Spatially congruent visual and tactile inputs modulate activity in multisensory areas, visual and somatosensory sensory cortices

NemoImage

13, Number

6, 2001, Part 2 of 2 Parts 1 D E bl@

ATTENTION

Spatially Congruent Visual and Tactile Inputs Modulate Activity in Multisensory Areas, Visual and SomatosensorySensoryCortices. Donna Lloyd, Peter Hansen, Gemma Calvert Fmrib Centre, University of Oxford, U.K. Introduction The detection of bimodal inputs is facilitated when they are in spatial correspondence. Electrophysiological studies have shown increased neuronal activity in multisensory brain areas in response to spatially concordant multisensory inputs but decreased activation in response to incongruent inputs (Stein, & Meredith 1993). Recent neuroimaging studies in humans suggests that multisensory effects in association areas modulate activity in sensory-specific cortices via back-projections (Calvett et al, 1999; Macaluso et al, 2000). The following study used event-related fMRI to determine sites of multisensory integration and their effect on primary sensory areas in the integration of spatially coincident visual and tactile stimuli. Methods 6 healthy participants’ were scanned in the following NRI experiment in a 3T scanner. An LED and a piezo-electric vibrator were placed close together on each big toe with both feet separated by 12 inches. Visual and tactile stimuli were presented simultaneously either to the same toe or opposite toes together (bimodal inputs) or individually (unimodal inputs). Participants’ were instructed to detect and respond to (via a button press) the modality indicated on a projector screen in front of them (either ‘VISION’ or ‘TOUCH’). Image analysis was carried out using tools from the PMRIB Source Library (www.fmrib.ox.ac.uk/fsl). Image processing used PEAT with PILM statistical analysis to model main effects and interactions. Group 2 (Gaussianised T) statistic images were thresholded using clusters determined by 2>1.8 and a cluster significance threshold of P=O.OS. Results Spatially congruent bimodal inputs significantly speeded detection of tactile stimuli (p < .002), but not visual stimuli (p = ,052 n.s). This picture was paralleled in the fMR1 data. Spatially congruent bimodal inputs produced increased activation compared to spatially incongruent inputs in three regions: intraparietal sulcus, insula and superior colliculus. These effects only occurred when participants’ were attending and responding to touch. When asked to attend and respond to visual stimuli, there was no relative enhancement when the bimodal stimuli were congruent. Attempts to detect response enhancements in unimodal cortices by ROI analysis of primary visual (Vl) and somatosensory (Sl) cortices related to congruent as opposed to incongruent visuotactile inputs revealed such effects in Sl and only when attending to touch (p < .05). Irrespective of attended modality, Vl and secondary sensory cortices did not show this effect. Conclusion In accordance with the behavioural results, there was a stronger fMRI effect of spatial congruency of bimodal inputs when participants’ detected tactile stimuli. This was reflected in the modulation of SI responses only to congruent inputs. This asymmetry between the effect of spatial congruence when detecting visual and tactile inputs is possibly due to relative transmission times of visual and tactile inputs from the foot. References Calve& G.A et al., (1999). NeuroReport, 10, 2619-2623. Macaluso et al., (2000). Science, 289, 1206-1208. Stein, B.E., & Meredith, M.A. (1993). The merging of the senses. MIT

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Press, CA, MA.