Biomedical subjects

Stanley J Bolanowski

Publications and source records attributed to Stanley J Bolanowski.

At least 19 recordsLinked to original sources

PubMed2006

Adaptations in human neuromuscular function following prolonged unweighting: II. Neurological properties and motor imagery efficacy.

Strength loss following disuse may result from alterations in muscle and/or neurological properties. In this paper, we report our findings on human plantar flexor neurological properties following 4 wk of limb suspension [unilateral lower limb suspension (ULLS)], along with the effect of motor imagery (MI) training on these properties. In the companion paper (Part I), we report our findings on the changes in skeletal muscle properties. Additionally, in the present paper, we analyze our findings to determine the relative contribution of neural and muscular factors in strength loss. Measurements of central activation, the H-reflex, and nerve conduction were made before and after 4 wk of ULLS (n = 18; 19-28 yr). A subset of the subjects (n = 6) performed PF MI training 4 days/wk. Following ULLS, we observed a significant increase in the soleus H-reflex (45.4 +/- 4.0 to 51.9 +/- 3.7% expressed relative to the maximal muscle action potential). Additionally, there were longer intervals between the delivery of an electrical stimulus to the tibial nerve and the corresponding muscle action potential (M-wave latency; mean prolongation 0.49 ms) and H-reflex wave (H-wave latency; mean prolongation 0.46 ms). The efficacy of MI on strength was ambiguous, with no significant effect detected (although a modest effect size was observed; eta2 = 0.18). These findings suggest that unweighting induces plastic changes in neural function that appear to be spatially distributed throughout the nervous system. In terms of the relative contribution of neural and muscular factors regulating strength loss, we observed that neural factors (primarily deficits in central activation) explained 48% of the variability in strength loss, whereas muscular factors (primarily sarcolemma function) explained 39% of the variability.

Action Potentials↗

PubMed2005

Perception of the tactile texture of raised-dot patterns: a multidimensional analysis.

An ALSCAL multidimensional scaling analysis in Euclidean space revealed that three orthogonal perceptual dimensions can account for the judged tactile dissimilarities of raised-dot patterns. Through magnitude estimates of various perceptual attributes, it was determined that the three dimensions consist of blur, roughness, and clarity. The only effect that selective adaptation of the Pacinian (P) channel had was to change the perceptual clarity of the raised dots against their background. Adaptation of the P channel with a 20 dB SL 250 Hz stimulus enhanced clarity. As indicated by magnitude estimates, adaptation of the P channel by the 250 Hz stimulus had no effect on the perceived roughness of the dot pattern but did cause the individual dots of the textured pattern to feel smoother. When the observer was required to estimate magnitude "overall roughness" defined as a combination of dot-pattern roughness and individual-dot roughness, adaptation of the P channel affected perceived roughness by reducing it. Taken as a whole, the results are consistent with the hypothesis that the NP channels and the P channel jointly influence the perception of textured surfaces.

Adaptation, Physiological↗

PubMed2005

Population-response model for vibrotactile spatial summation.

A computational model based on previous physiological and psychophysical data is presented for the human Pacinian (P) psychophysical channel. The model can predict the probability of detection in simple psychophysical tasks, and hence psychometric functions and thresholds. The model simulates stimulating variable and fixed glabrous skin sites with different-sized contactors and includes spatial variation of monkey P-fiber sensitivities. Therefore, it is especially suitable for studying spatial summation, i.e. the improvement of threshold with increasing contactor area. Selective contributions of neural integration (n.i.) and probability summation (p.s.) are also incorporated into the model. Model predictions are compared to psychophysical results of Gescheider et al. (2005). The performance of the model regarding the effects of contactor size is very good. In addition to predicting approximately 3 dB improvement of thresholds when the contactor area is doubled, the model also reveals nonlinear contributions of p.s. and n.i. Furthermore, the model asserts that thresholds are largely governed by neural integration when small contactors are used. These and other findings discussed in the article show that the presented model is a helpful tool for formulating testable hypotheses. Although the model can also simulate some temporal summation effects, simulation results do not conform well to previous data on temporal response properties. Thus, the model needs to be refined in that respect.

Cell Count↗

PubMed2005

A direct comparison of exogenous and endogenous inhibition of return and selective attention mechanisms in the somatosensory system.

