Feasibility of fNIRS Neurofeedback for Tactile Imagery

This study investigates the feasibility of using functional near-infrared spectroscopy (fNIRS)-based neurofeedback to facilitate voluntary modulation of brain activity during tactile imagery in healthy adults. Neurofeedback is a technique that provides individuals with real-time information about their brain activity, allowing them to learn to regulate specific neural processes through training. While neurofeedback has been widely studied using electroencephalography (EEG) and functional magnetic resonance imaging (fMRI), the application of fNIRS-based neurofeedback has become increasingly popular in recent years due to its portability and relatively low cost. Importantly, this study is among the first to explore the use of tactile imagery as a target mental strategy for neurofeedback training. Most previous neurofeedback paradigms have relied on motor imagery to induce modulation of sensorimotor brain activity. In contrast, the present study investigates whether tactile imagery can also be used to voluntarily regulate cortical activity when supported by real-time fNIRS feedback. Tactile imagery has been shown to activate cortical regions involved in somatosensory processing, including areas of the sensorimotor cortex. Training individuals to modulate these responses may have potential applications in neurorehabilitation, particularly in contexts such as sensorimotor recovery. However, before such applications can be considered, it is important to evaluate whether individuals can successfully learn to regulate task-related cortical hemodynamic responses during tactile imagery when provided with real-time feedback derived from fNIRS signals. The present study employs a randomized, double-blind experimental design with two groups: a neurofeedback (NF) group and a sham (SH) feedback control group. Forty healthy participants aged 18–40 will be recruited and randomly assigned to one of the two groups (20 participants per group). All participants will complete a single experimental session consisting of four neurofeedback runs. Each run will include ten trials, and each trial will consist of three phases: a baseline period (10 seconds), an upregulation period during which participants perform tactile imagery of sensations on the right hand (15 seconds), and a rest period (15 seconds). Short breaks of approximately 2–3 minutes will be provided between runs. Participants in the neurofeedback group will receive real-time visual feedback based on their own fNIRS signals during the tactile imagery upregulation phase. In contrast, participants in the sham feedback group will receive feedback that is not contingent on their actual neural activity but is instead generated from pre-recorded signals. Both participants and experimenters interacting with participants will be blinded to group allocation in order to minimize expectancy effects. To complement the neurophysiological measurements, subjective measures will also be collected. Participants will complete a vividness of tactile imagery questionnaire (VTIQ) before and after the neurofeedback training session. In addition, after each run participants will rate the level of effort required to perform the imagery task using a five-point Likert scale. These subjective measures will help characterize participants’ perceived engagement with the task and their ability to generate tactile imagery. The primary outcome of the study is the change in cortical activation measured by fNIRS during tactile imagery upregulation periods relative to baseline. Secondary outcomes include changes in neural activation across runs, subjective tactile imagery vividness scores, and self-reported effort ratings. The expected outcome of this research is to determine whether participants can modulate somatosensory-related cortical activity during tactile imagery when provided with fNIRS-based neurofeedback, and whether this modulation differs from sham feedback conditions. As a feasibility study, the findings will provide important information about the practicality of implementing tactile imagery neurofeedback using fNIRS, the degree of participant learning within a single session, and the variability of neural and subjective responses. These results may inform the design of future neurofeedback protocols and potential applications in clinical populations.