Hypercapnia affects the functional coupling of resting state electroencephalographic rhythms and cerebral haemodynamics in healthy elderly subjects and in patients with amnestic mild cognitive impairment Claudio Babiloni a,b,⇑ , Fabrizio Vecchio b,c , Riccardo Altavilla d , Francesco Tibuzzi c , Roberta Lizio b , Claudia Altamura d , Paola Palazzo d , Paola Maggio d , Francesca Ursini d , Matilde Ercolani c , Andrea Soricelli e,g , Giuseppe Noce e , Paolo Maria Rossini b,f , Fabrizio Vernieri d a Department of Physiology and Pharmacology, University of Rome ‘‘La Sapienza’’, Rome, Italy b IRCCS San Raffaele Pisana, Rome, Italy c A.Fa.R. Dip. Neurosci, Ospedale ‘San Giovanni Calibita’ Fatebenefratelli, Isola Tiberina, Rome, Italy d Unità di Neurologia, Università Campus Bio-Medico di Roma, Rome, Italy e IRCCS SDN, Napoli, Italy f Department of Geriatrics, Neuroscience & Orthopedics, Institute of Neurology Catholic University ‘‘Sacro Cuore’’, Rome, Italy g Department of Studies of Institutions and Territorial Systems, University of Naples Parthenope, Naples, Italy article info Article history: Accepted 3 October 2013 Available online 15 November 2013 Keywords: Hypercapnia (CO 2 ) Amnesic mild cognitive impairment (MCI) Resting state Electroencephalography (EEG) Near-infrared spectroscopy (NIRS) highlights  Coherence of resting state EEG rhythms is impaired in MCI patients.  MCI patients also showed poorer reactivity of resting state EEG rhythms coherence during CO 2 condition compared with Nold subjects.  VMR was not altered in both Nold and amnesic MCI subjects, while EEG coupling was especially sensitive to the effects of hypercapnia on the amnesic MCI subjects. abstract Objective: Cerebral vasomotor reactivity (VMR) and coherence of resting state electroencephalographic (EEG) rhythms are impaired in Alzheimer’s disease (AD) patients. Here we tested the hypothesis that these two variables could be related. Methods: We investigated VMR and coherence of resting state EEG rhythms in nine normal elderly (Nold) and in 10 amnesic mild cognitive impairment (MCI) subjects. Resting state eyes-closed EEG data were recorded at baseline pre-CO 2 (ambient air, 2 min), during 7% CO 2 /air mixture inhalation (hypercapnia, 90 s) and post-CO 2 (ambient air, 2 min) conditions. Simultaneous frontal bilateral near-infrared spectros- copy (NIRS) was performed to assess VMR by cortical oxy- and deoxy-haemoglobin concentration changes. EEG coherence across all electrodes was computed at delta (2–4 Hz), theta (4–8 Hz), alpha 1 (8–10.5 Hz), alpha 2 (10.5–13 Hz), beta 1 (13–20 Hz), beta 2 (20–30 Hz) and gamma (30–40 Hz) bands. Results: In Nold subjects, ‘total coherence’ of EEG across all frequency bands and electrode pairs decreased during hypercapnia, with full recovery during post-CO 2 . Total coherence resulted lower in pre-CO 2 and post-CO 2 and presented poor reactivity during CO 2 inhalation in MCI patients compared with Nold subjects. Hypercapnia increased oxy-haemoglobin and decreased deoxy-haemoglobin concen- trations in both groups. Furthermore, the extent of changes in these variables during CO 2 challenge was correlated with the EEG coherence, as a reflection of neurovascular coupling. 1388-2457/$36.00 Ó 2013 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved. http://dx.doi.org/10.1016/j.clinph.2013.10.002 ⇑ Corresponding author at: Department of Physiology and Pharmacology, University of Rome ‘‘La Sapienza’’, Rome, Italy. Tel.: +39 06 49910989; fax: +39 06 49910917. E-mail address: claudio.babiloni@uniroma1.it (C. Babiloni). Clinical Neurophysiology 125 (2014) 685–693 Contents lists available at ScienceDirect Clinical Neurophysiology journal homepage: www.elsevier.com/locate/clinph