Spatial localization of electrotactile stimuli on the fingertip in humans

This study was designed to determine the extent to which sensations elicited by discrete electrotactile stimulation can be spatially localized, with a qualitative comparison to mechanical stimulation, in a 2 x 2 electrode array on the fingertip. Electrotactile stimulation was delivered in two modes: (1) same current to all locations (constant) or (2) current adjusted to perceptual threshold of each location (varied). For each stimulus location, subjects were asked to identify the location of the stimulus. Mechanical stimulation of the same locations on the fingerpad was delivered through von Frey hairs (0.07, 0.2 and 0.4 g). The percentage of accurate responses was computed for all stimulation modes. We found that the accuracy of discrimination of stimulus location in both the constant (46%) and varied (40%) electrotactile stimulation modes was significantly higher than chance level (25%; p < 0.01). Furthermore, subjects were significantly more accurate in discriminating electrotactile stimuli in the constant than in the varied mode (p < 0.05). We also found that the accuracy of spatial discrimination was dependent on stimulation site for mechanical, but not electrotactile stimulation. Finally, we found a significant difference in accuracy over the duration of the experiment only for mechanical modes, which may indicate that electrotactile stimuli are less biased over time. These results suggest that, although low in accuracy, human subjects are able to extract spatial information from electrotactile stimuli. Further research is needed to optimize the amount of the information that can be delivered through electrotactile stimulation.     

Effects of contraction duration on low-frequency fatigue in voluntary and electrically induced exercise of quadriceps muscle in humans

The aims of this study were to investigate if low-frequency fatigue (LFF) dependent on the duration of repeated muscle contractions and to compare LFF in voluntary and electrically induced exercise. Male subjects performed three 9-min periods of repeated isometric knee extensions at 40% maximal voluntary contraction with contraction plus relaxation periods of 30 plus 60 s, 15 plus 30 s and 5 plus 10 s in protocols 1, 2 and 3, respectively. The same exercise protocols were repeated using feedback-controlled electrical stimulation at 40% maximal tetanic torque. Before and 15 min after each exercise period, knee extension torque at 1, 7, 10, 15, 20, 50 and 100 Hz was assessed. During voluntary exercise, electromyogram root mean square (EMG_rms) of the vastus lateralis muscle was evaluated. The 20-Hz torque:100-Hz torque (20:100 Hz torque) ratio was reduced more after electrically induced than after voluntary exercise (P < 0.05). During electrically induced exercise, the decrease in 20:100 Hz torque ratio was gradually (P < 0.05) reduced as the individual contractions shortened. During voluntary exercise, the decrease in 20:100 Hz torque ratio and the increase in EMG_rms were greater in protocol 1 (P < 0.01) than in protocols 2 and 3, which did not differ from each other. In conclusion, our results showed that LFF is dependent on the duration of individual muscle contractions during repetitive isometric exercise and that the electrically induced exercise produced a more pronounced LFF compared to voluntary exercise of submaximal intensity. It is suggested that compensatory recruitment of faster-contracting motor units is an additional factor affecting the severity of LFF during voluntary exercise. Accepted: 5 November 1997     

Age differences in tactile pattern recognition at the fingertip

Young (21–26 years, n?=?20) and old (55–86 years, n?=?25) participants were tested for their ability to recognize raised letters (6-mm high, 1-mm relief) by touch. Spatial resolution thresholds were also measured with grating domes to derive an index of the degree of afferent innervation at the fingertip. Letter recognition in the young group was very consistent and highly accurate (mean, 86% correct), contrasting with the performance of the old group, which was more variable and comparatively low in accuracy (mean, 53% correct). In both groups, spatial resolution thresholds accounted for a substantial portion of the variance in the performance, suggesting a strong link between age-dependent variations in tactile innervation and recognition accuracy. The patterns of errors in the old group showed that an inability to encode internal elements specific to certain letters was at the source of most confusion among letters. Whether this inability reflected only deficient peripheral encoding mechanisms or some other alterations at the central level is discussed.     

Study of sound localization by owls and its relevance to humans

Human psychoacoustical studies have been the main sources of information from which the brain mechanisms of sound localization are inferred. The value of animal models would be limited, if humans and the animals did not share the same perceptual experience and the neural mechanisms for it. Barn owls and humans use the same method of computing interaural time differences for localization in the horizontal plane. The behavioral performance of owls and its neural bases are consistent with some of the theories developed for human sound localization. Neural theories of sound localization largely owe their origin to the study of sound localization by humans, even though little is known about the physiological properties of the human auditory system. One of these ideas is binaural cross-correlation which assumes that the human brain performs a process similar to mathematical cross-correlation to measure the interaural time difference for localization in the horizontal plane. The most complete set of neural evidence for this theory comes from the study of sound localization and its brain mechanisms in barn owls, although partial support is also available from studies on laboratory mammals. Animal models of human sensory perception make two implicit assumptions; animals and humans experience the same percept and the same neural mechanism underlies the creation of the percept. These assumptions are hard to prove for obvious reason. This article reviews several lines of evidence that similar neural mechanisms must underlie the perception of sound locations in humans and owls.     

