Crossmodal influences on early somatosensory processing: interaction of vision, touch, and task-relevance

Abstract

Previous research suggests that somatosensory cortex is subject to modulation based on the relevancy of incoming somatosensory stimuli to behavioural goals. Recent fMRI findings provide evidence for modulation of primary somatosensory cortex when simultaneous visual and tactile stimuli were relevant to the performance of a motor task. The present study aimed to (1) determine the temporal characteristics of this modulation using event-related potentials (ERPs) and (2) investigate the role of task-relevance in mediating such a modulation. Electroencephalography was collected from healthy subjects during visual, vibrotactile or bimodal stimulation as they performed a sensory-guided motor task. Experiment 1 tested the hypothesis that simultaneous bimodal stimuli would be associated with modulation of somatosensory ERPs, and Experiment 2 tested the hypothesis that such effects would only be seen when both modalities are relevant. ERPs were time-locked to stimulus onset, and mean ERP amplitudes and latencies were extracted for the P50, P100, and N140. The bimodal condition in the first experiment was associated with larger amplitudes at both early and mid-latency components. The manipulation of task-relevance under bimodal conditions produced more complex results for the mid-latency components. For the P50, this enhancement was observed only when both stimuli were relevant, whereas the P100 was smallest when the tactile stimuli were not relevant to the response. These results provide evidence that crossmodal stimuli can modulate early somatosensory event-related potentials and that these effects are mediated by stimulus relevance.

Early modality-specific somatosensory cortical regions are modulated by attended visual stimuli: interaction of vision, touch and behavioral intent

“…The prevailing thought on the generators of the N140 is that it reflects activation of prefrontal cortex, an area that is known to play a role in retrieving and maintaining representations of stimulus relevancy in relation to behavioral goals (Desmedt and Tomberg, 1989; Allison et al, 1991; Pardo et al, 1991; Knight et al, 1995), however, the bilateral distribution of the N140 at parietal sites has also prompted some researchers to suggest a generator in S2 (Frot and Mauguiere, 1999), which as mentioned previously has been implicated in attention to tactile stimuli. Similar to the current study, the results of Dionne et al (2013) also showed different patterns of N140 modulation at frontal and parietal sites and these results provide further support that this component might be associated with multiple generators such that the frontal and parietal generators are sensitive to different factors. Given the results of these two studies, it seems that the parietal component of the N140 shows specificity for task demands but not crossmodal stimuli, and the frontal component is sensitive to both crossmodal stimuli in addition to task requirements.…”

“…As such the amplitudes of the early components reported here will not be affected by the small difference in stimulus durations for the tactile stimuli presented in the uni- and bimodal conditions of Experiment 1. This is supported by the similarities of the waveforms, especially the consistent timing of the P50, P100, and N140 components in the unimodal and bimodal conditions reported in previous studies using these same parameters (Dionne et al, 2013; Popovich and Staines, 2014). In addition, in the case when the visual stimulus precedes the tactile stimulus by 100 ms (VT Grade) shown in Figure 6 (red trace) there is some indication of alpha-like activity.…”

“…Studies employing an oddball detection task that required subjects to monitor both hands for deviant stimuli in one modality while ignoring the other and reporting detections with a verbal response also failed to find crossmodal effects on this potential (Eimer and Driver, 2000; Eimer, 2001). Dionne et al (2013) reported that the P100 was sensitive to the presence of crossmodal stimuli but not to the task-relevance of those stimuli during the performance of a graded motor task, yet that same effect was not observed in the current study. However, there are differences in the design of these two experiments that may account for this discrepancy.…”

“…Human and animal studies have shown that the mere presence of additional sensory input even when it is irrelevant for performance of a task can enhance neural excitability in the attended sensory modality (Calvert et al, 1997; Macaluso et al, 2000, 2002; Calvert, 2001; Foxe et al, 2002; Kayser et al, 2005, 2007; Lehmann et al, 2006; Pekkola et al, 2006; Lakatos et al, 2007; Meehan and Staines, 2009), suggesting that interactions between modality-specific cortical representations exist. By contrast, other studies have shown crossmodal enhancement in modality-specific sensory cortex only occurs when both stimulus events are relevant for behavior (Dionne et al, 2010, 2013). These findings suggest that crossmodal processing is likely governed by both bottom-up sensory–sensory interactions and top-down attentional mechanisms in order to allow for the selection, amplification, and integration of sensory input relevant for initiating goal-oriented responses.…”

“…In a non-gating context, recent findings using event-related potentials (ERPs) provide evidence that task-relevance of stimuli facilitates crossmodal modulation of early and mid-latency somatosensory-specific ERP components, namely the P50, a positive potential peaking at approximately 50 ms after presentation and generated in the primary somatosensory cortex (Hämäläinen et al, 1990), as well as the P100 and N140 (Dionne et al, 2013; Popovich and Staines, 2014) generated in secondary somatosensory cortex (Mima et al, 1998; Frot and Mauguiere, 1999; Gu, 2002) and influenced by attention. These results are novel as crossmodal effects on the somatosensory P50 have not been previously reported, and even attentional modulation of this potential is not consistently observed (Desmedt and Robertson, 1977; Michie et al, 1987; Eimer and Forster, 2003; Zopf et al, 2004; Schubert et al, 2008).…”