Performance Enhancement of MC-CDMA System through Novel Sensitive Bit Algorithm Aided Turbo Multi User Detection

Multi carrier code division multiple access (MC-CDMA) system is a promising multi carrier modulation (MCM) technique for high data rate wireless communication over frequency selective fading channels. MC-CDMA system is a combination of code division multiple access (CDMA) and orthogonal frequency division multiplexing (OFDM). The OFDM parts reduce multipath fading and inter symbol interference (ISI) and the CDMA part increases spectrum utilization. Advantages of this technique are its robustness in case of multipath propagation and improve security with the minimize ISI. Nevertheless, due to the loss of orthogonality at the receiver in a mobile environment, the multiple access interference (MAI) appears. The MAI is one of the factors that degrade the bit error rate (BER) performance of MC-CDMA system. The multiuser detection (MUD) and turbo coding are the two dominant techniques for enhancing the performance of the MC-CDMA systems in terms of BER as a solution of overcome to MAI effects. In this paper a low complexity iterative soft sensitive bits algorithm (SBA) aided logarithmic-Maximum a-Posteriori algorithm (Log MAP) based turbo MUD is proposed. Simulation results show that the proposed method provides better BER performance with low complexity decoding, by mitigating the detrimental effects of MAI.     

Amplitude cancellation reduces the size of motor unit potentials averaged from the surface EMG.

The purpose of the study was to evaluate the influence of selected physiological parameters on amplitude cancellation in the simulated surface electromyogram (EMG) and the consequences for spike-triggered averages of motor unit potentials derived from the interference and rectified EMG signals. The surface EMG was simulated from prescribed recruitment and rate coding characteristics of a motor unit population. The potentials of the motor units were detected on the skin over a hand muscle with a bipolar electrode configuration. Averages derived from the EMG signal were generated using the discharge times for each of the 24 motor units with lowest recruitment thresholds from a population of 120 across three conditions: 1) excitation level; 2) motor unit conduction velocity; and 3) motor unit synchronization. The area of the surface-detected potential was compared with potentials averaged from the interference, rectified, and no-cancellation EMGs. The no-cancellation EMG comprised motor unit potentials that were rectified before they were summed, thereby preventing cancellation between the opposite phases of the potentials. The percent decrease in area of potentials extracted from the rectified EMG was linearly related to the amount of amplitude cancellation in the interference EMG signal, with the amount of cancellation influenced by variation in excitation level and motor unit conduction velocity. Motor unit synchronization increased potentials derived from both the rectified and interference EMG signals, although cancellation limited the increase in area for both potentials. These findings document the influence of amplitude cancellation on motor unit potentials averaged from the surface EMG and the consequences for using the procedure to characterize motor unit properties.     

Measurement of rotational molecular motion by time-resolved saturation transfer electron paramagnetic resonance.

We have used saturation-recovery electron paramagnetic resonance (SR-EPR), a time-resolved saturation transfer EPR technique, to measure directly the microsecond rotational diffusion of spin-labeled proteins. SR-EPR uses an intense microwave pulse to saturate a spin population having narrow distribution of orientations with respect to the magnetic field. The time evolution of the signal is then observed. The signal increases in time as saturation is relieved by spin-lattice relaxation (Tl) as well as by saturation transfer due to spectral diffusion (Tsd), which is a function of rotational diffusion (Tr) and spectral position. In the presence of both events, the recovery is biphasic, with the initial phase related to both Tr and Tl, and the second phase determined only by Tl. We have measured the saturation recoveries of spin-labeled hemoglobin tumbling in media of known viscosities as a function of rotational correlation time (Tr) and pulse duration (tp). The Tr values estimated from the initial phase of recovery were in good agreement with theory. Variation of the pulse time can also be used to determine Tr. For tp less than Tsd, the recoveries were observed to be biphasic, for tp greater than Tsd a single-exponential. T1 values were determined from the recoveries after pulses quenching spectral diffusion or from the second phase of recovery after shorter pulses. These results demonstrate that SR-EPR is applicable to the study of motion of spin-labeled proteins. Its time resolution should provide a significant advantage over steady state techniques, particularly in the case of motional anisotropy or system heterogeneity.     

The Effects of Sex Hormonal Fluctuations during Menstrual Cycle on Cortical Excitability and Manual Dexterity (a Pilot Study)

Aim

To investigate whether hormonal fluctuations during the menstrual cycle affect corticospinal excitability, intracortical inhibition (ICI) or facilitation (ICF) in primary motor cortex, and also whether the hormonal fluctuations have any effect on manual dexterity in neurologically intact women.