Force-length, torque-angle and EMG-joint angle relationships of the human in vivo biceps brachii

The relationships of EMG and muscle force with elbow joint angle were investigated for muscle modelling purposes. Eight subjects had their arms fixed in an isometric elbow jig where the biceps brachii was electrically stimulated (30 Hz) and also in maximum voluntary contraction (MVC). Biceps EMG and elbow torque transduced at the wrist were recorded at 0.175 rad intervals through 1.75 rad of elbow extension. The results revealed that while the torque-length relationship displayed the classic inverted U pattern in both evoked and MVC conditions, the force-length relationship displayed a monotonically increasing pattern. Analyses of variance of the EMG data showed that there were no significant changes in the EMG amplitudes for the different joint angles during evoked or voluntary contractions. The result also showed that electrical stimulation can effectively isolated the torque-angle and force-length relationships of the biceps brachii and that the myoelectric signal during isometric contraction is uniform regardless of the length of the muscle or the joint angle.     

Conformational determinants of the intracellular localization of midkine

Midkine (MK) is a multifunctional growth factor and has been discovered to play important roles in carcinogenesis. MK has been reported to localize to the nucleus and nucleolus, however, the data are not consistent and the signals responsible for the localization are unknown. Here we reported that human MK exclusively localized to the nucleus and nucleolus in HepG2 cells by using GFP as a tracking molecule. In order to identify the motifs required for the nuclear localization and nucleolar accumulation, point- and deletion-mutations were introduced and the corresponding subcellular localizations were analyzed. Data revealed that (i) K79R81, K86K87, and the C-terminal tail of MK constitute the nuclear localization determinant of MK, and (ii) the C-terminal tail is the key element controlling MK nucleolar accumulation though the N-terminal tail, K79R81, and K86K87 also contribute to this process. Taken together, our results provide the first documentation about the determinants required for MK nuclear and nucleolar localization.     

Studies on after-taste of various taste stimuli in humans

This series of experiments was performed in order to evaluatethe physiological characteristics and patterns of after-tasteof various taste substances. The durations of after-taste followingmonosodium glutamate (MSG), inosine-5'-monophosphate (IMP) andguanosine-5'-monophosphate (GMP) (umami substances) were longerthan those for sucrose, NaCl, tartaric acid and quinine-HCIat concentrations corresponding to the recognition threshold.The periods of after-taste of solutions of MSG and IMP, andMSG and GMP, were longer than those for the single componentsolutions. Most subjects recognized sucrose as sweet, NaCl assalty, tartaric acid as sour and quinine-HCI as bitter, bothin terms of immediate taste and after-taste. According to thepatterns of after-taste for umami substances, the subjects weredivided into three groups. In group A, umami (appealing, savorytaste in Japanese cuisine) was the main quality of the after-tastesensation; in group B, an indefinite, equivocal taste was thecharacteristic quality of the aftertaste; and no differencewas reported in group C between the immediate taste and after-taste.These results suggest that the characteristics of after-tastefor MSG, IMP and GMP are different from those of the four basictastes.     

Ultrastructure of electrical synapses between nociceptive and anterior pagoda neurons in the CNS of the leech (Whitmania pigra)

We have used electron microscopy to measure quantitatively the morphology of electrical synapses in a circuit that has been proposed to account for the positional discrimination of the leech. Injection of a presynaptic nociceptive sensory neuron and the postsynaptic anterior pagoda neuron with HRP showed gap junctions in the neuropil. After double labeling, La³⁺-treated ganglia revealed labeled gap junctions from 2.0 to 3.5 nm wide. Between the labeled axon terminals, there were innexons with diameters of 8 to 10 nm. The innexon's central pore diameter was 2 nm, and the mean of the center-to-center distance between two innexons was 30 nm. Except for the gap junction areas of nociceptive sensory neuron axon terminals, the other ultrastructural parameters measured by freeze fracture were similar to those of samples labeled with HRP and filled with La³⁺. These data suggested that the gap width, innexon diameter, and its central pore do not on their own account for the mechanism of positional discrimination, which may depend rather on the differences in distribution and number of gap junctions. Electronic Publication     

Tactile-Vibration-Activated Foci in Insular and Parietal-Opercular Cortex Studied with Positron Emission Tomography: Mapping the Second Somatosensory Area in Humans

