Abstract
In recent times, we have witnessed a push towards restoring sensory perception to upper-limb amputees, which includes the whole spectrum from gentle touch to noxious stimuli. These are essential components for body protection as well as for restoring the sense of embodiment. Notwithstanding the considerable advances that have been made in designing suitable sensors and restoring tactile perceptions, pain perception dynamics and its decoding using effective bio-markers, are still not fully understood. Here, using electroencephalography (EEG) recordings, we identified and validated a spatio-temporal signature of brain activity during innocuous, moderately more intense, and noxious stimulation of an amputee’s phantom limb using transcutaneous nerve stimulation (TENS). Based on the spatio-temporal EEG features, we developed a system for detecting pain perception and reaction in the brain, which successfully classified three different stimulation conditions with a test accuracy of 94.66%, and we investigated the cortical activity in response to sensory stimuli in these conditions. Our findings suggest that the noxious stimulation activates the pre-motor cortex with the highest activation shown in the central cortex (Cz electrode) between 450 ms and 750 ms post-stimulation, whereas the highest activation for the moderately intense stimulation was found in the parietal lobe (P2, P4, and P6 electrodes). Further, we localized the cortical sources and observed early strong activation of the anterior cingulate cortex (ACC) corresponding to the noxious stimulus condition. Moreover, activation of the posterior cingulate cortex (PCC) was observed during the noxious sensation. Overall, although this is a single case study, this work presents a novel approach and a first attempt to analyze and classify neural activity when restoring sensory perception to amputees, which could chart a route ahead for designing a real-time pain reaction system in upper-limb prostheses.
Highlights
Nociception is commonly known as the sense of pain[1]
Based on the identified spatio-temporal brain activity patterns, we developed an offline system for detecting pain reaction in the brain which can recognize the three stimulation conditions from recorded EEG responses by using effective spatio-temporal bio-markers to identify the different brain regions involved in noxious stimuli processing as well as latency responses for each stimulation condition
The NOX stimulation was reported by the subject as uncomfortable but tolerable[7], the moderately intense (MOD) stimulation was reported as slightly more noticeable/intense compared to the INNO stimulation
Summary
Nociception is commonly known as the sense of pain[1]. Specialized receptors called nociceptors that cover the skin and organs react to harmful chemical, mechanical and thermal stimuli[2]. The signal activates the somatosensory cortex which is responsible for physical sensations; the signals are relayed to the frontal cortex where higher-order cognitive processing occurs, and to the limbic system, which is linked to emotions[5] This pain processing network, along with pain reflex pathways in the spinal cord[6], are considered of the utmost importance for body protection from damaging stimuli[7]. The overall goal of this study was to extend upon the work performed by Osborn et al.[7], where the reflex system was implemented in the arm prosthesis and the amputee was not involved in the withdrawing reaction This is thought to be of the utmost importance when designing a better bidirectional-control system between the human and the prosthesis, and increase the amputee’s sense of embodiment and the sense of ownership[19,20].
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