Encoding and processing of sensory information in neuronal spike trains

Recently, a statistical signal-processing technique has allowed the information carried by single spike trains of sensory neurons on time-varying stimuli to be characterized quantitatively in a variety of preparations. In weakly electric fish, its application to first-order sensory neurons encoding electric field amplitude (P-receptor afferents) showed that they convey accurate information on temporal modulations in a behaviorally relevant frequency range (<80 Hz). At the next stage of the electrosensory pathway (the electrosensory lateral line lobe, ELL), the information sampled by first-order neurons is used to extract upstrokes and downstrokes in the amplitude modulation waveform. By using signal-detection techniques, we determined that these temporal features are explicitly represented by short spike bursts of second-order neurons (ELL pyramidal cells). Our results suggest that the biophysical mechanism underlying this computation is of dendritic origin. We also investigated the accuracy with which upstrokes and downstrokes are encoded across two of the three somatotopic body maps of the ELL (centromedial and lateral). Pyramidal cells of the centromedial map, in particular I-cells, encode up- and downstrokes more reliably than those of the lateral map. This result correlates well with the significance of these temporal features for a particular behavior (the jamming avoidance response) as assessed by lesion experiments of the centromedial map

Albuminocytological dissociation in different electrophysiological gbs variants

The objective of our study was to determine the distribution of different electrophysiological variants of GBS and its relationship with albuminocytological dissociation (ACD). The rationale of the study was to determine whether presence or absence of albuminocytological dissociation has any association with NCS findings and whether can be relied upon as an indirect predictor of axonal variant which warrants poor patient out comes versus demyelinating. Materials and Methods: A consecutive series of 76 patients who presented at PIMS over a 12 month period with GBS were included. Nerve Conduction studies (NCS) and Electromyographic (EMG) findings with CSF characterization for albuminocytological dissociation were recorded. P value \u3c 0.05 was taken significant. Results: NCS revealed AIDP as the most common variant (44; 57.8%) followed by AMAN (19; 25%) and AMSAN (7; 9.2%).For 5(6.5%) patients with normal NCS, EMG revealed early neuropathic changes in 4 (80% of normal NCS; 5.2% of total) (suggesting axonal degeneration). Total axonal degenerative type accounted for (AMAN + AMSAN + axonal neuropathy on EMG=30) 39.4% while demyelinating (AIDP + prolonged/absent F-wave=45) 59.2%. ACD was found in 60 (78.9%) patients.There was no signification association between ACD and NCS variants (p\u3e0.05). Conclusion: AIDP is the most prevalent (58%) GBS variant in our population, at least in the vicinity of Islamabad. There is high prevalence of axonal variants (≈40% of total) as compared to Western countries. There is no correlation between ACD and NCS variants. ACD cannot be used as an independent predictor of NCS variant. Presence or absence of ACD has no definite predilection for axonal variant which itself warrants poor patient outcomes versus demyelinating type

Periodic solutions and refractory periods in the soliton theory for nerves and the locust femoral nerve

Close to melting transitions it is possible to propagate solitary electromechanical pulses which reflect many of the experimental features of the nerve pulse including mechanical dislocations and reversible heat production. Here we show that one also obtains the possibility of periodic pulse generation when the boundary condition for the nerve is the conservation of the overall length of the nerve. This condition generates an undershoot beneath the baseline (`hyperpolarization') and a `refractory period', i.e., a minimum distance between pulses. In this paper, we outline the theory for periodic solutions to the wave equation and compare these results to action potentials from the femoral nerve of the locust (locusta migratoria). In particular, we describe the frequently occurring minimum-distance doublet pulses seen in these neurons and compare them to the periodic pulse solutions.Comment: 10 pages, 6 Figure

Investigating human Schwann cell phenotypes and outcome measures of muscle reinnervation

