Rapid enhancement of touch from non-informative vision of the hand

Processing in one sensory modality may modulate processing in another. Here we investigate how simply viewing the hand can influence the sense of touch. Previous studies showed that non-informative vision of the hand enhances tactile acuity, relative to viewing an object at the same location. However, it remains unclear whether this Visual Enhancement of Touch (VET) involves a phasic enhancement of tactile processing circuits triggered by the visual event of seeing the hand, or more prolonged, tonic neuroplastic changes, such as recruitment of additional cortical areas for tactile processing. We recorded somatosensory evoked potentials (SEPs) evoked by electrical stimulation of the right middle finger, both before and shortly after viewing either the right hand, or a neutral object presented via a mirror. Crucially, and unlike prior studies, our visual exposures were unpredictable and brief, in addition to being non-informative about touch. Viewing the hand, as opposed to viewing an object, enhanced tactile spatial discrimination measured using grating orientation judgements, and also the P50 SEP component, which has been linked to early somatosensory cortical processing. This was a trial-specific, phasic effect, occurring within a few seconds of each visual onset, rather than an accumulating, tonic effect. Thus, somatosensory cortical modulation can be triggered even by a brief, non-informative glimpse of one’s hand. Such rapid multisensory modulation reveals novel aspects of the specialised brain systems for functionally representing the body

Intraneural stimulation elicits discrimination of textural features by artificial fingertip in intact and amputee humans.

Restoration of touch after hand amputation is a desirable feature of ideal prostheses. Here, we show that texture discrimination can be artificially provided in human subjects by implementing a neuromorphic real-time mechano-neuro-transduction (MNT), which emulates to some extent the firing dynamics of SA1 cutaneous afferents. The MNT process was used to modulate the temporal pattern of electrical spikes delivered to the human median nerve via percutaneous microstimulation in four intact subjects and via implanted intrafascicular stimulation in one transradial amputee. Both approaches allowed the subjects to reliably discriminate spatial coarseness of surfaces as confirmed also by a hybrid neural model of the median nerve. Moreover, MNT-evoked EEG activity showed physiologically plausible responses that were superimposable in time and topography to the ones elicited by a natural mechanical tactile stimulation. These findings can open up novel opportunities for sensory restoration in the next generation of neuro-prosthetic hands

Gamma Band Oscillation Response to Somatosensory Feedback Stimulation Schemes Constructed on Basis of Biphasic Neural Touch Representation

abstract: Prosthetic users abandon devices due to difficulties performing tasks without proper graded or interpretable feedback. The inability to adequately detect and correct error of the device leads to failure and frustration. In advanced prostheses, peripheral nerve stimulation can be used to deliver sensations, but standard schemes used in sensorized prosthetic systems induce percepts inconsistent with natural sensations, providing limited benefit. Recent uses of time varying stimulation strategies appear to produce more practical sensations, but without a clear path to pursue improvements. This dissertation examines the use of physiologically based stimulation strategies to elicit sensations that are more readily interpretable. A psychophysical experiment designed to investigate sensitivities to the discrimination of perturbation direction within precision grip suggests that perception is biomechanically referenced: increased sensitivities along the ulnar-radial axis align with potential anisotropic deformation of the finger pad, indicating somatosensation uses internal information rather than environmental. Contact-site and direction dependent deformation of the finger pad activates complimentary fast adapting and slow adapting mechanoreceptors, exhibiting parallel activity of the two associate temporal patterns: static and dynamic. The spectrum of temporal activity seen in somatosensory cortex can be explained by a combined representation of these distinct response dynamics, a phenomenon referred in this dissertation to “biphasic representation.” In a reach-to-precision-grasp task, neurons in somatosensory cortex were found to possess biphasic firing patterns in their responses to texture, orientation, and movement. Sensitivities seem to align with variable deformation and mechanoreceptor activity: movement and smooth texture responses align with potential fast adapting activation, non-movement and coarse texture responses align with potential increased slow adapting activation, and responses to orientation are conceptually consistent with coding of tangential load. Using evidence of biphasic representations’ association with perceptual priorities, gamma band phase locking is used to compare responses to peripheral nerve stimulation patterns and mechanical stimulation. Vibrotactile and punctate mechanical stimuli are used to represent the practical and impractical percepts commonly observed in peripheral nerve stimulation feedback. Standard patterns of constant parameters closely mimic impractical vibrotactile stimulation while biphasic patterns better mimic punctate stimulation and provide a platform to investigate intragrip dynamics representing contextual activation.Dissertation/ThesisDoctoral Dissertation Biomedical Engineering 201

