Neural mechanisms underlying touch-induced visual perceptual suppression: An fMRI study

A primary sensory cortical interareal feedforward inhibitory circuit for tacto-visual integration

Tactile sensation and vision are often both utilized for the exploration of objects that are within reach though it is not known whether or how these two distinct sensory systems combine such information. Here in mice, we used a combination of stereo photogrammetry for 3D reconstruction of the whisker array, brain-wide anatomical tracing and functional connectivity analysis to explore the possibility of tacto-visual convergence in sensory space and within the circuitry of the primary visual cortex (VISp). Strikingly, we find that stimulation of the contralateral whisker array suppresses visually evoked activity in a tacto-visual sub-region of VISp whose visual space representation closely overlaps with the whisker search space. This suppression is mediated by local fast-spiking interneurons that receive a direct cortico-cortical input predominantly from layer 6 neurons located in the posterior primary somatosensory barrel cortex (SSp-bfd). These data demonstrate functional convergence within and between two primary sensory cortical areas for multisensory object detection and recognition.

Auditory stimuli degrade visual performance in virtual reality

We report an auditory effect of visual performance degradation in a virtual reality (VR) setting, where the viewing conditions are significantly different from previous studies. With the presentation of temporally congruent but spatially incongruent sound, we can degrade visual performance significantly at detection and recognition levels. We further show that this effect is robust to different types and locations of both auditory and visual stimuli. We also analyze participants behavior with an eye tracker to study the underlying cause of the degradation effect. We find that the performance degradation occurs even in the absence of saccades towards the sound source, during normal gaze behavior. This suggests that this effect is not caused by oculomotor phenomena, but rather by neural interactions or attentional shifts.

Differential Effects of Sustained Manual Pressure Stimulation According to Site of Action

Sustained pressure stimulation of the body surface has been used in several physiotherapeutic techniques, such as reflex locomotion therapy. Clinical observations of global motor responses and subsequent motor behavioral changes after stimulation in certain sites suggest modulation of central sensorimotor control, however, the neuroanatomical correlates remain undescribed. We hypothesized that different body sites would specifically influence the sensorimotor system during the stimulation. We tested the hypothesis using functional magnetic resonance imaging (fMRI) in thirty healthy volunteers (mean age 24.2) scanned twice during intermittent manual pressure stimulation, once at the right lateral heel according to reflex locomotion therapy, and once at the right lateral ankle (control site). A flexible modeling approach with finite impulse response basis functions was employed since non-canonical hemodynamic response was expected. Subsequently, a clustering algorithm was used to separate areas with differential timecourses. Stimulation at both sites induced responses throughout the sensorimotor system that could be mostly separated into two anti-correlated subsystems with transient positive or negative signal change and rapid adaptation, although in heel stimulation, insulo-opercular cortices and pons showed sustained activation. In direct voxel-wise comparison, heel stimulation was associated with significantly higher activation levels in the contralateral primary motor cortex and decreased activation in the posterior parietal cortex. Thus, we demonstrate that the manual pressure stimulation affects multiple brain structures involved in motor control and the choice of stimulation site impacts the shape and amplitude of the blood oxygenation level-dependent response. We further discuss the relationship between the affected structures and behavioral changes after reflex locomotion therapy.

Effects of spatial consistency and individual difference on touch-induced visual suppression effect

Crossmodal studies have reported not only facilitatory but also inhibitory perceptual interactions. For instance, tactile stimulation to the index finger of a hand leads to the degradation of visual discrimination performance (touch-induced visual suppression, TIVS). It has been suggested that the magnitude of TIVS depends on the spatial congruency of visuo-tactile stimuli and on individual differences in task performance. We performed a detailed investigation of the effects of spatial consistency and individual differences on the occurrence of TIVS. The visual target and tactile stimulus were presented at co-localized, ipsilateral but not co-localized, or contralateral positions. The degree of autistic traits has been reported to be well variable among the general population and to reflect differences in sensory processing. Therefore, we assessed the magnitude of autistic traits using the autism-spectrum quotient (AQ) as an index of individual differences. TIVS occurred particularly at the ipsilateral but not co-localized position. In contrast, the magnitude of the TIVS was positively correlated with the AQ score when the stimuli were presented at the co-localized position. These findings suggest that the occurrence of TIVS can be modulated both by the spatial relationship between the visual and tactile stimuli and by individual differences in autistic traits.