Peripheral Nerve Injury (PNI) often causes partial or complete paralysis and/or loss of sensation of the segment of the body involved. Traumatic PNI is a global problem and can result in significant disability and socio-economic impacts. Clinical translation of new therapeutics for the treatment of PNI is challenged by the little information that is known about the cellular and molecular features that underpin human nerve regeneration. Moreover, clinical models and measurements that can quantify the efficacy of new treatments for PNI are not well established. Therefore, this PhD explored injured and healthy human nerve samples liberated from reconstructive nerve procedures to characterise the cellular and molecular features of human peripheral nerve degeneration. Associated with this theme of characterisation of human nerve injury, the recovery of motor units in reinnervated elbow flexor muscles following nerve transfer was quantified using Motor Unit Number Estimation (MUNE). In order to better understand the relationship of MUNE with the biological process of nerve regeneration, an animal model of nerve injury was used to investigate the association between MUNE and histological markers of regeneration. MUNE was found to be a sensitive marker of muscle reinnervation in human and animal models of nerve regeneration. Moreover, MUNE demonstrated a correlation with histological markers of muscle reinnervation. It is known that these changes in the number of motor units are accompanied by changes in muscle volume. Therefore, using the same surgical scenario of nerve transfer to reanimate elbow flexor muscles, this PhD measured the recovery of muscle volume following nerve transfer to reanimate elbow flexor muscles using quantitative Magnetic Resonance Imaging (MRI) techniques. It was found that MRI assessment of muscle volume is a measure that is sensitive to the biological process of nerve regeneration. With further data, this has the capacity to determine the efficacy of new therapeutics for the treatment of PNI and predict the likely functional recovery following PNI. In summary, the findings represent an important step towards understanding the in vivo cellular and molecular events in human nerve degeneration. In addition, MUNE and quantitative MRI techniques were found to represent sensitive and responsive measures of nerve regeneration. With further data, the findings presented here will help new therapeutic options for human nerve injury advance

Algorithms for Neural Prosthetic Applications

abstract: In the last 15 years, there has been a significant increase in the number of motor neural prostheses used for restoring limb function lost due to neurological disorders or accidents. The aim of this technology is to enable patients to control a motor prosthesis using their residual neural pathways (central or peripheral). Recent studies in non-human primates and humans have shown the possibility of controlling a prosthesis for accomplishing varied tasks such as self-feeding, typing, reaching, grasping, and performing fine dexterous movements. A neural decoding system comprises mainly of three components: (i) sensors to record neural signals, (ii) an algorithm to map neural recordings to upper limb kinematics and (iii) a prosthetic arm actuated by control signals generated by the algorithm. Machine learning algorithms that map input neural activity to the output kinematics (like finger trajectory) form the core of the neural decoding system. The choice of the algorithm is thus, mainly imposed by the neural signal of interest and the output parameter being decoded. The various parts of a neural decoding system are neural data, feature extraction, feature selection, and machine learning algorithm. There have been significant advances in the field of neural prosthetic applications. But there are challenges for translating a neural prosthesis from a laboratory setting to a clinical environment. To achieve a fully functional prosthetic device with maximum user compliance and acceptance, these factors need to be addressed and taken into consideration. Three challenges in developing robust neural decoding systems were addressed by exploring neural variability in the peripheral nervous system for dexterous finger movements, feature selection methods based on clinically relevant metrics and a novel method for decoding dexterous finger movements based on ensemble methods.Dissertation/ThesisDoctoral Dissertation Bioengineering 201

Neurophysiologic diagnosis, clinical symptoms and neuropathologic findings in polyneuropathies