Materials and Methods

Twenty volunteers (10 Female, 10 Male) were included in this study. The levels of progesterone and estradiol were measured from saliva during the women’s menstrual follicular, ovulation and mid-luteal phases. Motor evoked potentials were recorded from the right first dorsal interosseous muscle. Single and paired-pulse Transcranial Magnetic Stimulation (TMS) were delivered in a block of 20 stimuli. With paired-pulse technique, 3ms and 10ms inter-stimulus intervals were used to assess ICI and ICF, respectively. The Grooved Pegboard Test (GPT) was completed in each session before the TMS assessments. Male participants were tested at similar time intervals as female participants.

Results

Mixed design ANOVA revealed that GPT score in female participants was significantly lower at the mid-luteal phase compared to the ovulation phase (p = 0.017). However, it was not correlated with progesterone or estrogen fluctuations during the menstrual cycle. The results also showed that the effect of phase, sex and the interaction of phase by sex for resting motor threshold, ICI or ICF were not significant (p > 0.05).

Conclusion

Manual dexterity performance fluctuates during the menstrual cycle in neurologically intact women, which might be due to the balance of the neuromodulatory effects of P4 and E2 in the motor cortex during different phases.     

Influence of amplitude cancellation on the simulated surface electromyogram.

The purpose of the study was to quantify the influence of selected motor unit properties and patterns of activity on amplitude cancellation in the simulated surface electromyogram (EMG). The study involved computer simulations of a motor unit population with physiologically defined recruitment and rate coding characteristics that activated muscle fibers whose potentials were recorded on the skin over the muscle. Amplitude cancellation was quantified as the percent difference in signal amplitude when motor unit potentials were summed before and after rectification. The simulations involved varying the level of activation for the motor unit population, the recording configuration, the upper limit of motor unit recruitment, peak discharge rates, the amount of motor unit synchronization, muscle fiber length, the thickness of the subcutaneous tissue, and the motor unit properties that change with advancing age. The results confirmed a previous experimental report (Day SJ and Hulliger M, J Neurophysiol 86: 2144-2158, 2001) that amplitude cancellation in the surface EMG can reach 62% at maximal activation. A decrease in the range of amplitudes of the motor unit potentials, as can occur during fatiguing contractions, increased amplitude cancellation up to approximately 85%. Differences in the amount of amplitude cancellation were observed across all simulated conditions, and resulted in substantial changes in the absolute magnitude of the EMG signal. The most profound factors influencing amplitude cancellation were the number of active motor units and the duration of the action potentials. The effects of amplitude cancellation were minimal (<5%) when the EMG amplitude was normalized to maximal values, with the exception of variations in peak discharge rate and recruitment range, which resulted in differences up to 17% in the normalized EMG signal across conditions. These results indicate the amount of amplitude cancellation that can occur in various experimental conditions and its influence on absolute and relative measures of EMG amplitude.     

Sequential Activation of Classic PKC and Estrogen Receptor α Is Involved in Estradiol 17?-D-Glucuronide-Induced Cholestasis

Estradiol 17ß-d-glucuronide (E17G) induces acute cholestasis in rat with endocytic internalization of the canalicular transporters bile salt export pump (Abcb11) and multidrug resistance-associated protein 2 (Abcc2). Classical protein kinase C (cPKC) and PI3K pathways play complementary roles in E17G cholestasis. Since non-conjugated estradiol is capable of activating these pathways via estrogen receptor alpha (ERα), we assessed the participation of this receptor in the cholestatic manifestations of estradiol glucuronidated-metabolite E17G in perfused rat liver (PRL) and in isolated rat hepatocyte couplets (IRHC). In both models, E17G activated ERα. In PRL, E17G maximally decreased bile flow, and the excretions of dinitrophenyl-glutathione, and taurocholate (Abcc2 and Abcb11 substrates, respectively) by 60% approximately; preadministration of ICI 182,780 (ICI, ERα inhibitor) almost totally prevented these decreases. In IRHC, E17G decreased the canalicular vacuolar accumulation of cholyl-glycylamido-fluorescein (Abcb11 substrate) with an IC50 of 91±1 µM. ICI increased the IC50 to 184±1 µM, and similarly prevented the decrease in the canalicular vacuolar accumulation of the Abcc2 substrate, glutathione-methylfluorescein. ICI also completely prevented E17G-induced delocalization of Abcb11 and Abcc2 from the canalicular membrane, both in PRL and IRHC. The role of ERα in canalicular transporter internalization induced by E17G was confirmed in ERα-knocked-down hepatocytes cultured in collagen sandwich. In IRHC, the protection of ICI was additive to that produced by PI3K inhibitor wortmannin but not with that produced by cPKC inhibitor Gö6976, suggesting that ERα shared the signaling pathway of cPKC but not that of PI3K. Further analysis of ERα and cPKC activations induced by E17G, demonstrated that ICI did not affect cPKC activation whereas Gö6976 prevented that of ERα, indicating that cPKC activation precedes that of ERα. Conclusion: ERα is involved in the biliary secretory failure induced by E17G and its activation follows that of cPKC.     