Nerve Conduction study and Evoked potentials in Visually Challenged Persons

INTRODUCTION: The development and refinement of instrumentation has been a great asset in the diagnosis of neurologic diseases. First available study was in 1951 by GALLEGO A.1 Peripheral nerve conduction study is an extension of neurological examination. Data are available for normal persons and how it gets changed in diseases process. From 1975 onward numerous studies are published regarding normal data, techniques, methods and origin of waves etc. Peripheral nerve conduction studies are done in very few of the visually challenged. PubMed advanced search of “Somatosensory Evoked Potentials” and “visually challenged persons” yields no available data. AIM OF THE STUDY: 1. To study the peripheral nerve conduction in visually challenged persons. 2. To study auditory and somatosensory evoked potentials in visually challenged persons. 3. Comparison of previous available data with our control population. MATERIALS AND METHODS: The study was conducted on the patient attenders in neurology services at the institute of neurology, Madras Medical College and Rajiv Gandhi Government general Hospital from May 2011 to march 2013. Institutional ethical committee is applied and the committee approved the study. Informed consent was obtained from the participants. In the control group a volunteer read the information sheet and consent form are visually challenged persons are got by means of thumb impression. Visually challenged persons are chosen from a government blind school. Twenty five persons from school and twenty five persons of age matched controls are chosen. Inclusion and Exclusion criteria: Those who are visually challenged since childhood are selected Persons with other associated diseases are excluded. Participants age, sex, visual acuity and height are measured and documented. METHODS: Patients are advised to avoid applying oil after head bath on the day of test. His test is done in the sitting position with comfortable neck muscle relaxation or in the lying posture according to the patients relaxation. CONCLUSION: 1. The central conduction time is significantly short in the visually challenged persons using Braille reading. It favours that visually deprived persons uses the touch information in a efficient manner which help them for coping with their surroundings. 2. The fast conduction decreases with decreasing usage of braille reading. 3. Brainstem auditory evoked response is normal in visually challenged persons. 4. Brainstem auditory evoked response not faster when they are using recorded voice lesson learning. 5. Peak central conduction time does not correlate with age. 6. In Braille reading persons, sensory nerve conduction latency, amplitude, velocities are normal while the central conduction is short indicating faster conduction. 7. The faster central conduction is of significance in visually challenged as they rely on touch for their locomotion and many other day to day activities. Hence it may be better if they continue to use Braille which helps better touch perception. Where as when they switch to auditory learning the central conduction in somatosensory pathway slows to that of normal people, which may be a disadvantage to the visually challenged who has to "feel" the world that they cannot see. So we recommend that Braille usage to be continued in older visually challenged persons even though they may also use auditory learning

Sensorimotor integration in dystonia: pathophysiology and possible non-invasive approaches to therapy

