Time-Dependent Statistical and Correlation Properties of Neural Signals during Handwriting

To elucidate the cortical control of handwriting, we examined time-dependent statistical and correlational properties of simultaneously recorded 64-channel electroencephalograms (EEGs) and electromyograms (EMGs) of intrinsic hand muscles. We introduced a statistical method, which offered advantages compared to conventional coherence methods. In contrast to coherence methods, which operate in the frequency domain, our method enabled us to study the functional association between different neural regions in the time domain. In our experiments, subjects performed about 400 stereotypical trials during which they wrote a single character. These trials provided time-dependent EMG and EEG data capturing different handwriting epochs. The set of trials was treated as a statistical ensemble, and time-dependent correlation functions between neural signals were computed by averaging over that ensemble. We found that trial-to-trial variability of both the EMGs and EEGs was well described by a log-normal distribution with time-dependent parameters, which was clearly distinguished from the normal (Gaussian) distribution. We found strong and long-lasting EMG/EMG correlations, whereas EEG/EEG correlations, which were also quite strong, were short-lived with a characteristic correlation durations on the order of 100 ms or less. Our computations of correlation functions were restricted to the spectral range (13–30 Hz) of EEG signals where we found the strongest effects related to handwriting. Although, all subjects involved in our experiments were right-hand writers, we observed a clear symmetry between left and right motor areas: inter-channel correlations were strong if both channels were located over the left or right hemispheres, and 2–3 times weaker if the EEG channels were located over different hemispheres. Although we observed synchronized changes in the mean energies of EEG and EMG signals, we found that EEG/EMG correlations were much weaker than EEG/EEG and EMG/EMG correlations. The absence of strong correlations between EMG and EEG signals indicates that (i) a large fraction of the EEG signal includes electrical activity unrelated to low-level motor variability; (ii) neural processing of cortically-derived signals by spinal circuitry may reduce the correlation between EEG and EMG signals

Neuronal Variability during Handwriting: Lognormal Distribution

We examined time-dependent statistical properties of electromyographic (EMG) signals recorded from intrinsic hand muscles during handwriting. Our analysis showed that trial-to-trial neuronal variability of EMG signals is well described by the lognormal distribution clearly distinguished from the Gaussian (normal) distribution. This finding indicates that EMG formation cannot be described by a conventional model where the signal is normally distributed because it is composed by summation of many random sources. We found that the variability of temporal parameters of handwriting - handwriting duration and response time - is also well described by a lognormal distribution. Although, the exact mechanism of lognormal statistics remains an open question, the results obtained should significantly impact experimental research, theoretical modeling and bioengineering applications of motor networks. In particular, our results suggest that accounting for lognormal distribution of EMGs can improve biomimetic systems that strive to reproduce EMG signals in artificial actuators

Recognition of Handwriting from Electromyography

Handwriting – one of the most important developments in human culture – is also a methodological tool in several scientific disciplines, most importantly handwriting recognition methods, graphology and medical diagnostics. Previous studies have relied largely on the analyses of handwritten traces or kinematic analysis of handwriting; whereas electromyographic (EMG) signals associated with handwriting have received little attention. Here we show for the first time, a method in which EMG signals generated by hand and forearm muscles during handwriting activity are reliably translated into both algorithm-generated handwriting traces and font characters using decoding algorithms. Our results demonstrate the feasibility of recreating handwriting solely from EMG signals – the finding that can be utilized in computer peripherals and myoelectric prosthetic devices. Moreover, this approach may provide a rapid and sensitive method for diagnosing a variety of neurogenerative diseases before other symptoms become clear

Glial Modulation of CO\u3csub\u3e2\u3c/sub\u3e Chemosensory Excitability in the Retrotrapezoid Nucleus of Rodents

We investigated the possibility that astrocytes modify the extracellular milieu and thereby modify the activity of central CO2 chemosensory neurons. The ability of astrocytes to modify the extracellular milieu is heterogeneously distributed among chemosensory sites that have, at least nominally, the same function. The differences in astrocytic activity may make some central chemosensory sites better attuned to the local brain tissue environment and other chemosensory sites better suited to integrate chemosensory activity from multiple sites within and outside the central nervous system

Glial Modulation of CO\u3csub\u3e2\u3c/sub\u3e Chemosensory Excitability in the Retrotrapezoid Nucleus of Rodents

We investigated the possibility that astrocytes modify the extracellular milieu and thereby modify the activity of central CO2 chemosensory neurons. The ability of astrocytes to modify the extracellular milieu is heterogeneously distributed among chemosensory sites that have, at least nominally, the same function. The differences in astrocytic activity may make some central chemosensory sites better attuned to the local brain tissue environment and other chemosensory sites better suited to integrate chemosensory activity from multiple sites within and outside the central nervous system

Glial Modulation of Neuronal Excitability in the Medulla of Rodents

Brainstem regulation of CO2 chemoreception is essential in matching ventilation to the metabolic demands of the organism. The principal sites involved in sensing CO2 are widespread and located throughout the medulla. There is general agreement that the changes in pH associated with an increase in PCO2 represent the appropriate stimulus to the central chemoreceptors. Although all of the sensory transduction process of CO2 are not known, modulation of neuronal activity through purinergic mechanisms and proton block of outward cationic TASK channels have good experimental support. Within the medulla, sodium-bicarbonate cotransport (NBC) is expressed principally in astrocytes. NBC is electrogenic, and when medullary glia are depolarized by either by the direct actions of CO2 or secondarily by elevated extracellular potassium associated with neuronal activity, pHe falls dramatically. Thus, glia tend to amplify the neuronal response to any given level of hypercapnia and may modulate chemoreceptor output by regulating pHe. Modulation of the glia-neuronal lactate shuttle may also affect pHe. Inhibition of monocarboxylate transporter 2 (MCT) in neurons leads to an intracellular alkalosis of neurons, an extracellular acid shift and increase in ventilation. In addition, inhibition MCT2 increases glucose uptake suggesting both lactate and glucose are used concurrently by neurons

Glial Modulation of Neuronal Excitability in the Medulla of Rodents

Brainstem regulation of CO2 chemoreception is essential in matching ventilation to the metabolic demands of the organism. The principal sites involved in sensing CO2 are widespread and located throughout the medulla. There is general agreement that the changes in pH associated with an increase in PCO2 represent the appropriate stimulus to the central chemoreceptors. Although all of the sensory transduction process of CO2 are not known, modulation of neuronal activity through purinergic mechanisms and proton block of outward cationic TASK channels have good experimental support. Within the medulla, sodium-bicarbonate cotransport (NBC) is expressed principally in astrocytes. NBC is electrogenic, and when medullary glia are depolarized by either by the direct actions of CO2 or secondarily by elevated extracellular potassium associated with neuronal activity, pHe falls dramatically. Thus, glia tend to amplify the neuronal response to any given level of hypercapnia and may modulate chemoreceptor output by regulating pHe. Modulation of the glia-neuronal lactate shuttle may also affect pHe. Inhibition of monocarboxylate transporter 2 (MCT) in neurons leads to an intracellular alkalosis of neurons, an extracellular acid shift and increase in ventilation. In addition, inhibition MCT2 increases glucose uptake suggesting both lactate and glucose are used concurrently by neurons