A wavelet-based adaptive filter for removing ECG interference in EMGdi signals

Diaphragmatic electromyogram (EMGdi) signals convey important information on respiratory diseases. In this paper, an adaptive filter for removing the electrocardiographic (ECG) interference in EMGdi signals based on wavelet theory is proposed. Power spectrum analysis was performed to evaluate the proposed method. Simulation results show that the power spectral density (PSD) of the extracted EMGdi signal from an ECG corrupted signal is within 1.92% average error relative to the original EMGdi signal. Testing on clinical EMGdi data confirm that this method is also efficient in removing ECG artifacts from the corrupted clinical EMGdi signal.     

Spin label study of local anesthetic-lipid membrane interactions. Phase separation of the uncharged from and bilayer micellization by the charged form of tetracaine

The interaction between tetracaine and egg phosphatidylcholine (egg PC) multibilayers was examined. ESR spectra of an ester spin label indicate that at low uncharged anesthetic: lipid ratios, membrane organization decreases. At higher ratios, saturation and phase separation occur, as suggested by a second spectral component which appears when the water solubility of tetracaine is reached. However, experiments with the drug in the absence and in the presence of membranes, making use of a phospholipid spin label, suggest that the new phase does not consist of solid tetracaine alone. Location of the new phase in the membrane would require a change in partition coefficient, while its location outside would imply a mechanism whereby the anesthetic would come off the membrane as aggregate containing spin probe and phospholipid. Charged tetracaine forms micelles which disrupt-unilamellar egg PC vesicles (Fernandez, M.S. (1981) Biochim. Biophys. Acta 646, 27–30). Micellar tetracaine added to bilayers containing a PC spin probe changes the spectrum from one typical of a bilayer into one typical of micelles, indicating the formation of a tetracaine-egg PC mixed micelle. The effect is reversible upon dilution to concentrations below the critical micelle concentration of tetracaine. When membranes are prepared in the presence of a water-soluble spin label, TEMPOcholine, ascorbate destroys the signal of untrapped label; when mixed phospholipid-tetracaine are formed by addition of micellar tetracaine, this leads to a complete loss of the ESR signal. High drug concentrations are often used for anesthesia and could be related to morphological nerve damage caused by large doses of anesthetics.     

Spin label study of local anesthetic-lipid membrane interactions. Phase separation of the uncharged form and bilayer micellization by the charged form of tetracaine

The interaction between tetracaine and egg phosphatidylcholine (egg PC) multibilayers was examined. ESR spectra of an ester spin label indicate that at low uncharged anesthetic: lipid ratios, membrane organization decreases. At higher ratios, saturation and phase separation occur, as suggested by a second spectral component which appears when the water solubility of tetracaine is reached. However, experiments with the drug in the absence and in the presence of membranes, making use of a phospholipid spin label, suggest that the new phase does not consist of solid tetracaine alone. Location of the new phase in the membrane would require a change in partition coefficient, while its location outside would imply a mechanism whereby the anesthetic would come off the membrane as an aggregate containing spin probe and phospholipid. Charged tetracaine forms micelles which disrupt-unilamellar egg PC vesicles (Fernandez, M.S. (1981) Biochim. Biophys. Acta 646, 27-30). Micellar tetracaine added to bilayers containing a PC spin probe changes the spectrum from one typical of a bilayer into one typical of micelles, indicating the formation of a tetracaine-egg PC mixed micelle. The effect is reversible upon dilution to concentrations below the critical micelle concentration of tetracaine. When membranes are prepared in the presence of a water-soluble spin label, TEMPOcholine, ascorbate destroys the signal of untrapped label; when mixed phospholipid-tetracaine are formed by addition of micellar tetracaine, this leads to a complete loss of the ESR signal. High drug concentrations are often used for anesthesia and could be related to morphological nerve damage caused by large doses of anesthetics.     

