Central Somatosensory Research Articles

The Evolution of Hand Proprioceptive and Motor Impairments in the Sub-Acute Phase After Stroke.

Hand proprioception is essential for fine movements and therefore many activities of daily living. Although frequently impaired after stroke, it is unclear how hand proprioception evolves in the sub-acute phase and whether it follows a similar pattern of changes as motor impairments. This work investigates whether there is a corresponding pattern of changes over time in hand proprioception and motor function as comprehensively quantified by a combination of robotic, clinical, and neurophysiological assessments. Finger proprioception (position sense) and motor function (force, velocity, range of motion) were evaluated using robotic assessments at baseline (<3 months after stroke) and up to 4 weeks later (discharge). Clinical assessments (among others, Box & Block Test [BBT]) as well as Somatosensory/Motor Evoked Potentials (SSEP/MEP) were additionally performed. Complete datasets from 45 participants post-stroke were obtained. For 42% of all study participants proprioception and motor function had a dissociated pattern of changes (only 1 function considerably improved). This dissociation was either due to the absence of a measurable impairment in 1 modality at baseline, or due to a severe lesion of central somatosensory or motor tracts (absent SSEP/MEP). Better baseline BBT correlated with proprioceptive gains, while proprioceptive impairment at baseline did not correlate with change in BBT. Proprioception and motor function frequently followed a dissociated pattern of changes in sub-acute stroke. This highlights the importance of monitoring both functions, which could help to further personalize therapies.

Decreased Microstructural Integrity of the Central Somatosensory Tracts in Diabetic Peripheral Neuropathy.

Although diabetic peripheral neuropathy (DPN) is predominantly considered a disorder of the peripheral nerves, some evidence for central nervous system involvement has recently emerged. However, whether or to what extent the microstructure of central somatosensory tracts may be injured remains unknown. This work aimed to detect the microstructure of central somatosensory tracts in type 2 diabetic patients and to correlate it with the severity of DPN. A case-control study at a tertiary referral hospital took place with 57 individuals with type 2 diabetes (25 with DPN, 32 without DPN) and 33 nondiabetic controls. The fractional anisotropy (FA) values of 2 major somatosensory tracts (the spinothalamic tract and its thalamocortical [spino-thalamo-cortical, STC] pathway, the medial lemniscus and its thalamocortical [medial lemnisco-thalamo-cortical, MLTC] pathway) were assessed based on diffusion tensor tractography. Regression models were further applied to detect the association of FA values with the severity of DPN in diabetic patients. The mean FA values of left STC and left MLTC pathways were significantly lower in patients with DPN than those without DPN and controls. Moreover, FA values of left STC and left MLTC pathways were significantly associated with the severity of DPN (expressed as Toronto Clinical Scoring System values) in patients after adjusting for multiple confounders. Our findings demonstrated the axonal degeneration of central somatosensory tracts in type 2 diabetic patients with DPN. The parallel disease progression of the intracranial and extracranial somatosensory system merits further attention to the central nerves in diabetic patients with DPN.

Central Somatosensory Networks Respond to a De Novo Innervated Penis: A Proof of Concept in Three Spina Bifida Patients.

Spina bifida (SB) causes low spinal lesions, and patients often have absent genital sensation and a highly impaired sex life. TOMAX (TO MAX-imize sensation, sexuality and quality of life) is a surgical procedure whereby the penis is newly innervated using a sensory nerve originally targeting the inguinal area. Most TOMAX-treated SB patients initially experience penile stimulation as inguinal sensation, but eventually, the perception shifts to penis sensation with erotic feelings. The brain mechanisms mediating this perceptual shift, which are completely unknown, could hold relevance for understanding the brain's role in sexual development. The aim of this study was to study how a newly perceived penis would be mapped onto the brain after a lifelong disconnection. Three TOMAX-treated SB patients participated in a functional magnetic resonance imagery experiment while glans penis, inguinal area, and index finger were stimulated with a paint brush. Brush stimulation-induced activation of the primary somatosensory cortex (SI) and functional connectivity between SI and remote cerebral regions. Stimulation of the re-innervated side of the glans penis and the intact contralateral inguinal area activated a very similar location on SI. Yet, connectivity analysis identified distinct SI functional networks. In all three subjects, the middle cingulate cortex (MCC) and the parietal operculum-insular cortex (OIC) were functionally connected to SI activity during glans penis stimulation, but not to SI activity induced by inguinal stimulation. Investigating central somatosensory network activity to a de novo innervated penis in SB patients is feasible and informative. The consistent involvement of MCC and OIC above and beyond the brain network expected on the basis of inguinal stimulation suggests that these areas mediate the novel penis sensation in these patients. The potential role of MCC and OIC in this process is discussed, along with recommendations for further research.