The interaction of excitation and inhibition in responses due to attentional mechanisms in the visual system has been investigated. The studies reported herein use the tactile system of humans to test a specific hypothesis about the processes of attention that have never been directly addressed. Both exogenous and endogenous Inhibition of Return (IOR) reaction-time paradigms with a 100 Hz, 35 microm of peak displacement amplitude were used. In these experiments multiple Stimulus Onset Asynchronies were tested which made it difficult for subjects to learn timing patterns. We tested whether a detection time to a target which is to be attended to is a composite of at least two underlying mechanisms. These mechanisms were explored using exogenous and endogenous IOR experiments. It is hypothesized that these mechanisms work in a push-pull fashion: one deploying attention when new events occur, and the other withdrawing attention ("Disengagement") after it has been deployed. Based on the results, a new hypothesis is proposed stating that one form of attention (selective attention) competes with IOR in determining the time taken to detect a target in the tactile system.

Attention↗

PubMed2004

Probability of stimulus detection in a model population of rapidly adapting fibers.

The goal of this study is to establish a link between somatosensory physiology and psychophysics at the probabilistic level. The model for a population of monkey rapidly adapting (RA) mechanoreceptive fibers by Güçlü and Bolanowski (2002) was used to study the probability of stimulus detection when a 40 Hz sinusoidal stimulation is applied with a constant contactor size (2 mm radius) on the terminal phalanx. In the model, the detection was assumed to be mediated by one or more active fibers. Two hypothetical receptive field organizations (uniformly random and gaussian) with varying average innervation densities were considered. At a given stimulus-contactor location, changing the stimulus amplitude generates sigmoid probability-of-detection curves for both receptive field organizations. The psychophysical results superimposed on these probability curves suggest that 5 to 10 active fibers may be required for detection. The effects of the contactor location on the probability of detection reflect the pattern of innervation in the model. However, the psychophysical data do not match with the predictions from the populations with uniform or gaussian distributed receptive field centers. This result may be due to some unknown mechanical factors along the terminal phalanx, or simply because a different receptive field organization is present. It has been reported that human observers can detect one single spike in an RA fiber. By considering the probability of stimulus detection across subjects and RA populations, this article proves that more than one active fiber is indeed required for detection.

Action Potentials↗

PubMed2003

Intra- and interactive touch on the face.

Experiments were performed in which the subjective size of steel balls was judged by the method of absolute magnitude estimation (AME). The balls were rolled actively ("scripting") by the right index finger pad of the subject over the passively receiving areas of the face, namely the forehead, cheek and the vermilion border of the lower lip. These areas were stimulated on the subject's own person (intra-active touch), on another person's face (interactive touch) and by another person upon the face of the subject (interactive touch). Results indicate that size perception appears to be governed primarily by the mechanical characteristics of the stimuli, including the balls and the sites on the face. When the subject's finger was used to script upon another's face, there were significant differences among or between the sites. When another person scripted upon the subject's face there were no significant differences among any of the sites. The results are discussed considering mode of stimulation and tissue mechanics.

Cheek↗

PubMed2003

Distribution of the intensity-characteristic parameters of cat rapidly adapting mechanoreceptive fibers.

Modeling population responses of nerve fibers requires statistical characterization of fiber-response properties. The rate/intensity characteristics of cat rapidly adapting (RA) fibers were fitted by four-parameter, piece-wise linear functions using nonlinear regression (n = 14; R2 > 0.958). The parameters were tested against the null hypothesis that they are log normally distributed. The test fail to reject this hypothesis (Kolmogorov-Smirnov p>0.477). However, a significant statistical difference was found between the specific lognormal distributions obtained from monkey (Johnson, J Neurophysiol 37: 48-72, 1974) and cat for all four parameters (Kolmogorov-Smirnov, p<0.0075, p<0.05, p<0.0001, p<0.00007). Although the stimulus contactor size was not the same in monkey and cat studies, the differences between monkey and cat fibers are attributed to anatomical differences in the glabrous sin of both species. Modeling studies suggest that the absolute firing thresholds of RA fibers have a right-skewed distribution because of the anatomical constraints present in both species' skin. Meissner corpuscles, which are the sensory end-organs of RA fibers, are likely to be found deeper in the skin within dermal papilla, therefore, the thresholds can be elevated. However, the thresholds are bounded at lower end, probably due to the epidermal junction that acts as a superficial mechanical barrier for these corpuscles.

Afferent Pathways↗

PubMed2003

Organization of Meissner corpuscles in the glabrous skin of monkey and cat.