Dystonia is a condition characterized by excessive and sustained muscle contractions causing abnormal postures and involuntary movements. The pathophysiology of dystonia includes loss of inhibition and abnormal plasticity in the somatosensory and motor systems; however, their contribution to the phenomenology of dystonia is still uncertain, and the possibility to target these abnormalities in an attempt to devise new treatments has not been thoroughly explored. This thesis describes how abnormal inhibition and plasticity in the somatosensory system of dystonic patients can be manipulated to ameliorate motor symptoms by means of peripheral stimulation. First, we characterized electrophysiological and behavioural markers of inhibition in the primary somatosensory cortex in a group of patients with idiopathic cervical dystonia (CD). Outcome measures included a) somatosensory temporal discrimination threshold (STDT); b) paired-pulse somatosensory evoked potentials (PP-SEP) tested with interstimulus intervals (ISIs) of 5, 20 and 40 ms; c) spatial somatosensory inhibition ratio (SIR) by measuring SEP interaction between simultaneous stimulation of the digital nerves in thumb and index finger; d) high-frequency oscillations (HFO) extracted from SEP obtained with stimulation of digital nerves of the index finger. This first investigation demonstrated that increased STDT in dystonia is related to reduced activity of inhibitory circuits within the primary somatosensory cortex, as reflected by reduced PP-SEP inhibition at ISI of 5 ms and reduced area of the late part of the HFO (l-HFO). In a second set of experiments, we applied high frequency repetitive somatosensory stimulation (HF-RSS), a patterned electric stimulation applied to the skin through surface electrodes, to the index finger in a sample of healthy subjects, with the aim to manipulate excitability and inhibition of the primary somatosensory (S1) and motor (M1) cortices. The former was assessed by the same methods used before (STDT, PP-SEP, HFO), with the addition of two psychophysical tasks designed to assess tactile spatial discrimination (grating orientation and bumps tests). Assessment of physiology of M1 was performed by means of short intracortical inhibition (SICI) assessed with TMS; this was performed with multiple conditioning stimulus (CS) intensities (70%, 80%, 90% of the active motor threshold) and with a insterstimulus interval (ISI) between conditioning and test stimulus of 3 ms. It was found that HF-RSS increased inhibition in S1 tested by PP-SEP and HFO; these changes were correlated with improvement in STDT. HF-RSS also enhanced bumps detection, while there was no change in grating orientation test. Finally, there was an increase in SICI, suggesting widespread changes in cortical sensorimotor interactions. Overall, these findings demonstrated that HF-RSS is able to modify the effectiveness of inhibitory circuitry in S1 and M1. The results obtained so far led us to hypothesize that HF-RSS could restore inhibition in dystonic patients, similar to what observed in healthy subjects. To test this, we applied HF-RSS on the index finger in a sample of patients with CD, and tested its effects with some of the outcome measures used before (STDT, PP-SEP, HFO, SIR, SICI). Unexpectedly, the results were opposite to what was predicted. Patients with CD showed a consistent, paradoxical response: after HF-RSS, they had reduced suppression of PP-SEP, as well as decreased HFO area and SICI, and increased SIR. STDT deteriorated after the stimulation protocol, and correlated with reduced measures of inhibition within S1 (PP-SEP at 5 ms ISI, l-HFO area). It was hypothesized that patients with CD have abnormal homeostatic inhibitory plasticity within the sensorimotor cortex and that this is responsible for their abnormal response to HF-RSS. Interestingly, this alteration in plasticity seems to be specific to idiopathic dystonia: when the same protocol was applied to patients with dystonia caused by lesions in the basal ganglia, the response was similar to healthy controls. This result suggests that reduced somatosensory inhibition and abnormal cortical plasticity are not strictly required for the clinical expression of dystonia, and that the abnormalities reported in idiopathic dystonia are not necessarily linked to basal ganglia damage. We then directed our attention to another form of peripheral electrical stimulation, delivered at low frequency (LF-RSS). Previous literature demonstrated that this pattern of stimulation had effects opposite to HF-RSS on tactile performance in healthy subjects; therefore, given the previous findings of abnormal response to HF-RSS in CD, we hypothesized that an inverse response might occur in these patients following LF-RSS as well. Our hypothesis was confirmed by the observation that LF-RSS, applied to the fingers in patients with CD, induced an increase in inhibition in the primary somatosensory and motor cortices. This was reflected by an improvement of STDT and an increase in PP-SEP suppression, HFO area and SICI. With this in mind, in the final project of the thesis, we tested the effects of HF-RSS and LF-RSS applied directly over two affected muscles in different groups of patients with focal hand dystonia (FHD), in an attempt to modulate involuntary muscle activity and, consequently, to ameliorate motor symptoms. Whereas HF-RSS was delivered synchronously over the two muscles, LF-RSS was given either synchronously or asynchronously. Outcome measures included a) PP-SEP obtained by direct stimulation of affected muscles, with ISIs of 5 and 30 ms; b) quantification of electromyographic (EMG) activity from tested muscles; c) SICI recorded from the affected muscles, with CS intensities ranging from 50% to 100% RMT and with an ISI of 3 ms; d) evaluation of hand function, assessed by the box and blocks test (BBT) and the nine-hole peg test (NHPT); e) SIR by measuring SEP interaction between simultaneous stimulation of the two muscles receiving repetitive stimulation. We confirmed the paradoxical response of dystonic patients to HF-RSS, which was reflected in decreased PP-SEP suppression and SICI and increased SIR. Importantly, this was paralleled by an increase in involuntary EMG activity and worse scores at the BBT and NHPT. This results were opposite when LF-RSS was delivered, either in its synchronous or asynchronous version, the latter being slightly more effective. Thus, LF-RSS was able to increase PP-SEP suppression and SICI, decrease SIR and reduce involuntary EMG activity, with consequent improvement in performance in the BBT and NHPT. Overall, our data provide novel insight into the neural mechanisms underlying loss of inhibition and deranged somatosensory plasticity in idiopathic dystonia and bring preliminary evidence that peripheral electrical stimulation can be used as a treatment in idiopathic focal hand dystonia