Positron emission tomographic measurements were used to study the distribution of focal changes in cerebral blood flow (CBF) induced by vibrotactile stimulation of the hands and feet in 22 normal humans. Subjects received bolus intravenous saline injections containing ～ 60 mCi ¹⁵O-labeled water. Active regions during stimulation were defined relative to resting, nonstimulated states. Scan data from different subjects were averaged after stereotactic standardization. The results identified previously described foci of increased CBF in postrolandic sensory cortex (primary somatosensory cortex) and supplementary motor cortex. New statistical testing procedures provided independent demonstrations of two additional increases in regional CBF, bilaterally, within the sylvian fissure. One site along the parietal operculum corresponded to previous conjectures about a second somatosensory cortical area (SII) in humans. Another site also was found on the insula. No topographic organization was found in either location. The discussion considers these responsive areas to innocuous tactile stimuli in reference to suggestions about a role for SII in the perception of pain.     

Effect of electrical stimulation of the testis on the nucleus praeopticus pars magnocellularis of the frog,Rana tigrina

Summary The changes in the nucleus praeopticus (NPO) pars magnocellularis of the frog Rana tigrina were studied after electrical stimulation of the left testis. After a 3-min stimulation, the neurones of the nucleus showed a statistically significant increase in the nuclear and cellular diameters. The lateral neurones in particular showed a complete loss of Nissl substance and other acute chromatolytic changes. In the aldehyde fuchsin stained preparations, however, the perikarya appeared filled with clumps of intensely stained neurosecretory material (NSM) and disintegrating cell nuclei. The NSM was discharged in the axons, resulting in an increase in number and size of the Herring bodies. These changes were abolished in frogs whose testes had been pre-anaesthetized with xylocaine. Based on these observations, the possible existence of an afferent pathway from the testis to the NPO pars magnocellularis is suggested.     

Comparison of cortical activation patterns by somatosensory stimulation on the palm and dorsum of the hand

Abstract

Objectives: Little is known about differences of cortical activation according to body location. We attempted to compare brain activation patterns by somatosensory stimulation on the palm and dorsum of the hand, using functional magnetic resonance imaging (fMRI).

Method: We recruited 15 healthy right-handed volunteers for this study. fMRI was performed during touch stimulation using a rubber brush on an area of the same size on the palm or dorsum of the hand. Regions of interest (ROIs) were drawn at the primary sensory–motor cortex (SM1), posterior parietal cortex, and secondary somatosensory cortex.

Results: Group analysis of fMRI data indicated that touch stimulation on the palm resulted in production of more activated voxels in the contralateral SM1 and posterior parietal cortex than on the dorsum of the hand. The most activated ROI was found to be the contralateral SM1 by stimulation of the palm or dorsum, and the number of activated voxels (5875) of SM1 by palm stimulation was more than 2 times that (2282) of dorsum stimulation. The peak activated value in the SM1 by palm stimulation (16.43) was also higher than that of the dorsum (5.52).

Conclusion: We found that stimulation of the palm resulted in more cortical activation in the contralateral SM1 than stimulation of the dorsum. Our results suggested that the palm of the hand might have larger somatotopy of somatosensory representation for touch in the cerebral cortex than the dorsum of the hand. Our results would be useful as a rehabilitation strategy when more or less somatosensory stimulation of the hand is necessary.     

Identification of the subcellular localization of mycobacterial proteins using localization motifs

Mycobacterium, the most common disease-causing genus, infects billions of people and is notoriously difficult to treat. Understanding the subcellular localization of mycobacterial proteins can provide essential clues for protein function and drug discovery. In this article, we present a novel approach that focuses on local sequence information to identify localization motifs that are generated by a merging algorithm and are selected based on a binomially distributed model. These localization motifs are employed as features for identifying the subcellular localization of mycobacterial proteins. Our approach provides more accurate results than previous methods and was tested on an independent dataset recently obtained from an experimental study to provide a first and reasonably accurate prediction of subcellular localization. Our approach can also be used for large-scale prediction of new protein entries in the UniportKB database and of protein sequences obtained experimentally. In addition, our approach identified many local motifs involved with the subcellular localization that also interact with the environment. Thus, our method may have widespread applications both in the study of the functions of mycobacterial proteins and in the search for a potential vaccine target for designing drugs.     

Effects of various taste stimuli on heart rate in humans

Relationships between taste stimuli and heart rate were evaluated in 29 healthy university students. The test solutions were sucrose, NaCl, citric acid, quinine-HCl and monosodium glutamate (MSG). Heart rate increased by 7.1-13.6% for all the taste stimuli after use as compared with pre-stimuli values. The maximum increases in heart rate came approximately 25 s after the taste stimuli. After the increases, heart rate returned to pre-stimuli levels after between 80 and 100 s. Heart rate reached its maximum with citric acid. Recovery from the heart-rate increase was more delayed for quinine-HCl and MSG than for the other stimuli. Except for sucrose, increases in heart rate and the hedonic scale values of the taste solutions showed significant negative correlation. These findings show that the taste stimuli solutions increased the heart rate and that the increase differed with the concentration and taste solution used.     

