The multisensory attentional consequences of tool use : a functional magnetic resonance imaging study

Background: Tool use in humans requires that multisensory information is integrated across different locations, from objects seen to be distant from the hand, but felt indirectly at the hand via the tool. We tested the hypothesis that using a simple tool to perceive vibrotactile stimuli results in the enhanced processing of visual stimuli presented at the distal, functional part of the tool. Such a finding would be consistent with a shift of spatial attention to the location where the tool is used. Methodology/Principal Findings: We tested this hypothesis by scanning healthy human participants’ brains using functional magnetic resonance imaging, while they used a simple tool to discriminate between target vibrations, accompanied by congruent or incongruent visual distractors, on the same or opposite side to the tool. The attentional hypothesis was supported: BOLD response in occipital cortex, particularly in the right hemisphere lingual gyrus, varied significantly as a function of tool position, increasing contralaterally, and decreasing ipsilaterally to the tool. Furthermore, these modulations occurred despite the fact that participants were repeatedly instructed to ignore the visual stimuli, to respond only to the vibrotactile stimuli, and to maintain visual fixation centrally. In addition, the magnitude of multisensory (visual-vibrotactile) interactions in participants’ behavioural responses significantly predicted the BOLD response in occipital cortical areas that were also modulated as a function of both visual stimulus position and tool position. Conclusions/Significance: These results show that using a simple tool to locate and to perceive vibrotactile stimuli is accompanied by a shift of spatial attention to the location where the functional part of the tool is used, resulting in enhanced processing of visual stimuli at that location, and decreased processing at other locations. This was most clearly observed in the right hemisphere lingual gyrus. Such modulations of visual processing may reflect the functional importance of visuospatial information during human tool use

Reach-To-Grasp Movements: A Multimodal Techniques Study

The aim of the present study was to investigate the correlation between corticospinal activity, kinematics, and electromyography (EMG) associated with the execution of precision and whole-hand grasps (WHGs). To this end, motor-evoked potentials (MEPs) induced by transcranial magnetic stimulation (TMS), EMG, and 3-D motion capture data have been simultaneously recorded during the planning and the execution of prehensile actions toward either a small or a large object. Differences in the considered measures were expected to distinguish between the two types of grasping actions both in terms of action preparation and execution. The results indicate that the index finger (FDI) and the little finger (ADM) muscles showed different activation patterns during grasping execution, but only the FDI appeared to distinguish between the two types of actions during motor preparation. Kinematics analysis showed that precision grips differed from WHGs in terms of displayed fingers distance when shaping before object\u2019s contact, and in terms of timing and velocity patterns. Moreover, significant correlations suggest a relationship between the muscular activation and the temporal aspects concerned with the index finger\u2019s extension during whole-hand actions. Overall, the present data seem to suggest a crucial role played by index finger as an early \u201cmarker\u201d of differential motor preparation for different types of grasps and as a \u201cnavigator\u201d in guiding whole-hand prehensile actions. Aside from the novelty of the methodological approach characterizing the present study, the data provide new insights regarding the level of crosstalk among different levels concerned with the neuro-behavioral organization of reach-to-grasp movements

Tactile Modulation of the Sensory and Cortical Responses Elicited by Focal Cooling in Humans and Mice

Distinct sensory receptors transduce thermal and mechanical energies, but we have unified, coherent thermotactile experiences of the objects we touch. These experiences must emerge from the interaction of thermal and tactile signals within the nervous system. How do thermal and mechanical signals modify each other as they interact along the pathway from skin to conscious experience? In this thesis, we study how mechanical touch modulates cooling responses by combining psychophysics in humans and neural recordings in rodents. For this, we developed a novel stimulator to deliver focal, temperature-controlled cooling without touch. First, we used this method to study in humans the sensitivity to focal cooling with and without touch. We found that touch reduces the sensitivity to near-threshold cooling, which is perhaps analogous to the well-established ‘gating’ of pain by touch. Second, we studied the perceived intensity of cooling with and without touch. We found that tactile input enhances the perceived intensity of cooling. Third, we measured the responses of the mouse primary somatosensory cortex to cooling and mechanical stimuli using imaging and electrophysiological methods. We found multisensory stimuli elicited non-linear cortical responses at both the population and cellular level. Altogether, in this thesis, we show perceptual and cortical responses to non-tactile cooling for the first time. Based on our observations, we propose a new model to explain the interactions between cooling and mechanical signals in the nervous system. This thesis advances our understanding of how touch modulates cold sensations during thermotactile stimulation

Tactons: structured tactile messages for non-visual information display

Tactile displays are now becoming available in a form that can be easily used in a user interface. This paper describes a new form of tactile output. Tactons, or tactile icons, are structured, abstract messages that can be used to communicate messages non-visually. A range of different parameters can be used for Tacton construction including: frequency, amplitude and duration of a tactile pulse, plus other parameters such as rhythm and location. Tactons have the potential to improve interaction in a range of different areas, particularly where the visual display is overloaded, limited in size or not available, such as interfaces for blind people or in mobile and wearable devices. This paper describes Tactons, the parameters used to construct them and some possible ways to design them. Examples of where Tactons might prove useful in user interfaces are given