Limb-State Information Encoded by Peripheral and Central Somatosensory Neurons: Implications for an Afferent Interface

A major issue to be addressed in the development of neural interfaces for prosthetic control is the need for somatosensory feedback. Here, we investigate two possible strategies: electrical stimulation of either dorsal root ganglia (DRG) or primary somatosensory cortex (S1). In each approach, we must determine a model that reflects the representation of limb state in terms of neural discharge. This model can then be used to design stimuli that artificially activate the nervous system to convey information about limb state to the subject. Electrically activating DRG neurons using naturalistic stimulus patterns, modeled on recordings made during passive limb movement, evoked activity in S1 that was similar to that of the original movement. We also found that S1 neural populations could accurately discriminate different patterns of DRG stimulation across a wide range of stimulus pulse-rates. In studying the neural coding in S1, we also decoded the kinematics of active limb movement using multi-electrode recordings in the monkey. Neurons having both proprioceptive and cutaneous receptive fields contributed equally to this decoding. Some neurons were most informative of limb state in the recent past, but many others appeared to signal upcoming movements suggesting that they also were modulated by an efference copy signal. Finally, we show that a monkey was able to detect stimulation through a large percentage of electrodes implanted in area 2. We discuss the design of appropriate stimulus paradigms for conveying time-varying limb state information, and the relative merits and limitations of central and peripheral approaches.

Functional Imaging of Central Nervous System Involvement in Complex Regional Pain Syndrome

In complex regional pain syndrome (CRPS), functional imaging studies gave evidence for an important role of the central nervous system (CNS) in the pathogenesis of the disease. Especially, reorganization in central somatosensory and motor networks was demonstrated, leading to an altered central processing of tactile and nociceptive stimuli, as well as to an altered cerebral organization of movement. These findings may explain a number of clinical signs and symptoms occurring in the course of the disease and seem to be closely related to chronic pain in CRPS. Neurorehabilitative strategies, which target cortical areas and aim to restore impaired sensorimotor function in patients with CRPS, therefore, may be effective not only in restoring impaired function but also in pain reduction. This article reviews findings of functional imaging studies, which have been conducted to clarify CNS involvement in the course of CRPS.

Idiopathic restless legs syndrome: Abnormalities in central somatosensory processing

Neurophysiological studies have shown an impairment of temperature perception in secondary and idiopathic restless legs syndrome (RLS). It is unclear whether these deficits are caused by peripheral nerve fibre damage or by central impairment of somatosensory processing. The aim of the present study was (1) to determine the frequency of thermal hypaesthesia in a large population of secondary and idiopathic RLS patients; (2) to differentiate between a peripheral and central disturbance of somatosensory processing and (3) to correlate these findings with the clinical manifestation of the disease. From the results of clinical examination, nerve conduction studies and blood samples the patients were divided into secondary and idiopathic RLS groups. The severity of RLS symptoms was assessed by standardized questionnaires. Quantitative sensory testing (QST) assessing temperature perception was performed in all patients. The peripheral function of small nerve fibres was evaluated by the quantitative nociceptor axon reflex test (QNART). 22 secondary and 20 idiopathic RLS patients participated in the study. Impairment of temperature perception (QST) was found in 72% of the secondary RLS patients and in 55% of idiopathic RLS patients. The peripheral C–fibre function (QNART) was normal in idiopathic RLS patients. In contrast it was significantly impaired in secondary RLS patients compared with idiopathic RLS patients and age matched controls. There was no correlation between the results obtained in QST and clinical scores. Impairment of temperature perception is present in a high percentage of RLS patients. In secondary RLS the sensory deficits are at least in part caused by small fibre neuropathy. In idiopathic RLS a functional impairment of central somatosensory processing is present.

