Contingent negative variation indicates phasic arousal for externally cued unilateral eye blink in human subjects Hans Strenge a, * , Peter Kropp a , Johanna Hoffmeister a , Annapia Verri b , Cristina Galli b , Wolf-Dieter Gerber a a Institute of Medical Psychology, Center of Nervous Diseases, University Kiel, Niemannsweg 147, 24105 Kiel, Germany b Istituto Neurologico'Casimiro Mondino', Via Palestro 3, 27100 Pavia, Italy Received 17 February 1999; accepted 8 March 1999 Abstract The contingent negative variation (CNV) as a slow cortical potential was used to investigate cortical processing of externally cued, voluntary unilateral eye blink. Probands blinked as a response within a modi®ed two-stimulus reaction time paradigm. Reaction time and amplitudes of CNV were determined. The activity of the orbicularis oculi muscles (OO) was registered by surface electromyography (EMG). Probands who performed unilateral eye blinks with accurately inhibiting contralateral OO activity showed a signi®cantly higher negativity of the early CNV component compared with the bilateral eye blink condition. This effect was con®ned to the beginning of unilateral blinking performance. It is suggested that the unilateral eye blink is a challenging motor task, initially requiring an increased cortically driven arousal and attention as revealed by increased early CNV components. q 1999 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Contingent negative variation; Arousal; Eye blink; Unilateral performance; Performance accuracy Blinking is an almost automatic function in spite of the highly integrated motor interaction, with a combination of contraction of the orbicularis oculi (OO) and relaxation of levator palpebrae muscles, involved [14]. A number of studies have shown that blinking is a conjugate behaviour [9] and that suppression of eyelid closure requires more effort than compensation of insuf®cient blinking [5]. It can be supposed that pure unilateral blinking may constitute a demanding motor task with more complex cortical proces- sing, including neuronal inhibition, than stereotypical bilat- eral eyelid closure. The contingent negative variation (CNV) is a surface- negative slow cortical potential elicited between the warn- ing (S1) and the imperative (S2) stimuli when a response to S2 is required. CNV represents the neuronal activity neces- sary for sensorimotor integration or association and is related to planning or execution of externally-paced, volun- tary movements [8]. CNV with the use of extended S1±S2 intervals consists of two parts, the early CNV and late CNV. The early CNV represents an orientation response related to the processing of S1 [13]. It is prone to habituation [10]. The late CNV is related both to motor preparation and anticipa- tion of the forthcoming external cue [4]. In order to examine the cortical preparation for externally cued unilateral and bilateral blinking, we studied the CNV with blinking as a response task in a reaction time paradigm in healthy subjects. Twenty-seven healthy right-handed students (12 females, 15 males, median age 25 years, range 21±29 years) without history of neuromuscular disorders participated in the experiment. All probands gave informed consent. The task was a modi®ed two-stimulus reaction time GO/NOGO CNV paradigm in which S1 signalled the response required at S2. The trials consisted of tone bursts (75 dB a): a warning stimulus S1 (duration 100 ms; GO: 1000 Hz; NOGO: 200 Hz, in quasi-random order), followed 3 s later by an impera- tive stimulus S2 (2500 Hz) with an intensity below that of the startle response threshold and acoustically elicited blink re¯ex. S2 lasted a maximum of 1500 ms and was deacti- vated by forceful eyelid closure. The randomized intervals between S2 and the next S1 varied between 6 and 10 s. A CNV session consisted of 40 trials. The motor tasks were (i) bilateral blinking (GO) and (ii) unilateral blinking with the right eye only (NOGO). Neuroscience Letters 266 (1999) 57±60 0304-3940/99/$ - see front matter q 1999 Elsevier Science Ireland Ltd. All rights reserved. PII: S0304-3940(99)00261-X * Corresponding author. Tel.: 149-431-597-2647; fax: 149-431- 597-2711. E-mail address: strenge@med-psych.uni-kiel.de (H. Strenge)