Different binding modes of free and carrier-protein-coupled nicotine in a human monoclonal antibody

Nicotine is the principal addictive component of tobacco. Blocking its passage from the lung to the brain with nicotine-specific antibodies is a promising approach for the treatment of smoking addiction. We have determined the crystal structure of nicotine bound to the Fab fragment of a fully human monoclonal antibody (mAb) at 1.85 Å resolution. Nicotine is almost completely (> 99%) buried in the interface between the variable domains of heavy and light chains. The high affinity of the mAb is the result of a charge–charge interaction, a hydrogen bond, and several hydrophobic contacts. Additionally, similarly to nicotinic acetylcholine receptors in the brain, two cation–π interactions are present between the pyrrolidine charge and nearby aromatic side chains. The selectivity of the mAb for nicotine versus cotinine, which is the major metabolite of nicotine and differs in only one oxygen atom, is caused by steric constraints in the binding site. The mAb was isolated from B cells of an individual immunized with a nicotine–carrier protein conjugate vaccine. Surprisingly, the nicotine was bound to the Fab fragment in an orientation that was not compatible with binding to the nicotine–carrier protein conjugate. The structure of the Fab fragment in complex with the nicotine–linker derivative that was used for the production of the conjugate vaccine revealed a similar position of the pyridine ring of the nicotine moiety, but the pyrrolidine ring was rotated by about 180°. This allowed the linker part to reach to the Fab surface while high-affinity interactions with the nicotine moiety were maintained.     

Evidence for perception of fine echo delay and phase by the FM bat,Eptesicus fuscus

The big brown bat, Eptesicus fuscus, can perceive small changes in the delay of FM sonar echoes and shifts in echo phase, which interact with delay. Using spectral cues caused by interference, Eptesicus also can perceive the individual delays of two overlapping FM echoes at small delay separations. These results have been criticized as due to spectral artifacts caused by overlap between stimulus echoes and extraneous sounds (Pollak 1993). However, no amplitude or spectral variations larger than 0.05 dB accompany delay or phase changes produced by the electronic apparatus. No reverberation falls in the narrow span of delays required to produce the bat's performance curve from echo interference cues. Consistent differences in the durations of sonar sounds for 6 bats that perform the same in the experiments demonstrate that overlap between stimulus echoes and extraneous echoes is not necessary, and changes in the amount of echo overlap have no effect on performance. Noise-induced random variations in echo spectra outweigh putative spectral artifacts, and deliberately-introduced spectral artifacts do not improve performance overall but instead yield new time-frequency images. Amplitude-latency trading of perceived delay, proposed as a demonstration that the latency of neural discharges encodes delay (Pollak et al. 1977), confirms that the bat's fine delay and phase perception depends on a temporal neural code. The perceived delays depend on stimulus delays, not the delays of extraneous sounds. The rejected criticisms are based on physiological results with random-phase FM stimuli which are irrelevant to neural coding of fine echo delay and phase.The contents of this paper first appeared in October 1990 in a letter to G.D. Pollak in response to his unpublished criticisms of echo-jitter experiments. These responses also have been presented at the 1991 and 1992 Association for Research in Otolaryngology midwinter meetings and at the 1992 3rd International Congress of Neuroethology. Several of the control experiments also appeared in Simmons et al. (1990b). The now-published criticisms (Pollak 1993, the preceding paper) have not addressed these responses, including the prior published data demonstrating that the stimulus conditions asserted by these criticisms do not in fact occur.     

Signal peptide mimics conjugated to peptide nucleic acid: a promising solution for improving cell membrane permeability

The specific binding ability and biostability of PNA (peptide nucleic acid) with DNA or RNA make PNA not only a good tool for the studies of molecular biology but also the candidate for gene-targeting drugs. However, the main obstacle for its potential usage as a therapeutic is the low cell uptake caused by the poor cell membrane permeability. In this paper the hydrophobic pentadecapeptide and two signal peptide mimics, hexa- and decapeptides ending with a positively charged amino acid, were proposed as the linked carrier for the transportation of PNA T10 through the cell membrane; stable spin label was coupled to the peptide-PNA conjugate so that the ESR measurements can be used for the assessment of their transmembrane movements. The syntheses of spin-labeled peptide-PNA conjugates were carried out on MBHA resin with Boc strategy. The cell membrane permeability of the spin-labeled conjugates of peptides and PNA can be determined with ESR, during the incubation of erythrocyte with the samples. According to ESR measurements, the three conjugates exhibit enhanced uptake into erythrocytes. The hexa- and decapeptide-modified PNA showed suitable water solubility. The peptide-PNA conjugates retained their binding ability to complementary DNA. The results suggest that peptide modification of PNA might be a promising solution for improving cell membrane permeability toward PNA.     

