View source for Evidence for limbic system activation during CO2-stimulated breathing in man

''Corfield DR, Fink GR, Ramsay SC, Murphy K, Harty HR, Watson JD, Adams L, Frack- owiak RS, and Guz A (1995) Evidence for limbic system activation during CO2-stimulated breathing in man. J Physiol 488 ( Pt 1): 77–84''

'''[http://onlinelibrary.wiley.com/doi/10.1113/jphysiol.1995.sp020947/epdf Link to Article]'''

'''Abstract:''' 1. The role of supra-brainstem structures in the ventilatory response to inhaled CO2 is unknown. The present study uses positron emission tomography (PET), with infusion of H2(15)O, to measure changes in relative regional cerebral blood flow (rCBF) in order to identify sites of increased neuronal activation during CO2-stimulated breathing (CO2-SB) in awake man. 2. Five male volunteers were scanned during CO2-SB (mean +/- S.E.M.; end-tidal PCO2, 50.3 +/- 1.7 mmHg; respiratory frequency, 16.4 +/- 2.7 min-1; tidal volume, 1.8 +/- 0.2 l). As control, scans were performed during 'passive' isocapnic (elevated fraction of inspired CO2) positive pressure ventilation (end-tidal PCO2, 38.4 +/- 1.0 mmHg; respiratory frequency, 15.5 +/- 2.2 min-1; tidal volume, 1.6 +/- 0.2 l). With CO2-SB, all subjects reported dyspnoea. 3. The anatomical locations of the increases in relative rCBF (CO2-SB versus control) were obtained using magnetic resonance imaging. 4. Group analysis identified neuronal activation within the upper brainstem, midbrain and hypothalamus, thalamus, hippocampus and parahippocampus, fusiform gyrus, cingulate area, insula, frontal cortex, temporo-occipital cortex and parietal cortex. No neuronal activation was seen within the primary motor cortex (at sites previously shown to be associated with volitional breathing). 5. These results suggest neuronal activation within the limbic system; this activation may be important in the sensory and/or motor respiratory responses to hypercapnia in awake man.

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*Study from 5 human volunteers using PET and MRI to identify regions of increased blood flow during CO2-induced hyperpnea. A number of limbic regions underwent increased perfusion during hypercapnic periods. Compare to different regions of increased blood flow found during elevated heart rate and blood pressure by Critchley et al.
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