Reconstructing neural-population responses in the form of spatial event plots assumes that the receptors are organized in a dense linear array. We have found that this assumption is not valid by determining the spatial organization of Meissner corpuscles (MCs) in the glabrous skin of both cat and monkey. The tissue was excised from animals that had been cardiac perfused with 4% paraformaldehyde. One-micrometer plastic sections revealed that the morphology of these receptors is different in the two animal species. However, in both species, they reside in approximately the same place in the dermal pegs of the skin, between the epidermal ridges, and electrophysiologically they both respond to ramp-and-hold stimuli with a rapidly adapting firing pattern. Thus, in this study we will refer to the receptors of the cat as "Meissner-like". In monkey, MCs are located in the dermal papillae between the epidermal limiting and intermediate ridges, forming orderly rows, the contours of which follow the overlying fingerprint. Although the average density of MCs is 45/mm2, they are distributed along the dermal pegs in such a manner as to give rise to three significantly ( p < 0.017) different average distances between corpuscles. We note that "fingerprints" vary in topography across the hand and this is also reflected in the underlying MC arrays. In the cat, these "Meissner-like" receptors display no specific pattern and have a density much lower than in the monkey. Cat glabrous skin does not have "fingerprints". The results emphasize that the spatial organization of tactile receptors must be taken into account when interpreting reconstructed population responses.

Animals↗

PubMed2003

Temporal gap detection in tactile channels.

The ability of observers to detect temporal gaps in bursts of sinusoids or bursts of band-limited noise was measured to assess the temporal acuity of Pacinian (P) and non-Pacinian (NP) tactile information processing channels. The P channel was isolated by delivering high frequency sinusoids or high frequency noise through a large 1.5-cm2 contactor to the thenar eminence. The NP channels were isolated from the P channel by delivering these stimuli as well as stimuli with lower frequencies through a small 0.01-cm2 contactor to the same site. Gap detection thresholds were higher for gaps in noise than for gaps in sinusoids but did not differ among conditions designed to isolate P and NP channels. The finding that temporal acuity does not differ among channels supports the hypothesis that, after termination of a stimulus, the P and NP channels exhibit the same amount of neural persistence. Also consistent with this hypothesis are the earlier findings that the enhancement of the sensation magnitude of a stimulus by a prior stimulus (Verrillo and Gescheider, Percept Psychophys 18: 128-136, 1975) and the duration of sensation after the termination of a stimulus (Gescheider et al., J Acoust Soc Am 91: 1690-1696, 1992) are independent of stimulus frequency. One important implication of this hypothesis, if true, is that the presence of temporal summation in the P channel and its absence in the NP channels, results, not from the lack of neural persistence in the NP channels, but instead, in marked contrast to the P channel, from the lack of a mechanism for integrating persistent neural activity over time.

Adult↗

PubMed2003

Frequency responses of cat rapidly adapting mechanoreceptive fibers.

The frequency responses of 11 rapidly adapting (RA) fibers in cat were studied by representing the average firing rate as a function of sinusoidal stimulus amplitude and stimulus frequency. Specifically, rate-intensity functions at different stimulation frequencies were fitted by four-parameter (a0, a1, a2, a3), piece-wise linear functions using nonlinear regression (n = 59; R2 > 0.877). Rate-intensity functions at intermediate frequencies were found by linear interpolation. The result of this analysis is rate-amplitude-frequency functions plotted as two-dimensional surfaces. The surfaces consist of five regions separated and sufficiently defined by four space curves. At 14 different frequencies, the statistical distribution of each rate-intensity-function parameter could be approximated by a particular lognormal distribution (n = 56; R2 > 0.796). The Kolmogorov-Smirnov test fails to reject this hypothesis for each combination of frequency and parameter (56 tests; p > 0.39). Therefore, at a given frequency, the variation of the parameters can be represented by lognormal distributions with specific means and standard deviations. Responses of six RA fibers, which are different from the data-set used for modeling, were compared with the stochastic model at different frequencies. The parameters of those fibers were tested against the null hypotheses that they were sampled from the particular parameter distributions dictated by the model. The Kolmogorov-Smirnov test fails to reject all the hypotheses at the alpha = 0.05 level (44 tests). At the alpha = 0.10 level, only a few test parameters were found to be departing from the model (a0 and a1 at 5 Hz; a2 at 20 Hz; a2 and a3 at 50 Hz). The remaining test parameters could be accurately described by the model. Having confirmed the validity of the model, the logarithmic means and the logarithmic standard deviations of the lognormally distributed rate-intensity-function parameters were estimated in the frequency range of 4-200 Hz. The rate-amplitude-frequency surfaces sampled from the established stochastic model completely characterize the rate responses of RA fibers to sinusoidal stimuli and are superior to tuning curves which require selecting criterion responses. The current rate-response model is promising for future computational work, especially on population modeling.