Effervescence Assisted Fusion Technique to Enhance the Solubility of Drugs

The solubility of five poorly soluble drugs was enhanced by using an effervescence assisted solid dispersion (EASD) technique. EASDs were prepared by using modified fusion method. Drug and hydrophilic carrier were melted, and in this molten mixture, effervescence was generated by adding effervescence couple comprising organic acid (citric acid) and carbonic base (sodium bicarbonate). Solubility of drug powders, solid dispersions, and EASDs was determined at 25°C using shake flask method. Atorvastatin calcium, cefuroxime axetil, clotrimazole, ketoconazole, and metronidazole benzoate were estimated using a spectrophotometer at 246, 280, 260, 230, and 232 nm (λ_max), respectively. Solubility of atorvastatin calcium (from 100 to 345 μg/ml), cefuroxime axetil (from 441 to 1948 μg/ml), clotrimazole (from 63 to 677 μg/ml), ketoconazole (from 16 to 500 μg/ml), and metronidazole benzoate (from 112 to 208 μg/ml) in EASDs was enhanced by 3.45-, 4.4-, 10.7-, 31.2-, and 1.8-fold, respectively. Scanning electron micrographs of drug powder, solid dispersion, and EASDs were compared. Scanning electron micrographs of EASDs showed a uniform distribution of drug particles in the carrier matrix. Morphology (size and shape) of cefuroxime axetil particles was altered in solid dispersion as well as in EASD. EASDs showed better solubility enhancement than conventional solid dispersions. The present technique is better suitable for drugs having a low melting point or melt without charring. Effervescence assisted fusion technique of preparing solid dispersions can be employed for enhancing solubility, dissolution, and bioavailability of poorly soluble drugs.KEY WORDS: dissolution, effervescence, fusion, solid dispersion, solubility     

Single small-interfering RNA expression vector for silencing multiple transforming growth factor-β pathway components

Although RNA interference (RNAi) is a popular technique, no method for simultaneous silencing of multiple targets by small-hairpin RNA (shRNA)-expressing RNAi vectors has yet been established. Although gene silencing can be achieved by synthetic small-interfering RNA (siRNA) duplexes, the approach is transient and largely dependent on the transfection efficiency of the host cell. We offer a solution: a simple, restriction enzyme-generated stable RNAi technique that can efficiently silence multiple targets with a single RNAi vector and a single selection marker. In this study, we succeeded in simultaneous stable knockdown of transforming growth factor β (TGF-β) pathway-related Smads—Smad2, Smad3 and Smad4—at the cellular level. We observed distinct phenotypic changes in TGF-β-dependent cellular functions such as invasion, wound healing and apoptosis. This method is best suited for an analysis of complex signal transduction pathways in which silencing of a single gene cannot account for the whole process.     

Salmonella detection in foods and feeds in 27 hours by an enzyme immunoassay

A heterogeneous enzyme immunoassay (EIA), which could be completed within 27 h, was developed for the detection of salmonellae in foods. Samples were subjected to the usual non-selective enrichment for 16–18 at 35°C and to a short (6 h) post-enrichment in a moderately selective broth. The EIA was carried out on polystyrene microtitration plates. A pooled polyvalent Salmonella flagellar antiserum and a protein A-alkaline phosphatase conjugate were used. The sensitivity of the enzyme immunoassay compared favorably with that of the conventional cultural technique for detection of Salmonella in 40 naturally contaminated food and feed samples. No sample was positive only by the cultural technique; samples positive only by the enzyme immunoassay were observed for feeds. Some specimens yielded high background values indicating possible interference from food proteins.     

