Abstract
Neuronal excitation and inhibition occur in the brain at the same time, and brain activation reflects changes in the sum of excitation and inhibition. This principle has been well-established in lower-level sensory systems, including vision and touch, based on animal studies. However, it is unclear how the somatosensory system processes the balance between excitation and inhibition. In the present ERP study, we modified the traditional spatial attention paradigm by adding double stimuli presentations at short intervals (i.e., 10, 30, and 100 ms). Seventeen subjects participated in the experiment. Five types of stimulation were used in the experiment: a single stimulus (one raised pin for 40 ms), standard stimulus (eight pins for 40 ms), and double stimuli presented at intervals of 10, 30, and 100 ms. The subjects were asked to attend to a particular finger and detect whether the standard stimulus was presented to that finger. The results showed a clear attention-related ERP component in the single stimulus condition, but the suppression components associated with the three interval conditions seemed to be dominant in somatosensory areas. In particular, we found the strongest suppression effect in the ISI-30 condition (interval of 30 ms) and that the suppression and enhancement effects seemed to be counterbalanced in both the ISI-10 and ISI-100 conditions (intervals of 10 and 100 ms, respectively). This type of processing may allow humans to easily discriminate between multiple stimuli on the same body part.
Highlights
When spatial attention to auditory (Alho et al, 1999; Karns and Knight, 2009) or visual stimuli (Noesselt et al, 2002; Macaluso et al, 2005) was modulated, evoked potentials were generated in the primary auditory or visual cortices
This study used double asynchronous stimulation to investigate the relationship between spatial attention enhancement and double asynchronous stimulation-induced suppression of brain activity in human SI
As the interstimulus intervals increased, a V-shaped effect was observed. We suggest that this occurs through an attention enhancement and a double stimulationsuppression effect
Summary
When spatial attention to auditory (Alho et al, 1999; Karns and Knight, 2009) or visual stimuli (Noesselt et al, 2002; Macaluso et al, 2005) was modulated, evoked potentials were generated in the primary auditory or visual cortices. Animal studies (Pilz et al, 2004; Braun et al, 2005; Reed et al, 2010) used double stimuli to show that the second stimulus suppresses the response to the first stimulus This suggested that spatiotemporal interactions modulate the Double Stimuli Suppression in SI response magnitude in human SI. Some ERP studies used a mechanical tactile stimulus and found a contralateral N80 component with sustained attention and a bilateral P100 component with spatial attention in the early stages (Eimer and Driver, 2000; Eimer and Forster, 2003b; Zopf et al, 2004). Other ERP and SEP studies of mechanical tactile stimuli (Eimer and Forster, 2003a; Eimer et al, 2004; Forster and Gillmeister, 2011; Katus et al, 2012) showed that amplitudes of mid-latency components such as N140 and P200 were enhanced in response to tactile stimuli presented to the attended hand
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