Action Potentials↗

PubMed2003

Correlation of spatial event plots with simulated population responses of mechanoreceptive fibers.

The experimental setup for generating spatial event plots (SEPs) from single mechanoreceptive fibers of the skin was computationally simulated. The generic fibers used in the simulations were similar to the rapidly adapting fibers (RAs), and had variable refractoriness and receptive-field size. The speed, lateral shift, and the contact width of the drum scanned across the receptive field of the fiber are adjustable parameters. The stimulus patterns used on the drum mimicked stimuli used by several other investigators. These were dot patterns, grating patterns, and the letter "E". First, the effects of simulation parameters on the SEPs were studied. The simulation output confirms the results of physiological experiments that SEPs contain information on the spatiotemporal resolution of the fiber. The next series of simulations involved generating SEPs of fibers obtained from the same or varying spatial distributions of receptive fields. Three hypothetical distributions were used: homogeneous rectangular, uniformly random, and Gaussian. The momentary population response at each case was found using the technique by Johansson and Vallbo (Brain Res 184: 353-366, 1980). The population responses were not isomorphic images of the stimulus patterns due to the variations in field sizes and locations. However, every fiber, no matter which distribution it came from, generated almost identical SEPs given similar response properties. Furthermore, the SEPs looked like the outline of the stimulus. These observations show that SEPs do not contain information about the population response. Therefore, reconstructing the population response using SEPs can result in misleading conclusions on central-nervous-system processing and should be viewed cautiously when formulating psychophysical/physiological linking hypotheses.

Animals↗

PubMed2003

Effects of temperature on the subjective magnitude of vibration.

Absolute magnitude estimation (AME) was used to determine the effects of skin temperature on the subjective magnitude of vibration delivered to the thenar eminence of the right hand. Measurements were made at three frequencies chosen to selectively activate cutaneous mechanoreceptor channels, namely NP I and NP III (Meissner and Merkel cell-neurite receptors, respectively) at 15 Hz, Pacinian (250 Hz, 400 Hz) and NP III (Ruffini endings) at 400 Hz. Skin temperatures at 15, 20 and 40 degrees C were tested at 11 suprathreshold displacement levels. It was concluded that the subjective magnitude of vibration is influenced by temperature in the Pacinian channel, but in the NP I and NP III channels the temperature of the skin did not have an effect upon judgements of subjective magnitude. This is consistent with earlier work by Verrillo and Bolanowski (J Acoust Soc Am 80: 528-532, 1986) and Bolanowski et al. (J Acoust Soc Am 84: 1680-1694, 1988); both studies show only modest effects of temperature at threshold at frequencies below approximately 40 Hz.

Adult↗

PubMed2002

Voltage-gated sodium channels are present on both the neural and capsular structures of Pacinian corpuscles.

It has long been accepted that action potentials arising from Pacinian corpuscles (PCs) originate at the first node of Ranvier located within the PC and that the mechanotransduction events (receptor potentials) are formed by stretch-activated channels selectively sensitive predominantly to Na+. Also, it has been shown previously that tetrodotoxin (TTX) affects the receptor potential suggesting that transduction may involve voltage-sensitive Na+ channels. To determine whether voltage-sensitive Na+ channels exist in the membrane thought to be responsible for transduction, immunocytochemical studies were performed using polyclonal antibodies raised in rabbit against the alpha subunit of rat type I and type II voltage-gated sodium channels. The results show the presence of label on the neurite and axolemma, as well as in the node regions. Interestingly, labeling is also found on the inner and outer lamellae that form the non-neural accessory structure surrounding the neurite. The presence of this label in the surrounding lamellae suggests that voltage-sensitive Na+ channels, that are involved in both transduction and action-potential generation, may be made available to the neurite via transport from the lamellae, a mechanism perhaps operating in parallel to axoplasmic transport.

Animals↗

PubMed2002

Effect of aging on the subjective magnitude of vibration.

Two groups of subjects were tested using the method of Absolute Magnitude Estimation (AME) to determine the effect of age on the subjective intensity of vibration delivered to the skin of the hand. The mean age of the younger group was 23.5 years and that of the older group was 68.6 years. Average thresholds in the older group were higher in both the Pacinian (P) and non-Pacinian channel (NP II). The subjective magnitude of vibration was substantially lower at all intensities in the older group. Individual results clearly showed that the P channel saturates near the detection threshold of the NP II channel.

Adult↗

PubMed2002

A four-channel analysis of the tactile sensitivity of the fingertip: frequency selectivity, spatial summation, and temporal summation.

