, a significant bilateral increase was observed. blood dynamics in relation to the activity of largeIn contrast, a significant bilateral decrease was clusters of cells. In birds, links between bloodobserved within the poststimulus period. Further- oxygen level-dependent (BOLD), hemodynamics,more, the number of Hb and HbO2 pulses was less and neuronal activation was not previously knownhigh for the auditory-hippocampal areas (0.25 to (Boumans et al, 2007; Voss et al, 2007; Vignal et al,1.25 mm and À0.25 to À1.25 mm, respectively) than 2008). By choosing anesthetic conditions, sequencesfor the more lateral positions, showing that recou- of stimuli and spatiotemporal parameters similar topling was faster in these areas (Figures 2B and 5). other published BOLD experiments (Table 1), we sought to establish a robust correlation between the BOLD signal and changes in Hb and HbO2 concen-Discussion trations. The diffuse optical method has the potential toOur study shows for the first time the changes of differentiate hemoglobin dynamics; however, theyblood oxygen in a small songbird during stimulation have limited spatial resolution. Conversely, BOLDin vivo. The most intense responses to similar stimuli functional magnetic resonance imaging has achievedhave been observed in the NCM and field L, using high spatial resolution but is more susceptible to Journal of Cerebral Blood Flow & Metabolism (2010), 1–8
  6. 6. Brain oxygen uncoupling/recoupling S Mottin et al6 Table 1 Comparisons between BOLD spatiotemporal parameters and POT parameters Male zebra finch Male zebra finch Male starling Male zebra (Voss et al, 2007) (Boumans et al, 2007) (Van Meir et al, 2005) finch (POT) Time resolution 4 seconds Between 3 and 5 seconds 0.033 seconds for DTr 6 seconds 0.666 seconds for DC Time stimulus paradigm 32 seconds 40 seconds 30 seconds ON–30 seconds OFF 20 seconds ON–32 seconds OFF ON–40 seconds OFF and 60 seconds ON–60 seconds OFF ON–60 seconds OFF Thickness of slice 1 mm 0.5 mm 0.7–0.8 mm 0.25 mm Number of slices 8 sagittal slices 1 Tilted coronal slice 2 sagittal slices 20 sagittal slices BOLD, blood oxygen level dependent; POT, picosecond optical tomography. BOLD spatiotemporal parameters in male zebra finches (Voss et al, 2007; Boumans et al, 2007) and male starlings (Van Meir et al, 2005) are shown. For POT parameters (DTr, transmittance changes; DC, concentration changes of hemoglobin), the thickness of the ‘diffuse slice’ is measured at the surface of the scalp. 1 Mole/L hematological features of tachymetabolic vertebrates appear to have converged to an equivalent oxygen supply. In mammals, the coupling of blood trans- HbO2 Concentration changes -(Hb) Concentration changes port and cerebral metabolic rates in physiologically o o BOLD Signal Changes active brain states has been the subject of debate, o o o and different theoretical models for it have been o o proposed (Banaji et al, 2008; Ress et al, 2009). In 0 humans, contrary to the ‘canonical hemodynamic o response function’ (used by software packages, o i.e., SPM;, BOLD responses reveal several disparities (Aguirre et al, 1998), and some authors (Vanzetta and Grinvald, 2008; Ress et al, 2009) suggest that the differences -1 Mole/L between BOLD responses are related to differences in Stimulus Silence the properties of blood vessel networks between mammals. Despite these differences, the BOLD over- Figure 6 Typical time course of BOLD signal (dashed line) in zebra finches is compared with the time course of HbO2 (curve shoot is always observed in the sensory systems of with the symbol ‘o’) and Hb concentration changes measured by tachymetabolic vertebrates. Nevertheless, in the POT in the caudal-medial areas. Minus Hb (ÀHb) concentration zebra finch, transient events seem to be more is shown for better comparison with the BOLD signal. BOLD, pronounced than in comparable small rodents, blood oxygen level dependent; HbO2, oxyhemoglobin; POT, perhaps because of differences in blood vessel picosecond optical tomography. networks. The biphasic changes in HbO2 (early decrease and increase) measured by POT reveal a temporal pattern limited ability to monitor hemoglobin dynamics. The similar to the biphasic response of tissue oxygen BOLD time courses exhibit a sharp increase and (decrease and increase) in the auditory cortex an overshoot at the beginning of the stimulus and (Masamoto et al, 2003) and to the biphasic response an undershoot during the poststimulus period. The (initial constriction followed by dilation) of isolated BOLD undershoot reveals two oscillations that have penetrating cerebral arterioles following an elevation not been discussed previously, and these poststimu- of K + or adenosine triphosphate (Dietrich et al, lus BOLD pulses are more pronounced in field L than 2009). For the poststimulus period, recoupling seems in the NCM (Voss et al, 2007; Boumans et al, 2007). to be more complex than expected because (1) HbO2 As known in mammals, we showed (Figure 6) that in and Hb pulses were less localized than during birds there was a direct link between the BOLD