Influence of motor units recruitment and firing rate on the soundmyogram and EMG characteristics in cat gastrocnemius

The separate contributions of the recruitment level and of the firing rate of the motor units on the soundmyogram and electromyogram time domain parameters were investigated during stimulation of the motor nerve of the cat gastrocnemius muscle. Upon orderly increase in the number of active motor units at a fixed firing rate, both the peak to peak amplitude (P-P_max) and the root mean square (RMS) of the sound myogram increased. At full recruitment the increase in firing rate from 2.5 to 50 Hz induced an exponential decline in the P-P_max. The RMS, however, followed this trend only from 15 to 50 Hz while showing an increase from 2.5 to 10 Hz. During simultaneous changes of recruitment and firing rate, the effect of increasing the number of motor units on the P-P_max and RMS is dampened by the increasing firing rate. The peak to peak amplitude of the EMG compound action potential increased with the number of active motor units. Moreover, its amplitude was not influenced by the firing rate. The EMG RMS, however, increases as a function of the firing rate. The results indicate that both the number and the firing rate of the active motor units contribute to the determination of the soundmyogram characteristics. Moreover, the peculiar changes of the soundmyogram time domain properties, compared to the ones of the EMG, allow one to differentiate the influence of the motor units number and firing rate on the electrical and mechanical performance of the muscle when stimulated.     

Effects of Maintenance Electroshock on the Oxidative Damage Parameters in the Rat Brain

Although several advances have occurred over the past 20 years concerning refining the use and administration of electroconvulsive therapy to minimize side effects of this treatment, little progress has been made in understanding the mechanisms underlying its therapeutic or adverse effects. This work was performed in order to determine the level of oxidative damage at different times after the maintenance electroconvulsive shock (ECS). Male Wistar rats (250–300 g) received a protocol mimicking therapeutic of maintenance or simulated ECS (Sham) and were subsequently sacrificed immediately after, 48 h and 7 days after the last maintenance electroconvulsive shock. We measured oxidative damage parameters (thiobarbituric acid reactive species for lipid peroxidation and protein carbonyls for protein damage, respectively) in hippocampus, cortex, cerebellum and striatum. We demonstrated no alteration in the lipid peroxidation and protein damage in the four structures studied immediately after, 48 h and 7 days after a last maintenance electroconvulsive shock. Our findings, for the first time, demonstrated that after ECS maintenance we did protocol minimal oxidative damage in the brain regions, predominating absence of damage on the findings.     

Antidromic propagation of action potentials in branched axons: implications for the mechanisms of action of deep brain stimulation

Electrical stimulation of the central nervous system creates both orthodromically propagating action potentials, by stimulation of local cells and passing axons, and antidromically propagating action potentials, by stimulation of presynaptic axons and terminals. Our aim was to understand how antidromic action potentials navigate through complex arborizations, such as those of thalamic and basal ganglia afferents-sites of electrical activation during deep brain stimulation. We developed computational models to study the propagation of antidromic action potentials past the bifurcation in branched axons. In both unmyelinated and myelinated branched axons, when the diameters of each axon branch remained under a specific threshold (set by the antidromic geometric ratio), antidromic propagation occurred robustly; action potentials traveled both antidromically into the primary segment as well as "re-orthodromically" into the terminal secondary segment. Propagation occurred across a broad range of stimulation frequencies, axon segment geometries, and concentrations of extracellular potassium, but was strongly dependent on the geometry of the node of Ranvier at the axonal bifurcation. Thus, antidromic activation of axon terminals can, through axon collaterals, lead to widespread activation or inhibition of targets remote from the site of stimulation. These effects should be included when interpreting the results of functional imaging or evoked potential studies on the mechanisms of action of DBS.     

Studies on cadmium localization in the water fern Azolla

Uptake of cadmium by the water fern Azolla filiculoides (Lamarck) was characterized, and the localization of the metal in the roots and shoots as well as its effects on some essential elements were studied. Cadmium was accumulated at a rapid rate in Azolla plants within 1 h and then more gradually up to 77 h. Cadmium content was increased in the inner epidermis, cortex and bundle cell walls of the root between 33 and 77 h. This accumulation was characterized by the appearance of small dark grains with high content of cadmium, phosphate and calcium along the epidermal cells. The shoots of Azolla plants grown in the presence of cadmium showed high content of cadmium only in the ventral lobe submerged in the growth medium, suggesting that cadmium was absorbed directly from the medium. The effect of cadmium on essential elements in Azolla was characterized by simultaneous increases in calcium and cadmium content in the root and shoot and by decreases in magnesium content in the root and potassium content in the shoot.