Multimodal cue integration in balance and spatial orientation

The global objective of this thesis was to make a significant contribution to our understanding of how the human brain integrates multisensory, multimodal information to inform our motion through space. The primary objectives were to discern whether visual system differentially encodes visual motion coherence and how both allocentric visual cues interact with vestibular system to tell us where and when we are in physical space. A secondary objective was to develop current techniques for the recording and analysis of visuo-vestibular sensory information for the purpose of multisensory, multimodal integration. I studied the response of cortical visual motion area V5/MT+ to random dot kinematograms (RDK) of varying motion coherence, from complete coherence to random. I used the probability of observing TMS (transcranial magnetic stimulation) evoked phosphenes before and after the RDK as a measure of cortical excitability change. I could not show what I had hypothesised: that coherent and random motion elicited a similar net effect upon V5/MT+ excitability, with intermediary coherences of motion having comparatively less effect. However, I argue that a large factor was insufficient sample size to find the effects given the analyses used. The results do show trends consistent with coherent and random net effects being achieved by different modes of cortical activation, and the study will inform future investigation with the paradigm used. I also measured cortical excitability change at a range of relative TMS intensities. This elicited a significant differential effect consistent with the theory that TMS facilitates neurons as a function of the amount of signal they carry. In a separate TMS evoked phosphene study, I show an interaction between whole body rotation in yaw and the ability to observe phosphenes in V5/MT+; as a function of the TMS intensity used and the velocity of whole body rotation used, relative to perceptual thresholds. As I found no main effects, I could not show whether the findings were consistent with a model of reciprocal visual and vestibular cortical inhibition. My work can be considered a feasibility study to inform further investigation. I also used a visual-vestibular mismatch paradigm to probe how erroneous visual landmark cues update veridical vestibular estimates of angular position and motion duration. I used visual masking to reduce the reliability of the visual landmark cues, prevent visual capture and to also elicit subliminal encodement. I found that reversion to vestibular estimates of angular position was made as a function of the noise inherent in the masked visual landmark cues. I found that it was possible to subliminally encode visual landmarks to update vestibularly derived estimates of motion duration. Lastly, I investigated the combination of a two-interval forced choice technique to record estimates of vestibularly derived angular position and a Bayesian Inference technique to parameterize the characteristics of the angular position estimates. I show this combination provides accurate estimates at the subject level and is suitable for incorporation in a Bayesian inference model of multimodal integration. The hypothesis I aim to test in the future is that if visual landmark and vestibular cues of angular position operate within different spatial reference frames, they cannot be optimally integrated in the brain analogous to a Bayesian Inference model of the multimodal integration.Open Acces

The role of the right temporoparietal junction in perceptual conflict: detection or resolution?

The right temporoparietal junction (rTPJ) is a polysensory cortical area that plays a key role in perception and awareness. Neuroimaging evidence shows activation of rTPJ in intersensory and sensorimotor conflict situations, but it remains unclear whether this activity reflects detection or resolution of such conflicts. To address this question, we manipulated the relationship between touch and vision using the so-called mirror-box illusion. Participants' hands lay on either side of a mirror, which occluded their left hand and reflected their right hand, but created the illusion that they were looking directly at their left hand. The experimenter simultaneously touched either the middle (D3) or the ring finger (D4) of each hand. Participants judged, which finger was touched on their occluded left hand. The visual stimulus corresponding to the touch on the right hand was therefore either congruent (same finger as touch) or incongruent (different finger from touch) with the task-relevant touch on the left hand. Single-pulse transcranial magnetic stimulation (TMS) was delivered to the rTPJ immediately after touch. Accuracy in localizing the left touch was worse for D4 than for D3, particularly when visual stimulation was incongruent. However, following TMS, accuracy improved selectively for D4 in incongruent trials, suggesting that the effects of the conflicting visual information were reduced. These findings suggest a role of rTPJ in detecting, rather than resolving, intersensory conflict

Monitoring cortical excitability during repetitive transcranial magnetic stimulation in children with ADHD: a single-blind, sham-controlled TMS-EEG study

Background: Repetitive transcranial magnetic stimulation (rTMS) allows non-invasive stimulation of the human brain. However, no suitable marker has yet been established to monitor the immediate rTMS effects on cortical areas in children. Objective: TMS-evoked EEG potentials (TEPs) could present a well-suited marker for real-time monitoring. Monitoring is particularly important in children where only few data about rTMS effects and safety are currently available. Methods: In a single-blind sham-controlled study, twenty-five school-aged children with ADHD received subthreshold 1 Hz-rTMS to the primary motor cortex. The TMS-evoked N100 was measured by 64-channel-EEG pre, during and post rTMS, and compared to sham stimulation as an intraindividual control condition. Results: TMS-evoked N100 amplitude decreased during 1 Hz-rTMS and, at the group level, reached a stable plateau after approximately 500 pulses. N100 amplitude to supra-threshold single pulses post rTMS confirmed the amplitude reduction in comparison to the pre-rTMS level while sham stimulation had no influence. EEG source analysis indicated that the TMS-evoked N100 change reflected rTMS effects in the stimulated motor cortex. Amplitude changes in TMS-evoked N100 and MEPs (pre versus post 1 Hz-rTMS) correlated significantly, but this correlation was also found for pre versus post sham stimulation. Conclusion: The TMS-evoked N100 represents a promising candidate marker to monitor rTMS effects on cortical excitability in children with ADHD. TMS-evoked N100 can be employed to monitor real-time effects of TMS for subthreshold intensities. Though TMS-evoked N100 was a more sensitive parameter for rTMS-specific changes than MEPs in our sample, further studies are necessary to demonstrate whether clinical rTMS effects can be predicted from rTMS-induced changes in TMS-evoked N100 amplitude and to clarify the relationship between rTMS-induced changes in TMS-evoked N100 and MEP amplitudes. The TMS-evoked N100 amplitude reduction after 1 Hz-rTMS could either reflect a globally decreased cortical response to the TMS pulse or a specific decrease in inhibition