Mielopatía cervical: análisis retrospectivo de los resultados quirúrgicos de 54 pacientes tratados mediante discectomía y fusión intersomática por vía anterior

Patients and methodsWe perform a retrospective analysis of clinical results in 53 consecutive patients surgically treated for cervical myelopathy or myelo-radiculopathy with anterior cervical discectomy and interbody fusión by means of the Cloward procedure. Results64.2% of the patients had good outcome as measured by the improvement in one or more grades in the Nurick's scale. No mortality related to the surgical procedure was noted, although 9.4% of the cases suffered neurological deterioration. Correct fusión was achieved in 92.5% of the patients, with a rate of post-surgical kyphosis of 9.4%. Multivariate analysis identified as factors related to the clinical outcome: age (p=0.008), vascular risk factors (p=0.031), duration of symptoms (p=0.002), pre-surgical neurological status (p<0.001), neuroradiological diagnosis (p=0.014), intramedullary high signal intensity changes in T2-weighted images (p=0.008), prolongation of the central somatosensory or motor conduction times (p=0.004) and neurologic complications (p=0.012) ConclusionsTreatment optimisation of the patient suffering cervical spondylotic myelopathy requires individualised evaluation. Prospective randomised studies are needed to answer the questions when and how to opérate.

Changes of non-affected upper limb cortical representation in paraplegic patients as assessed by fMRI.

Peripheral and central nervous system lesions can induce reorganization within central somatosensory and motor body representations. We report changes in brain activation patterns during movements of non-affected body parts in paraplegic patients with spinal cord injury (SCI). Nine SCI patients and 12 healthy controls underwent blood oxygen level dependent signal functional MRI during sequential finger-to-thumb opposition, flexion and extension of wrist and of elbow, and horizontal movements of the tongue. Single subject and group analyses were performed, and the activation volumes, maximum t values and centres of gravity were calculated. The somatotopical upper limb and tongue representations in the contralateral primary motor cortex (M1) in the SCI patients were preserved without any shift of activation towards the deefferented and deafferented M1 foot area. During finger movements, however, the SCI patients showed an increased volume in M1 activation. Increased activation was also found in non-primary motor and parietal areas, as well as in the cerebellum during movements of the fingers, wrist and elbow, whereas no changes were present during tongue movements. These results document that, in paraplegic patients, the representation of the non-impaired upper limb muscles is modified, though without any topographical reorganization in M1. The extensive changes in primary and non-primary motor areas, and in subcortical regions demonstrate that even distant neuronal damage has impact upon the activation of the whole sensorimotor system.

Maps of optical differential pathlength factor of human adult forehead, somatosensory motor and occipital regions at multi-wavelengths in NIR

The optical differential pathlength factor (DPF) is an important parameter for physiological measurement using near infrared spectroscopy, but for the human adult head it has been available only for the forehead. Here we report measured DPF results for the forehead, somatosensory motor and occipital regions from measurements on 11 adult volunteers using a time-resolved optical imaging system. The optode separation was about 30 mm and the wavelengths used were 759 nm, 799 nm and 834 nm. Measured DPFs were 7.25 for the central forehead and 6.25 for the temple region at 799 nm. For the central somatosensory and occipital areas (10 mm above the inion), DPFs at 799 nm are 7.5 and 8.75, respectively. Less than 10% decreases of DPF for all these regions were observed when the wavelength increased from 759 nm to 834 nm. To compare these DPF maps with the anatomical structure of the head, a Monte Carlo simulation was carried out to calculate DPF for these regions by using a two-layered semi-infinite model and assuming the thickness of the upper layer to be the sum of the thicknesses of scalp and skull, which was measured from MRI images of a subject's head. The DPF data will be useful for quantitative monitoring of the haemodynamic changes occurring in adult heads.

TRAUMATIC NEURALGIAS: Complex Regional Pain Syndromes (Reflex Sympathetic Dystrophy and Causalgia): Clinical Characteristics, Pathophysiologic Mechanisms and Therapy

Complex regional pain syndromes (CPRS) may develop as a disproportionate consequence of a trauma affecting the limbs without (CRPS I, reflex sympathetic dystrophy) or with (CRPS II, causalgia) obvious nerve lesions. The clinical picture of CRPS consists of asymmetrical distal extremity pain, swelling, and autonomic (sympathetic) and motor symptoms. Changes in the peripheral and central somatosensory, autonomic and motor processing, and a pathologic interaction of sympathetic and afferent systems are discussed as underlying pathophysiologic mechanisms. Therapeutic strategies include pharmacologic pain relief, sympatholytic interventions, and rehabilitation.