Thresholds were measured for the detection of vibratory stimuli of variable frequency and duration applied to the index fingertip and thenar eminence through contactors of different sizes. The effects of stimulus frequency could be accounted for by the frequency characteristics of the Pacinian (P), non-Pacinian (NP) I, and NP III channels previously determined for the thenar eminence (Bolanowski et al., J Acoust Soc Am 84: 1680-1694, 1988; Gescheider et al., Somatosens Mot Res 18: 191-201, 2001). The effect of changing stimulus duration was also essentially identical for both sites, demonstrating the same amount of temporal summation in the P channel. Although the effect of changing stimulus frequency and changing stimulus duration did not differ for the two sites, the effect of varying the size of the stimulus was significantly greater for the thenar eminence than for the fingertip. The attenuated amount of spatial summation on the fingertip was interpreted as an indication that the mechanism of spatial summation consists of the operations of both neural integration and probability summation.

Adolescent↗

PubMedDate not supplied

Modeling population responses of rapidly-adapting mechanoreceptive fibers.

The population response of rapidly-adapting (RA) fibers is one component of the physiological substrate of the sense of touch. Herein, we describe a computational scheme based on the population-response model by K.O. Johnson (J. Neurophysiol. 37: 48-72, 1974) which we extended by permitting the capability to include the spatial distributions of receptors in the glabrous skin linked to RA fibers. The hypothetical cases simulated were rectangular, uniformly random and proximo-distally Gaussian distributions. Each spatial organization produced qualitatively distinct population-response profiles that also varied due to stimulus parameters. The effects of stimulus amplitude, average innervation density and contactor-probe location were studied by considering various response measures: number of active fibers, summated firing rate and the average firing rate of a subset of the modeled population. The outcome of the measures were statistically compared among simulated anatomical distributions. The response is the same for rectangular and uniformly random distributions, both of which have a homogeneous innervation density. However, the Gaussian distribution produced statistically different responses when the measure was not averaged over the subset population which represented the receptive field of a higher-order neuron. These results indicate that, as well as stimulus parameters, the anatomical organization is a significant determinant of the population response. Therefore, reconstructing population activity for testing psychophysical hypotheses must presently be done with care until the organization of the receptors within the skin has been clarified.

Action Potentials↗

PubMedDate not supplied

End-to-end linkage (EEL) clustering algorithm: a study on the distribution of Meissner corpuscles in the skin.

A novel hierarchical clustering algorithm was applied to the distribution of Meissner corpuscles in the skin of mammals. This method, called end-to-end linkage (EEL), is useful for grouping data that consists of chain-like contingencies in the multivariable space. Unlike the traditional techniques which uncover hyperspherical clusters (e.g. single linkage), EEL considers the shortest distance between the predefined end pairs of the two clusters as an inter-group distance. This scheme allows characterizing the internal structure of data better than other hierarchical techniques. The anatomical data used in the case study is important for studying the sense of touch. The results show a substantial improvement over the traditional single-linkage method. On average, the number of correctly classified corpuscles is increased to twice the number identified by the single-linkage method. EEL can also be used for analyzing other sensory modalities where geometric relationships need to be explored. In addition, the report contains corpuscle density and epidermal-ridge width data obtained from several species.

Algorithms↗

PubMedDate not supplied

Tristate markov model for the firing statistics of rapidly-adapting mechanoreceptive fibers.

Rapidly-adapting (RA) mechanoreceptive fibers, which are associated with Meissner corpuscles, mediate one component of the neural information that contributes to the sense of touch. Responses of cat RA fibers subject to 40-Hz sinusoidal stimulation were modeled as a Markov process. Since an RA fiber generates one, two or no spikes in each cycle of the stimulus, the fiber's activity was considered to exist in one of these three possible states. By analyzing empirically generated spike trains, the probability of each state and the probabilities of transitions between the three states were found as a function of the average firing rate of the fiber. The average firing rate depends on the stimulus amplitude. In addition, the phase of each spike with respect to the stimulus cycle was represented by a Laplace distribution. Based on empirical data, the mean and the standard deviation of this distribution decrease as the stimulus amplitude is increased. The entire stochastic model was implemented on a computer to simulate the responses of RA fibers. The post-stimulus time, inter-spike interval and period histograms generated from the simulations match the histograms obtained from the empirical data well as quantified by relative errors. This temporal model can be combined with a population model for average rate to derive a spatio-temporal description of the responses of somatosensory afferents. The effects of changing the stimulation frequency are discussed.

Action Potentials↗