Tactile width discrimination processing has been extensively studied in rodents and has demonstrated multiple relevant basic mechanisms. Despite this relevance, the number of studies of width discrimination in humans has been scarce. During the present dissertation, neurophysiological correlates of width discrimination were analyzed through electroencephalography recordings in participants performing a width discrimination task in active or passive modes. Analysis of power in the delta, theta, alpha, beta, and gamma frequency bands revealed differences in the power for different frequency bands and electrodes recorded. Active width discrimination processing was characterized by an increase in the power of delta, theta and gamma frequency bands in electrodes F3 and F4, and an increase in power in the gamma frequency band in T4. Passive tactile width processing was characterized by an increase in the power of delta in electrodes Fp1 and T4, and an increase in gamma frequency band in Tp10. Altogether these results suggest that active and passive tactile width discrimination processing are characterized by an asymmetrical network involving prefrontal, frontal and temporal electrodes, in delta, theta, and gamma frequency bands.

Introduction: Tactile information processing requires the integration of sensory, motor, and cognitive information. Width discrimination has been extensively studied in rodents, but not in humans. Methods: Here, we describe Electroencephalography (EEG) signals in humans performing a tactile width discrimination task. The first goal of this study was to describe changes in neural activity occurring during the discrimination and the response periods. The second goal was to relate specific changes in neural activity to the performance in the task. Results: Comparison of changes in power between two different periods of the task, corresponding to the discrimination of the tactile stimulus and the motor response, revealed the engagement of an asymmetrical network associated with fronto-temporo-parieto-occipital electrodes and across multiple frequency bands. Analysis of ratios of higher [Ratio 1: (0.5–20 Hz)/(0.5–45 Hz)] or lower frequencies [Ratio 2: (0.5–4.5 Hz)/(0.5–9 Hz)], during the discrimination period revealed that activity recorded from frontal-parietal electrodes was correlated to tactile width discrimination performance between-subjects, independently of task difficulty. Meanwhile, the dynamics in parieto-occipital electrodes were correlated to the changes in performance within-subjects (i.e., between the first and the second blocks) independently of task difficulty. In addition, analysis of information transfer, using Granger causality, further demonstrated that improvements in performance between blocks were characterized by an overall reduction in information transfer to the ipsilateral parietal electrode (P4) and an increase in information transfer to the contralateral parietal electrode (P3). Discussion: The main finding of this study is that fronto-parietal electrodes encoded between-subjects’ performances while parieto-occipital electrodes encoded within-subjects’ performances, supporting the notion that tactile width discrimination processing is associated with a complex asymmetrical network involving fronto-parieto-occipital electrodes.

Brain–machine interfaces combining visual, auditory, and tactile feedback have been previously used to generate embodiment experiences during spinal cord injury (SCI) rehabilitation. It is not known if adding temperature to these modalities can result in discomfort with embodiment experiences. Here, comfort levels with the embodiment experiences were investigated in an intervention that required a chronic pain SCI patient to generate lower limb motor imagery commands in an immersive environment combining visual (virtual reality -VR), auditory, tactile, and thermal feedback. Assessments were made pre-/ post-, throughout the intervention (Weeks 0–5), and at 7 weeks follow up. Overall, high levels of embodiment in the adapted three-domain scale of embodiment were found throughout the sessions. No significant adverse effects of VR were reported. Although sessions induced only a modest reduction in pain levels, an overall reduction occurred in all pain scales (Faces, Intensity, and Verbal) at follow up. A high degree of comfort in the comfort scale for the thermal-tactile sleeve, in both the thermal and tactile feedback components of the sleeve was reported. This study supports the feasibility of combining multimodal stimulation involving visual (VR), auditory, tactile, and thermal feedback to generate embodiment experiences in neurorehabilitation programs.

We review the literature on sensory, short-term, long-term, and working memory for tactile and haptic inputs, focusing on research using interference tasks and issues arising from the use of this methodology. We then present two studies that investigated the effects of haptic, verbal, spatial, and motor interference on haptic object recognition. Experiment 1 was an old/new object recognition task with the interference tasks performed during encoding of the study objects. Experiment 2 was a sequential object-matching task with the interference tasks performed in the retention interval between presenting the two objects. Different results were found across the two experiments and the pattern of interference obtained was different again in two similar studies that also used interference tasks to investigate haptic object recognition (. Lacey & Campbell, 2006). Haptic, spatial, visual, and verbal interference all significantly disrupted performance on the primary haptic object recognition task in some studies but not in others. We argue that the selection and use of primary and secondary tasks in interference studies need to be more theoretically motivated and, where possible, standardized before general conclusions can be drawn about haptic memory using this methodology. However, notwithstanding these issues, the current findings suggest that verbal and visual processes have a role during the haptic encoding of objects whereas haptic and spatial, but not motor, processes are important for maintaining the representations of objects presented haptically. We further suggest that whereas verbal strategies may be employed in some haptic memory tasks, the underlying representations are likely spatial in nature.