Frequency Response of a Protein to Local Conformational Perturbations

Signals created by local perturbations are known to propagate long distances through proteins via backbone connectivity and nonbonded interactions. In the current study, signal propagation from the flexible ligand binding loop to the rest of Protein Tyrosine Phosphatase 1B (PTP1B) was investigated using frequency response techniques. Using restrained Targeted Molecular Dynamics (TMD) potential on WPD and R loops, PTP1B was driven between its crystal structure conformations at different frequencies. Propagation of the local perturbation signal was manifested via peaks at the fundamental frequency and upper harmonics of 1/f distributed spectral density of atomic variables, such as C_α atoms, dihedral angles, or polar interaction distances. Frequency of perturbation was adjusted high enough (simulation length >∼10×period of a perturbation cycle) not to be clouded by random diffusional fluctuations, and low enough (<∼0.8 ns⁻¹) not to attenuate the propagating signal and enhance the contribution of the side-chains to the dissipation of the signals. Employing Discrete Fourier Transform (DFT) to TMD simulation trajectories of 16 cycles of conformational transitions at periods of 1.2 to 5 ns yielded C_α displacements consistent with those obtained from crystal structures. Identification of the perturbed atomic variables by statistical t-tests on log-log scale spectral densities revealed the extent of signal propagation in PTP1B, while phase angles of the filtered trajectories at the fundamental frequency were used to cluster collectively fluctuating elements. Hydrophobic interactions were found to have a higher contribution to signal transduction between side-chains compared to the role of polar interactions. Most of in-phase fluctuating residues on the signaling pathway were found to have high identity among PTP domains, and located over a wide region of PTP1B including the allosteric site. Due to its simplicity and efficiency, the suggested technique may find wide applications in identification of signaling pathways of different proteins.     

Epoch length to accurately estimate the amplitude of interference EMG is likely the result of unavoidable amplitude cancellation

Researchers and clinicians routinely rely on interference electromyograms (EMGs) to estimate muscle forces and command signals in the neuromuscular system (e.g., amplitude, timing, and frequency content). The amplitude cancellation intrinsic to interference EMG, however, raises important questions about how to optimize these estimates. For example, what should the length of the epoch (time window) be to average an EMG signal to reliably estimate muscle forces and command signals? Shorter epochs are most practical, and significant reductions in epoch have been reported with high-pass filtering and whitening. Given that this processing attenuates power at frequencies of interest (<250 Hz), however, it is unclear how it improves the extraction of physiologically relevant information. We examined the influence of amplitude cancellation and high-pass filtering on the epoch necessary to accurately estimate the “true” average EMG amplitude calculated from a 28 s EMG trace (EMG_ref) during simulated constant isometric conditions. Monte Carlo iterations of a motor-unit model simulating 28 s of surface EMG produced 245 simulations under two conditions: with and without amplitude cancellation. For each simulation, we calculated the epoch necessary to generate average full-wave rectified EMG amplitudes that settled within 5% of EMGref. For the no-cancellation EMG, the necessary epochs were short (e.g., <100 ms). For the more realistic interference EMG (i.e., cancellation condition), epochs shortened dramatically after using high-pass filter cutoffs above 250 Hz, producing epochs short enough to be practical (i.e., <500 ms). We conclude that the need to use long epochs to accurately estimate EMG amplitude is likely the result of unavoidable amplitude cancellation, which helps to clarify why high-pass filtering (>250 Hz) improves EMG estimates.     

1H-NMR characterization of the human myocardium myoglobin and erythrocyte hemoglobin signais

The ¹H-NMR signal of deoxy Mb provides a unique opportunity to measure tissue oxygenation in vivo. To utilize the technique for human application, however, requires a specific spectral characterization of both human Mb and erythrocyte Hb. We report that the proximal histidyl-NH signal of human deoxy Mb resonates at 80.3 ppm at 25°C and maintains a 3.9 ppm separation with the corresponding Hb A signal throughout the physioiogical temperature range. In the particular case of the human thenar muscle, the deoxy Mb signal is clearly detectable without any interference from Hb.     

Variance-based signal conditioning technique: Comparison to a wavelet-based technique to improve spike detection in multiunit intrafascicular recordings

Detection of single unit action potentials (APs) from peripheral nerve recordings is complicated by low signal-to-noise ratio (SNR) due to the activity of nearby muscles, interference from more distant nerve fibers, and thermal noise from the neural interface. In this study, we propose a novel signal conditioning technique for multiunit signals (i.e. a signal comprised of multiple units coming from different nerve fibers), based on the variance to be applied prior to detection of APs. The proposed technique was tested on experimental and simulated intrafascicular recordings; and was compared to a wavelet-based conditioning (also applied before AP detection). The outputs of both conditioning schemes were sent to an AP detection algorithm that used a simple threshold (equal to the standard deviation of the signal). The overall performance of the detection phase was superior when using the wavelet-based conditioned signal especially for SNR ≤ 2 dB. However, when using the variance-based conditioned signal, the AP detection phase resulted in lower number of false positives for SNR > 2 dB. The novel variance-based method improves the SNR by attenuating the background noise between APs and can be applied as pre-conditioning processing for AP detection.