title: Electrical stimulation of the frontal cortex enhances slow-frequency EEG activity and sleepiness.
abstract: Our aim was to enhance the spontaneous slow-frequency EEG activity during the resting state using oscillating transcranial direct currents (tDCS) with a stimulation frequency that resembles the spontaneous oscillations of sleep onset. Accordingly, in this preliminary study, we assessed EEG after-effects of a frontal oscillatory tDCS with different frequency (0.8 vs. 5 Hz) and polarity (anodal, cathodal, and sham). Two single-blind experiments compared the after effects on the resting EEG of oscillatory tDCS [Exp. 1=0.8 Hz, 10 subjects (26.2 ± 2.5 years); Exp. 2=5 Hz, 10 subjects (27.4 ± 2.4 years)] by manipulating its polarity. EEG signals recorded (28 scalp derivations) before and after stimulation [slow oscillations (0.5-1 Hz), delta (1-4 Hz), theta (5-7 Hz), alpha (8-12 Hz), beta 1 (13-15 Hz) and beta 2 (16-24 Hz)] were compared between conditions as a function of polarity (anodal vs. cathodal vs. sham) and frequency of stimulation (0.8 vs. 5 Hz). We found a significant relative enhancement of the delta activity after the anodal tDCS at 5 Hz compared to that at 0.8 Hz. This increase, even though not reaching the statistical significance compared to sham, is concomitant to a significant increase of subjective sleepiness, as assessed by a visual analog scale. These two phenomena are linearly related with a regional specificity, correlations being restricted to cortical areas perifocal to the stimulation site. We have shown that a frontal oscillating anodal tDCS at 5 Hz results in an effective change of both subjective sleepiness and spontaneous slow-frequency EEG activity. These changes are critically associated to both stimulation polarity (anodal) and frequency (5 Hz). However, evidence of frequency-dependence seems more unequivocal than evidence of polarity-dependence.
authors.affiliation: Department of Psychology, University of Rome "Sapienza", Via dei Marsi 78, 00185 Rome, Italy; IRCCS San Raffaele Pisana, Via della Pisana 235, 00163 Rome, Italy. Electronic address: aurora.datri@uniroma1.it.
authors.forename: A
authors.initials: A
authors.lastname: D'Atri
authors.affiliation: Department of Psychology, University of Rome "Sapienza", Via dei Marsi 78, 00185 Rome, Italy. Electronic address: elisa.desimoni@uniroma1.it.
authors.forename: E
authors.initials: E
authors.lastname: De Simoni
authors.affiliation: Department of Psychology, University of Rome "Sapienza", Via dei Marsi 78, 00185 Rome, Italy. Electronic address: maurizio.gorgoni@uniroma1.it.
authors.forename: M
authors.initials: M
authors.lastname: Gorgoni
authors.affiliation: Department of Biotechnological and Applied Clinical Sciences, University of L'Aquila, Via Vetoio (Coppito 2), 67100 Coppito (L'Aquila), Italy. Electronic address: michele.ferrara@univaq.it.
authors.forename: M
authors.initials: M
authors.lastname: Ferrara
authors.affiliation: Department of Psychology, University of Rome "Sapienza", Via dei Marsi 78, 00185 Rome, Italy. Electronic address: fabio.ferlazzo@uniroma1.it.
authors.forename: F
authors.initials: F
authors.lastname: Ferlazzo
authors.affiliation: IRCCS San Raffaele Pisana, Via della Pisana 235, 00163 Rome, Italy; Institute of Neurology, Catholic University of The Sacred Heart, Largo Agostino Gemelli 8, 00168 Rome, Italy. Electronic address: paolomaria.rossini@afar.it.
authors.forename: P M
authors.initials: PM
authors.lastname: Rossini
authors.affiliation: Department of Psychology, University of Rome "Sapienza", Via dei Marsi 78, 00185 Rome, Italy; IRCCS San Raffaele Pisana, Via della Pisana 235, 00163 Rome, Italy. Electronic address: luigi.degennaro@uniroma1.it.
authors.forename: L
authors.initials: L
authors.lastname: De Gennaro
mesh_terms: D000293:Adolescent; D000328:Adult; D003700:Delta Rhythm / Q000502:physiology; D004569:Electroencephalography; D005260:Female; D005625:Frontal Lobe / Q000502:physiology*; D006801:Humans; D016014:Linear Models; D017286:Polysomnography; D012146:Rest; D016037:Single-Blind Method; D012890:Sleep / Q000502:physiology*; D065908:Transcranial Direct Current Stimulation / Q000379:methods*; D055815:Young Adult
keywords: EEG synchronization; frontal cortex; oscillatory transcranial direct current stimulation (osc-tDCS); resting EEG; sleep onset; sleepiness