Somatosensory and Auditory Brain Stem Conduction after Head Injury: A Comparison with Clinical Features in Prediction of Outcome

Abstract Evoked potential conduction times in brain stem auditory (BCT) and central somatosensory pathways (CCT) were recorded from 23 normal subjects and 101 patients with severe head injury. Abnormalities in the CCT and the BCT findings correlated with the clinical indices of brain damage (coma score, motor response, pupil response, and spontaneous and reflex eye movements) in the head-injured patients and each correlated with outcome at 6 months from the injury. The CCT in the “best” hemisphere produced the strongest correlation with outcome (P&amp;lt;0.001). The correlation of the CCT with outcome was stronger in the 47 patients examined 2 to 3 days after the injury (P&amp;lt;0.001) compared to the 34 patients examined within 24 hours after the injury (P&amp;lt;0.02). No such difference was noted for the BCT. Serial studies within the first 2 weeks of injury did not show a consistent pattern and repetition of the investigation over this period did not provide any additional information. We used an INDEP-SELECT discriminant analysis program to determine whether information from the evoked potential data could improve prediction of outcome based on clinical data alone. With the addition of the CCT, the predictive accuracy (expressed as the correct classification probability) increased only slightly from 77 to 80%, and the difference was not significant. We conclude that central somatosensory and auditory brain stem conduction times provide useful prognostic information in paralyzed or sedated patients, but when neurological examination is feasible the benefits of evoked potential analysis do not justify the effort involved in data collection.

Somatosensory and auditory brain stem conduction after head injury

Evoked potential conduction times in brain stem auditory (BCT) and central somatosensory pathways (CCT) were recorded from 23 normal subjects and 101 patients with severe head injury. Abnormalities in the CCT and the BCT findings correlated with the clinical indices of brain damage (coma score, motor response, pupil response, and spontaneous and reflex eye movements) in the head-injured patients and each correlated with outcome at 6 months from the injury. The CCT in the "best" hemisphere produced the strongest correlation with outcome (P less than 0.001). The correlation of the CCT with outcome was stronger in the 47 patients examined 2 to 3 days after the injury (P less than 0.001) compared to the 34 patients examined within 24 hours after the injury (P less than 0.02). No such difference was noted for the BCT. Serial studies within the first 2 weeks of injury did not show a consistent pattern and repetition of the investigation over this period did not provide any additional information. We used an INDEP-SELECT discriminant analysis program to determine whether information from the evoked potential data could improve prediction of outcome based on clinical data alone. With the addition of the CCT, the predictive accuracy (expressed as the correct classification probability) increased only slightly from 77 to 80%, and the difference was not significant. We conclude that central somatosensory and auditory brain stem conduction times provide useful prognostic information in paralyzed or sedated patients, but when neurological examination is feasible the benefits of evoked potential analysis do not justify the effort involved in data collection.

Somatosensory and brainstem auditory evoked potentials in alcoholic liver disease with and without encephalopathy

Median somatosensory and brainstem auditory evoked potentials (SEP and BAEP) were studied in chronic alcoholics with and without complications of alcoholic liver disease. The alcoholics were divided into 4 groups: Group 1 with minimally abnormal liver function tests; Group 2 with hepatic failure; Group 3 with mild to moderate hepatic encephalopathy; and Group 4 with severe encephalopathy. A control group consisted of age-matched normal subjects. In the alcoholic groups, BAEPs showed a significant prolongation in the latencies of peaks III to VI and interpeaks I–III, III–V, and I–V. The peak latency prolongation was associated with a reduction in all peak amplitudes. In median SEPs, the cervical N13 and cortical N20 latencies were significantly delayed in the alcoholic groups. The amplitude of all cortical SEP components within 150 msec analysis time was also significantly reduced. In addition, the alcoholic groups had slowing in median nerve conduction and prolongation in central conduction time (N13 to N20 interpeak latency). In both BAEPs and SEPs, there were no differences in the peak amplitude and the peak latency among the alcoholic groups except for the late cortical SEP components which showed progressive prolongation and eventual absence from Groups 2 to 4. The present data indicate that chronic alcoholics have subclinical dysfunction in the central somatosensory and brainstem auditory pathways irrespective of the complications of alcoholic liver disease. However, the late components of the cortical SEPs can be affected in hepatic failure and hepatic encephalopathy.

Electrophysiologic features of abetalipoproteinemia: functional consequences of vitamin E deficiency.

We performed electrophysiologic testing in 10 patients with abetalipoproteinemia (ABL). Peripheral nerve studies implied an axonal disorder. Visual evoked potentials demonstrated prolonged P100 latency in three patients and abnormal electroretinograms in six. Somatosensory evoked potentials indicated dorsal column dysfunction in eight patients. Brainstem auditory evoked potentials were normal. Findings were consistent with the known neuropathology of ABL and of experimental vitamin E deficiency. Stabilization or improvement in electrophysiologic findings occurred with vitamin E supplementation. Neurophysiologic tests document retinal, central somatosensory and peripheral nerve lesions in vitamin E deficiency and provide an objective indication of response to treatment.