activation (Figure 2B), (2) the recoupling of the signal and minus Hb (ÀHb). However, ÀHb exhibited activated auditory regions was faster than for other a faster response to changes in stimulus (Figure 6), regions (Figure 5), and (3) the early HbO2 pulse suggesting that the BOLD signal is a more ‘convo- arrived before the Hb pulse (Figure 3). Therefore, luted response’ to hemodynamic than ÀHb. BOLD and POT recoupling pulses in birds seem to be Birds and mammals have well-pronounced pial more spatiotemporally structured than nonlinear arterial ramifications (Mc Hedlishvili and Kuridze, ‘passive elastic sloshing’, as expected (Ress et al, 1984). Birds have (1) bigger red blood cells by a factor 2009). of 3 and a far larger capillary diameter, (2) less red We imaged the sinus sagittalis superior (position blood cells per volume of blood by a factor of 1/3, 0 mm in Figure 2B), and no significant changes were and (3) a hemoglobin concentration in red blood observed during the activation period. However, this cells comparable with that of small rodents (Altman result should be considered carefully because distin- and Dittmer, 1971). The pial angioarchitecture and guishing arterial, capillary, and venous compartmentsJournal of Cerebral Blood Flow & Metabolism (2010), 1–8
  7. 7. Brain oxygen uncoupling/recoupling S Mottin et al 7is not straightforward in optical neuroimaging (Hillman fluctuations in the human motor cortex during restet al, 2007). using echo-planar MRI. J Cereb Blood Flow Metab 17: Systems with a low ratio of energy storage to 301–8energy consumption, end products, and heat genera- Boumans T, Theunissen FE, Poirier C, Van Der Linden A (2007) Neural representation of spectral and temporaltion have to respond ‘instantaneously’ to activation. features of song in the auditory forebrain. Eur J NeurosciThe understanding of the time course of uncoupling/ 26:2613–26recoupling and spontaneous oscillations (Steinmeier Calderon-Arnulphi M, Alaraj A, Slavin KV (2009) Nearet al, 1996; Biswal et al, 1997; Fox and Raichle, 2007; infrared technology in neuroscience: past, present andRess et al, 2009) emphasize the role of nonisochoric future. Neurol Res 31:605–14processes in this response. Despite the constraints Chin SL, Petit S, Borne F, Miyazaki K (1999) The whiteof an instantaneous response, the sensory systems light supercontinuum is indeed an ultrafast white lightof all tachymetabolic animals seem to be robust laser. Jpn J Appl Phys Part 2 Letters 38:L126–8when faced with the ordinary perturbations they Clayton CF (2007) Molecular neurobiology of bird song. In:were designed to handle, but fragile when faced Handbook of Neurochemistry and Molecular Neurobiol- ogy (Lajtha A, ed), US: Springer, 373–417with unexpected or strong perturbations (Niven and Dietrich HH, Horiuchi T, Chuanxi X, Hongo K, Falck JR,Laughlin, 2008). Our approach shows the occurrence Dacey RG (2009) Mechanism of ATP-induced local andof strong reactivity in the cerebral vessels of the bird, conducted vasomotor responses in isolated rat cerebralan animal with a long lifespan (Barja and Herrero, penetrating arterioles. J Vasc Res 46:253–641998; Moe et al, 2009). Several studies (Mitschelen Fox MD, Raichle ME (2007) Spontaneous fluctuations inet al, 2009) indicate that age-related changes in brain activity observed with functional magnetic reso-vascular reactivity are important contributing factors nance imaging. Nat Rev Neurosci 8:700–11to mild cognitive impairment in aging mammals. Gibson AP, Austin T, Everdell NL, Schweiger M, ArridgeContrary to the accepted dogma, the role of oxidative SR, Meek JH, Wyatt JS, Delpy DT, Hebden JC (2006)stress as a determinant of longevity is still open to Three-dimensional whole-head optical passive motor evoked responses in the tomography of neonate. Neuro-question (Mitschelen et al, 2009; Moe et al, 2009). image 30:521–8Our results could thus shed light on this crucial Hillman EMC, Devor A, Bouchard MB, Dunn AK, Kraussquestion, i.e., the link between brain aging and GW, Skoch J, Bacskai BJ, Dale AM, Boas DA (2007)vascular reactivity. Depth-resolved optical imaging and microscopy of vascular compartment dynamics during somatosensory stimulation. Neuroimage 35:89–104 Jarvis ED, Gunturkun O, Bruce L, Csillag A, Karten H, ¨ ¨ ¨Acknowledgements Kuenzel W, Medina L, Paxinos G, Perkel DJ, Shimizu T,The authors thank Clementine Vignal and Nicolas Striedter G, Wild JM, Ball GF, Dugas-Ford J, Durand SE,Mathevon for their technical participation and Hough SE, Husband S, Kubikova L, Lee DW, Mello CV, Powers A, Siang C, Smulders TV, Wada K, White SA,bioacoustic data. The authors also thank Colette Yamamoto K, Yu J, Reiner A, Butler AB (2005) AvianBouchut, Sabine Palle, and Pierre Laporte for brains and a new understanding of vertebrate braintheir help. evolution. Nat Rev Neurosci 6:151–9 Kasischke KA, Vishwasrao HD, Fisher PJ, Zipfel WR, Webb WW (2004) Neural activity triggers neuronal oxidativeDisclosure/conflict of interest metabolism followed by astrocytic glycolysis. 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