Event-related potential studies of somatosensory detection and discrimination.

This thesis contains four studies, the first examining methodology issues and four subsequent ones examining somatosensory cortical processing using event-related potentials (ERPs). The methodology section consists of 2 experiments. The first compared the latency variability in stimulus presentation between 3 computers. The second monitored the applied force of the vibration stimuli under experimental conditions to ensure that the chosen method for somatosensory stimulus presentation was consistent and reliable. The next study involved 3 experiments that aimed to characterize the mid to long latency somatosensory event-related potentials to different duration vibratory stimuli using both intracranial and scalp recording. The results revealed differences in the waveform morphology of the responses to and on-off responses, which had not previously been noted in the somatosensory system. The third and fourth studies each consisted of 2 experiments. These examined the discrimination between vibratory stimuli using an odd-ball paradigm to try to obtain a possible 'mismatch' response, similar to that reported in the auditory system. The aim of this study was to clarify some of the discrepancies in the literature surrounding the somatosensory mismatch response and to further characterize this response. The results from intracranial and scalp ERP recordings showed a two-component, negative-positive mismatch response over the anterior parietal region and a negative component over the superior pre-frontal region in response to changes in both frequency and duration. The negative component over the frontal region had never before been described. The last study explored possible interactions between somatosensory and auditory cortical potentials in response to spatially and temporally synchronized auditory and vibratory stimuli. The results showed clear interactions in the cortical responses to combined auditory and somatosensory stimuli in both standard and mismatch conditions

Enhancing touch sensibility with sensory electrical stimulation and sensory retraining

A large proportion of stroke survivors suffer from sensory loss, negatively impacting their independence, quality of life, and neurorehabilitation prognosis. Despite the high prevalence of somatosensory impairments, our understanding of somatosensory interventions such as sensory electrical stimulation (SES) in neurorehabilitation is limited. We aimed to study the effectiveness of SES combined with a sensory discrimination task in a well-controlled virtual environment in healthy participants, setting a foundation for its potential application in stroke rehabilitation. We employed electroencephalography (EEG) to gain a better understanding of the underlying neural mechanisms and dynamics associated with sensory training and SES. We conducted a single-session experiment with 26 healthy participants who explored a set of three visually identical virtual textures—haptically rendered by a robotic device and that differed in their spatial period—while physically guided by the robot to identify the odd texture. The experiment consisted of three phases: pre-intervention, intervention, and post-intervention. Half the participants received subthreshold whole-hand SES during the intervention, while the other half received sham stimulation. We evaluated changes in task performance—assessed by the probability of correct responses—before and after intervention and between groups. We also evaluated differences in the exploration behavior, e.g., scanning speed. EEG was employed to examine the effects of the intervention on brain activity, particularly in the alpha frequency band (8–13 Hz) associated with sensory processing. We found that participants in the SES group improved their task performance after intervention and their scanning speed during and after intervention, while the sham group did not improve their task performance. However, the differences in task performance improvements between groups only approached significance. Furthermore, we found that alpha power was sensitive to the effects of SES; participants in the stimulation group exhibited enhanced brain signals associated with improved touch sensitivity likely due to the effects of SES on the central nervous system, while the increase in alpha power for the sham group was less pronounced. Our findings suggest that SES enhances texture discrimination after training and has a positive effect on sensory-related brain areas. Further research involving brain-injured patients is needed to confirm the potential benefit of our solution in neurorehabilitation.</p