Tausta: Polyneuropatia (PNP) on ääreishermoston sairaus, joka aiheuttaa laaja-alaisia, yleensä symmetrisiä vaurioita ääreishermostossa. PNP:aan johtavia syitä on satoja. Tavoitteet: Löytää parhaat neurofysiologiset menetelmät uremian, myelooman hoidossa käytettävän talidomidin sekä Fabryn taudin aiheuttaman PNP:n diagnosoimiseksi. Fabryn taudissa tutkin lisäksi ohutsäieneuropatian aiheuttamia neuropatologisia löydöksiä iholta otetusta koepalasta. Tutkimuksissa kartoitettiin lisäksi PNP:n aiheuttamien subjektiivisten oireiden korrelaatio neurofysiologisten ja neuropatologisten löydösten kanssa. Munuaisten vajaatoimintaa sairastavilla potilailla tavoitteena oli tutkia dialyysihoidon tehon vaikutusta autonomisen hermoston toimintaan sekä yhden dialyysikerran vaikutusta neurofysiologisiin löydöksiin. Aineisto ja menetelmät: I: Tutkittiin 21 uremiapotilaan sensoristen ja motoristen hermojen vasteet, värinä- sekä lämpötuntokynnykset ennen ja jälkeen hemodialyysin. Subjektiiviset PNP oireet kartoitettiin PNP oireita kysyvillä kaavakkeella. II:12 talidomidi hoitoa saavaa myeloomapotilasta, tutkimuksen menetelmät olivat samat kuin tutkimuksessa I. III: 12 Fabryn tautia sairastavaa potilasta, edellä mainittujen neurofysiologisten tutkimusten lisäksi potilailta otettiin ihobiopsia säären alueelta. Ihobiopsiasta laskettiin ohuiden hermosyiden määrä koepalan värjäyksen jälkeen. Subjektiiviset PNP oireet kartoitettiin kyselykaavakkeella. Sydämen sykevaihtelu tutkittiin levossa taajuustason analyysillä. IV: 32 uremiapotilaan autonomisen hermoston toimintaa tutkittiin sydämen sykevaihtelun aikatason analysillä, paksujen myelinoituneiden säikeiden toimintaa tutkittiin perifeeristen sensoristen hermojen mittauksilla toistetusti noin 2.9 vuoden aikana. Tulokset: Ureemisen PNP:n diagnostiikassa herkimmät tutkimukset ovat F-aaltojen parametrit alaraajojen motorisista hermoista, värinätuntokynnys alaraajoista sekä suralishermon amplitudi. Positiiviset PNP oireet uremiassa korreloivat värinätunto-kynnyksen sekä sensoristen hermojen neurografialöydösten kanssa. Neurofysiologisten tutkimusten ajankohdalla dialyysiajankohtaan nähden ei ole merkitystä. Talidomidi-PNP on pääasiassa sensorinen, mutta motoriset syyt ovat lievästi vaurioituneet. Talidomidi PNP:ssa subjektiiviset oireet korreloivat huonosti neurofysiologisten löydösten kanssa. Fabryn taudissa naisilla on oletettua enemmän ohutsäieneuropatian aiheuttamia oireita ja löydöksiä. Paksujen säikeiden löydöksiä ei tullut esiin. Ohutsäieneuropatian diagnostiikassa ihobiopsia ja kvantitatiiviset tuntokynnysmittaustestit täydentävät toisiaan. Tehokas dialyysi parantaa autonomisen hermoston toimintaa uremiapotilailla. Päätelmät: Erityyppisten polyneuropatioiden diagnostiikassa pitää etukäteen valita PNP tyypille oikeat tutkimusmenetelmät raskaiden tutkimuspatterien vähentämiseksi sekä diagnostiikan parantamiseksi. PNP:n aiheuttamat oireet ja kliiniset löydökset pitää aina tutkia, mutta yksin ne eivät ole herkkiä PNP:n diagnostiikassa.Backround: Polyneuropathy (PNP) is a disorder of the peripheral nervous system that causes widespread, usually symmetric, abnormalities of peripheral nerves. Numerous underlying conditions can cause PNP. Aims: To evaluate the subjective PNP symptoms and the most useful neurophysiologic tests for the diagnosis of uremic PNP, thalidomide induced PNP in myeloma patients, and PNP in Fabry disease. Another aspect of the study was to determine the correlation between subjective symptoms and neurophysiologic and neuropathologic findings in patients with PNP. In uremic patients, the aim was also to study the effect of one dialysis session on neurophysiologic parameters. Also the effect of dialysis on the function of autonomic nervous system was evaluated. Subjects and methods: (I) 21 uremic patients, sensory and motor conduction studies, vibratory- and thermal detection thresholds before and after dialysis. The clinical findings and subjective symptoms were studied using a standardized questionnaire. (II) 12 myeloma patients with thalidomide therapy, the methods were the same as in study I. (III) 12 patients with Fabry disease, same methods as in studies I and II, also skin biopsy for the detection of intraepidermal nerve fibre density. (IV) 32 uremic patients, autonomic nervous system was studied with time-domain measures, thick myelinated fibers were studied with sensory neurography. Results: The F- wave parameters, vibratory perception threshold from lower limbs, and the sural amplitude were the best parameters in the diagnosis of uremic PNP. Positive PNP symptoms in uremic patients correlated with vibratory perception threshold and sensory neurography. The neurophysiologic test can be done either before or after dialysis. Thalidomide PNP is predominantly sensory, but motor fibers are also slightly affected. The subjective sensory PNP symptoms did not correlate with neurophysiologic findings. In Fabry disease, women had more PNP symptoms than expected. Thick myelinated fibers are not affected in Fabry disease. In the diagnosis of small-fibre PNP, the skin biopsy and quantitative sensory tests complement each other. Effective dialysis therapy had a positive effect to cardiac autonomic function. Conclusions: When diagnosing PNP, it is important to use standardized neurophysiologic tests that reflect the function of different types of nerve fibres. These tests should have proper reference values and they should be sensitive in detecting the particular type of PNP that is suspected. The patient’s subjective symptoms, family history and clinical findings give valuable information, and should always be evaluated together with the neurophysiologic tests.Siirretty Doriast