Research report Differential modulation of temporal and frontal components of the somatosensory N140 and the effect of interstimulus interval in a selective attention task Tetsuo Kida a, * , Yoshiaki Nishihira b , Toshiaki Wasaka a , Hiroki Nakata a , Masanori Sakamoto c a Doctoral Program in Health and Sports Sciences, University of Tsukuba, Tennoudai 1-1-1, Tsukuba, Japan b Institute of Health and Sports Sciences, University of Tsukuba, Tennoudai 1-1-1, Tsukuba, Japan c Faculty of Education, Division of Health and Sports Education, United of Graduate School of Education, Tokyo Gakugei University, Japan Accepted 29 October 2003 Abstract The modulation of the somatosensory N140 was examined in a selective attention task where a control condition was applied and the interstimulus interval (ISI) was varied. Electrical stimuli were randomly presented to the left index ( p = 0.4) and middle fingers ( p = 0.1), and right index ( p = 0.4) and middle fingers ( p = 0.1). In the attend-right condition, subjects were instructed to count silently the number of infrequent target stimuli presented to the right middle finger, and to the left middle finger in the attend-left condition. They had no task in the control condition. Each condition was performed with two different sets of ISI (mean 400 vs. 800 ms). The somatosensory N140 elicited by frequent standard stimuli was analyzed. The N140 amplitude was larger for the attended ERP compared to the control and unattended ERPs. This attention effect was more marked at the frontal electrodes compared to the temporal electrodes contralateral to the stimulation side. Furthermore, the attention effect at the frontal electrode was larger when the ISI was 800 ms than when it was 400 ms. The N140 amplitude did not differ between the control and unattended ERPs, which might show that a small processing negativity (PN) occurred during the control condition or difference in vigilance level between them. In conclusion, the early lateral (‘‘temporal’’) and late midline (‘‘frontal’’) components of the N1 (N140) show different behavior, and thus may have different functional significance. Enhancement of the attention effect at the frontal electrode in the longer ISI condition supports the hypothesis that it is related to stronger, voluntary maintenance of the attentional trace. D 2003 Elsevier B.V. All rights reserved. Theme: Neural basis of behavior Topic: Physiology learning and memory Keywords: Attention; Somatosensory; N140; Interstimulus interval; Attentional trace 1. Introduction The somatosensory N140 increases with selective atten- tion [4,5,7,8,12,14,18,19]. This enhancement has been interpreted to result from both an endogenous negative component (i.e., processing negativity: PN, [20–23,27]) superimposed on the attended SEP [1,2,18,19], and changes in exogenous components [14]. In contrast to many inves- tigations in auditory and visual N1 components, however, the effects of attention on the somatosensory N140 during a selective attention task remain a matter of debate. In the present study, we examined the attentional mod- ulation of somatosensory N140 during performance of a selective attention task with different interstimulus intervals (interstimulus interval (ISI): mean 400 vs. 800 ms). Michie [18] reported that the P1 and N1 did not increase with selective spatial attention, but the attended P2 amplitude was smaller than unattended P2 and attended N2 was larger than unattended N2. This was interpreted as an overlapping endogenous negative component. They also reported no effect of the ISI on the ERP. In their later study, however, they found the attention effect on the P105 and N150, which was also interpreted as the somatosensory PN [19]. This 0926-6410/$ - see front matter D 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.cogbrainres.2003.10.016 * Corresponding author. Tel.: +81-29-8532607; fax: +81-29-8532607. E-mail address: nikita@seiri.taiiku.tsukuba.ac.jp (T. Kida). www.elsevier.com/locate/cogbrainres Cognitive Brain Research 19 (2004) 33 – 39