Enhancing touch sensibility with sensory electrical stimulation and sensory retraining

A large proportion of stroke survivors suffer from sensory loss, negatively impacting their independence, quality of life, and neurorehabilitation prognosis. Despite the high prevalence of somatosensory impairments, our understanding of somatosensory interventions such as sensory electrical stimulation (SES) in neurorehabilitation is limited. We aimed to study the effectiveness of SES combined with a sensory discrimination task in a well-controlled virtual environment in healthy participants, setting a foundation for its potential application in stroke rehabilitation. We employed electroencephalography (EEG) to gain a better understanding of the underlying neural mechanisms and dynamics associated with sensory training and SES. We conducted a single-session experiment with 26 healthy participants who explored a set of three visually identical virtual textures—haptically rendered by a robotic device and that differed in their spatial period—while physically guided by the robot to identify the odd texture. The experiment consisted of three phases: pre-intervention, intervention, and post-intervention. Half the participants received subthreshold whole-hand SES during the intervention, while the other half received sham stimulation. We evaluated changes in task performance—assessed by the probability of correct responses—before and after intervention and between groups. We also evaluated differences in the exploration behavior, e.g., scanning speed. EEG was employed to examine the effects of the intervention on brain activity, particularly in the alpha frequency band (8–13 Hz) associated with sensory processing. We found that participants in the SES group improved their task performance after intervention and their scanning speed during and after intervention, while the sham group did not improve their task performance. However, the differences in task performance improvements between groups only approached significance. Furthermore, we found that alpha power was sensitive to the effects of SES; participants in the stimulation group exhibited enhanced brain signals associated with improved touch sensitivity likely due to the effects of SES on the central nervous system, while the increase in alpha power for the sham group was less pronounced. Our findings suggest that SES enhances texture discrimination after training and has a positive effect on sensory-related brain areas. Further research involving brain-injured patients is needed to confirm the potential benefit of our solution in neurorehabilitation.</p

Contextual signals in visual cortex:How sounds, state, and task setting shape how we see

What we see is not always what we get. Even though the light that hits the retina might convey the same images, how visual information is processed and what we eventually do with it depend on many contextual factors. In this thesis, we show in a series of experiments how the sensory processing of the same visual input in the visual cortex of mice is affected by our internal state, movements, other senses and any task we are performing. We found that recurrent activity originating within higher visual areas modulates activity in the primary visual cortex (V1) and selectivity amplifies weak compared to strong sensory-evoked responses. Second, visual stimuli evoked similar early activity in V1, but later activity strongly depended on whether mice were trained to report the visual stimuli, and on the specific task. Specifically, adding a second modality to the task demands extended the temporal window during which V1 was causally involved in visual perception. Third, we report that not only visual stimuli but also sounds led to strong responses in V1, composed of distinct auditory-related and motor-related activity. Finally, we studied the role of Posterior Parietal Cortex in an audiovisual change detection task. Despite extensive single-neuron and population-level encoding of task-relevant visual and auditory stimuli, as well as upcoming behavioral responses, optogenetic inactivation did not affect task performance. Whereas these contextual factors have previously been studied in isolation, we obtain a more integrated understanding of how factors beyond visual information determine what we actually see